C3.4 Answers - BSCSTripleScience - home · PDF file · 2011-05-16Also much stronger...

© Edexcel Limited 2007Extension Units Science Teacher’s Guide130

C3.4 1 Bells, pipes and wires

Students’ Book pages

1 Any five from: shiny, strong, sonorous (makes a ringing sound when hit), high density, high melting point, high boiling point, good conductor of heat and/or electricity, malleable (bendy) or ductile.

2 a Strong, sonorous; b shiny.

3 Density takes account of the volume as well as the mass. If you are going to use �heavy’ as a description, you would have to control for equal-sized objects.

4 Any three transition metals, e.g. cobalt, nickel, silver, gold, mercury, titanium.

5 Good conductor of electricity, ductile.

6 a To protect you from getting a shock, to stop the current carrying wires touching and shorting out (or other equivalent answer based on safety);

b flexible.

7 Iron, platinum.

8 Five examples given below – treat other answers on their merits.

Name Use Property

iron/steel tubular bells sonorous

brass French horn malleable

steel construction strong

copper electrical wires good conductor

platinum catalytic converter speeds up the reaction

Summary exercise

transition, high, heat, density, properties, ductile, catalysts

Higher questions

1 Similarities include: good conductors of heat, electricity, flexible (malleable), ductile, sonorous. Differences include: magnesium and aluminium are lower density, more reactive, both pale silvery grey.

2 Only very small amounts are used, therefore cost is kept down (finely divided to increase surface area). Catalyst is not used up during a reaction therefore the platinum will, in theory, last indefinitely.

Extension questions

1 a Plastics are insoluble in water. Metals will have a small level of solubility, which means the water will contain small amounts of dissolved metal ions, which can then get into the bloodstream. This is a particular issue with lead, which is toxic.

(The effect is worse in soft-water areas where solubility will be higher.)

b Pb. The symbol is linked to the Latin name. Plumbers were people who worked with lead (Pb). �ater pipes used to be made of lead because it is flexible and could be bent into shape.

c Similarities e.g. good conductor, high density; differences e.g. softer, more flexible, less shiny, lower melting point.

d Plastics are flexible, corrosion-resistant and less expensive than copper, therefore used for pipes, for preference. Copper is a good conductor of heat so it helps to spread the heat around the tank. Also much stronger than most plastics – the size of hot-water tanks would mean that plastics would be liable to crack/leak.

2 Steel is strong and relatively cheap, and is used for bulk construction work such as pylons. Aluminium has a lower density than copper, so it is better for supporting the cables – savings can then be made in the construction and spacing of pylons. It conducts well enough to do the job. As well as being denser, copper is also much more expensive and therefore uneconomic for large-scale uses.

Worksheet C3.4 1a

iron – catalyst in the manufacture of ammonia – can form bonds with nitrogen and hydrogen that hold them together on the surface of the metal so that they can reactcopper – electrical cables – good conductor of electricitybrass – jewellery, ornaments and musical instruments – a golden-coloured alloy of copper and zinc that is shiny and hard-wearingnickel – to make stainless steel – will make an alloy with iron that is silver-coloured, hard-wearing and will not rustmercury – in thermometers to measure temperature; in barometers to measure air pressure – the only metallic element that is a liquid at room temperaturetungsten – filament in light bulbs – can be drawn into very thin wires; has a very high melting pointchromium – metallic coating on bumpers from classic cars of the 1950s and 1960s – very shiny, silver colour and resists corrosion

Worksheet C3.4 1b

1 a Tungsten; b mercury; c iron; d lead; e aluminium.

2 Density of 19.4 means that the word �heavy’ is certainly valid. Students may argue that the use of �stone’ for a metal is not appropriate.

3 Copper, silver and gold. All these metals are in the same vertical column (group).

AnswersC3.4

© Edexcel Limited 2007 Extension Units Science Teacher’s Guide 131

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4 Platinum, tungsten, mercury and gold. All in the same horizontal row (period).

5 Mercury is a liquid at room temperature, therefore can’t be made into a wire to allow the thickness to be measured.

6 a True, e.g. by reference to tungsten, platinum and iron.

b Insufficient evidence – only two non-transition metals listed, one is low density and the other high density.

c False – a few metals do follow this pattern, but there are many exceptions (notably lead and mercury).

d False – no obvious correlation (e.g. compare tungsten and silver).

e True/insufficient evidence. There is sufficient similarity in melting point, rank order of density and electrical conductivity to support this statement, although a more cautious student could reasonably claim that more data on a wider range of properties would be needed before coming to a conclusion.

C3.4 2 Paints, dyes and pigments


1 The liquid is cloudy/misty/opaque.

2 a Titanium; b cobalt or copper; c chromium.

3 Evaporation is a physical change in which a liquid turns into a gas. Oxidation is a chemical reaction of the substance with oxygen to form a new product.

4 All the liquids are clear/transparent/see-through.

5 A substance that binds the dye to the cloth.

6 Deep colours were difficult to produce and therefore very expensive. It was only the rich (such as the royal family) who could afford these colours.

7 Dyes are usually soluble and bind to the fabric. Pigments are insoluble (precipitates).

Summary exercise

transition, coloured, insoluble, soluble, dyes, direct, mordant

Higher questions

1 Mistakes include: pigments are insoluble in water; lead is not a transition metal; some dyes (direct dyes) do bond directly to the fabric; mordants are used to bind dyes (and they are not catalysts).

2 If oxygen reacts with the paint, the water level would be expected to rise up the tube (by about 20% if all the oxygen is used up). If evaporation takes place, the level of water in the tube would either stay constant (if the vapour all re-condensed) or go down.

Extension questions

1 a Advantages – wide range of colours, cheap, easily available to all. Disadvantages – some chemicals involved in manufacture are toxic and/or corrosive and/or carcincogenic, so can be dangerous to the work force, or cause pollution problems due to discharges from factories. Relies on renewable resources that could perhaps be put to better use in other ways.

b A return to wholly organic products is likely to result in an increase in price and a decrease in choice/range of colours, etc. Overall, it depends what you mean by �based on’: we could use renewable (biomass) materials as the raw materials in the manufacturing process – these would arguably be organic (although not in the way that is usually meant by the term).

2 Perkin was the scientist who invented the first artificial dye (mauve). This was the first time clothes in this colour had been widely available to everyone at a price they could afford. Previously mauve and purple had been a very expensive (and therefore highly fashionable) colour. The first manufactured, mass-produced dye was invented in the 1850s.

Worksheet C3.4 2b

1 3000 BCE.

2 a Iron; b chromium; c titanium.

3 Advantage – renewable source of raw materials; disadvantages – colours often fade, dyes are usually expensive/need a lot of raw material to produce a good colour.

4 a Dyes are soluble, pigments are insoluble.b Most dyes are compounds of C, H, N and O.

Pigments often contain transition metals.

5 It is called a tonic because it had medicinal properties. It would have had value in a tropical climate, such as in parts of India, in protecting against malaria.

6 Anilin.

7 Pigment – insoluble in water.

Answers ➞ continuedC3.4


Answers ➞ continuedC3.4 Answers ➞ continuedC3.4

C3.4 3 Cosmetics and alcohols


1 A liquid that dissolves another substance (the solute).

2 a �ater.b Various answers may be suggested, e.g. making

the product appear more scientific, or appearing to be better value.

3 Alcohol.

4 Carbon, hydrogen, oxygen.

5 Both contain the same elements with C/H linked in similar ways, both contain OH groups.

6 Propanol contains one more carbon atom (and two extra hydrogens).

7 a H2O;b both contain oxygen and hydrogen/ OH group.

8 �ater does not mix very well with oils (and other organic products), many of which are used in cosmetics. Other solvents, such as alcohols, are useful because they will dissolve organic products and also mix with water.

Summary exercise

hydroxyl, oxygen, hydrogen, functional group, carbon, homologous series, solvents, miscible, immiscible

Higher questions

1 a They both contain the same functional group (the OH or hydroxyl group) but contain different numbers of carbon atoms.

b They have different numbers of OH groups in the molecule (and the same carbon chain length).

2 a

C

H

H

C

H

H

C

H

O

HH

H

CC

H

H

H

O

H

H

C

H

H

H

propan-1-ol propan-2-olb Propan-3-ol would be the same as propan-2-ol.

Extension questions

1 �ater and alcohols both contain OH groups. Substances with similar structures usually mix well together. There is sufficient similarity between water and short-chain alcohols for them to mix well. As the chain length becomes greater, the similarity becomes less and therefore the solubility decreases.

2 �Prop-’ is the prefix used for compounds with three carbons (cf propanol). It contains OH groups, so the ending is �-ol’ and there are three of them (hence �tri’). They are located one on each of the three carbon atoms (hence 1,2,3).

Worksheet C3.4 3a

1 Ethanol is a good solvent for both oil-based and water-based products.

2 pH=7, neutral.

3 Ethanol should be easy to set alight – it burns with a clean, blue (almost invisible) flame.

4 Colour change (orange green). Ethanol will be oxidised to ethanal or ethanoic acid (vinegar). Some change of smell may be detectable.

5 Alcohol in the breath passed over acidified dichromate crystals in a tube. If the crystals changed colour from orange to green, this was evidence of drinking. A more accurate blood test then followed before any prosecutions could take place.

Worksheet C3.4 3b

1 Fermentation.

2 a ethanol+oxygen carbon dioxide+waterb hydrogen and carbon; c oxygen; d carbon; e ethanol already has some oxygen in the molecule,

so less is needed from the air for combustion. Incomplete combustion of hydrocarbons leads to formation of soot/carbon, which gives the smoky flame.

3 Methylated spirit contains methanol, which means the ethanol is not fit to drink, and therefore not liable to duty in the same way as alcoholic drinks.

4 a

Name of alcohol

Number of carbon atoms

Chemical formula

Displayed formula

methanol 1 CH3OH O HH C

H

H

ethanol 2 C2H5OH C

H

H

C

H

H

O HH

propanol 3 C3H7OH C

H

H

C

H

H

C

H

H

OH H

butanol 4 C4H9OH CC

H

H

H

H

H CC

H

H

H

H

O H

b two hydrogens are added for each carbon;c CnH2n+1OH, or CnH2n+2O;

d homologous series.


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C3.4 4 Sweet and sour chemicals


1 Preserves food/prevents growth of bacteria (or equivalent). Gives the food a tangy/sharp taste.

2 Organic acids contain carbon. They are weaker/have a higher pH than inorganic acids.

3 a Bubbles/fizzing; or magnesium dissolves into the acid/forms a solution;

b reaction is slower/less violent (or equivalent answer).

4 Similar: both contain two carbons; both contain carbon, hydrogen, oxygen. Different: ethanoic acid has two hydrogens fewer; one more oxygen; contains a double bond.

5 a The marker will dry up totally (as all the solvent would evaporate).

b �ater evaporates much more slowly and therefore the marker would take much longer to �dry out’.

6 Liquids that mix well together.

7 a Any two from: ethanol, water, ethanoic acid.b Ester (or a named ester) and water, or oil and

water. (Treat alternative suggestions on their merits.)

8 Treat suggestions on their merits using relevant information from Students’ Book or prior knowledge.

Summary exercise

organic, carbon, inorganic, hydrogen, alcohols, solvents/flavourings (either order), miscible, immiscible

Higher questions

1 Answers should be linked to the fact that alcohols, water and acids all contain OH groups whereas esters do not.

2 a Ethyl butanoate; b propyl pentanoate; c butyl ethanoate.

Extension questions

1

Compound Ethanol Ethanoic acid

number of carbon atoms 2 2

number of hydrogen atoms 6 4

number of oxygen atoms 1 2

Ethanoic acid contains one extra oxygen atom compared with ethanol (an argument based on the fact that there are fewer hydrogen atoms in ethanoic acid would also be correct, although this is not linked to the text or the learning objectives for the unit).

2 Missing substance is water.

Equation C2H5OH+O2 CH3CO2H+H2Oor alternatively C2H6O+O2 C2H4O2+H2O

Worksheet C3.4 4.a

1 Hydrogen.

2 Carbon dioxide.

3 In part 2 acid is concentrated, whereas in part 1 the acid was dilute (mostly water).

4 a To speed up the reaction.b Ethanol (and ethyl ethanoate) are flammable.

Heating directly with a naked flame would pose an unacceptable fire risk.

5 C, E, F.

Worksheet C3.4 4b

Flavour and ester name

Alcohol and acid used

Displayed formula of ester

rum (ethyl methanoate)

ethanol and methanoic acid

E

banana (iso-pentyl ethanoate)

iso-pentanol and ethanoic acid

D

orange (octyl ethanoate)

octanol and ethanoic acid

A

pear (propyl ethanoate)

propanol and ethanoic acid

C

pineapple (ethyl butanoate)

ethanol and butanoic acid

G

apricot (pentyl butanoate)

pentanol and butanoic acid

F

raspberry (iso-butyl methanoate)

iso-butanol and methanoic acid

B

Worksheet C3.4 4.c

1 Vinegar is sharp/tangy/sour.

2 a Hydrogen;b burns with a squeaky pop;c magnesium+ethanoic acid magnesium

ethanoate+hydrogen

3 a Carbon dioxide;b turns limewater milky;c sodium carbonate+ethanoic acid sodium

ethanoate+carbon dioxide+water

4 a �eaker;b i universal indicator would give orange colour

with ethanoic and red with the other acids; ii add a piece of magnesium to samples of both

acids – slower reaction with magnesium;c inorganic.



5 a Ethanol or ethanoic acid;b ethyl ethanoate or water; c ethyl ethanoate; d ethanol.

6 a A substance that speeds up a reaction without being used up itself.

b The sulphuric acid doesn’t get used up/change into another substance, so will not appear in the equation.

c Dilute sulphuric acid will contain more water. Concentrated acid will contain more acid/less water/be purer.

d Dilute sulphuric acid will contain less of the active chemical/the dilute acid will not be strong enough to have an effect (or similar answer).

C3.4 5 Cells and batteries


1 Chemical electrical.

2 A battery is made of a number of cells joined together.

3 3 V.

4 a Four; b six.

5 A battery – each pair of zinc and copper plates (plus the cloth) was a single cell. There were many cells in the pile.

6 It has to contain some moisture otherwise it won’t conduct/the paste inside the cell is moist/there is moisture but no free-running liquid (or equivalent answer).

7 a Cell will stop working/equipment may be damaged by leaking chemicals/corrosive chemicals could come into contact with the skin.

b Cell would stop working/won’t conduct/no electricity produced (or equivalent).

8 a Less use of resources/raw materials. Reduced pressure on landfill sites. Less risk of toxic/harmful chemicals leaking into environment/water supplies/soil.

b In the long run, yes – reduced replacement costs for new cells. In the short term, no, as cells are more expensive to buy and you may also need to buy a charger.

c An individual 1.5 V �battery’ is actually a cell. Two or more would be a battery.

Summary exercisechemical, electrical, battery, copper, carbon/zinc (either order), primary, secondary

Higher questions

1 Probably not – a simple application of the conservation of energy principle means that you’d have to use energy to recharge the cells. A sophisticated answer would consider the energy costs involved in manufacture and transport, as well as energy losses in transmission from power stations when re-charging.

2 Errors include: zinc carbon cells are not rechargeable – this could be nickel cadmium, or nickel metal hydride; it would be a 3V battery (not a cell). You would need two cells (not four) or a more reactive metal (e.g. lithium).

Extension questions

1 a Zinc negative, manganese oxide positive.b Oxygen is added (or argument based on loss of

electrons).c In Mn2O3 ratio is 1:1.5, so this is less oxygen

(relatively speaking) than in MnO2, which has a 1:2 ratio. Removal of oxygen is a reduction reaction.

d The cell is an alkaline cell and potassium hydroxide is an alkali.

Worksheet C3.4 5a

Order of statements: 1, 5, 4, 2, 7, 3, 8, 3.

Further work: the �dry cell’ uses a paste rather than a liquid as the electrolyte (conducting medium) and an oxidising agent is added to ensure that water is formed rather than hydrogen gas.

Worksheet C3.4 5b

1 a Zinc/carbon or alkaline, or mercury button;b lead/acid, or nickel/cadmium or lithium ion;c lead/acid; d lithium ion; e zinc/carbon.

2 Treat answers on their merits, depending on the range of products chosen. In the main, the manufacturers are likely to have chosen the best battery for the job, although with the reducing price of some button cells, this may tip the balance from the more traditional alkaline or zinc/carbon cells for some torches or portable music players.

C3.4 6 Electrolysis


1 a The bulb is on; b bubbles/fizzing at the electrodes.

2 a Hydrogen and chlorine;b chlorine from the salt and hydrogen from the

water.


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3 a Atom; b ion; c atom; d ion; e ion; f ion.

4 Cathode has a negative charge, metal ions have a positive charge, opposite charges attract.

5 Anode – chloride ions are negative and will be attracted to the anode/chlorine is a non-metal, and in general non-metals are produced at the anode.

6 Diagram should show copper chloride solution as the electrolyte, electrodes correctly labelled and a completed circuit back to a battery or DC supply. Copper metal is formed as a coating on the cathode and chlorine gas is given off at the anode.

Summary exercise

electrolysis, liquid, electrolyte, electrodes, anode, cathode, ions, charge, attracted, opposite

Higher questions

1 Pure salt – ions trapped in solid lattice and cannot move (strong forces of attraction), therefore non conductor.Pure water – (mostly) made of molecules, therefore no charged ions (actually about one pair of ions per 10 million molecules but this knowledge not expected at this level), so poor conductor.Salt water – contains ions which are free to move as they are in the liquid state.

2 If salt water is very dilute, the concentration of chloride ions is small. This reduces the chance of chlorine being discharged. There is a greater chance of a reaction with water molecules which have a higher �concentration’ in a dilute solution (i.e. much greater proportion of solvent molecules) to produce oxygen.

Extension questions

1 a Heated above the melting point/melted/heated until it melts.

b Similarity: both are liquids. Difference: molten salt is a pure substance, salt water is a mixture, or molten salt is very hot, salt water is usually cold/can only be heated up to (about) 100 °C. (Treat other suggestions on their merits.)

c Salt is made of (positive and negative) ions that form a (giant) lattice/crystal. Opposite charges attract and so the bonding in salt is very strong. A lot of energy is needed to overcome these forces of attraction and turn salt into a liquid, therefore melting point is very high.

d i Chlorine; ii sodium.e Salt water gives hydrogen at the cathode.f Sodium is a very reactive metal. Any sodium

produced would immediately react with the water, producing hydrogen.

Worksheet C3.4 6a

1 a Copper, lead (or possibly zinc).b Any three from: sodium, magnesium, potassium,

calcium (and possibly zinc).c Metals in part a are less reactive than metals

in part b.

2 a H2O.b More (about twice as much) gas (hydrogen) is

given off at the cathode compared with the anode (oxygen).

3 a Calcium carbonate is insoluble in water, so no/very few ions in solution/all the ions stay in the solid, where they are not free to move.

b Sucrose molecules are uncharged/sucrose is not made of ions/molecules will not be attracted to either electrode (or equivalent answer).

4 There are ions in solution that can carry the current, so the bulb will still light, as the solution is a conductor. Because the current reverses direction, the ions will first move one way and then the other (50 times per second). So there is no net ion flow and therefore no decomposition.

Worksheet C3.4 6b

1 They are all non-metals.

2 Hydrogen gas is given off.

3 Cathode.

4 a Hydrogen at cathode, bromine at anode;b hydrogen at cathode, oxygen at anode.

5 Positive – attracted to the cathode, which is negative (opposite charges attract).

6 Hydrogen comes from the water present as the solvent in the solution.

7 �ater has the formula H2O and therefore contains twice as much hydrogen as oxygen, or sulphuric acid contains hydrogen and therefore the electrolyte and the solvent both contain hydrogen.

8 Solid salt won’t conduct, therefore no reaction. Salt water will conduct, but gives hydrogen rather than sodium at the cathode.

9 a This conclusion is consistent with the evidence presented and is therefore reasonable on that basis. The nature of the metal is irrelevant to the anode reaction and therefore it is actually a coincidence in this case. A high-level answer would examine both these possibilities and conclude that there is insufficient evidence to come to a definite conclusion.

b A good test would be to choose a combination of an unreactive metal and a non-metal that is known to be discharged at the anode (e.g. copper chloride or silver bromide).



c A logical analysis of the results in the table should suggest that the anode and cathode reactions can be considered independently, and therefore that halogens would be discharged from halide solutions irrespective of the reactivity of the metal. Treat alternative arguments on their merits.

C3.4 7 Purifying and plating metals


1 a Impure copper; b pure copper; c copper sulphate solution.

2 They fall to the bottom of the electrolysis cell.

3 It may contain some valuable materials (e.g. silver or gold).

4 �hen one metal is coated onto the surface of another.

5 1975 coin is non-magnetic (bronze), new one is copper-plated steel (magnetic).

6 Gold is too expensive.

7 Steel (bumper) cathode, chromium anode. Electrolyte would be a chromium compound, e.g. chromium sulphate or chromium chloride. Diagram to show a steel can as the cathode, immersed in a bath of tin sulphate solution, and a tin anode. Circuit should be completed. A higher-level answer would include a consideration of how you might attach the can so that you wouldn’t end up with an �unplated’ section of can.

Summary exercise

electrolysis, impure, anode, pure, negative, copper, electroplating, iron, cathode

Higher questions

1 Steel at the cathode, chromium at the anode. A suitable electrolyte would be a (soluble) chromium compound such as chromium sulphate.

2 Copper, gold and tin are unreactive metals. They are difficult to turn from their atoms into their ions, but easy to turn back again. An alternative argument would say that if the metal atoms are unreactive, the metal ions are reactive. More reactive metals are difficult to turn from ions into atoms. In solution, the water will decompose (giving hydrogen) in preference to electroplating taking place.

Extension questions

1 Coating may be broken, exposing the food to the iron. Iron is more reactive than tin and is therefore more likely to react with the contents of the can, especially if the juice is acidic. There is therefore a danger of food spoilage and/or dangerously high levels of iron being present in the food.

2 If you wanted to coat an object with silver. Examples could be jewellery, ornaments or a brass instrument. This would improve the appearance and/or value, and could also improve the resistance to corrosion. An alternative argument might be that you were trying to create the appearance of a pure silver item (and hence the prestige) without incurring the cost – silver plate would be cheaper than pure silver.

Worksheet C3.4 7a

1 Cleaning the copper foil with sandpaper, or using a low current/voltage.

2 Stays the same – colour (intensity) of the solution does not change during the experiment.

3 Nickel anode will have decreased in mass/got smaller. The extent to which this is obvious to the observer would depend on the size of the anode to start with and the length of time the current has been passed.

4 Nickel atoms from the anode will dissolve into the solution/oxidise and turn into nickel ions (by losing two electrons). (Positively charged) nickel ions in solution will be attracted across to the cathode (negative electrode). At the cathode, nickel ions will be converted back (reduced) to nickel atoms when they gain two electrons.


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Worksheet C3.4 7b

Metal Ch

emic

al

sym

bo

l

Coated onto Reason

chromium Cr car bumpers and bike handlebars

very shiny, silvery coloured and does not rust

silver Ag knives and forks

looks impressive and is much cheaper than the pure metal

nickel Ni engineering components and ball bearings

hard wearing and resists corrosion

tin Sn steel cans for food

non-toxic and does not rust or corrode

gold Au headphone jacks and other electrical contacts

very good electrical conductor, and can be deposited in a very thin layer

Worksheet C3.4 7c1 a Nickel electrode=anode;

b copper electrode=cathode;c nickel sulphate solution=electrolyte.

2 a Solid; b aqueous (dissolved in water); c electron.

3 The anode dissolves/goes into solution/is oxidised/reduces in mass.

4 a Cathode (copper/negative electrode). This electrode is negative. Nickel ions are positive. Opposite charges attract;

b arrow showing movement from anode (nickel) to cathode (copper);

c arrow next to (or through) bulb pointing vertically downwards.

5 Ni2+ (aq)+2e– Ni (s)

6 a D; b C; c C or E; d A, B and E.

C3.4 8 Electrolysis, ions and oxidation


1 Student’s own diagram.

2 a Cu 2+(aq); b Cu(s).

3 a Decreases; b increases; c stays the same.

4 a Electron; b (copper and sulphate) ions.

5 a magnesium+oxygen magnesium oxideb magnesium+chlorine magnesium chloride

6 a Reduction; b neither; c reduction; d oxidation; e reduction.

Summary exercise

electrolysis, loses, positively, ion, oxidation, negatively, gains, atom, reduction, electrons

Higher questions

1 Cu2+(aq)+2e– Cu(s).

2 The cathode should have a mass of 160g. The decrease in the mass of the anode should be equal to the increase in the mass of the cathode.

Extension questions

1 Copper ions should be shown moving from the anode towards the cathode. Oxidation is occurring at the anode, reduction at the cathode.

2 a Fe−3e– Fe3+ b Ni 2++2e– Nic 2H++2e– H2 d Pb2+−2e– Pb4+

e 2O2–−4e– O2

Worksheet C3.4 8a

1 a Decreases; b increases.

2 Student’s own answer.

3 If the decrease in the anode mass was exactly the same as the increase in the cathode mass, this would support the idea that the anode was pure. A greater loss of mass at the anode would suggest that impurities had come off the anode along with the copper. Additional visual evidence would include the appearance of solid impurities underneath the anode or the discoloration of the solution.

4 Cathode. This is where solid copper is deposited (see state symbols); or cathode has a negative charge and can supply extra electrons.

5 Cu (s)−2e– Cu2+ (aq)

Worksheet C3.4 8b

1 A, C, E, F, G (experiments where time varies but current is constant). Student’s own graph.

2 Graph is a straight line that goes through the origin.

3 This is not a wrong measurement. The time is being varied along with the current, and once this factor is taken into account the results are sensible.

4 There is clearly a lack of systematic planning in the data collection, and it is difficult to get a clear set of comparisons on the effect of current. However, the



experiment is not entirely hopeless, and there is one pair of experiments (A and I) that does allow a fair and direct comparison of the effect of current to be made. If the mass/time relationship is accepted, then other comparisons can also be inferred.

5 Time should be held constant at 10 min, and three other values of current chosen that progress in equal increments or bear a simple relationship to those for which data already exist (e.g. 0.5, 1.25, 1.5, 2.0 or 3.0 amps). This would be expected to show a proportional relationship (the data in the table give 0.20 g copper per amp based on a 10-minute experiment). Students could either mention a straight line graph of results, or make specific predictions about the values chosen (�1.25 amps would give 0.25 g copper because 1.25 is half of 2.5 and 0.25 is half of 0.50’).

6 Inderjit’s statement is a simplified version of Faraday’s Law, and is therefore correct scientifically and links exactly with the data in the table. Plotting the mass of copper against the product of (current×time) would give a straight line graph. Specific examples from the table could also be used to illustrate the principle (e.g. experiments A and B, which lead to the same outcome; or experiments D and J, where apparently very disparate figures lead to a simple ratio of 2:1 if you calculate current×time. This is in exact agreement with the mass ratio in these cases).

C3.4 9 The alkali metals


1 a Potassium, oxygen, hydrogen;b because it was difficult to decompose, and up to

that point no one had succeeded in doing so;c the fact that he had made small, metallic globules,

which burnt with a bright flame.

2 a Reduction. Gain of electrons as you go from potassium ions (1+) to potassium metal (or removal of oxygen from potassium hydroxide).

b Na++e– Na

3 Grey/silver colour. Can be shiny when freshly cut (although this isn’t that obvious from the photo).

4 a 180 °C;b lithium (smallest), sodium, potassium (largest);c the larger the atom, the lower the melting point;d answer in the range 30–60 °C.

5 lithium+water lithium hydroxide+hydrogen

2Li(s)+2H2O(l) 2LiOH(aq)+H2(g)

potassium+water potassium hydroxide + hydrogen

2K(s)+2H2O(l) 2KOH(aq)+H2(g)

6 a Gas burns with a squeaky pop;b test with universal indicator – turns purple; or

test with litmus – turns blue (or use of any other suitable indicator).

7 Metals are very reactive – storing under (unreactive) oil prevents the metals from coming into contact with air (oxygen) or water.

8 Similarities: e.g. colour (silver/grey), conducts heat and electricity well, both malleable. Differences: e.g. Na has much lower melting point, is much softer, more reactive with air, water and acids.

Summary exercise

potassium, increases, lithium, decreases, electrolysis, sodium, cathode, reduction, gain, hydrogen

Higher questions

1 Reduction. Metal ions gain an electron: M++e– M

2 Electrons are negative, nuclei are positive, therefore there will be an attractive force between them. Force also depends on distance, and in the larger atoms the (outer) electrons will be further from the nucleus. The force of attraction will be weaker and the melting point lower. (A full treatment would also take into account the increased nuclear charge and the screening effect of inner shell electrons, but that depth of answer would not be expected at GCSE.)

Extension questions

1 Electrolysis of salt water produces hydrogen, not sodium. Sodium is too reactive to produce from electrolysis of aqueous solutions, as hydrogen will always be discharged in preference to reactive metals (or argument on the basis that any sodium formed at the electrode would immediately react with the water, forming hydrogen).

2 Manufacture is by electrolysis of molten salt. Some of Davy’s experiments also used molten sodium compounds, but he tended to use alkalis, in this case caustic soda (sodium hydroxide), rather than salt. Sodium hydroxide absorbs moisture spontaneously – Davy also used this property to electrolyse moist, solid sodium hydroxide. Large-scale manufacture today uses salt as a cheaper and safer raw material.

Worksheet C3.4 9a

1 a 11; b 37.

2 a 4; b 20.

3 Allow any answer in the range 50–70 °C (actual value is 64 °C).

4 Lithium, sodium and potassium all have density less than 1.0.


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5 a Student’s own graph.b Increase in atomic radius leads to decrease in

boiling point (inverse relationship).c Data for rubidium and caesium do not exactly

follow the trend – a case could be made for either of these being an anomaly. Alternatively, it could be argued that they both fall within the limits of �experimental error’ – that there is no anomaly and that they are both close to the line of best fit.

6 Ionisation energy decreases as you go down the group.

7 a True – smooth trend from 520 (Li, at no. 3) to 380 (Cs, at no. 55);

b partly true – either sodium or potassium could be cited as an anomaly to the general trend;

c false – the general trend is in the opposite direction;

d partly true – this formula holds for Li, Na and K, but not for Rb or Cs.

Worksheet C3.4 9b

1 a Positive (+1); b negative (–1).

2 Numbers are the same.

3 a 2,1; b 2,8,1.

4 a Opposite charges attract (like charges repel);b greater force when closer.

5 a Na – e– Na+

b Oxidation – sodium atom has lost an electron.

6 a Student’s own graph.b Greater number of electrons is linked to larger

atomic radius. This is because with more electrons there are more shells, and each shell is (on average) further away from the nucleus than the previous one.

7 �hen alkali metals react, they lose an electron to become an ion. The outer shell electron is the one that will be lost. The force of attraction between the nucleus and the outer shell electron will decrease with increasing distance, so it is easier to remove the electron when the atom is larger. Caesium, with the largest atom, therefore has the highest reactivity and lithium, with the smallest atom, has the lowest reactivity.

C3.4 10 Glass


1 Sand (silicon dioxide, silica).

2 a Lowers the melting point of the sand;b improves the strength and durability of the glass.

3 Grey=silicon, red=oxygen. More oxygen than silicon/twice as many red �atoms’ as grey ones/red:grey ratio is 2:1.

4 a Iron or chromium; b boron; c cobalt; d lead.

5 Re-use means that the glass bottle stays intact and is refilled after washing. Recycling means that the glass is melted down and reformed into a new bottle or other object.

6 Glass will break and therefore be a safety hazard (e.g. to animals, young children or cyclists). Glass is non-biodegradable and will therefore not break down biologically (or chemically) in the environment. There will therefore be a reliance on physical breakdown (e.g. by crushing), which will be slow. Throwing away will also contribute to the volume of waste in landfill sites.

7 Most plastics will soften or even melt at the temperatures needed for steam cleaning.

8 Clear=transparent or see-through. The majority of glass is clear (although some may be clear green or clear brown). Colourless is the opposite of coloured. Clear is the opposite of cloudy or opaque.

9 Student’s own table.

Summary exercise

silicon, oxygen, high, sodium, lower, calcium, lead, re-used, recycled

Higher questions

1 a CO2.b Carbon dioxide is a colourless gas. Silicon dioxide

is a crystalline solid with a high melting point and varying colour – often yellow/orange.

c Carbon dioxide – simple molecules (weak forces between one molecule and another). Silicon dioxide – giant molecules. Strong bonds extend throughout the lattice. Giant structure means the molecule is a solid with bonds that are difficult to break. (An answer stating that the (covalent) bonds are stronger in SiO2 is wrong. The individual covalent bonds in CO2 are very strong (805 kJ/mol) – it’s the intermolecular forces (between one molecule and another) that are weak. The silicon–oxygen bonds in SiO2, while still strong (466 kJ/mol), are weaker than those in CO2 – as a first approximation the fact that you are comparing single bonds in SiO2 with double bonds in CO2 would be reasonable at GCSE level.)

d silicon dioxide+sodium carbonate sodium silicate+carbon dioxide

SiO2+Na2CO3 Na2SiO3+CO2



2 a UV radiation is harmful to humans/can cause cancer/some types are capable of ionising molecules/can damage DNA. Glass will help protect against harmful UV radiation.

b Melting point of silica is about 2000 °C. Although raw material costs are cheap, energy costs will be very significant in heating the sand to this temperature. Energy costs for soda glass are much less, and the sodium carbonate is not a particularly expensive material (based on salt, which is also a cheap and readily available material).

Extension questions

1 a i Fixed shape, denser than water, can both be sonorous, formed into tubes or rods.

ii Transparent, glass will flow and form �drops’ when heated.

b Experimental results will take an enormously long time to collect. Evidence is mainly historical, based on observations of glass windows in ancient buildings, many of which have glass that is slightly thicker at the bottom. The dispute is in the interpretation of this evidence – it could show that the glass has �flowed’ down under the influence of gravity over the centuries. An alternative explanation is that the technology for making flat glass was not well developed in the middle ages. The panes of glass were inherently thicker at one end due to the way the glass was manufactured, and the appearance of �flow’ is an illusion that can’t be reproduced under proper experimental conditions. The debate continues!

2 Raw materials – glass based on sand (non-renewable, but no immediate shortage in supply); plastics are currently oil-based (non-renewable, limited known supplies and diminishing rapidly in this country, so dependent on imports, e.g. from Russia, Saudi Arabia, Iraq). Oil can also be used as fuel. Plastics could switch to alternative, renewable sources in future (e.g. biomass), but potential conflict with use of land for food crops.Transport – plastics much lighter, therefore reduced energy cost for moving goods around the country.Recycling – both glass and plastics can be recycled. In both cases there may be issues of separating different types. Some plastic bottles have different types of plastics stuck together, making recycling more difficult.Re-use – glass more easy to re-use (e.g. doorstep milk deliveries). Use of bottle deposits for glass bottles to encourage recycling is now coming back in again after several decades where it was deemed uneconomic and �old-fashioned’.Disposal – neither is biodegradable and both will contribute to landfill problems. Plastics can be disposed of in incinerators, although potential problem of toxic fumes with some types of plastic (e.g. PVC).

Worksheet C3.4 10a

boro-silicate A–B–C–E

glass fibre B–D–A–C

lead crystal C–E–D–A

soda-lime D–A–E–B

light barium crown glass E–C–B–D

Worksheet C3.4 10b

1 3.6 m tonnes.

2 2.53.6

=69.4%.

3 Recycled and crushed glass. Two sources are manufacturer’s rejects and household or business recycling.

4 Any three from: reduced use of raw materials (sand, limestone); savings in energy consumption; less waste going to landfill sites; reduced emissions of CO2.

5 a 6.5 kg.b (less than) 1 kg.

6 sodium carbonate sodium oxide+carbon dioxide

7 In road building (glasphalt) and as a sand substitute for golf course bunkers.

8 Treat suggestions on their merits, e.g. increased or mandatory doorstep collection from more homes; compulsory deposits on glass bottles; increasing landfill taxes; collection charges for rubbish with zero charge for recycling; more recycling bins in public buildings and on the streets; better publicity; educational awareness in schools.

C3.4 11 Caustic soda: an important alkali


1 50 million tonnes.

2 20% (100×10/50)

3 Potassium hydroxide.

4 a Chlorine; b hydrogen.

5 Universal indicator turns blue/purple.

6 Any three from: soap, paper, oven cleaners, (viscose) fibres.

7 a e.g. wool, cotton or linen; b e.g. nylon or polyester.

8 The raw material is natural, as are the individual cellulose molecules, but the fibres themselves are made by a chemical manufacturing process, so


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viscose is not wholly artificial (the natural cellulose molecule is still intact), but neither is it a natural fibre in the same way as, say, wool.

9 There are many important uses that depend on alkali production (e.g. soap and paper manufacture). Sodium hydroxide is made from salt, which is readily available as a raw material. Sodium hydroxide is therefore preferred to other alkalis (e.g. potassium hydroxide or rubidium hydroxide), which would do the job as well but would be much more difficult to manufacture in such large quantities.

Summary exercise

alkali, electrolysis, brine, cathode, chlorine, anode, caustic, corrosive, paper, wood

Higher questions

1 a sodium hydroxide+chlorine sodium chlorate (I)+sodium chloride+water

b 2NaOH+Cl2 NaOCl+NaCl+H2O

2 Energy costs are likely to be high in any process involving electrolysis. In this case, the raw material (salt water) is very cheap, and in most chemical processes there is a high degree of automation meaning that labour costs are a relatively small part of the overall cost.

Extension questions

1 Neither. Sodium stays as sodium ions (1+) and when hydroxide ions are formed from water there is no gain or loss of electrons overall. (H2O H++OH–) (The decomposition of water to make hydrogen gas (and hydroxide ions) at the cathode is a reduction reaction and credit could be given for an argument based on this line of reasoning.)

2 a Electrolysis of brine/salt water solution;b electrolysis of molten salt;c both processes involve electrolysis, so there

wouldn’t be any saving on electricity costs. Additionally, the brine process is run at room temperature while sodium manufacture is at 800 °C+, so far from saving energy, the student’s suggestion would involve a significant increase in overall energy costs.

Worksheet C3.4 11a

1 a Acid; b alkali.

2 �Swimming pool’ smell.

3 Hydrochloric or chloric acid.

4 The colour of the indicator changes from red to a paler orange colour, and maybe even to colourless.

5 There would not have been a complete circuit and no current would have flowed.

6 The metal could have reacted/dissolved and contaminated the solution; or the metal could have acted as an �anode’ in the cathode compartment.

7 Na+ and Cl–

8 a Cl–; b Na+

9 Oxidation – loss of electrons.

Worksheet C3.4 11b

1 a Salt water/brine; b chlorine and sodium hydroxide; c sodium hydroxide; d hydrogen.

2 The two main products would mix together and react.

3 It is a liquid, which is a good conductor of electricity.

4 Hydrogen.

5 Na++e– Na

6 A mixture (alloy) of another metal with mercury.

7 Low reactivity/does not react with water or alkali.

8 a Mercury is toxic; b in theory all the mercury is recycled so none

should be released into the environment.

9 sodium+water sodium hydroxide+hydrogen

10 Original demand was particularly for soap and paper manufacture. The development of modern plastics, especially PVC, means that demand for chlorine has risen rapidly in the past 50 years. Demand for soap has dropped as it has been replaced by soapless detergents.

C3.4 12 Why is sulphuric acid so important?


1 Fertilisers, paints, fibres, detergents.

2 3.4 (170/50)

3 Nitrogen, phosphorus, potassium.

4 a calcium phosphate+sulphuric acid calcium hydrogen phosphate+calcium sulphate

b ammonia+sulphuric acid ammonium sulphate

5 Rock phosphate is insoluble, so the phosphorus cannot dissolve in water to be absorbed by plants through the roots. Pure ammonia is a gas, so would evaporate very readily from the soil (although it is possible to use liquid ammonia injected under the soil surface). Ammonia solution would also suffer from significant evaporation losses.



6 TiO2

7 Iron compounds are coloured. The presence of iron compounds would affect the �whiteness’ of the titanium dioxide pigment.

8 Student’s own table/chart.

Summary exercise

large, most, fertilisers, ammonium, calcium, superphosphate, titanium, iron

Higher questions

1 TiOSO4+H2O TiO2+H2SO4

2 The use of organic fertilisers such as compost or manure would be needed, or use of alternative, less intensive agricultural methods such as crop rotation or allowing fields to lie fallow for a period.

Extension questions

1 Issues will include: definitions of what we mean by �more healthy’; length of time needed to carry out a study; problems in assembling a suitably large sample; making sure the sample is fairly drawn and representative of the population as a whole; difficulties in maintaining appropriate controls on diet, and possible ethical issues if you are deliberately feeding someone on a diet you believe to be unhealthy; problems in finding volunteers to take part in a study; accuracy in participants recording details if you are relying on diet diary methods.

3 Equation is not balanced – two sulphate groups on right-hand side and only one on left-hand side. Balanced equation is:

FeTiO3+2H2SO4 TiOSO4+FeSO4+2H2O

Worksheet C3.4 12a

1 ammonia+sulphuric acid ammonium sulphate or ammonium hydroxide+sulphuric acid ammonium sulphate+water

2 Neutralisation.

3 Excess ammonia.

4 Evaporates into the air.

5 Sulphuric acid fumes might have been given off.

6 a Could get �spitting’ of hot solid from the dish. Dish could crack. Prolonged heating could give fumes of sulphuric acid and/or ammonia.

b You would get a white powder rather than good crystals.

Worksheet C3.4 12b

1 Sulphides.

2 United States.

3 Fertiliser.

4 Explosives.

5 Super phosphate.

6 Sulphates.

7 Detergents.

8 Paints.

9 Acid rain.

10 Ammonia.

11 Plastics.

12 Pickling.

13 Dyes.

C3.4 13 The Contact process


1 Sulphuric acid.

2 Sulphur (or iron pyrites), air, water.

3 Economics – product sold at a competitive price while still allowing the chemical company to make a profit. Environmental – avoids the discharge of unacceptable levels of toxic gases (principally SO2) into the atmosphere.

4 To speed up the reaction.

5 a Increases;b conversion rate drops rapidly at temperatures

higher than 450 °C (e.g. down to 92% at 500 °C).

6 a Student’s own graph.b One converter would leave over a third (37%)

of the reactants unreacted, wasting materials and giving significant pollution problems; four converters achieve 99.5% conversion rate, only 0.5% remains unreacted – not economic to add a further converter, and discharges would now be within allowed limits.

7 a Pollution problems with discharge of toxic gases;b potential risk of explosion (or at the very least,

leakage of gases);c overheating and vaporisation of sulphuric acid

– corrosive fumes a danger to work force.

8 Temperature: 450 °C; pressure: just above atmospheric pressure; catalyst: vanadium oxide; gas ratio: excess air (more than suggested by the equation).


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Summary exercise

Contact, dioxide, trioxide, oxidation, more, lower, higher, less, reduction, water

Higher questions

1 SO3+H2SO4 H2S2O7H2S2O7+H2O 2 H2SO4

2 The company might be issued with a warning notice in the first instance. This could then be followed by prosecution which could lead to a fine or, in extreme circumstances, the closure of the factory. There would also be the risk of bad publicity in the local press.

Extension questions

1 327 kg (1000×32/98).

2 Platinum is more expensive than vanadium oxide, and as 99.5% conversion can be achieved with the cheaper vanadium oxide catalyst, this is good enough.

Worksheet C3.4 13a

1 Observations: fizzing, magnesium dissolves into the acid, tube gets warm. Test for gas: burns with a squeaky pop. Products: magnesium sulphate+hydrogen.

2 Observations: fizzing, sodium carbonate dissolves into the acid (if acid is in excess). Test for gas: turns limewater milky and puts out a burning splint. Products: sodium sulphate+carbon dioxide+water.

3 Observations: copper oxide dissolves in the acid to form a clear blue solution. Products: copper sulphate+water.

4 a Gas given off, purple vapour, dark grey/purple solid formed in the tube;

b iodine;c iodide ions (I–) to iodine atoms/molecules

involves loss of electrons.

5 a Removing water;b carbon, hydrogen, oxygen;c turns black and holes appear in the paper

– eventually forms a black sludge.d The black solid is carbon. The sulphuric acid

is removing the elements of water (hydrogen and oxygen) from the carbohydrate, leaving the carbon behind.

6 a A carbohydrate.b It starts by going yellow, then brown and

eventually black.c As in 5, a dehydration reaction is occurring

and carbon is being formed when the sugar is dehydrated.

d Steam is given off, and the blackened sugar starts to rise out of the beaker.

e The reaction is exothermic. Sulphuric acid removes the water from the sugar leaving carbon – this is the black colour. The increase in temperature makes the reaction go faster, which generates more heat. The heat is sufficient to boil the water, which turns to steam, forcing its way through the sugar/carbon and making it rise up out of the beaker as a solid foam. This then hardens as it cools.

Worksheet C3.4 13b

1 a SO2; b SO3; c H2SO4.

2 a S(s)+O2(g) SO2(g)b SO3(g)+H2O(l) H2SO4(l)

3 99.5%.

4 The higher the temperature, the lower the conversion to sulphur trioxide.

5 Student’s own graph.

6 600 °C.

7 This is a compromise between reaction speed and conversion to sulphur trioxide. At 450 °C you can still get 97% conversion rate and the reaction will go fast enough to give a good yield of product. Below 450 °C the reaction is too slow; above 450 °C and the yield drops off significantly.

Worksheet C3.4 13c

1

1 420 600 180 63 63

2 450 510 60 21 84

3 450 475 25 9 93

4 420 435 15 6.5 99.5

2 Exothermic – the temperature in each reaction bed goes up, showing that heat has been given out.

3 Student’s own graph.

4 The higher the conversion rate, the higher the temperature change. The relationship is almost directly proportional.

5 The gas temperature at the start of the second (and subsequent) reactor beds is always less than the exit temperature from the previous reactor bed.

6 The hot gases from reactor bed 1 exit at 600 °C. The heat from this reaction is used to warm up the incoming gases.



7 The overall conversion rate would only be 93%. This would mean that an unacceptably high amount of SO2 would be discharged into the atmosphere, breaching discharge limits.

8 Four reaction beds achieve 99.5% conversion, so there is only 0.5% unreacted gas. The four beds give an economic return and ensure compliance with environmental regulations, so further reactors would be a waste.

C3.4 14 Detergents


1 �ater doesn’t always �wet’ fabrics very well, and doesn’t mix with oil or grease.

2 The liquids would separate into two layers, with the cooking oil on top.

3 hydrophobic hydrophilic

4 Able to be broken down by living organisms (bacteria) in the environment. Detergents that are non-biodegradable will be discharged into rivers, where they will cause foaming on the water. This looks unsightly and can be hazardous to wildlife.

5 Biological detergents contain enzymes that will act in a similar way to those inside the body, to digest protein-based stains (those based on �biological’ products such as meat, blood and eggs).

6 Student’s own answer.

Summary exercise

solvent, dissolve, attract, surface, drops, decreases, increases, hydrophilic, hydrophobic

Higher questions

1 Gravity will also be acting on the droplet and pulling it downwards. This will create a strain at the �neck’ of the drop which will eventually be too great, and the drop will start to fall. (As air resistance takes effect the drop will start to become more spherical again.)

2 Any branched chain hydrocarbon with the same molecular formula would be an acceptable answer.

Extension questions

1 a Positive;b negative; opposite charges attract, so anions

would be negative if they are attracted to the anode;

c cationic surfactant – positive (attracted to the (negative) cathode); non-ionic – no charge (ions are charged, so non-ionic surfactant isn’t).

2 Student’s own diagams.

Worksheet C3.4 14a

1–3 Answers will link to products used and results obtained.

4 Answers could include cost-analysis data (e.g. price per gram) to link with experimental data, or alternative types of laboratory test (e.g. how much detergent you need to get a good lather), or testing of detergents in a �real-life’ situation (e.g. comparing their effectiveness in washing up dirty dishes, or with dirty fabric samples).

5 Advertisers’ claims are often based on dubious science. You would need information on sample size and whether the sample was a representative one, how the experiments were carried out, and whether the data quoted were based on objective measurable facts or simply opinion.

Worksheet C3.4 14b

1 Oil wells are often many miles from the places where the oil is going to be refined and used (e.g. transportation from Russia or Iraq to western Europe).

2 1967

3 �hen oil spreads out across the surface of water.

4 Oil doesn’t mix with/dissolve in water, and it is less dense/floats on the surface.

5 It can damage the insulating properties of fur and/or feathers. The feathers of a bird may stick together so it can’t fly. The oil is toxic and may be swallowed by the animals. Toxic products may accumulate in the food chain and other animals could become poisoned by eating contaminated fish or other sea creatures.

6 Detergents can help disperse the oil and allow it to mix in with the water (and therefore spread out).

7 Any two from: booms (floating barriers), skimmers (boats which can scoop up the oil) or sponges.

8 Ideas could include: expensive to use so much detergent; difficult to spray detergent onto such a large area; other methods are quicker/more effective; recovery methods may allow some of the oil to be re-used.

9 Animals depend on a certain natural level of oil in fur and feathers for waterproofing. Excess detergent could remove the natural oils as well as the polluting ones.


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C3.4 15 Soap


1 Fats/oils and alkali.

2 Esters (of fatty acids).

3 Carbon, hydrogen, oxygen.

4 alcohol+fatty acid ester+water

5 Hydrophilic end is the –COO– group, hydrophobic end is the carbon chain.

6 Palm oil or olive oil.

7 They react with the grease that will be baked onto the oven and turn it into soap, which will assist with the cleaning process.

8 a About 10–11; b 5.5; c (weak) acid.

9 Similarities – both made from oils; both have molecules with hydrophilic and hydrophobic ends; both help oils and grease to dissolve; both form lather with soft water. Differences – soap made with alkali, non-soapy detergents with acids; soap usually made with organically based fats and oils, non-soap detergent (NSD) from petroleum-based oils; soap can also be made with solid (animal) fats; pH of soap is usually above 7, with NSD below 7; NSD will also form a lather with hard water, soap will not.

Summary exercise

fats, hydroxide, alkali, esters, acid, hydrophobic, salt, hydrophilic

Higher questions

1 a

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

C

H

H

O HC

O

H

b C16H32O2 (or C15H31CO2H)

2 C15H31CO2H+NaOH C15H31CO2Na+H2O

Extension questions

1 Depends critically on the source of fat used. Soaps based on animal fats such as lard would probably be unacceptable to vegetarians. Other soaps are based on vegetable oils and therefore would pose no ethical problems.

2 Student’s own answers.

Worksheet C3.4 15a

1 Fat or oil and sodium hydroxide.

2 Add salt (to lower solubility of soap) and allow hot liquid to cool. (Could also allow boiling to reduce the volume of liquid/evaporate off some of the water.)

3 Student’s own results.

4 The pH is still likely to be quite high (11 or 12). Commercial products are likely to be lower, although they will still be alkaline (typically 9 or 10), some quite strongly so.

5 Depends on pH value, but probably not safe, would need further cleaning treatment/washing to remove excess alkali. Even when this has taken place, some people don’t like using soap because of the drying effect it has on their skin, reacting with the natural oils.

Worksheet C3.4 15b

1 Babylon.

2 From the animal sacrifices on Mount Sapo in Rome.

3 Animal fat and potash (potassium oxide/hydroxide).

4 The ashes from the fire were boiled with water in a pot to make �potash’. This contained the alkali that we now know as potassium hydroxide. �hen the idea of chemical elements was first introduced, potash was believed to be an element. �hen Davy carried out his experiment to show that potash was actually a compound, the metal formed from potash was called potassium.

5 Cleaning grease from textiles, especially wool.

6 The raw material (tallow) was used for lighting (candles) as well as soap-making. Taxing soap would have been a good source of revenue for the government, as well as a popular move to prevent the price of candles going up beyond the reach of the general public.

7 Treat answers on their merits, but most students would probably come down on the side of the government – domestic lighting could be justified as more important than �beauty products’. Modern parallels would be the lower rate of VAT on energy supplies – 5% as opposed to the general rate of 17.5% – and the government winter fuel payments to pensioners.

8 Gas lighting reduced the need for candles (and in the process gave people a much brighter light source). This allowed the use of the raw material to be switched to soap-making without penalising the general public by making candles very scarce and/or pushing up the price to an unreasonable level.

9 Student’s own research.



C3.4 16 Hard and soft water


1 Better lather with soft water, and reaction of soap with hard water produces scum/makes water go cloudy/gives a white precipitate.

2 Non-soap detergents produce a good lather, even with hard water.

3 Hard water contains minerals (especially calcium), which are good for healthy teeth and bones. Many people also find the taste is better.

4 magnesium sulphate+sodium stearate magnesium stearate+sodium sulphate

5 a Calcium carbonate; b calcium hydrogen carbonate.

6 Precipitate of calcium carbonate is formed when water is heated:calcium hydrogen carbonate calcium carbonate+water+carbon dioxide

7 Calcium carbonate is shown as (s), not (aq).

8 �hen you use it, the calcium is gone.

9 A balanced answer will quote some of the advantages and disadvantages mentioned in the text and in 1–3.

Summary exercise

soft, hard, *scum, calcium/magnesium (either order), sodium, *precipitate, hydrogen, carbonate, limescale

[*These two words could be swapped and the passage would still make sense.]

Higher questions

1 Temporary hardness is reversed on boiling as the calcium ions come out of solution, forming a precipitate of calcium carbonate (limescale):

Ca(HCO3)2(aq) CaCO3(s)+CO2(g)+H2O(l)

2 �ater containing calcium or magnesium sulphate is unaffected by boiling (other than an increase in the solubility of these compounds), so the calcium and magnesium stay in solution and the water remains hard.

Extension questions

1 Dissolved calcium and magnesium ions cause hardness. Rainwater itself will be soft. Unless the roof tiles contain minerals including calcium or magnesium (unlikely), the water is likely to be soft.

2 Minerals can be deposited inside the steam jets, blocking them up and/or depositing limescale onto the clothes being ironed. This would be a bigger problem in a hard-water area as there will be a greater concentration of dissolved minerals in the water.

Worksheet C3.4 16a

1 Sea water and limewater will be hardest. Mineral water is likely to be hard, but this will depend on the precise composition of the brand used. Tap water will vary from area to area. Rain water will be soft, and distilled water should be the softest.

2 Sea water is hard – dissolved solids (especially magnesium compounds in this case) will react with the soap.

3 Goes cloudy/milky. �hite precipitate/�bits’/scum forms in the water.

4 Treat answers on their merits, but a fair test should have an objective measure in terms of amount of lather (e.g. �at least 1 cm on the surface’) or time (e.g. �you can still see some bubbles after 30 seconds’).

5 To ensure water samples are not contaminated/no soap from one experiment is carried over into the next experiment (or equivalent answer).

6 It is very pure/contains no impurities/minerals/calcium/magnesium to react with the soap.

7 If the water is hard, there is likely to be a significant amount of calcium and/or magnesium in the water. If it is soft (less likely), either the overall mineral content is low, or sodium and potassium will be the main metals present.

8 Chalk and limestone areas will have hard water. Other rocks (e.g. sandstone and granite) will give soft water. �ater supplies may come from underground aquifers and therefore surface geology may not be a good guide. �ater supplies may come from a more remote location (e.g. Birmingham’s water comes from �ales), so the local geology may be misleading.

9 Steam irons need soft water. Rainwater would be suitable for this purpose. The collection method may make it less suitable – a water butt may contain various ingredients that may make you think twice about using it on your clothes.

Worksheet C3.4 16b

A 2 IV

B 1 III

C 4 V

D 5 I

E 3 II


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1 a Distillation; b ion-exchange resin/filter.

2 a Bubble bath or foam bath;b other types of washing powder and liquid

detergent had not been invented.

Worksheet C3.4 16c

1 Student’s own graph/chart.

2 a Bloxworth; b Ambleton.

3 Dutton.

4 Goes cloudy/milky. �hite precipitate/�bits’/scum form in the water.

5 Limestone

6 Ambleton – amount of soap needed for a good lather goes down slightly on boiling (therefore some temporary hardness) but still needs 14.8 cm3 of soap (the highest figure) so most of the hardness remains even after boiling.

7 Chesterford – there is a big drop in the amount of soap needed after boiling. The calcium previously in the water (as calcium hydrogen carbonate, which is soluble) will have been precipitated as limescale (calcium carbonate).

8 So that you had a good standard of comparison. In test 1 you can see that all three samples contain some minerals that cause hardness; in tests 2 and 3 you can be sure that the lower figures (about 1.5 cm3) really do represent soft water.

9 Yes – it is working efficiently. The results for samples passed through the softener are similar to those for distilled water, indicating that all the chemicals responsible for causing hardness have been removed.

C3.4 17 Questions


1 a Good conductor of electricity.

b Shiny/hard-wearing.

c Low reactivity/resists corrosion/hard-wearing.

d Sonorous.

e Resists corrosion/shiny/strong.

f Shiny/resists corrosion/low reactivity.

g Good conductor of heat/high melting point/low density.

h High density.

2 The scientific consensus is that carbon would be classified as a non-metal, although it is sometimes

included in the �semi-metals’ category. On the evidence presented, it is possible to make a case for either conclusion.

3 a Titanium dioxide; b vanadium oxide; c iron sulphide; d copper; e chromium; f copper oxide.

4 a Answers may include some of the following points: all sites are near the coast or major rivers, allowing import of raw materials via large ships. They are all near major centres of population, and will have good road (motorway) and rail contacts. The �irral is also close to the main deposits of salt in Cheshire, and all sites will have access to salt water from the sea. Any site on the north-east coast will be close to oil and gas supplies from the North Sea. Sites in the north of England will also be closer to the main areas of higher rainfall and mountains (Lake District, Peak District, Snowdonia), giving access to large volumes of fresh water and electricity from hydro-electric schemes.

b Treat answers on their merits, but most locations would be unlikely to be suitable for major heavy chemical industry because of a lack of one or more of the main factors mentioned above.

5 a aqua; b sodium chloride; c silicon dioxide; d sodium hydroxide; e citric acid; f sodium laureth sulphate; g magnesium chloride or magnesium nitrateh sorbitol or glycerol or propylene glycol; i benzyl benzoate.

6 a Sodium hydroxide;b reacts with grease that might be blocking the

drain, forming soap;c neutralisation;d salt/sodium chloride;e sodium hydroxide+chlorine sodium

hypochlorite+sodium chloride+waterf 2NaOH+Cl2 NaOCl+NaCl+H2Og a substance with no charge/made of molecules

which acts as a surface active agent/reduces the surface tension in the water;

h soap is made of ions/contains the (negative) stearate ion/would be an anionic surfactant.

7 a Dilute sulphuric acid;b six;c oxidation. Lead atoms have lost (two) electrons;d Pb−2e– Pb2+

e gain of (two) electrons/loss of oxygen atoms;f chemical energy in fuel and air kinetic energy

(in engine and dynamo) electrical energy chemical (potential) energy (stored in battery)

g Pb2+(aq)+2H2O(l) – 2e– PbO2(s)+4H+(aq) Pb2++2e– Pb

C3.4 Answers - BSCSTripleScience - home · PDF file · 2011-05-16Also much stronger...

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Transcript of C3.4 Answers - BSCSTripleScience - home · PDF file · 2011-05-16Also much stronger...