Metals Jonathan Diab

8.3.1

Outline and examine some uses of different metals through history, including contemporary uses as uncombined metals or as alloys

The first metals used by humans were those that were found in their elemental form, that is, uncombined with other elements. Gold, Silver and copper can be found as almost pure elements in various parts of the world and were initially used to make jewellery, ornaments and tools. The ability of these metals to be beaten and bent into various shapes and their relative scarcity made them prized possessions.

Early uses of copperInitially copper was used to make ornaments, tools, weapons and cooking implements. The Egyptians made and wore copper beads and used copper pipes to convey water. The excellent thermal conductivity of copper made it ideal as a cooking pot, a use that continues to the present day.One of the disadvantages of copper, regarding its use in weapons and tools, is that it is a rather soft metal. The chance discovery that a small amount of tin added to the copper increased the hardness of the metal was a major breakthrough.

Bronze: an alloy of copperThe deliberate addition of tin to copper to produce a much harder metal alloy, bronze, was of such importance that this stage of human cultural development is called the Bronze age (3000- 1000 BC). Bronze had many advantages over copper. Bronze cutting tools, such as axes and knives, maintain good cutting edges and are easily resharpened. Bronze shields and armour were much stronger that any other material available at the time. This was of strategic significance to nations waging war on their neighbours. Bronze also casts extremely well and is very durable. Statues many thousands of years old are evidence of the durability of bronze and the metallurgical skills of ancient civilisations.

Contemporary uses of copperContemporary uses of copper are mostly related to its excellent electrical and thermal conductivity, resistance to corrosion and ability to form a huge range of alloys. Copper is second only to silver as an electrical conductor and is used extensively in electrical cables and wiring, appliances, electrical generators and motors. Copper pipes, tanks and hot water systems are used for plumbing because copper does not corrode in hot water.Copper piping is also used in air- conditioning units and heat exchangers such as car radiators because it loses heat quickly. Coppers ability to form a wide range of alloys (more than one thousand different alloys have been formed) is one of the main reasons that copper remains one of the most important metals today.

The use of iron through historyThe iron age began around 1000BC. During this period, iron replaced Bronze in many applications, particularly the manufacture of tools and weapons. Pure iron is, however, susceptible to corrosion (rusting) and is relatively soft. It is likely that artisans discovered by accident that iron contaminated with carbon forms an alloy (steel) that is more corrosion resistant and harder than pure iron. The further discovery that the steel becomes even harder and keeps a better edge by heating it to a moderate temperature and then dunking it is cold water meant that bronze was eventually replaced by iron in many applications.Although carbon steels (iron- carbon alloys) were probably first made about 1000BC, the large- scale production of steel did not begin until the middle of the nineteenth century. Today there are many types of steel that have various uses, particularly in building construction and in the manufacture of cars, machinery and household appliances. Iron remains the most abundant, useful and important of all metals.

Contemporary uses of metalsCopper and iron are still widely used today. However, other metals such as aluminium and titanium are now also of considerable importance.

AluminiumDespite being the most abundant metal in the Earths crust and possessing some remarkable useful properties, aluminium was not used extensively until the beginning of the twentieth century. The reason for this is that aluminium was extremely difficult and expensive to extract from it ore, bauxite, which contains the mineral gibbsite, Al2O3.3H2O, together with various impurities.After a commercially viable method of extracting Aluminium had been developed, the use of aluminium increased dramatically.Due to its low density and its resistance to corrosion, aluminium has displaced steel in many commercial and industrial situations. For example, aluminium is used widely in building construction as roofing, window frames, appliance trim and decorative furniture. It is also used in the manufacture of a range of domestic utensils such as saucepans, frying pans, drink cans and cooking foil.Aluminium is also an excellent electrical and thermal conductor and is highly reflective, making it useful in such diverse applications as electrical transmission lines, telescope reflectors, food packaging and saucepans.Aluminium can be strengthened by the addition of small amounts of other metals such as titanium to produce many alloys that are valued for their low density and strength. As a result they are extensively used in spacecraft, aircraft and boat construction

TitaniumAlthough titanium was discovered in 1791, it was not until 1910 that the pure metal was isolated.Titanium is the 9th most abundant element in the Earths crust, occurring primarily in the minerals rutile and ilmenite. Pure titanium is a lustrous solid, similar in appearance to stainless steel. It melts at high temperatures, has a low density and great strength and is very resistant to corrosion. Alloys of titanium are very strong and are used in situations where lightweight strength and resistance to high temperatures are required, such as in jet engine components, aircraft, spacecraft and missiles.Titanium alloys are biocompatible and therefore can be used for surgical implants such as artificial knee and hip joints.Because titanium is so resistant to corrosion, it is used in marine environments as propellers and other ship parts and in chemical factories where corrosive acids are used. Titanium is also added to other metals such as aluminium, iron, manganese and molybdenum to improve their strength.

MetalPropertiesUses

Copper

Excellent thermal and electrical conductor, malleable and ductile, low reactivity, readily forms alloys

Electrical cables and wiring, radiators, refrigeration systems, water pipes, alloys including bronze (casting) and brass (fittings and fixtures)

Iron

Soft, malleable, magnetic, good thermal and electrical conductor, fairly reactive, readily forms alloys

Due to its susceptibility to corrosion it is usually converted to steel, which is used in buildings and bridges, automobiles, machinery and appliances

Aluminium

Low density, relatively soft when pure, excellent thermal and electrical conductor, malleable and ductile, good reflector of heat and light, readily forms alloysSaucepans, frying pans, drink pan, cooking foil, food packaging, roofing, window frames, appliance trim, decorative furniture, electrical cables, aircraft and boat construction

TitaniumGreat strength, high melting point, low density, low reactivity, readily forms alloys

In lightweight, high- strength alloys used in high temperature environments, e.g. spacecraft and aircraft, pipes and linings for vats where acids are used

ChromiumShiny silver appearance, resists corrosion, readily forms alloys

Plating other metals, as an additive in steel alloys, e.g. stainless steel

CobaltMagnetic, readily forms alloysIn alloys such as alnico to manufacture permanent magnets

NickelMagnetic, readily forms alloysAs an additive in steel alloys, invar (Fe, Ni) used in scientific instruments, as an alloy (Ni, Cu) in making coins, nichrome (Ni, Cr) used in electrical heating elements

ZincFairly reactive but forms protective oxide layer, readily forms alloysIn galvanising iron, in the outer casing and negative electrode of dry cells, alloy (brass) used in fittings and fixtures

GoldShiny gold appearance, excellent thermal and electrical conductor, unreactive, readily forms alloysElectrical connections, jewellery, monetary standard, dentistry

Describe the use of common alloys including steel, brass and solder and explain how these relate to their properties

SteelIron, in various forms of steel, is used extensively in building construction and the manufacture of cars and other machinery. These steels usually contain small amounts of carbon alloyed with iron. The properties of carbon steels can be changed by altering the amounts of carbon added to the iron. Increasing the proportion of carbon increases the strength and hardness of the steel produced. They can be further changed by working the steel in forging and rolling processes, and by heat treatment such as annealing, quenching and tempering.Some specialist steels contain small amounts of other metals. For example, stainless steel used in cutlery and sinks consists of iron alloyed with chromium and nickel. Some steels have other metals added to form alloy steels with special properties.

Type

Element Alloying With IronMajor Properties

Uses

Carbon Steels

Mild steel

{Li, Ca, Ba} > {Mg, Al, Fe, Zn} > {Sn, Pb} > Cu > {Ag, Au, Pt}

By using galvanic cells to calculate a more accurate measurement of a metals reactiveness, we get the following reactivity series:

K Na Li Ba Ca Mg Al Zn Fe Sn Pb Cu Ag Pt Au

The sequence is an activity series for the common metals. All the reactions here involve the metal atoms losing electrons to become metal ions. The series lists the metals in order of decreasing ease of losing electrons: metals to the left lose electrons more easily than metals to the right.Loss of electrons means oxidation, so the activity series lists the metals in order of decreasing ease of oxidation: K, Na, Li are more easily oxidised than Ag, Pt, Au.

Identify the reaction of metals with acids as requiring the transfer of electrons

Acids are substances, which in solution produce hydrogen ions H+. When metals react with acid, they form hydrogen gas. It isnt the acid that reacts with the metal, but rather the hydrogen in the acid. This reaction causes a change in the ions in which some mixtures will oxidise (lose electrons) while others will undergo reduction (gain electrons). Both may occur at the same time. This is called a redox reaction (reduction-oxidation) or electron-transfer reaction. These reactions cause the atoms of metals to lose electrons and become positive ions.

Outline examples of the selection of metals for different purposes based on their reactivity, with a particular emphasis on current developments in the use of metals.

Metals are usually used in certain areas because of their reactivity levels with certain other substances or elements, usually oxygen, water and dilute acids.

Gold is known to be the most unreactive metal currently used. It retains its shiny lustre and resists corroding, explaining why it has been used for thousands of years as jewellery and ornaments.

Magnesium is a very reactive metal and is usually used as a sacrificial anode, meaning that it is purposely used to corrode before other metals. For example, ships and wharfs sometimes have large blocks of magnesium attached so that they can react with the oxygen before the steel used does. When burned in oxygen, magnesium produces a bright white light. This characteristic of it has caused it to be used in photographic flashbulbs and is actively used in modern fireworks.

Calcium is also an extremely reactive metal and its use is restricted to certain situations where its reactivity can be used to advantage. It is added to some steels to remove traces of remaining unwanted oxygen, sulphur and phosphorus. It is also used in electronic vacuum tubes to react with oxygen, allowing for a much more effective vacuum.

Zinc is used to coat iron. Iron is dipped into molten zinc helping to protect it in two ways. The first, the zinc forms a protective coating for the iron, excluding all oxygen and reacts with the air to form an impervious layer that protects the iron from corrosion. The second is, if the zinc does happen to become exposed, it acts as a sacrificial anode, reacting with the oxygen and allowing the iron to last longer. Zincs reactivity also allows it to be used in dry cells and button cells in which it oxidises, losing electrons which travel through an external circuit, producing an electric current.

Tin and chromium are widely used to coat other metals, usually steel, because of their shiny appearance and their low reactivity. They do no react with air and water very easily, resisting corrosion. They are used to coat many steels. Tin is used as a coating for food cans such as baked beans and canned fruit because of its low reactivity. Chromium was used to coat the bumpers of many older cars. Both tin and chromium form an oxide layer which protects the underlying metal from corrosion.

Outline the relationship between the relative activities of metals and their positions on the periodic table

A comparison of the activity series for metals with the position of these metals in the periodic table reveals some interesting relationships. The activity series shows that Group 1 metals are the most reactive followed by Group 2 metals. Group 3 (Al) comes next in reactivity followed by some transition metals (Zn, Fe), then the metals of Group 4 (Sn, Pb). At the end of the series are more transition metals (Cu, Ag, Pt, Au). The activity series also shows that in Groups 1 and 2 reactivity increases from top to bottom (Li to k, Mg to Ba). The relative reactivity of metals also correlates well with an important physical property called first ionisation energy.

Identify the importance of first ionisation energy in determining the relative reactivity of metals

The first ionisation energy of an element is the energy required to remove an electron from a gaseous atom of the element. It is the energy change for the process:

Y(g) Y+(g) + e-

Where Y is any element. By determining the strength of the first ionisation of a metal, an overall judgement of reactivity can be made about the metal. The first ionisation energy measures the ease of removing an electron from a metal atom: the lower the ionisation energy, the easier it is to remove an electron.

The relative ease with which a metal loses its valence electrons is a major factor affecting its reactivity. Very reactive metals such as potassium and sodium lose their valence electrons relatively easily. Less reactive metals such as copper do not lose their valence electrons as readily, and gold and silver rarely lose their electrons at all. Ionisation energy is a measure of the energy needed to remove an electron from the electrostatic attractive force of the positively charged nucleus. The ionisation energy of an atom or ion is defined as the amount of energy required to remove the most loosely bound electron from the atom or ion in the gaseous state. The energy required to remove the first electron from an atom is called the first ionisation energy. In general, reactive metals tend to have low ionisation energies and less reactive metals have higher ionisation energies. The reactivity of metals increase as their ionisation energy decreases.

8.3.3

Identify an appropriate model that has been developed to describe atomic structure

There are many models that have been created to represent the atomic structure but the most accepted is Bohrs model in which atoms exist with a nucleus filled with neutrons and protons and are orbited by electrons in different energy levels or shells. The negatively charged electrons continuously move around the atom by electro-static forces caused by the positive charged protons.

Outline the history of the development of the periodic table including its origins, the original data used to construct it and the predictions made after is constructions.

Early in the nineteenth century as more and more elements became known, attempts were made to see patterns in their properties. In 1829 with about 40 elements known, the German chemist, Dobereiner, drew attention to several groups of three elements (which he called triads) with very similar properties;

Lithium, sodium, potassiumCalcium, strontium, bariumChlorine, bromine, iodine

In 1864 with over 60 known elements, John Newlands, an Englishman, proposed a law of octaves: when the elements were arranged in order of increasing atomic weight, the eighth element starting from a given one is a kind of repetition of the first like the eighth note in an octave of music. His law identified many similarities among the elements, but erroneously required similarities where none existed.

In 1869, Dimitri Mendeleev, a Russian, and Lothar Meyer, a German, independently produced the forerunner of the modern periodic table. They arranged the elements in order of increasing atomic weight, and placed elements having similar properties under one another to obtain a table which illustrated what they called the periodic law:

Properties of the elements vary periodically with their atomic weights.

This table was far more successful than that of Newlands, primarily because Mendeleev recognised that there were probably elements in existence that had not been discovered at that time. He left gaps in his table in order to place similar elements to fill the gaps. He was able to go further, predicting the properties of six such elements, three of which he called eka-silicon, eka-boron and eka-aluminium in which eka means like.

Over the following years, atomic weights became more accurately known and some discrepancies emerged in this periodic table. In a few cases, in order to fit similar elements under one another, it was necessary to invert the order of atomic weights. This problem was resolved in 1914 when the British scientist, Henry Moseley, determined what we now call the atomic number of each of the elements. He proposed that it, rather than atomic weight, was the basic feature, which determined properties. Moseley proposed a modified periodic law:

Properties of the elements vary periodically with their atomic numbers.

This law puts argon and potassium, cobalt and nickel and tellurium and iodine in their right orders.Once it was recognised that properties were depedent upon the number of protons (atomic number) and hence upon the numbers of electrons, tendencies towards relating the layout of the periodic table to electron configuration developed, and so the current form of the table was gradually devised.

Explain the relationship between the position of elements in the Periodic table and

Electrical ConductivityAcross a period, the electrical conductivity of elements decreases because elements are less metallic. Non metals do not have free mobile electrons in their crystal lattice. Down a group, the electrical conductivity of elements increases because they are more metallic. Down a group, the valence shell is further away from the nucleus and can more easily escape into the lattice.

Ionisation EnergyIonization energy in the energy required to remove an electron from an atom of the element in the gaseous state. Across a period, the ionization energy increases because the atomic radius decreases across a period. The valence electrons closer to the nucleus experience a stronger nuclear pull. Down a group, the ionization energy decreases because the atomic radius is bigger and outer electrons are not as attracted to the nucleus of atoms.

Atomic RadiusWhen the atomic radius of elements is plotted against atomic number, a pattern emerges in which there are a set of sharp maxima, corresponding to the alkali metals (Li, Na, K, Rb, Cs Group 1). The minima occur at the noble gases (Ne, Ar, Kr, Xe, Rn Group 8). This means that atomic radius decreases from left to right across any period of the table. Going down a group, the atomic radius increases. This occurs because each new period adds another electron shell or energy level that is more distant from the nucleus than the previous energy level.

Melting PointThe melting points of the elements also show a slight pattern when graphed against atomic number. There is a sharp set of minima that correspond to the noble gases. The maxima are less well defined: the first two correspond to the elements carbon and silicon while the others correspond to transition metals. Across a period, the melting point increases from group 1 to group 4 then decrease from group 5 to group 8. The lattice changes from metallic bonding to covalent network and then covalent molecular. Down a group, it decreases from groups 1 to 4 and increases from groups 5 to 8

Boiling PointAcross a period, the boiling point increases from group 1 to group 4 then decrease from group 5 to group 8. The lattice changes from metallic bonding to covalent network and then covalent molecular. Down a group, it decreases from groups 1 to 4 and increases from groups 5 to 8

Combing Power (Valency)The combining power of a group increases down the periodic table. Across the periodic table, the combining power decreases.

ElectronegativityThe electronegativity of an element is a measure of the ability of an atom of that element to attract bonding electrons towards itself when it forms compounds. Electronegativity increases from left to right across a period (omitting noble gases) and decreases from top to bottom.We can decide whether two elements form an ionic or covalent compound by using the following guideline:

If the difference in electronegativities of two elements is greater than 1.5, the elements will form an ionic compound; otherwise the compound will be covalent.

ReactivityThe reactivity between metals and non-metals on the periodic table differ. For metallic elements, reactivity decreases from left to right across a period of the table and increases from top to bottom down a group. Reactivity for non-metals increases from left to right across a period and decreases from top to bottom down a group.

8.3.4

Define the mole as the number of atoms in exactly 12g of carbon-12 (avogadros number)

There are 6.02 x 1023 atoms in 12g of carbon. Since 6.02 x 1023 atoms of carbon have a mass of 12 grams, then for titanium (atomic weight 48), 6.02 x 1023 atoms (each which are 4 times as heavy as carbon) must have a mass of 4 x 12 = 48 grams. If for any element we take the mass, which in grams is numerically equal to the atomic weight, then it contains 6.02 x 1023 atoms. Therefore, a mole of a substance is that quantity which contains as many elementary units (atoms, molecules, ions etc.) as there are in exactly 12 grams of the carbon-12 isotope. We call this number (6.02 x 1023) the Avogadro Constant.The molar mass is the mass of a mole of the substance. It can be used for both elements and compounds. Compare mass changes in samples of metals when they combine with oxygen

Number of moles = Mass / Mass of one mole=Mass / Molar Mass= Mass / atomic or molecular weight in grams

Divide mass by atomic or molecular weight to find number of molesSimilarly, Multiply Number of Moles by atomic or molecular weight to find Mass

Number of atoms = Number of moles x the Avogadro ConstantOr Molecules = Number of Moles x 6.02 x 1023

Multiply the Number of Moles by 6.02 x 1023 to find the number of atoms or moleculesSimilarly, Divide Number of atoms or molecules by 6.02 x 1023 to find the Number of Moles.

To convert Mass to Atoms or Molecules, we must go through moles. That is;

Mass Moles Atoms or Molecules

Describe the contribution of Gay-Lussac to the understanding of gaseous reactions and apply this to an understanding of the mole concept

After studying the volumes in which gases reacted, Gay-Lussac, in 1808, proposed the law of combing volumes: When measured at constant temperature and pressure, the volumes of gases taking part in a chemical reaction show simple whole number ratios to one another. Gay-Lussacs findings played a critical role in developing the mole concept in that his findings helped to develop the idea to use ratios to make hypothesis

Recount Avogadros law and describe its importance in developing the mole concept

Avogadro, using the findings of Gay-Lussac, proposed the following: When measured at the same temperature and pressure, equal volumes of gases contain the same number of molecules. Avogadros hypothesis allowed chemists to use quantitative analyses of compounds and reactions to determine formulae for compounds and hence relative atomic masses for elements.

Distinguish between empirical formulae and molecular formulae

The empirical formula of a compound is the formula that tells us the ratio in which the atoms are present in the compound.The molecular formula o a compound is the formula that tells us how many of each type of atom are present in a molecule of the compound. The empirical formula of a compound specifies the simplest whole- number ratio of the numbers of atoms or ions of each element in the compound. This contrasts with the molecular formula, which specifies the actual number of atoms of each element in a molecule. For the compound hydrogen peroxide, the molecular formula is H2O2. Each Hydrogen peroxide molecule contains 2 hydrogen atoms and 2 oxygen atoms bonded together. However, the empirical formula of hydrogen peroxide is HO. This represents the simplest whole- number ratio of the numbers of atoms of each element.In many compounds, such as water (H2O), ammonia (NH3) and carbon dioxide (CO2), the empirical and molecular formulas are the same. Where the empirical and molecular formulas are different, the molecular formula is always a multiple of the empirical formula.It is possible for different compounds to have the same empirical formula but they have to have different molecular formulas. Acetylene and benzene are two compounds with the empirical formula CH. The molecular formulas for these compounds are C2H2 and C6H6 respectively.The empirical formula of a substance can be established experimentally. This is achieved by determining the percentage composition of the substance by chemical analysis. This is then used to calculate the empirical formula of the substance.

8.3.5

Define the terms mineral and ore with reference to economic and non-economic deposits of natural resources

A Mineral is a pure (or nearly pure) crystalline compound that occurs in the Earths crust. They are termed minerals based upon the above criteria, not on the economics of a particular mine.An Ore is a compound or mixture of compounds from which it is economic (or commercially profitable) to extract a desired substance such as a metal. If the mineral is present in sufficient quantity to make the mining and extraction of the metal economically viable, than it is called an ore.

Describe the relationship between the commercial prices of common metals, their actual abundances and relative costs of production

There are many factors that affect the price of metals in society. Factors that affect the price of metals are: The abundance and location of ores of the metal (less abundant ores will generally attract higher royalties and so will be more expensive) The cost of extracting the metal from the ore The cost of transporting the metal or its ores to the required location (rare metals or their ores may need to be shipped from remote locations, while for abundant metals, conveniently located ore deposits can be used) The world-wide demand for the metal; if the demand is high, the price rises; if it slumps, price falls: the supply and demand factorThese factors affect the cost of one metal relative to another. General economic conditions such as booming or stagnating economies also affect metal prices, but they generally have a similar effect on all metals.

Explain why ores are non-renewable resources

Metal ores are non-renewable resources. They were formed when the earth was formed and there is no way of forming anymore of them.

Describe the separation process, chemical reactions and energy considerations involved in the extraction of copper from one of its ores

Copper is principally extracted from sulfide ores, particularly chalcopyrite (CuFeS2). The copper ore may be on the surface and easy to excavate, or may be underground and require more sophisticated methods of excavation. The crude ore from the mine often contains less than 0.5% copper by mass and must be milled before the metal can be extracted. Milling refers to the concentration or purification of an ore. Copper is concentrated using a method called froth flotation. In this process, air is bubbled through a suspension of the pulverised ore in water containing a flotation agent. The desired copper mineral particles adhere to rising bubbles and are skimmed off as froth, leaving the unwanted silicate minerals to settle out. In this way, the copper ore is separated from the gangue.The concentrated ore, which is now about 15% copper, is then roasted in air, which converts the FeS to FeO but leaves the CuS unaffected.

2CuFeS2 (S) + 3O2 (g) 2CuS(s) + 2FeO(s) + 2SO2 (g)

the product is then heated at 1100oC with ground limestone, sand and additional concentrated ore. This converts the FeO to a molten slag and converts the copper(11) sulfide to copper(1) sulfide.

FeO(s) + SiO2 (s) FeSiO3 (l)

In the final smelting step, the copper(1) sulfide is roasted in air so that part of it is converted to copper(1) oxide.

2Cu2S(s) + 3O2 (g) 2Cu2O(s) + 2SO2 (g)

The two copper(1) compounds, copper(1) sulfide and copper (1) oxide, then react together to form copper metal and sulphur dioxide.

2Cu2O(s) + Cu2S(s) 6Cu(l) + SO2 (g)

This process requires a significant input of energy to maintain the temperatures required for this reaction.The smelting process produces crude copper of about 98% purity, with is called blister copper because of the bubbly appearance produced by escaping sulphur dioxide. To obtain the 99.9% purity required for electrical wiring, the blister copper is refined electrolytically.The impure blister copper is cast into slabs and made the anode (positive electrode) of an electrolytic cell. The cathode is a thin sheet of pure copper and the electrolyte is copper(11) sulfate solution, acidified with sulfuric acid.

The copper and reactive metal impurities (such as zinc, iron and nickel) present in the anode dissolve and enter the solution as ions. As the anode slab dissolves, the more inert metal impurities such as gold, silver and platinum fall to the bottom of the cell. In a finely divided state, they form an anode slime, which is a profitable source of these metals.

A small voltage is used so that pure copper deposits at the cathode (negative electrode). The ions of the more reactive metals remain in solution. These are removed periodically so that their concentrations do not build up sufficiently to cause them to also deposit at the cathode. The copper that deposits at the cathode is extremely pure because almost all of the impurities present in the blister copper have been removed

Recount the steps taken to recycle aluminium

To recycle aluminium, used drink cans, car engines, boats and household appliances are collected and transported to a central processing plant where the aluminium is separated from impurities like labelling, food remnants and dirt. Sometimes, the aluminium is separated into groups of different aluminium alloys after the first separating procedure. It is then smelted in order to recast the metal into ingots. These ingots are then transported back to producers who use them to recreate new products.

Water

8.4.1

Define the terms solute, solvent and solution

Solutions - mixtures containing quantities of dissolved substances. Solutions are defined as homogeneous mixtures.Solute - the substance that is dissolved in another substance or solutionSolvent - the liquid that does the dissolving

Identify the importance of water as a solvent

Water is the most widely used solvent both by humans and by nature. In all living matter most of the chemical reactions responsible for life occur in water solutions, or aqueous solutions. Water dissolves nutrients from soil and carries them in solution to living cells. Water also carries waste products away from cells (again in solution). The human body is over two thirds water, with blood, our life-maintaining transport system, being over 80% water. Without water, blood would not be able to flow in arteries, veins and capillaries and transport essential nutrients and waste products. Water is also a major component of our lymph system, and the moisture lining our lungs allows the gases oxygen and carbon dioxide to be transferred between the air we breathe and our respiratory system.

Compare the state, percentage and distribution of water in the biosphere, lithosphere, hydrosphere and atmosphere

Liquid water covers nearly 70% of the Earths surface in the form of oceans, seas, lakes, ground water and rivers, which are collectively referred to as the hydrosphere. Water also occurs in vast quantities beneath the surface as ground water stored in aquifers, layers of water-bearing rocks. The Great Artesian Basin from Queensland through NSW and into Victoria and SA is an example.The polar ice caps cover another portion of our planet, dominating the regions north of the Arctic Circle and south of the Antarctic circle. The solid water found in the polar ice caps, above the snowline at higher altitudes and in glaciers, usually contains lower concentrations of dissolved salts because water generally freezes as a pure substance.

Our atmosphere contains varying amounts of gaseous water, water vapour, in the range 0-5%. Although this represents only a small percentage of the atmosphere, it allows for the transport of vast quantities of water through the Earths water cycle.

Water in the Lithosphere can occur as moisture or permafrost within solid and rocks, and as water of crystallisation within minerals. Water of crystallisation or water of hydration refers to water molecules that form part of the crystal structure of many ionic substances. Common examples are hydrated copper (11) sulfate, CuSO4.5H2O, which has 5 water molecules associates with each formula unit, and hydrated Sodium Carbonate, Na2CO3.10H2O.

Zone of the EarthWater Present as% of the zone that is water

AtmosphereVapour or tiny liquid droplets (in clouds)0.5 to 5%

HydrosphereLiquid (with other substances dissolved in it) and solids (in polar icecaps)>95% in oceans, >99% in polar icecaps, lakes and rivers

LithosphereAs ground water and chemically bound as water of crystallisation in many minerals