Questionsheet FORMULAE AND MOLECULAR EQUATIONS … · · 2011-09-21FORMULAE AND MOLECULAR...

FORMULAE, EQUATIONS & MOLESAS TOPIC 2

FORMULAE AND MOLECULAR EQUATIONS

IONIC EQUATIONS

MOLES

EMPIRICAL FORMULAE

MOLECULAR FORMULAE

USES OF FORMULAE

YIELD CALCULATIONS

CALCULATION OF REACTING MASSES

CALCULATIONS INVOLVING GASES

CALCULATIONS INVOLVING THE IDEAL GAS EQUATION

EXPERIMENT TO FIND THE FORMULA OF A METAL OXIDE

EXPERIMENT TO DETERMINE THE FORMULA OF ANHYDRATED SALT

EXPERIMENT TO DETERMINE OF THE RELATIVE MOLECULARMASS OF A GAS BY DIRECT WEIGHING

USING THE IDEAL GAS EQUATION EXPERIMENT TODETERMINE THE RELATIVE MOLECULAR MASS OF A GAS

Questionsheet 1

Questionsheet 2

Questionsheet 3

Questionsheet 4

Questionsheet 5

Questionsheet 6

Questionsheet 7

Questionsheet 8

Questionsheet 9

Questionsheet 10

Questionsheet 11

Questionsheet 12

Questionsheet 13

Questionsheet 14

QUESTIONSHEETS AS LevelCHEMISTRY

17 marks

15 marks

14 marks

16 marks

17 marks

16 marks

16 marks

17 marks

21 marks

41 marks

12 marks

9 marks

12 marks

10 marks

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Curriculum Press • Bank House • 105 King Street • Wellington • Shropshire • TF1 1NU

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AuthorsTrevor Birt John BrockingtonDonald E Caddy Kevin FrobisherAndrew Jones Andy ShepherdAdrian Bond Stuart Barker

EditorsJohn BrockingtonStuart Barker

Do notwrite inmargin

TOPIC 2 Questionsheet 1

TOTAL /

AS Level

17

a) Explain why the formula of aluminium sulfate is Al2(SO

4)

3; not AlSO

4.

...........................................................................................................................................................................

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....................................................................................................................................................................... [3]

b) (i) Write down the formulae of the following compounds.

Copper(II) sulfate .................................................................................................................................. [1]

Sodium hydroxide ................................................................................................................................. [1]

Copper(II) hydroxide ............................................................................................................................ [1]

Sodium sulfate ....................................................................................................................................... [1]

(ii) Write a balanced molecular equation, including state symbols, for the reaction between copper(II) sulfateand sodium hydroxide in aqueous solution to give a precipitate of copper(II)hydroxide and a solution ofsodium sulfate.

....................................................................................................................................................................... [2]

c) (i) Equations I and II relate to the Haber process and contact process, respectively. Both are incorrect. Ineach case state the fault (or faults) and then write down the correct equation.Equation I N(g) + 3H(g) ¾ NH

3(g)

Fault(s) ................................................................................................................................................. [1]

Correct equation ................................................................................................................................ [1]

Equation II SO2(g) + O

2(g) ¾ SO

3(g)

Fault(s) ................................................................................................................................................. [1]

Correct equation ................................................................................................................................ [1]

(ii) The equations in c) (i) are each written with a ¾ sign instead of an arrow. What is the reason for this?

....................................................................................................................................................................... [1]

d) Iron and HCl react together according to the following basic equation: Fe + 2HC1 → FeCl2 + H

2

Depending on the reaction conditions the product may be (i) solid, anhydrous iron(II) chloride, (ii) an aqueoussolution of iron(II) chloride, or (iii) crystals of iron(II) chloride-4-water. Select suitable state symbols andmake any other necessary modifications to the basic equation to represent the formation of each of theseproducts.(i) Passing dry hydrogen chloride gas over heated iron to give anhydrous iron(II) chloride.

....................................................................................................................................................................... [1]

(ii) Dissolving iron in hydrochloric acid to give a solution of iron(II) chloride.

....................................................................................................................................................................... [1]

(iii) Dissolving iron in hydrochloric acid and then crystallising the solution to give iron(II) chloride-4-water.

....................................................................................................................................................................... [1]

FORMULAE AND MOLECULAR EQUATIONS



TOTAL /

AS Level

15

IONIC EQUATIONS

Note State symbols should be included in all the ionic equations in this Questionsheet.

a) An extract from a textbook reads as follows: “An ionic equation focuses attention on the essential chemistry,because it shows only those ions or molecules which take part in the reaction. Spectator ions do not appear.”(i) What are ‘spectator ions’?

....................................................................................................................................................................... [1]

(ii) What is wrong with the following ionic equation?

Cl2(aq) + 2K+(aq) + 2Br-(aq) → Br

2(aq) + 2K+(aq) + 2C1-(aq)

....................................................................................................................................................................... [1]

(iii) Rewrite the ionic equation in a) (ii) correctly.

....................................................................................................................................................................... [1]

b) (i) Write a balanced molecular equation (with state symbols) for calcium carbonate dissolving in hydrochloricacid to give an aqueous solution of calcium chloride, water and carbon dioxide.

....................................................................................................................................................................... [2]

(ii) Rewrite the equation in b) (i) as an ionic equation.

....................................................................................................................................................................... [2]

c) (i) Write an ionic equation for sodium chloride and silver nitrate reacting together in aqueous solution to givea precipitate of silver chloride and a solution of sodium nitrate.

....................................................................................................................................................................... [2]

(ii) What difference (if any) would there be in the ionic equation if sodium chloride were to be replaced bypotassium chloride?

....................................................................................................................................................................... [1]

d) (i) Write ionic equations for the following reactions.

I Hydrochloric acid and sodium hydroxide in aqueous solution.

....................................................................................................................................................................... [1]

II Nitric acid and potassium hydroxide in aqueous solution.

....................................................................................................................................................................... [1]

(ii) In the light of your answers to d) (i), suggest why the enthalpy change (heat given out) is approximatelythe same for both reactions.

....................................................................................................................................................................... [1]

e) The reaction between potassium manganate(VII) and iron(II) sulfate in the presence of dilute sulfuric acidis represented by the following ionic equation:

MnO4

-(aq) + 5Fe2+(aq) + 8H+(aq) →→→→→ Mn2+(aq) + 5Fe3+(aq) + 4H2O(1)

Use the appropriate spectator ions to expand the ionic equation into a molecular equation.

....................................................................................................................................................................... [2]



TOTAL /

AS Level

MOLES

a) Define the chemical term mole.

...........................................................................................................................................................................

....................................................................................................................................................................... [3]

b) Calculate the mass of each of the following:

(i) 1 mol of atomic nitrogen.

....................................................................................................................................................................... [1]

(ii) 1 mol of molecular nitrogen.

....................................................................................................................................................................... [1]

c) How many moles are there in each of the following?

(i) 0.48 g magnesium.

....................................................................................................................................................................... [1]

(ii) 100 kg calcium hydroxide.

...........................................................................................................................................................................

....................................................................................................................................................................... [1]

(iii) 2 tonnes Sulfur.

...........................................................................................................................................................................

....................................................................................................................................................................... [1]

d) Calculate the percentage by mass of tin in tin(IV) chloride, SnCl4.

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

e) 2 mol of a compound has a mass of 117.0 g. What is its relative molecular mass?

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

f) What is the total number of moles of particles (ions, molecules) present in 0.35 mol of copper(II) Sulfate-5-water, CuSO

4.5H

2O?

...........................................................................................................................................................................

...........................................................................................................................................................................

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

14



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AS Level

a) Explain the meaning of the term empirical formula.

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

b) A compound contains 29.1 % of sodium , 40.5 % of Sulfur and 30.4 % of oxygen. Calculate its empiricalformula.

...........................................................................................................................................................................

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....................................................................................................................................................................... [3]

c) 10.00 g of an oxide of lead, when reduced, produced 9.07 g of metal. Determine the empirical formula of theoxide.

...........................................................................................................................................................................

...........................................................................................................................................................................

...........................................................................................................................................................................

....................................................................................................................................................................... [4]

d) 4.00 g of sodium are burnt in excess oxygen, to produce 6.78 g of a yellow solid E. Find the empirical formulaof E.

...........................................................................................................................................................................

...........................................................................................................................................................................

...........................................................................................................................................................................

....................................................................................................................................................................... [4]

e) Compound F contains 39.74 % carbon, 7.28 % hydrogen and 52.98 % bromine. Show that the empiricalformula is C

5H

11Br.

...........................................................................................................................................................................

...........................................................................................................................................................................

...........................................................................................................................................................................

....................................................................................................................................................................... [3]

16

EMPIRICAL FORMULAE



TOTAL /

AS Level

a) (i) Explain the meaning of the term molecular formula.

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

(ii) If the empirical formula of a compound is known, what additional information is required in order todetermine its molecular formula?

....................................................................................................................................................................... [1]

(iii) Calculate the percentages by mass of phosphorus, oxygen and chlorine in the compound POCl3.

...........................................................................................................................................................................

...........................................................................................................................................................................

....................................................................................................................................................................... [3]

b) A hydrocarbon D is known to have a formula CnH

(2n+2). It is found to have a relative molecular mass of 156.

Deduce its molecular formula.

...........................................................................................................................................................................

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

c) A salt of silver comprises silver, carbon and oxygen only. It contains 7.89 % carbon and 21.06 % oxygen bymass and has a relative formula mass of 304. Determine the empirical and molecular formulae of this salt.

...........................................................................................................................................................................

...........................................................................................................................................................................

...........................................................................................................................................................................

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....................................................................................................................................................................... [4]

d) The empirical formula of a diprotic acid is CHO2 . 0.125 g of the acid was neutralised by a solution containing

0.111 g of sodium hydroxide. Calculate its molecular formula.

...........................................................................................................................................................................

...........................................................................................................................................................................

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....................................................................................................................................................................... [5]

17

MOLECULAR FORMULAE



TOTAL /

AS Level

a) Calculate the mass of combined strontium in a 125 g tube of toothpaste, which contains 10 % by mass ofstrontium chloride-6-water, SrCl

2.6H

2O.

...........................................................................................................................................................................

...........................................................................................................................................................................

...........................................................................................................................................................................

...........................................................................................................................................................................

....................................................................................................................................................................... [4]

b) What mass of tetraethyllead (TEL), Pb(C2H

5)

4, would have to be added to 1000 dm3 of petrol to give a lead

content of 0.1 g dm-3?

...........................................................................................................................................................................

...........................................................................................................................................................................

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....................................................................................................................................................................... [4]

c) How much sodium fluoride should be added to 10 tonnes of drinking water to provide a fluoride ionconcentration of 1 part per million?

...........................................................................................................................................................................

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....................................................................................................................................................................... [4]

d) A motorist can be prosecuted if the ethanol content of his/her blood is greater that ‘80 mg per 100 ml’ ofblood. How many moles of ethanol would there be in 1 dm3 of the blood of a motorist who was ‘at the limit’?

...........................................................................................................................................................................

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....................................................................................................................................................................... [4]

USES OF FORMULAE

16



TOTAL /

AS Level

YIELD CALCULATIONS

a) (i) What mass of aluminium could theoretically be obtained by the electrolysis of 1 tonne of aluminiumoxide, Al

2O

3?

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

(ii) In a particular plant, the yield obtained is 90 %. What mass of aluminium oxide would be needed toproduce 1 tonne of aluminium?

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

b) In the preparation of nitrobenzene, C6H

5NO

2, one mole of product is obtained theoretically from one mole of

benzene, C6H

6. In one particular experiment, a student obtained 43.0 g of nitrobenzene from 40.0 g of benzene.

(i) What mass of nitrobenzene should, in theory, have been produced?

...........................................................................................................................................................................

....................................................................................................................................................................... [3]

(ii) Calculate the percentage yield obtained in this experiment.

....................................................................................................................................................................... [1]

(iii) Give two reasons why the yield may have been less than that predicted.

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

c) An aqueous solution of sodium hydroxide, containing 35.0 g NaOH, was reacted with dilute Sulfuric acidcontaining 49.0 g H

2SO

4. The resulting solution was evaporated to dryness and strongly heated to produce

anhydrous sodium Sulfate.

(i) Write the overall equation for the reaction.

....................................................................................................................................................................... [1]

(ii) Calculate the number of moles of both sodium hydroxide and sulfuric acid and, by referring to yourequation, state which of these substances is deficient.

Moles of NaOH ..................................................................................................................................... [1]

Moles of H2SO

4................................................................................................................................... [1]

Deficient reactant .................................................................................................................................. [1]

(iii) Calculate the theoretical yield of anhydrous sodium sulfate.

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

16



TOTAL /

AS Level

Mg S MgS+ ⎯ →⎯..........

a) Calculate the mass of sodium hydrogencarbonate that must be heated to obtain 100 g of sodium carbonate:

...........................................................................................................................................................................

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....................................................................................................................................................................... [3]

b) Copper could be recovered from copper(II) sulfate solution by a displacement reaction with aluminium.

(i) Write the equation for this reaction.

....................................................................................................................................................................... [2]

(ii) What is the minimum mass of aluminium that would be required to recover 1 kg of copper?

...........................................................................................................................................................................

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....................................................................................................................................................................... [4]

c) During steel making, sulfur is removed from molten iron by adding magnesium:

If a 100 tonne batch of molten iron contains 0.25% sulfur, how many kilograms of magnesium are neededto remove it?

...........................................................................................................................................................................

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d) Haematite is an ore of iron, containing 30 % by mass of iron(III) oxide, Fe2O

3. In a particular blast furnace,

95 % of the iron is extracted. What mass of haematite is required to produce 10 tonnes of pure iron?

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CALCULATION OF REACTING MASSES

17

→2 3 2 3 2 2NaHCO Na CO H O CO.......... + +



TOTAL /

AS Level


a) Calculate the volume of hydrogen produced at room temperature and pressure by 3.25 g of zinc metal whenreacted with excess acid. Zn(s) + H

2SO

4(aq) → ZnSO

4 (aq) + H

2(g)

...........................................................................................................................................................................

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....................................................................................................................................................................... [3]

b) 0.160 g of calcium carbide (CaC2) was treated with excess water. Calculate the volume of ethyne (C

2H

2) gas

produced at room temperature and pressure. CaC2(s) + 2H

2O(l) → C

2H

2(g) + Ca(OH)

2(s)

...........................................................................................................................................................................

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....................................................................................................................................................................... [3]

c) 0.480 g of aluminium carbide (Al4C

3) was treated with excess water. Calculate the volume of methane (CH

4)

gas produced at room temperature and pressure. Al4C

3(s) + 12H

2O(l) → 3CH

4(g) + 4Al(OH)

3(s)

...........................................................................................................................................................................

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....................................................................................................................................................................... [3]

d) Lithium hydroxide is used to absorb carbon dioxide in space suits. Calculate the volume of carbon dioxidemeasured at room temperature and pressure absorbed by 1.00 g of lithium hydroxide.2LiOH(s) + CO

2(g)

→ Li

2CO

3(s) + H

2O(l)

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....................................................................................................................................................................... [3]

13(Continued...)

For all these questions assume that 1 mole of any gas occupies 24 dm3 at room temperature andpressure



TOTAL /

AS Level


TOPIC 2 Questionsheet 9 Continued

21

e) Calculate the volume of carbon dioxide measured at room temperature and pressure absorbed by 1.00 g ofcalcium hydroxide. Ca(OH)

2(s) + CO

2(g)

→ CaCO

3(s) + H

2O(l)

...........................................................................................................................................................................

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....................................................................................................................................................................... [3]

f) Some drain cleaners use aluminium powder and sodium hydroxide. When placed in water the aluminiumpowder reacts with the sodium hydroxide as follows to give hydrogen and heat.

2Al(s) + 2NaOH(aq) + 6H

2O(l) → 2NaAl(OH)

4(aq) + 3H

2(g)

Calculate the volume of hydrogen produced at room temperature and pressure from 1.00 g of aluminium.

...........................................................................................................................................................................

...........................................................................................................................................................................

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....................................................................................................................................................................... [3]

g) Sodium azide (NaN3) on heating decomposes to nitrogen gas as follows: 2NaN

3(s)

→ 2Na(s) + 3N

2(g)

Calculate the volume of gases produced from 100 g of sodium azide at room temperature and pressure. Thisis the basis of an air bag system for cars, in which sodium azide is mixed with an oxidiser of iron oxide andsilicon dioxide.

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TOTAL /

AS Level

0.688 g of a hydrocarbon occupied 472cm3 at 98 kPa and 67 0C.

a) Calculate the(i) mol of hydrocarbon in 0.688 g

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(ii) relative molecular mass of the hydrocarbon.

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....................................................................................................................................................................... [2]

b) (i) Suggest the molecular formula and name of the hydrocarbon

....................................................................................................................................................................... [2](ii) Give an equation for the complete combustion of the hydrocarbon

....................................................................................................................................................................... [2](iii) Calculate the volume of oxygen needed to completely react with 0.21 g of the hydrocarbon under the

same conditions.

...........................................................................................................................................................................

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....................................................................................................................................................................... [3]


13


NOTE In this Questionsheet, assume that the ideal gas constant R = 8.31 J K-1 mol-1

QUESTION 1



TOTAL /

AS Level TOPIC 2 Questionsheet 10 Continued

13

1500cm3 dry chlorine reacted with 1.40g iron at 300C and 99.5 kPa. Following the complete reaction of the iron,552cm3 chlorine remained.

a) Calculate:(i) the volume of chlorine reacted with the iron

....................................................................................................................................................................... [1]

(ii) the volume of one mole of gas under these conditions

...........................................................................................................................................................................

...........................................................................................................................................................................

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....................................................................................................................................................................... [3]

(iii) the mol chlorine reacted with the iron

...........................................................................................................................................................................

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....................................................................................................................................................................... [2]

(iv) the mol iron reacted

...........................................................................................................................................................................

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....................................................................................................................................................................... [2]

b) Show how many mol of chlorine would react with one mole of iron in this reaction

...........................................................................................................................................................................

...........................................................................................................................................................................

....................................................................................................................................................................... [2]c) From your answer to b) suggest an equation for the reaction

....................................................................................................................................................................... [2]d) Suggest why the chlorine was dry

....................................................................................................................................................................... [2]



QUESTION 2



TOTAL /

AS Level TOPIC 2 Questionsheet 10 Continued

1.08 g of a Group 2 metal completely reacted with an excess of hydrochloric acid and 1120 cm3 hydrogen formedat 96.5 kPa and 16 oC

a) Give an ionic equation for the reaction using M as the symbol of the metal.

....................................................................................................................................................................... [2]

b) Calculate the volume of one mole of gas under these conditions

...........................................................................................................................................................................

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....................................................................................................................................................................... [3]

c) Calculate the mol of hydrogen formed

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d) Calculate the relative atomic mass of the metal and suggest the identity

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e) If the experiment had been carried out at 24 oC and 100 kPa using 0.50 g calcium and 231 cm3 hydrogenformed, calculate the percentage of the metal that was unreacted

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QUESTION 3


15



TOTAL /

AS Level TOPIC 2 Questionsheet 11

EXPERIMENT TO FIND THE FORMULA OF A METAL OXIDE

A porcelain boat was weighed empty and then filled with a metal oxide and reweighed. The apparatus was setup as in the diagram and the oxide heated in a stream of hydrogen until there was no further loss in mass of theboat and its contents. This removes the oxygen, leaving the metal.

Complete the table below and then calculate the formula of the oxide

a) Results for an oxide of copper

Mass of boat and metal oxide before heating = 11.25 g

Mass of boat empty = 9.90 g

Mass of metal oxide = [1]

Mass of boat and metal oxide after heating = 11.10 g


Mass of metal = [1]

Calculation (use atomic masses: Cu = 64, O=16)

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....................................................................................................................................................................... [4]

Complete the table below and then calculate the formula of the oxide

b) Results for an oxide of iron

Mass of boat and metal oxide before heating = 9.29 g


Mass of metal oxide = [1]

Mass of boat and metal oxide after heating = 9.21 g


Mass of metal = [1]

Calculation (use atomic masses: Fe = 56, O=16)

Metal oxide

Porcelain boatHeat

Hydrogen Gases out

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12



TOTAL /


EXPERIMENT TO DETERMINE THE FORMULA OF AN HYDRATED SALT

In an experiment to determine the formula of hydrated salts, a sample of hydrated barium chloride was heated ina previously weighed crucible until a constant mass was reached. The results are given below.

Results

Mass of crucible + lid + barium chloride crystals = 17.44 g

Mass of crucible + lid empty = 15.00 g

Mass of hydrated barium chloride crystals = [1]

Mass of crucible + lid + barium chloride after heating = 17.08 g

Mass of crucible + lid empty = 15.00 g

Mass of anhydrous barium chloride = [1]

Mass of hydrated barium chloride crystals = [1]

Mass of anhydrous barium chloride = [1]

Mass of water of crystallisation = [1]

Complete the table above and then determine the value of n in the formula BaCl2·nH

2O

Show all the steps in your calculation with full explanation.

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9



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EXPERIMENT TO DETERMINE OF THE RELATIVE MOLECULARMASS OF A GAS BY DIRECT WEIGHING

Woodenblock

Cap

In an experiment the following method was followed.1. Weigh the 20 cm3 syringe empty (with vacuum), using a wooden block to hold back the plunger.2. Flush out the syringe with the gas twice, before filling to the mark with the gas and using the wooden block as

the guide.3. Weigh the syringe + gas + wooden block.4. Repeat steps 2 and 3 with other gases.5. Repeat step 1 and average the two results.6. Put the results in the table below.

Gas Mass of gas Average mass Mass of gas Mass of 24 dm3 Calculated Mr from A

r

+ syringe of syringe empty of the gas of constituent atoms

O2

29.618 g 29.592 g

CO2

29.635 g 29.592 g

N2O 29.628 g 29.592 g

SO2

29.644 g 29.592 g

C4H

1029.639 g 29.592 g

CH4

29.606 g 29.592 g

C2H

229.614 g 29.592 g

a) Complete the above table. [4]

b) Plot a graph of Mass of 24 dm3 of the gas against Mr

[2]

c) Is there a correlation between the mass of 24 dm3 of gas and the Mr value?

....................................................................................................................................................................... [1]

d) Comment on the reliability of the results.

...........................................................................................................................................................................

....................................................................................................................................................................... [2]

e) What are the main errors in the experiment?

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12



TOTAL /


USING THE IDEAL GAS EQUATION EXPERIMENT TODETERMINE THE RELATIVE MOLECULAR MASS OF A GAS

In an experiment to determine the relative molecular mass of trichloromethane, the following method carried out.Trichloromethane is a volatile liquid that boils at 62°C.1. Set up the apparatus as shown in the diagram, but without the hypodermic syringe. Put 5 cm3 of air into the

syringe and wait until the readings are steady.2. Rinse the hypodermic syringe with the test liquid, then fill the hypodermic syringe with the test liquid. Make

sure that all the air is expelled from the hypodermic syringe, and then seal the end with silicone rubber.3. Weigh the hypodermic syringe, then inject about 0.2 cm3 of liquid into the graduated gas syringe and immediately

reweigh the syringe.4. Record the value of the reading on the scale of the graduated syringe when it is steady. Also note the

temperature and the atmospheric pressure.

ResultsMass of hypodermic syringe and liquid before injection = 11.28 gMass of hypodermic syringe and liquid after injection = 11.12 gTemperature of vapour = 100°CAtmospheric pressure = 105 kPaVolume of syringe at start with air only = 5 cm3

Volume of syringe with air and vapour = 39 cm3

(The gas constant R = 8.31 JK-1mol-1)

a) Calculate the relative molecular mass of trichloromethane (CHCl3) using the results of the experiment.

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b) Calculate a value from relative atomic masses. ............................................................................................. [1]

c) What are the likely significant errors in the experiment?

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....................................................................................................................................................................... [4]

Rubber capHypodermic syringe

Thermometer

Steam

Steam

10

Questionsheet FORMULAE AND MOLECULAR EQUATIONS … · · 2011-09-21FORMULAE AND MOLECULAR...

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Transcript of Questionsheet FORMULAE AND MOLECULAR EQUATIONS … · · 2011-09-21FORMULAE AND MOLECULAR...