Syllabus Edition

First teaching 2020

Last exams 2024

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Atoms, Molecules & Stoichiometry (CIE AS Chemistry)

Exam Questions

3 hours45 questions
1a4 marks

Explain what is meant by the terms

Relative atomic mass

[2] 

Relative isotopic mass

 [2]

1b3 marks
i)
State the symbols used for relative atomic mass and relative molecular mass.
[1]
 
ii)
Describe how to calculate the relative molecular mass of a compound.
[1]
 
iii)
State the difference between relative molecular mass and relative formula mass.
[1]
1c1 mark

Ionic compounds such as sodium chloride are arranged in a giant three-dimensional lattice structure, with a regular and repeating pattern of positive and negative ions.

State the formula unit of sodium chloride.

1d
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4 marks

Complete Table 1.1

Table 1.1
 
Chemical Formula Relative molecular / formula mass
Magnesium oxide MgO  
Sulfuric acid H2SO4  
Ammonium phosphate (NH4)3PO4  
Copper(II) sulfate pentahydrate CuSO4•5H2O  
  

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2a1 mark
Give the number of particles in one mole of a chemical.
 

2b3 marks

i)       Give the number and type of atoms present in a molecule of water. 

[2]
 
ii)
Calculate the total number of particles and atoms present in one mole of water. 

[1]
2c4 marks

i)

Give the number and type of ions present in one mole of sodium carbonate, Na2CO3.
[2]
 
ii)
Calculate the number of metal ions present in two moles of sodium carbonate.

[2]

2d
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7 marks

i)       State the conditions when one mole of a gas occupies a volume of 24.0 dm3.

[2]
ii)
Complete Table 2.1.
Table 2.1
 
Gas Number of moles Volume of gas (dm3) Number of molecules present
Nitrogen 2.0 48.0  
Sulfur dioxide   1.8  
Carbon monoxide     9.03 x 1023
 
[5]

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3a3 marks

Complete Table 3.1.

Table 3.1
 
Ion Formula
Nitrate NO3
  CO32–
Sulfate  
  OH
  NH4+
Zinc(II)  
  Ag+
  HCO3
Phosphate  

 

3b3 marks

Complete Table 3.2.

Table 3.2
 
Ionic compound Formula
Sodium chloride NaCl
Potassium oxide  
  Al2(CO3)3
Copper(II) nitrate  

3c3 marks

Aqueous silver nitrate should not be acidified with hydrochloric acid as it forms a white precipitate of silver chloride, AgCl, and nitric acid.

i)
Write the chemical equation for the reaction of silver nitrate with hydrochloric acid. Your answer should include state symbols.
[2]
ii)
Silver ions from the silver nitrate and hydrogen ions from the hydrochloric acid are responsible for the formation of silver chloride.
Ag+ + Cl → AgCl

Suggest why the nitrate ions and hydrogens do not appear in this ionic equation.

[1]

3d3 marks

Aqueous barium chloride should not be acidified with sulfuric acid as it forms a white precipitate of barium sulfate and hydrochloric acid.

i)
Write the chemical equation for the reaction of barium chloride with sulfuric acid. Your answer should include state symbols.
[2]
ii)
Write the ionic equation for the formation of barium sulfate. 
[1]

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4a4 marks

Copper(II) chloride can be produced by the reaction of hydrochloric acid with different copper(II) compounds.

i)
Suggest why the reaction of copper with hydrochloric acid is not used to form copper(II) chloride.
[1]

ii)
Complete Table 4.1 by writing the chemical equation for the formation of copper(II) chloride using hydrochloric acid and the copper(II) compounds.
Table 4.1
 
Copper(II) compound Chemical equation
Copper(II) oxide,
CuO
....................................................................................................
Copper(II) hydroxide,
Cu(OH)2
....................................................................................................
Copper(II) carbonate,
CuCO3
....................................................................................................
 
[3]
4b
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3 marks

11.93 g of copper(II) oxide is reacted with 50 cm3 of 2.0 mol dm-3 hydrochloric acid.

i)
Calculate the number of moles of copper(II) oxide and hydrochloric acid.
[2]
ii)
Explain which chemical is the limiting reagent.
[1]
4c
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3 marks

22.43 g of copper(II) hydroxide reacts with hydrochloric acid to form 23.63 g of copper(II) chloride.

Complete Table 4.2 to calculate the percentage yield of this reaction.

Table 4.2
 
Relative formula mass of copper(II) hydroxide ........................................
Moles of copper(II) hydroxide ........................................
Relative formula mass of copper(II) chloride ........................................
Theoretical yield of copper(II) chloride ........................................
Percentage yield of copper(II) chloride ........................................
 
4d
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2 marks

22.23 g of copper(II) carbonate reacts with hydrochloric acid at room temperature and pressure. One of the products is a gas.

You should use your answer to part (a)(ii) to help answer this question.

Calculate the volume, in cm3, of the gas produced.

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5a2 marks
Explain the meaning of the terms empirical formula and molecular formula.
 

5b4 marks

Three organic compounds are shown in Fig. 5.1.

1-2-5b-e-ch2o-empirical-formula-chemicals
Fig. 5.1
 
i)
Give the molecular formula of each compound.
 
Acetic acid ..............................
 
Glucose ..............................
 
Lactic acid ..............................
[3]
 
ii)
Give the empirical formula of all three compounds.
 
[1]
5c
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5 marks

An unknown hydrocarbon contains 85.7% carbon. The relative molecular mass of the unknown hydrocarbon is 56.0. 

i)
Calculate the empirical formula of the unknown hydrocarbon. Show your working.
[3]
 
ii)
Determine the molecular formula of the unknown hydrocarbon. Show your working.
[2]
5d1 mark

Explain the difference between an anydrous salt and a hydrated salt.

5e
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3 marks

Gypsum is a salt that can contain water of crystallisation. In its anhydrous form, the chemical formula of gypsum is CaSO4. 1.80 g of water is added to 6.81 g of gypsum to form the hydrated salt, CaSO4•xH2O. 

Calculate the value of x in CaSO4•xH2O. Show your working.

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1a
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4 marks

This question is about the formation and reaction of silane, SiH4.

0.5 g of quartz sand and 0.5 g of powdered silica are mixed with 2.4 g of magnesium powder. The resulting mixture is placed in a pot half filled with sand. A magnesium ribbon fuse is added and the mixture is ignited to form magnesium oxide and solid magnesium silicide, Mg2Si.

 
i)
Write an equation for this reaction.
Include state symbols. 
[2] 
ii)
Determine the limiting reagent in this reaction.
Show your working.
[2]
1b3 marks

The magnesium silicide is reacted with hydrochloric acid according to the following equation:

Mg2Si (s) + 4HCl (aq) → 2MgCl2 (aq) + SiH4 (g)
 

The gaseous silane formed spontaneously ignites in air. 

State the type of reaction and write the chemical equation for this reaction.

Include state symbols.

1c
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3 marks

An alternative method to produce silane involves the reaction of silicon with hydrochloric acid to form trichlorosilane, HSiCl3.

Si (s) + 3HCl (aq) → HSiCl3 (l) + H2 (g) 
 

Calculate the maximum mass of trichlorosilane produced from the reaction of 35.125 g of silicon.

1d
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2 marks

Another method of silane production involves the reduction of silicon dioxide by aluminium and hydrogen gas.

3SiO2 (s) + 6H2 (g) + 4Al (s) → 3SiH4 (g) + 2Al2O3 (s)

What is the volume, in dm3, of hydrogen gas required to produce 10 dm3 of silane gas? Explain your answer.

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2a
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2 marks

Cobalt(II) sulfate is used in storage batteries, electroplating baths and as an additive to soils and animal feeds.

A sample of hydrated cobalt sulfate, CoSO4•xH2O, has a relative formula mass of 173.0.

Calculate a value for 'x'.

2b
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4 marks

A student completed an experiment to determine the value of ‘x’ in a hydrated salt.

They heated a solid sample of the salt, CoSO4.xH2O, in a crucible for 60 seconds and recorded the following set of results.

Table 2.1
 

Mass of empty crucible (g)

29.22

Mass of crucible and solid before heating (g)

32.67

Mass of crucible and solid after heating (g)

32.02

 

Use the data obtained by the student in Table 2.1 to calculate a value for ‘x’.

2c3 marks

The actual value for x in CoSO4.xH2O is 6.

i)
Suggest one reason for the difference between your calculated value in part (b) and the actual value.
[1]
 
ii)
Explain how you could improve the experiment the student did, using the same equipment, to achieve a value closer to the correct value for x.
[2]
2d1 mark

Cobalt(II) sulfate undergoes a displacement reaction with magnesium because magnesium is a more reactive metal than cobalt.

Write an ionic equation for this reaction. State symbols are not required.

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3a2 marks

Chevreul's salt or copper(I, II) sulfite dihydrate, Cu3(SO3)2•2H2O, is an unusual hydrated salt as it contains copper in both of its common oxidation states.

The first step in the formation of Chevreul's salt is the reaction of aqueous copper sulfate with a solution of potassium metabisulfite, K2S2O5.

Balance the equation for the reaction to form the anhydrous Chevreul's salt.

__CuSO4 + __K2S2O5 → Cu3(SO3)2 + 4K2SO4 + __SO2 
3b
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3 marks

The chemical formula of Chevreul's salt is sometimes written as Cu2SO3•CuSO3•2H2O to show that it contains copper(I) sulfite and copper(II) sulfite.

Calculate the percentage by mass of copper(I) ions in copper(I) sulfite

Show your working.

3c2 marks

Chevreul's salt can react with ammonia solution to form a deep blue solution of the tetraamminecopper(II) complex, [Cu(NH3)4]2+ (aq). It can also react with hydrochloric acid to form a white solid of copper(I) chloride, water and sulfur dioxide.

Write an ionic equation for the formation of copper(I) chloride from Chevreul's salt. State symbols are not required.

3d
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3 marks

When Chevreul's salt is heated in an inert atmosphere, it is stable to around 200 oC. Above this temperature, a variety of compounds can be produced although the final product of sustained heating at high temperatures is copper(II) oxide.

During the heating process, a sample of the mixture is taken. After separation, the most common compound was analysed and found to contain 39.8% copper, 20.1% sulfur and the rest oxygen.

Calculate the empirical formula of the most common compound. Show your working.

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4a1 mark

The reaction of nitrous oxide gas, N2O (g), with carbon disulfide vapour, CS2 (g), is an example of a chemical luminescence reaction producing a flame with a bright blue light.

2N2O (g) + CS2 (g) → 2S (s) + 2N2 (g) + CO2 (g)

The brightness of the light produced was a reason why this reaction was once used in low-light photography.

When nitrous oxide and carbon disulfide are placed together there is no immediate reaction.

Explain how a flame can help initiate the reaction.

4b
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3 marks

A measuring cylinder containing 100 cm3 of nitrous oxide is used in a demonstration of the reaction between nitrous oxide and carbon disulfide.

i)
Calculate the number of moles of nitrous oxide in the measuring cylinder.
[1]
ii)
Calculate the minimum number of carbon disulfide molecules required to react with the nitrous oxide at room temperature.
[2]
4c3 marks

In a second demonstration, 10.8 dm3 of nitrous oxide is reacted with 5.6 dm3 carbon disulfide vapour.

i)
Explain which reagent is in excess. Show your working.
[2]
ii)
Calculate the maximum mass of sulfur that will be produced from this demonstration. 
[1]
4d
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3 marks

The demonstration is performed a third time to determine the percentage yield of sulfur of the reaction.

For this demonstration, 16.50 dm3 of nitrous oxide is reacted with an excess of carbon disulfide at room temperature and pressure. This produces 14.32 g of sulfur.

Calculate the percentage yield for this demonstration. 

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5a1 mark

Iron compounds have a variety of uses. Many iron compounds are found in fertilisers and as food additives and supplements.

Iron sulfate is used to treat and prevent iron deficiency anaemia.

Suggest two possible formulae for iron sulfate.

5b
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4 marks

Iron reacts with chlorine to form iron(III) chloride.

i)
Write an equation for this reaction of iron with chlorine. 
State symbols are not required.
[1]
 
ii)
Calculate the mass of iron(III) chloride produced from 5.02 g of iron, assuming a 78% yield.
[3]
5c
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3 marks

Iron(III) oxide is reduced to Fe with carbon at a temperature of 1200 °C in the blast furnace. 

2Fe2O3 + 3C → 4Fe + 3CO2 

An example reaction is set up by heating 9.86 g of iron(III) oxide with an excess of carbon powder. After the reaction is complete, it is left to cool to room temperature. 

Calculate the volume of carbon dioxide, at room temperature, that is produced by this reduction of 9.86 g of iron(III) oxide.

5d
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3 marks

A student reacts 4.95 g of iron(III) oxide with 1.12 g of carbon.

The resulting products are 3.46 g of iron and 2.60 g of carbon monoxide.

Determine the balanced equation for the reaction. Show your working.

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1a
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4 marks

Magnesium carbonate is a common antacid that is used to react with and neutralise excess stomach acid, HCl. 

MgCO3 (s) + 2HCl (aq) rightwards arrow MgCl2 (aq) + CO2 (g) + H2O (l)

The total mass of the reactants is 9.91 g.

Calculate the volume of carbon dioxide that is produced at room temperature and pressure.


Volume of CO2 = .................. dm3
1b
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3 marks

Another magnesium salt, magnesium sulfate, can exist in hydrated or anhydrous forms.

6.31 g of a sample of magnesium sulphate, MgSO4.xH2O, was strongly heated until a mass of 3.61 g of solid remained with no further change in mass recorded.

Calculate the number of moles of water of crystallisation, x, in the magnesium sulphate sample.

moles of water = ..................... mol

1c
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3 marks

Another sample of hydrated magnesium sulphate, MgSO4.xH2O, is found to contain 51.1% water by mass.

Calculate the number of moles of water of crystallisation, x, in this sample.


moles of water = ..................... mol

1d2 marks

Describe the effect on the value of x obtained if the salt was not heated strongly to a constant mass.

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2a
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4 marks

Fireworks contain elements to give them their colour, as well as oxygen-containing compounds to facilitate speedy combustion.

In a firework, solid potassium nitrate, KNO3, decomposes to form solid potassium nitrite, KNO2, and oxygen, O2.

Calculate the mass, in g, of potassium nitrate, KNO3, required to make 1.5 g of oxygen. Give your answer to 2 significant figures.

mass of KNO3 = .................. g

2b
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1 mark

Calculate the volume, in dm3, of gas that is produced when solid potassium nitrate, KNO3, decomposes at room temperature and pressure. Give your answer to 2 significant figures. 

volume of gas = ................ dm3

2c
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4 marks

Potassium can form a superoxide, KO2 (s), which will react with carbon dioxide, CO2 (g), to produce potassium carbonate, K2CO3 (s) and oxygen, O2 (g).

Calculate the volume, in dm3, of carbon dioxide which will react with 5.00 g of the superoxide. Give your answer to 3 significant figures. 


volume of CO2 = .................. dm3

2d3 marks

2.61 g of potassium carbonate, K2CO3, was produced during the reaction in part (c).

Calculate the percentage yield of potassium carbonate. Give your answer to 2 decimal places. 


% yield = ................... %
 

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3a
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1 mark

The coca-cola company states that a 12 oz can of coke contains 34 mg of caffeine, Mr = 194.19 g mol-1.

Calculate the number of moles of caffeine in a can of coke.


moles of caffeine = .................... mol

3b
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3 marks

Caffeine is made up of 49.48%  carbon, 5.20% hydrogen, 28.85% nitrogen and the rest is oxygen.

Calculate the empirical formula of caffeine.

3c
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1 mark

Calculate the molecular formula of caffeine using your answer from part (b).

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4a
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3 marks

This question is about the reactions of ionic compounds.

Sodium carbonate is manufactured in a two-stage process as shown.

 
NaCl + NH3 + CO2 +  H2O → NaHCO3 + NH4Cl
 
2NaHCO3 → Na2CO3 + H2O + CO2
 

Calculate the maximum mass of sodium carbonate that can be obtained from 0.75 kg of sodium chloride.



mass of Na2CO3 = ..................... (g)
4b
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4 marks

Norgessaltpeter, Ca(NO3)2, was the first nitrogen fertiliser to be manufactured in Norway. It is produced by the reaction of calcium carbonate with nitric acid.

In an experiment, an excess of powdered calcium carbonate was added to 37.4 cm3 of 0.531 mol dm–3 nitric acid.

Calculate the minimum mass of CaCO3 that should be added to react with all of the nitric acid. Give your answer to an appropriate number of significant figures.


mass of CaCO3 = ....................

4c
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4 marks

A 0.0830 mol sample of pure zinc oxide was added to 75.0 cm3 of 0.90 mol dm−3 hydrochloric acid.

Assuming the reaction has a percentage yield of 60.6%, calculate the mass of anhydrous zinc chloride that could be obtained from the products of this reaction.


mass of zinc chloride = ................. g

4d
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5 marks

Magnesium nitride, Mg3N2, reacts with water to form magnesium hydroxide and ammonia.

Calculate the number of molecules of ammonia gas produced by the reaction of 12.62 g of magnesium nitride.


number of molecules = ............................

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5a5 marks

Apatite is a general term used for a family of various calcium phosphate compounds commonly found in rocks and minerals, bones and teeth.

i)
State the formula of calcium phosphate.
[1]
 
ii)
Hydroxylapatite, Ca5(PO4)3OH, is one member of the apatite family and is a major component of bone.
Give the oxidation number of calcium in hydroxyapatite. Explain your answer.
[3]
 
iii)
Another member of the apatite family is chlorapatite.
Suggest the formula of chlorapatite.
[1]
5b2 marks

Fluorapatite, Ca5(PO4)3F, reacts with sulfuric acid to form hydrogen phosphate, calcium sulfate and hydrogen fluoride.

Write the balanced chemical equation for this reaction.

5c
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5 marks

Fluorapatite, Ca5(PO4)3F, can also react with sulfuric acid to form calcium dihydrogenphosphate, Ca(H2PO4)2, calcium sulfate and hydrogen fluoride.

2Ca5(PO4)3F + 7H2SO4 → 3Ca(H2PO4)2 + 7CaSO4 + 2HF

Calculate the mass of calcium dihydrogenphosphate formed when 50.2 g of Ca5(PO4)3F reacts with 87.9 g H2SO4.


mass of Ca(H2PO4)= ............................ g
 

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