Formulae & Relative Masses (Cambridge (CIE) IGCSE Chemistry)

Exam Questions

2 hours32 questions
1a1 mark

When cobalt(II) oxide, CoO, is heated in air an oxide with the formula Co3O4 is formed.

Balance the equation for this reaction.

…....... CoO + O2 → 2Co3O4

1b
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2 marks

Sulfuric acid is a compound.

The formula of sulfuric acid is H2SO4.

Complete Table 1.1 to calculate the relative molecular mass of sulfuric acid.

Table 1.1

atom

number of atoms

relative atomic mass

 

hydrogen

2

1

2 × 1 = 2

sulfur

 

 

 

oxygen

 

 

 

relative molecular mass = .............................

1c1 mark

Hydrogen is a fuel which can be obtained from water by electrolysis.

Refinery gas and petrol are fuels obtained by the fractional distillation of petroleum.

Complete the equation for the burning of hydrogen.

.......... H2 (g) + O2 (g) → ..........H2O (l) 

1d2 marks

State the meaning of (g) and (l).

(g):

(l):

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2a2 marks

In a blast furnace used for the extraction of iron, carbon reacts with oxygen from the air to form carbon monoxide.

Complete the chemical equation for this reaction.

....C + ..... →  2CO

2b1 mark

The structure of a compound of iron is shown.

q2f-0620_s19_qp_31

Deduce the molecular formula of this compound to show the number of iron, carbon and oxygen atoms.

2c2 marks

Iodine reacts with aqueous sodium thiosulfate, Na2S2O3.

Balance the chemical equation for this reaction.

.....Na2S2O3 + I2 → Na2S4O6 + .....NaI

2d
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2 marks

Complete the table to calculate the relative formula mass of anhydrous copper(II) sulfate, CuSO4.

Use your Periodic Table to help you.

type of atom

number of atoms

relative atomic mass

 

copper

1

64

1 × 64 = 64

sulfur

 

 

 

oxygen

 

 

 

relative formula mass =_______________  

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3a1 mark

This question is about iron and compounds of iron.

Iron can be converted into steel in a basic oxygen converter.

Oxygen is blown into the impure molten iron to remove some of the impurities.

Oxygen reacts with the carbon in the impure iron to form carbon dioxide.

Write a chemical equation for this reaction.

3b2 marks

This question is about bromine and compounds of bromine.

Bromine reacts with hydrogen sulfide, H2S.

Complete the chemical equation for this reaction.

....... + H2S →  .....HBr + S

3c
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2 marks

This question is about cobalt and compounds of cobalt.

Complete the table to calculate the relative formula mass of anhydrous cobalt(II) sulfate, CoSO4. Use your Periodic Table to help you.

type of atom

number of atoms

relative atomic mass

 

cobalt

 

 

 

sulfur

1

32

1 × 32 = 32

oxygen

 

 

 

relative formula mass =   ______________ 

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4a1 mark

Extended Only

The names and formulae for some compounds are shown.

aluminium nitrate, Al(NO3)3 magnesium nitrate, Mg(NO3)2 sodium nitrate, NaNO3

Deduce the formula for calcium nitrate.

4b2 marks

Sodium reacts with molten sodium hydroxide.

Complete the chemical equation for this reaction.

2Na + ......NaOH → ......Na2O + H2

4c1 mark

The structure of a carboxylic acid is shown.

q4bii_0620-s20-qp-32_cie-igcse-chemistry

Deduce the formula of this carboxylic acid to show the number of atoms of carbon, hydrogen and oxygen.

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5a2 marks

This question is about reactions involving calcium compounds.

Heating calcium carbonate, CaCO3, produces calcium oxide, CaO, and one other gaseous product.

Write the word equation for this reaction.

5b1 mark

Extended Only

Write a balanced chemical equation for heating calcium carbonate, CaCO3, to form calcium oxide, CaO, and one other gaseous product.

5c
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1 mark

Calcium hydroxide, Ca(OH)2 can be made by the reaction of calcium oxide, CaO, with water.

CaO + H2O → Ca(OH)2 

112 g of calcium oxide reacts with 36 g of water.

 Calculate the mass of calcium hydroxide that is produced.

____________________ g

5d
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2 marks

Calcium hydroxide can be used to test for the presence of carbon dioxide.

If carbon dioxide is present, the calcium hydroxide will form a milky white precipitate of calcium carbonate.

The formula of calcium carbonate is CaCO3

Calculate the relative formula mass (Mr) of calcium carbonate.

Relative atomic masses (Ar): C = 12   O = 16   Ca = 40

5e
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2 marks

Calculate the percentage of oxygen in calcium carbonate, CaCO3, using the following equation.

Percentage by mass = fraction numerator A subscript straight r cross times space number space of space atoms over denominator M subscript straight r space of space the space compound end fraction space cross times space 100

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1a3 marks

Extended Only

Use your copy of the Periodic Table to help you answer these questions.

Predict the formula of each of the following compounds.

i) aluminium fluoride

[1]

ii) arsenic oxide

[1]

iii) silicon bromide

[1]

1b3 marks

Extended Only

Deduce the formula of each of the following ions.

i) phosphide

[1]

ii) barium

[1]

iii) francium

[1]

1c3 marks

Extended Only

Draw a diagram showing the arrangement of the valency electrons in one molecule of the covalent compound carbon dioxide.

Use o to represent an electron from a carbon atom. Use x to represent an electron from an oxygen atom.

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2a4 marks

The law of constant composition states that all pure samples of a compound contain the same elements in the same proportion by weight. A typical experiment to test this law is to prepare the same compound by different methods and then show that the samples have the same composition. Methods of making copper(II) oxide include:

  • heating copper carbonate,

  • heating copper hydroxide,

  • heating copper nitrate,

  • heating copper foil in air.

Complete the following equations.

i) CuCO3 → ............. + .............

[1]

ii) Cu(OH)2 → ............. + .............

[1]

iii) 2Cu(NO3)2 → ............. + 4NO2 + .............

[2]

2b5 marks

Copper oxide can be reduced to copper by heating in hydrogen.

i) What colour change would you observe during the reduction?

[1]

ii) Explain why the copper must be allowed to cool in hydrogen before it is exposed to air.

[2]

iii) Name another gas which can reduce copper(II) oxide to copper.

[1]

iv) Name a solid which can reduce copper(II) oxide to copper.

[1]

2c
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4 marks

The table below shows the results obtained by reducing the copper(II) oxide produced by different methods to copper.

i) Complete the table.

source of copper(II) oxide

mass of copper(II) oxide / g

mass of copper / g

percentage copper / %

CuCO3

2.37

1.89

79.7

Cu(OH)2

2.51

1.99

 

Cu(NO3)2

2.11

1.68

 

Cu and O2

2.29

1.94

 

[2]

ii) One of the samples of copper(II) oxide is impure. Identify this sample and suggest an explanation why the percentage of copper in this sample is bigger than in the other three samples.

[2]

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3a1 mark

Extended Only

Iron pyrite, FeS2, is known as Fool’s Gold because it is a shiny yellow solid which is similar in appearance to gold. Iron pyrite is an ionic compound. Gold is a metallic element.

Iron pyrite, FeS2, contains positive and negative ions. The positive ion is Fe2+. Deduce the formula of the negative ion.

3b2 marks

A student is provided with a sample of iron pyrite and a sample of gold.

Suggest how the student could distinguish between the two substances.

3c2 marks

Sulfur dioxide is produced on a large scale by heating iron pyrite strongly in air. The iron pyrite reacts with oxygen in the air producing iron(III) oxide, Fe2O3, and sulfur dioxide.

Construct a chemical equation for the reaction between iron pyrite and oxygen.

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4a2 marks

Extended Only

Element X can undergo the following physical changes.

Element X is a Group III metal. It burns in air to form an oxide X2O3.

Write a symbol equation for this reaction.

4b2 marks

Extended Only

Aqueous silver nitrate is added to aqueous magnesium chloride. A white precipitate forms. Write an ionic equation for this reaction. Include state symbols.

4c2 marks

Complete the chemical equation for the reaction of chlorine with phosphorus.

......Cl2 + 2P → ......PCl5

4d2 marks

Aqueous potassium iodide reacts with aqueous copper(II) sulfate to produce iodine.

Balance the chemical equation for this reaction.

KI + CuSO4 → CuI + I2 + K2SO4

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5a1 mark

This question is about elements X, Y and Z. An atom of element X is represented as straight X presubscript 16 presuperscript 34

What is the electronic structure of the ion X2–?

5b1 mark

This question is about elements X, Y and Z.

Identify the atom against which the relative masses of all other atoms are compared.

5c2 marks

Extended Only

Magnesium oxide, MgO, is formed when magnesium burns in oxygen.

Write the chemical equation for the reaction that occurs when magnesium burns in oxygen.

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6a1 mark

Separate: Chemistry and Extended Only

The structures of five organic compounds, A, B, C, D and E, are shown. Answer the questions that follow. Each letter may be used once, more than once or not at all.

q1a-0620-s20-qp-43

Give the letter of the compound that has the empirical formula CH2.

6b1 mark

An endothermic reaction occurs when calcium nitrate is heated.

Balance the equation for this reaction.

.....Ca(NO3)2 → .....CaO + .....NO2 + .....O2

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7a2 marks

This question is about iron and iron compounds.

Iron reacts with chlorine to form iron(III) chloride, Fe2Cl6.

Balance the chemical equation for this reaction.

.....Fe + .....Cl2 → Fe2Cl6

7b1 mark

The structure of an ion is shown.

q2d-0620_s19_qp_33

Deduce the molecular formula of this ion to show the number of iron, carbon and nitrogen atoms.

7c2 marks

This question is about chlorine and compounds of chlorine.

Chlorine reacts with warm turpentine, C10H16.

Balance the chemical equation for this reaction.

C10H16 + 8Cl2   → .....C + .....HCl

7d
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1 mark

The equation shows the effect of heat on anhydrous zinc sulfate.  

 ZnSO4 rightwards arrow with heat on top ZnO + SO3

When 12.60 g of anhydrous zinc sulfate is heated, the mass of zinc oxide formed is 6.34 g.

Calculate the mass of zinc oxide formed when 63.0 g of anhydrous zinc sulfate is heated.

mass of zinc oxide = _______________

7e
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2 marks

Complete the table to calculate the relative formula mass of anhydrous zinc sulfate, ZnSO4. Use your Periodic Table to help you.

type of atom

number of atoms

relative atomic mass

 

zinc

1

65

1 × 65 = 65

sulfur

 

 

 

oxygen

 

 

 

relative formula mass = _________________

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1a1 mark

Extended Only

Fluorine forms both ionic and covalent compounds. Magnesium reacts with fluorine to form the ionic compound magnesium fluoride. The electronic structures of an atom of magnesium and an atom of fluorine are shown.

q2a-0620-s20-qp-42

What is the formula of magnesium fluoride?

1b2 marks

When copper is reacted with hot concentrated sulfuric acid, sulfur dioxide gas is formed.

Balance the chemical equation for this reaction.

Cu + .......H2SO4 → CuSO4 + SO2 + .......H2O

1c2 marks

Extended Only

When sulfuric acid reacts with ammonia the salt produced is ammonium sulfate.

Write the chemical equation for this reaction.   

1d2 marks

Extended Only

Barium sulfate is an insoluble salt. Barium sulfate can be made from aqueous ammonium sulfate using a precipitation reaction.

Write an ionic equation for this precipitation reaction. Include state symbols.

1e2 marks

Extended Only

Oxygen is produced by the decomposition of hydrogen peroxide. Manganese(IV) oxide is the catalyst for this reaction.

Oxygen can also be produced by the decomposition of potassium chlorate(V), KClO3.

The only products of this decomposition are potassium chloride and oxygen.

Write a chemical equation for this decomposition.

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2a3 marks

Extended Only

This question is about titanium.

Titanium is a transition metal that is extracted from titanium dioxide in a two-stage industrial process.

In the first stage, titanium dioxide reacts with carbon and chlorine to form titanium tetrachloride and carbon monoxide.

Write the balanced symbol equation for this reaction.

2b1 mark

Explain how your chemical symbol equation in part (a) demonstrates the law of conservation of mass.

2c2 marks

Identify two hazards associated with Stage 1.

2d
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2 marks

Separate: Chemistry and Extended Only

Calculate, to three significant figures, the percentage by mass of chlorine in titanium tetrachloride. 

(Ar:  Ti = 48   Cl = 35.5)

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3a2 marks

Extended Only

Magnesium displaces copper from copper sulfate solution.

Write the balanced symbol equation for the reaction.

You should include state symbols. 

3b2 marks

Extended Only

State two changes that would be observed during the displacement reaction.

3c2 marks

Extended Only

Write the ionic equation for the displacement of copper from copper sulfate by magnesium. You should include state symbols.

3d2 marks

Extended Only 

Displacement reactions are examples of redox reactions.

Explain why the displacement reaction between magnesium and copper sulfate is both reduction and oxidation.

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4a1 mark

Extended Only

This question is about lead nitrate.

Lead nitrate is an ionic compound. 

It consists of Pb2+ and NO3- ions. 

What is the chemical formula of lead nitrate?

4b
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2 marks

Separate: Chemistry and Extended Only

Calculate the percentage by mass of oxygen in lead nitrate, Pb(NO3)2.

4c3 marks

Extended Only

A displacement reaction occurs between solutions of lead nitrate and potassium iodide, KI, to form solid lead(II) iodide and aqueous potassium nitrate.

Write the balanced symbol equation, including state symbols, for this reaction.

4d2 marks

Separate: Chemistry Only

Table 1 summarises the solubility of a selection of ionic compounds in water.

Table 1

Soluble

Insoluble

All nitrates

 

Most common chlorides

Silver chloride, lead chloride

Most common sulfates

Lead sulfate, barium sulfate, calcium sulfate

Sodium carbonate, potassium carbonate, ammonium carbonate

Most common carbonates

The displacement reaction between lead nitrate and potassium iodide forms a yellow precipitate.

Justify which chemical is responsible for the yellow colour.

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5a2 marks

The relative atomic mass, Ar, for each element is shown in the Periodic Table. 

Define the term relative atomic mass. 

5b
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2 marks

Separate: Chemistry and Extended Only

The element gallium has a relative atomic mass of 69.735 and only contains two isotopes. A sample of gallium contained the isotope 69Ga, with a relative abundance of 63.25 %. Calculate the mass number of the other isotope. You must show all your working.

5c1 mark

Extended Only

Define the term empirical formula.

5d
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3 marks

Separate: Chemistry and Extended Only

An unknown compound contains carbon, hydrogen and oxygen.

It consists of 18% carbon,and 73 % oxygen.

Calculate the empirical formula of the unknown compound

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