What is the moles equation?

Number of moles = mass in grams ÷ relative formula mass (Mr). Rearrange it to find a mass: mass = moles × Mr.

How do I find a reacting mass?

Find the moles of the substance you know, use the ratio in the balanced equation to get the moles of the one you want, then multiply by its Mr.

Are moles on Foundation tier?

No. In AQA Combined Science the mole and its calculations are Higher tier only. Relative formula mass and conservation of mass are on both tiers.

GCSE chemistry moles questions with worked answers

6 marksFoundation and Higher5.3.1.2 Relative formula mass

AQA Trilogy 8464

Spec and skills

Paper scope: C1
Spec 5.3.1.2
Original practice question
Answer and supported method checks

Calcium hydroxide has formula

\mathrm{Ca(OH)_2}

. Relative atomic masses: Ca = 40, O = 16, H = 1.

.1

Calculate its relative formula mass.

[3 marks]

.2

Calculate the percentage by mass of oxygen in calcium hydroxide.

[3 marks]

5 marksHigher5.3.2.2 Amounts of substances in equations

AQA Trilogy 8464

Spec and skills

Paper scope: C1
Spec 5.3.2.2
Original practice question
Answer and supported method checks

Calcium carbonate decomposes when heated.

\mathrm{CaCO_{3} \rightarrow CaO + CO_{2}}

A_r

: C = 12, O = 16, Ca = 40

.1

Calculate the mass of calcium oxide produced from 25 g of calcium carbonate.

[3 marks]

.2

Explain why 25 g of calcium carbonate does not produce 25 g of calcium oxide.

[2 marks]

4 marksHigher5.3.2.3 Using moles to balance equations5.3.2.1 Moles

AQA Trilogy 8464

Spec and skills

Paper scope: C1
Spec 5.3.2.3
Spec 5.3.2.1
Original practice question
Answer and supported method checks

11.2 g of iron reacts completely with 21.3 g of chlorine,

\mathrm{Cl_{2}}

, to form 32.5 g of iron chloride,

\mathrm{FeCl_{3}}

.

A_r

: Cl = 35.5, Fe = 56

.1

Calculate the number of moles of iron that reacted.

[1 mark]

.2

Use the masses to write the balanced equation for the reaction, with the smallest whole-number balancing numbers.

[3 marks]

5 marksHigher5.3.2.2 Amounts of substances in equations

AQA Trilogy 8464

Spec and skills

Paper scope: C1
Spec 5.3.2.2
Original practice question
Answer and supported method checks

Hydrogen burns in oxygen to form water.

\mathrm{2H_{2} + O_{2} \rightarrow 2H_{2}O}

A_r

: H = 1, O = 16

.1

Calculate the mass of water formed when 8.0 g of hydrogen burns completely.

[3 marks]

.2

Calculate the mass of oxygen needed to burn the 8.0 g of hydrogen.

[2 marks]

7 marksHigher5.3.2.1 Moles

AQA Trilogy 8464

Spec and skills

Paper scope: C1
Spec 5.3.2.1
Original practice question
Answer and supported method checks

Aluminium reacts with chlorine to form aluminium chloride. In one experiment 5.4 g aluminium combines with 21.3 g chlorine.

A_r

: Al = 27, Cl = 35.5. Chlorine gas is

\mathrm{Cl_2}

.

.1

Calculate the number of moles of chlorine molecules that reacted.

[3 marks]

.2

Use the data to write the balanced equation forming AlCl3.

[2 marks]

.3

Explain why the reacting mass ratio cannot be used directly as the equation coefficients.

[2 marks]

6 marksHigher5.3.2.1 Moles

AQA Trilogy 8464

Spec and skills

Paper scope: C1
Spec 5.3.2.1
Original practice question
Answer and supported method checks

Two separate samples each have mass 8.0 g. One is oxygen gas,

\mathrm{O_2}

, and the other is sulfur dioxide,

\mathrm{SO_2}

.

A_r

: O = 16, S = 32.

.1

Calculate the amount of oxygen molecules in the oxygen sample.

[2 marks]

.2

Calculate the amount of sulfur dioxide molecules in its sample.

[2 marks]

.3

Explain which sample contains more molecules and by what factor.

[2 marks]

GCSE chemistry moles questions with worked answers (AQA Combined Science)

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Questions people ask

What is the moles equation?

How do I find a reacting mass?

Are moles on Foundation tier?