Edexcel IGCSE Chemistry: Chemical Formulae, Equations & Calculations Question Bank

Practise balancing equations and using formulae, Mr and mole ratios for reacting masses, yields and composition.

Exam points

balance formula units and state symbols before taking stoichiometric ratios
convert between mass and moles using Mr, then apply the balanced-equation ratio
calculate percentage composition, yield or empirical formula from supplied data

Covered syllabus points

1.25 Chemical equations 1.26 Relative formula mass 1.27 The mole 1.28 Amount of substance calculations 1.29 Reacting masses 1.30 Percentage yield 1.31 Experimental formulae 1.32 Empirical and molecular formulae 1.33 Formula calculations 1.34C Solution concentration calculations 1.35C Gas volume calculations 1.36 Metal oxide formula practical

[Maximum number: 5]

This question is about magnesium metal and its compounds.

(a)

Magnesium burns in oxygen gas to form solid magnesium oxide.

[ 2 ]

(i)

Complete the chemical equation for the reaction by balancing the equation and adding the state symbols.

Figure for Question (i) — Edexcel IGCSE Chemistry

[ 2 ]

$\ce{2Mg(s) + O2(g) -> 2MgO(s)}$

Marking guidance:
- 1 mark for balancing.
- 1 mark for state symbols.
- Allow multiples or fractions, but $\ce{O2}$ must also be changed to score the balancing mark.

(b)

A student uses this method to make a solution of magnesium chloride.

Step 1. measure $25 \mathrm{~cm}^{3}$ of dilute hydrochloric acid into a beaker
Step 2 add magnesium powder a little at a time
Step 3 keep adding magnesium powder until it is in excess
Step 4 remove the excess magnesium powder by filtration

This is the equation for the reaction.

Figure for Question (b) — Edexcel IGCSE Chemistry

[ 3 ]

(i)

Calculate the minimum mass of magnesium needed to react with $25.0 \mathrm{~cm}^{3}$ of $2.00 \mathrm{~mol} / \mathrm{dm}^{3}$ hydrochloric acid.
[for $\mathrm{Mg}, \mathrm{A}_{\mathrm{r}}=24$ ]

mass = g

[ 3 ]

[Maximum number: 1]

Crude oil is a mixture of hydrocarbons.

One of the hydrocarbons in the refinery gas fraction is an alkane with the structural formula $\mathrm{CH}_{3} \mathrm{CH}_{2} \mathrm{CH}_{2} \mathrm{CH}_{3}$

Calculate the relative molecular mass $\left(M_{\mathrm{r}}\right)$ of this alkane.

M_{r}=

[Maximum number: 3]

The diagram shows the positions of some elements in part of the Periodic Table.

Na Al S Cl
K Xe
In

Table for Question (e) Chemical formulae, equations and calculations question 3 — Edexcel IGCSE Chemistry

A teacher adds a small piece of sodium to a glass trough containing water and universal indicator.

The universal indicator changes colour.
The equation for the reaction is

2 \mathrm{Na}(\mathrm{~s})+2 \mathrm{H}_{2} \mathrm{O}(\mathrm{l}) \rightarrow 2 \mathrm{NaOH}(\mathrm{aq})+\mathrm{H}_{2}(\mathrm{~g})

The reaction with sodium produces 0.036 g of hydrogen gas.

One mole of hydrogen gas contains $6.0 \times 10^{23}$ molecules.
Calculate the number of molecules of hydrogen gas produced in the reaction with sodium.

Give your answer to two significant figures.
number of molecules of hydrogen gas =

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Covered syllabus points

(e) Chemical formulae, equations and calculations question 1

Question (a)

Question (i)

Question (b)

Question (i)

(e) Chemical formulae, equations and calculations question 2

(e) Chemical formulae, equations and calculations question 3