Cambridge IGCSE · Chemistry (0620)

Relative masses of atoms and molecules: Practice Questions

5 multiple-choice questions marked as you go, and 5 written questions with worked solutions. All on Relative masses of atoms and molecules.

10 questions23 marksFree, no account

Question 1

1 mark

Which statement best describes the relative atomic mass, \( A_r \), of an element?

Question 2

1 mark

Calcium oxide reacts with carbon dioxide to form calcium carbonate according to the equation:
\( CaO + CO_2 \rightarrow CaCO_3 \)
Using simple proportions, what mass of calcium carbonate is produced from \( 14g \) of calcium oxide?
(Relative formula masses: \( CaO = 56, CaCO_3 = 100 \))

Question 3

1 mark

An element X has two isotopes with mass numbers 107 and 109. If the relative atomic mass of X is 107.8, what is the percentage abundance of the isotope with mass number 107?

Question 4

1 mark

What is the relative molecular mass, \( M_r \), of ethane, \( C_2H_6 \)?
(Relative atomic masses: \( C = 12, H = 1 \))

Question 5

1 mark

A sample of element Boron contains two isotopes, \( ^{10}B \) and \( ^{11}B \). The abundance of \( ^{10}B \) is \( 20\% \) and the abundance of \( ^{11}B \) is \( 80\% \).
Calculate the relative atomic mass of Boron.

Question 6

2 marks

Define relative molecular mass, \(M_r\), with reference to the carbon-12 isotope.

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Question 7

3 marks

Calculate the total mass of products formed when \(4.0\text{ g}\) of calcium reacts completely with \(1.6\text{ g}\) of oxygen, based on the principle of conservation of mass.

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Question 8

6 marks

The element copper exists as two isotopes, \(^{63}Cu\) and \(^{65}Cu\). If the relative atomic mass of copper is \(63.5\), calculate the percentage abundance of the lighter isotope.

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Question 9

3 marks

(a) Define relative molecular mass, \(M_r\).

(b) Calculate the relative formula mass of hydrated aluminium sulfate, \(Al_2(SO_4)_3 \cdot 18H_2O\).
(Relative atomic masses: Al = 27, S = 32, O = 16, H = 1)

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Question 10

4 marks

A metal \( X \) forms an oxide with the formula \( X_2O_3 \). It is found that 1.08 g of the metal reacts completely with oxygen to form 2.04 g of the oxide.

(a) Calculate the mass of oxygen present in the 2.04 g sample of the oxide.
(b) Use the mass ratio and the known relative atomic mass of oxygen to calculate the relative atomic mass, \( A_r \), of metal \( X \).
(c) Identify the metal \( X \) using the Periodic Table.

(Relative atomic mass: \( O = 16.0 \))

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