2.1 Relative Masses of Atoms & Molecules | CIE A Level Chemistry Topic Questions 2025

1a4 marks

Explain what is meant by the terms

Relative atomic mass

[2]

Relative isotopic mass

[2]

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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]

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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.

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1d

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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1a

3 marks

Copper is an easily moulded base metal that is often added to precious metals to improve their elasticity, flexibility, hardness, colour, and resistance to corrosion.

Table 3.1 shows the number of protons, neutrons and electrons of different isotopes and ions of copper.

Table 3.1

Species	Protons	Neutrons	Electrons
		34	27
⁶⁵Cu⁺	29

i)

Complete Table 3.1.

[2]

ii)

Give the full electron configuration of the Cu⁺ ion.

[1]

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1b

3 marks

Calculate the percentage abundance of ⁶³Cu with a mass of 62.9296 and ⁶⁵Cu with a mass of 64.9278, when the average mass of the Cu isotope is 63.546.

Express your answer to an appropriate number of significant figures.

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1c2 marks

Explain why the isotopes of copper exhibit the same chemical reactions but their densities differ.

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1d2 marks

Copper can form a salt with chlorine to form copper(II) chloride. This reacts with sodium phosphate to form two different salts only.

Write a balanced equation for this reaction.

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1a

1 mark

The element chromium has several naturally occurring isotopes whose abundances are shown in Table 1.1

Table 1.1

Mass number	% abundance
50	4.345
52	83.789
53	9.501
54	2.365

Calculate the relative atomic mass of chromium to two decimal places.

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1b1 mark

Chromium can form a variety of compounds. Chromium(III) chloride hydrate is the dark green complex [CrCl₂(H₂O)₄]Cl.

Write the full electronic configuration for the chromium ion in this compound.

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1c

1 mark

Calculate the relative molecular mass of [CrCl₂(H₂O)₄]Cl.

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Relative Masses of Atoms & Molecules (CIE A Level Chemistry)

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