ASChemistryCIEExam Questions2. Atoms, Molecules & Stoichiometry2.1 Relative Masses of Atoms & Molecules

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First teaching 2023

First exams 2025

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Relative Masses of Atoms & Molecules (CIE AS Chemistry)

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2.1 Relative Masses of Atoms & Molecules

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2.1 Relative Masses of Atoms & Molecules

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11 mark

The atomic mass is a way of representing the mass of an atom.

Which of the following definitions is correct for the term atomic mass?

  • The mass of an electron

  • 1/12 the mass of carbon-12 atom

  • The mass of hydrogen-1 atom

  • The mass of a proton

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21 mark

Which of the following show the relative formula mass of ammonium sulfate, (NH4)2SO4?

Use of the data booklet is relevant to this question.

  • 98.1

  • 98

  • 132.1

  • 132

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31 mark

Iron has many different naturally occurring isotopes.

Isotope

% Abundance

Atomic mass

54Fe

5.845

53.9396

56Fe

91.754

55.9349

57Fe

2.119

56.9354

58Fe

0.282

57.9333

Using the information given, what is the average atomic mass of iron?

  • 56.1858 amu

  • 55.500 amu

  • 59.270 amu

  • 55.845 amu

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1
Sme Calculator1 mark

A sample of neon contains the isotopes 20Ne and 21Ne.

The relative atomic mass of the neon sample is 20.2.

What is the percentage of 21Ne atoms in the sample of neon?

  • 8.0%

  • 20%

  • 80%

  • 92%

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2
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A sample of metal Z was analysed by mass spectrometry. The relative abundance of each isotope in a mass spectrum of the sample is shown.

m/z value

70

72

74

Relative abundance (%)

24.4

32.4

43.2

What is the relative atomic mass of metal Z to 3 significant figures?

  • 72.33

  • 72.4

  • 72.45

  • 72.2

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3
Sme Calculator1 mark

A copper compound has a formula CuSO4•xH2O and a molar mass of 231.6.

What is the value of x?

  • 2

  • 3

  • 4

  • 5

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11 mark

An element consists of two isotopes 69X and 71X, whose abundances are 60% and 40% respectively. What is the relative atomic mass of element X?

  • 69.2

  • 69.8

  • 70.0

  • 70.2

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21 mark

A sample of strontium was analysed by mass spectroscopy. Some of the relative abundances of each isotope are shown below.

Strontium has a relative atomic mass of 87.71.

m / z value

84

86

87

88

% abundance

0.56

To be found

To be found

82.58

 

Which % abundance values below are correct for strontium-86 and strontium-87 respectively?

  • 6.86% and 9.86%

  • 9.90% and 6.96%

  • 7.00% and 9.54%

  • 8.67% and 8.19%

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31 mark

Aspirin is a common analgesic used for the relief of aches and pains.

13

Which row correctly describes aspirin?

 

Empirical formula

Molecular formula

Mr / g mol-1

A

C2H2O

C9H8O4 

180.0

B

C3H3O

C9H12O4 

184.0

C

C9H12O4 

C9H12O4 

184.0

D

C9H8O4 

C9H8O4 

180.0

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