A LevelChemistryCambridge (CIE)Exam Questions2. Atoms, Molecules & StoichiometryRelative Masses of Atoms & Molecules

Relative Masses of Atoms & Molecules (Cambridge (CIE) A Level Chemistry): Exam Questions

Exam code: 9701

47 mins15 questions

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Relative Masses of Atoms & Molecules

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1a
4 marks

Define the following terms.

Relative atomic mass

[2]

Relative isotopic mass

[2]

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1b
3 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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1c
1 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
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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
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2 marks

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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1b
1 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
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1 mark

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

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2a
2 marks

Nitrous oxide is used as a sedative in dentistry and has the formula N2O. Different sources of N2O contain different ratios of 14N and 15N.           

State the name of the instrument used to distinguish between 14N and 15N and outline two characteristic differences seen in the analysis of 14N and 15N.

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2b
2 marks

A sample of nitrous oxide was enriched so that it contained 4% by mass of 15N. Calculate the relative molecular mass of the resulting nitrous oxide.

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2c
2 marks

An atom has twice as many protons, and twice as many neutrons, as an atom of 15N.

Determine the chemical symbol for this atom, including the mass number, and deduce the number of electrons.

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3a
2 marks

Ethanoic acid has a relative molecular mass of 60.0.

Define the term relative molecular mass.

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3b
1 mark

State the empirical formula of ethanoic acid.

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3c
2 marks

Ethanoic acid reacts with aqueous sodium carbonate to form a neutral salt solution and a gas.

i) Name the salt produced in this reaction.

[1]

ii) Calculate its relative formula mass.

[1]

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1a
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3 marks

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

Table 3.1

Species

Protons

Neutrons

Electrons

34

27

65Cu+

29

i) Complete Table 3.1.

[2]

ii) State the full electronic configuration of the Cu+ ion.

[1]

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1b
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3 marks

63Cu has a relative isotopic mass of 62.9296 and 65Cu has a relative isotopic mass of 64.9278. The relative atomic mass of copper is 63.546.

Calculate the percentage abundance of each isotope of copper. Show your working.

Express your answer to an appropriate number of significant figures.

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1c
2 marks

Explain why isotopes of copper have the same chemical properties but different densities.

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1d
2 marks

Copper(II) chloride reacts with sodium phosphate to form two salts only.

Write a balanced equation for this reaction.

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