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AS Chemistry
Unit 1 Practice Exam Questions – Test 2

Name………………………………………………………..

1.	Magnesium exists naturally as a mixture of its isotopes, ^24Mg, ^25Mg and ^26Mg.
The isotopes in magnesium can be separated by mass spectrometry. The diagram below shows a mass spectrometer.
(i)	Complete the table below to show the composition of the ^25Mg and ^26Mg isotopes.
protons | neutrons | electrons
^25Mg | | |
^26Mg | | |
[2]
 
(ii)	Complete the electronic configuration of an atom of ^24Mg.
1s^2 ....................................................................................................................
[1]
(iii)	Results from the mass spectrum of a sample of magnesium are shown below.
isotope | ^24Mg | ^25Mg | ^26Mg
relative isotopic mass | 24.00 | 25.00 | 26.00
% abundance | 78.60 | 10.11 | 11.29
Calculate the relative atomic mass of the sample of magnesium.
Give your answer to two decimal places.
answer ...............................
[2]
[Total 5 marks]
2.	Magnesium has a giant metallic structure held together by metallic bonding.
(i)	Draw a labelled diagram to show metallic bonding.
[2]
(ii)	Use your diagram to explain how magnesium conducts electricity.
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[1]
[Total 3 marks]

3.	Magnesium reacts with oxygen to form magnesium oxide.
2Mg(s) + O_2(g) ® 2MgO(s)
(i)	Use oxidation numbers to show that oxygen has been reduced in its reaction with magnesium.
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[2]
(ii)	Draw a ‘dot-and-cross’ diagram to show the arrangement of electrons in magnesium oxide. Show outer electron shells only and include any charges.
[2]
[Total 4 marks]
 
4.	Old samples of magnesium oxide become contaminated with magnesium carbonate.
(i)	Suggest how this contamination takes place.
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[1]
(ii)	A student added an excess of hydrochloric acid to an old sample of magnesium oxide that is contaminated with magnesium carbonate.
State two observations that the student would make.
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[2]
 (iii)	Explain, with the aid of equations, why the resulting solution contained only one dissolved compound of magnesium.
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[3]
[Total 6 marks]

5.	This question is about the simple molecular compounds water, ammonia and sulphur dioxide.
Pairs of electrons in molecules may be present as bonding pairs or as lone pairs.
(i)	Complete the table below for water, ammonia and sulphur dioxide.
molecule | H_2O | NH_3 | SO_2

number of bonding pairs of electrons

4
(2 double bonds)

number of lone pairs of electrons
around central atom

1

[2]
(ii)	Use your answers to (a)(i) to help you draw the shape of a molecule of NH_3 and of SO_2. Clearly show values of the bond angles in your diagrams.
molecule | NH_3 | SO_2

shape of
molecule with
bond angles

[4]
[Total 6 marks]
6.	Describe and explain the density of ice compared with water.
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[Total 2 marks]
7.	A student carried out an experiment using chlorine gas, Cl_2(g).
	The student bubbled chlorine through an aqueous solution of potassium bromide, KBr(aq). A reaction took place.
(i)	What colour is the solution after the reaction has taken place?
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[1]
(ii)	Write an equation for this reaction.
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[2]

(iii)	This reaction takes place because chlorine has a stronger oxidising power than bromine. Explain why chlorine has a stronger oxidising power than bromine.
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[3]
[Total 6 marks]

8.	A student carried out two experiments using chlorine gas, Cl_2(g).
(a)	In the first experiment, the student bubbled chlorine through 120 cm^3 of an aqueous solution of 0.275 mol dm^–3 sodium hydroxide, NaOH(aq).
The equation for this reaction is shown below.
Cl_2(g) + 2NaOH(aq) ® NaCl(aq) + NaClO(aq) + H_2O(l)
Under the reaction conditions, 1 mole of Cl_2(g) occupies 24.0 dm^3.

(i)	What is meant by the term the mole?
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[1]
(ii)	How many moles of NaOH were in the 120 cm^3 volume of NaOH(aq)?
answer ....................... mol
[1]
(iii)	Calculate the volume of Cl_2(g) that was needed to react with the NaOH(aq) used.
answer ...............................
[2]
(iv)	What is a common use for the solution that the student prepared?
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[1]
(b)	In the second experiment, the student repeated the procedure in (a) but with hot concentrated sodium hydroxide. A different reaction took place in which sodium chlorate (V) was formed instead of NaClO.
Suggest the formula of sodium chlorate (V).
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[1]
[Total 6 marks]

9.	In this question, you are provided with information about ionisation energies of elements. You are also provided with some additional information that will help you answer part (b).
(a)	Define the term first ionisation energy.
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[3]
(b)	In this question, one mark is available for the quality of use and organisation of scientific terms.
Table 1 provides data on elements in Period 2 of the Periodic Table.
	Table 2 shows the first 6 successive ionisation energies of an element X, which is in Period 3 of the Periodic Table.
·	Using Table 1, describe and explain the trend in first ionisation energies shown by the Period 2 elements, Li–N.
·	Using Table 2, identify element X. Explain how you decided on your answer.
[10]
element | Li | Be | B | C | N
number of protons | 3 | 4 | 5 | 6 | 7

electron
configuration

1s^2 2s^1

1s^2 2s^2

1s^2 2s^2 2p^1

1s^2 2s^2 2p^2

1s^2 2s^2 2p^3

1st ionisation energy
/ kJ mol^–1

520

900

801

1086

1402

		Table 1

element | ionisation energy / kJ mol^–1
| 1st | 2nd | 3rd | 4th | 5th | 6th
X | 578 | 1817 | 2745 | 11 578 | 14 831 | 18 378
		Table 2
[Total 13 marks]

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10.	Both calcium carbonate, CaCO_3, and calcium oxide, CaO, are white solids.Dilute hydrochloric acid, HCl, can be used to identify whether a sample of white solid is CaCO_3 or CaO.
(i)	Write equations, including state symbols, for the reaction of HCl with CaCO_3 and the reaction of HCl with CaO.
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[3]
(ii)	How would observation of the reactions with hydrochloric acid allow the identification of the white solid?
CaCO_3 .............................................................................................................
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CaO ................................................................................................................
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[1]
[Total 4 marks]
11.	Antimony, Sb, is a metal used in alloys to make lead harder. Bullets contain about 1% of antimony for this reason.Antimony has two main isotopes.
(i)	What do you understand by the term isotopes?
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[1]
(ii)	Complete the table below to show the properties of particles that make up isotopes.
proton | neutron | electron
relative mass | | |
relative charge | | |
[2]
[Total 3 marks]
12.	Relative atomic mass, A_r, can be used to compare the masses of atoms of different elements.
(i)	Explain what you understand by the term relative atomic mass.
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 [3]
(ii)	The antimony in a bullet was analysed by a forensic scientist to help solve a crime. The antimony was found to have the following percentage composition by mass: ^121Sb, 57.21%; ^123Sb, 42.79%.
	Calculate a value for the relative atomic mass of the antimony. Give your answer to 4 significant figures.
A_r ...................................
[2]
[Total 5 marks]
13.	Antimony is in Group 5 of the Periodic Table. It forms a compound with hydrogen that has the formula SbH_3.
(i)	Predict the bond angle in SbH_3.
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[1]
(ii)	Explain why a molecule of SbH_3 has this bond angle.
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 [2]
[Total 3 marks]
14.	Antimony is found naturally in a number of minerals including stibnite. Stibnite typically contains 5% of Sb_2S_3. Antimony can be obtained by reducing Sb_2S_3 with scrap iron.
		Sb_2S_3 + 3Fe ® 2Sb + 3FeS
(i)	How many moles of Sb_2S_3 are in 500 kg of a typical sample of stibnite containing 5% by mass of Sb_2S_3?
molar mass of Sb_2S_3 = 340 g mol^–1; relative atomic mass of Sb = 122
……………… mol
[2]
(ii)	Calculate the mass of antimony that could be obtained by processing 500 kg of stibnite.
mass = ……………… kg
[2]
[Total 4 marks]

Harris Academy Chafford Hundred