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AS Chemistry
Unit 1 Practice Exam Questions – Test 4
Name………………………………………………………..
Harris Academy Chafford Hundred
1
1.
A student had a stomach-ache and needed to take something to neutralise excess
stomach acid. He decided to take some Milk of Magnesia, which is an aqueous
suspension of magnesium hydroxide, Mg(OH)2.
(a)
The main acid in the stomach is hydrochloric acid, HCl(aq), and the unbalanced
equation for the reaction that takes place with Milk of Magnesia is shown below.
.....Mg(OH)2(s)  .....HCl(aq)  .....MgCl2(aq)  .....H2O(l)
Balance the equation by adding numbers where necessary in the unbalanced
equation above.
[1]
(b)
The student’s stomach contained 500 cm3 of stomach fluid with an acid
concentration of 0.108 mol dm–3. The student swallowed some Milk of Magnesia
containing 2.42 g Mg(OH)2. He wondered whether this dose was sufficient to
neutralise the stomach acid.
Assume that all the acid in the stomach fluid was 0.108 mol dm–3 hydrochloric
acid.
(i)
How many moles of HCl were in the 500 cm3 of stomach fluid?
[1]
(ii)
Calculate the mass of Mg(OH)2 necessary to neutralise this stomach fluid.
[3]
(iii)
Determine whether the student swallowed too much, too little, or just the
right amount of Milk of Magnesia to neutralise the stomach acid.
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[1]
[Total 6 marks]
Harris Academy Chafford Hundred
2
2.
Chewing chalk has been used for many years to combat excess stomach acid and
indigestion tablets often contain calcium carbonate, CaCO3. Suggest, with the aid of an
equation, how these tablets work.
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[Total 2 marks]
3.
Chlorine is used in the preparation of many commercially important materials such as
bleach and iodine.
Bleach is a solution of sodium chlorate(l), NaOCl, made by dissolving chlorine in
aqueous sodium hydroxide.
Cl2(g)  2NaOH(aq)  NaOCl(aq)  NaCl(aq)  H2O(l)
Determine the changes in oxidation number of chlorine during the preparation of bleach
and comment on your results.
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[Total 3 marks]
4.
Iodine is extracted commercially from seawater with chlorine gas. Seawater contains
very small quantities of dissolved iodide ions, which are oxidised to iodine by the
chlorine gas.
(i)
Write an ionic equation for the reaction that has taken place.
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[2]
Harris Academy Chafford Hundred
3
(ii)
Use your understanding of electronic structure to explain why chlorine is a
stronger oxidising agent than iodine.
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[2]
[Total 4 marks]
5.
In this question, one mark is available for the quality of use and organisation of
scientific terms.
Nitrogen and oxygen are elements in Period 2 of the Periodic Table. The hydrogen
compounds of oxygen and nitrogen, H2O and NH3, both form hydrogen bonds.
(i)
Draw a diagram containing two H2O molecules to show what is meant by
hydrogen bonding. On your diagram, show any lone pairs present and relevant
dipoles.
[3]
(ii)
State and explain two anomalous properties of water resulting from hydrogen
bonding.
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[4]
[Total 7 marks]
Harris Academy Chafford Hundred
4
6.
The ‘dot-and-cross’ diagram of an ammonia molecule is shown below.
H
N
H
H
Predict, with reasons, the bond angle in an ammonia molecule.
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[Total 4 marks]
Harris Academy Chafford Hundred
5
7.
The atomic radii of nitrogen and oxygen are shown below.
element
nitrogen
oxygen
atomic radius/nm
0.075
0.073
Explain why a nitrogen atom is larger than an oxygen atom.
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[Total 4 marks]
8.
Ammonia reacts with sulphuric acid, as shown in the equation below.
2NH3(g)  H2SO4(aq)  (NH4)2SO4(aq)
(i)
Complete the statement below to describe how ammonia is behaving in this
reaction.
Ammonia is behaving as a ..................... because
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[2]
Harris Academy Chafford Hundred
6
(ii)
State one important use for the compound (NH4)2SO4.
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[1]
(iii)
Apart from the manufacture of (NH4)2SO4, state one other large-scale use of
ammonia.
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[1]
[Total 4 marks]
9.
The Group 7 element bromine was discovered in 1826. Bromine gets its name from the
Greek brōmos meaning stench because of its strong smell.
Bromine consists of a mixture of two isotopes, 79Br and 81Br.
(i)
What is the difference between the atomic structures of 79Br and 81Br?
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[2]
(ii)
State two similarities between the atomic structures of 79Br and 81Br.
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[2]
[Total 4 marks]
10.
The electronic configuration of a bromine atom can be written in terms of sub-shells.
(i)
Complete the electronic configuration of a bromine atom.
1s22s22p63s23p6 ................................................................................................
[2]
Harris Academy Chafford Hundred
7
(ii)
Why is bromine classified as a p-block element?
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[1]
[Total 3 marks]
11.
Bromine forms three compounds with phosphorus. The compounds have the molecular
formulae PBr3, PBr5 and P2Br4.
(i)
Explain what is meant by the term molecular formula.
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[1]
(ii)
PBr3 can be prepared by heating bromine with phosphorus, P4.
Write a balanced equation for this reaction.
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[1]
(iii)
Compound A is one of the three bromides of phosphorus above. It has the
following percentage composition by mass: P, 16.2; Br, 83.8.
Use this percentage composition to calculate the empirical formula and to
determine the identity of compound A.
empirical formula ......................................
identity of compound A ......................................
[3]
[Total 5 marks]
Harris Academy Chafford Hundred
8
12.
Water and carbon dioxide both consist of covalent molecules.
State what is meant by a covalent bond.
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[Total 2 marks]
13.
Draw ‘dot-and-cross’ diagrams for a molecule of water and a molecule of carbon
dioxide. Show outer electron shells only.
water
carbon dioxide
[Total 3 marks]
Harris Academy Chafford Hundred
9
14.
The shape of a water molecule is different from the shape of a carbon dioxide
molecule.
(i)
Draw the shapes of these molecules and state the bond angles.
water
carbon dioxide
bond angle in water = ..............
bond angle in carbon dioxide = ..............
[4]
(ii)
Explain why a water molecule has a different shape from a carbon dioxide
molecule.
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[2]
[Total 6 marks]
15.
An understanding of electronegativity helps to explain why some covalent bonds are
polar.
(i)
Define the term electronegativity.
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[2]
Harris Academy Chafford Hundred
10
(ii)
Water and carbon dioxide both have polar bonds. Explain why water has polar
molecules but carbon dioxide has non-polar molecules.
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[2]
[Total 4 marks]
16.
The first ionisation energies of the elements H to K are shown below. Use this diagram
to help with your answers to this question.
2500
1st ionisation energy
/ kJ mol–1
He
Ne
2000
H
O
Be
1000
Ar
F
N
1500
P
C
Mg
S
Si
B
500
Li
Na
Al
K
0
0
1
2
3
4
5
6
7
8
9 10 11 12 13 14 15 16 17 18 19 20
atomic number
(a)
Define the term first ionisation energy.
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[3]
Harris Academy Chafford Hundred
11
(b)
Explain why the first ionisation energies show a general increase across Period 2
(Li to Ne).
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[2]
[Total 5 marks]
17.
State and explain the trend in first ionisation energies shown by the elements with the
atomic numbers 2, 10 and 18.
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[Total 4 marks]
Harris Academy Chafford Hundred
12