AS Chemistry
Atoms, Bonds and Groups
Unit 1 - F321
Revision Pack 
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Chemistry Group:

1.	The Group 7 element bromine was discovered by Balard in 1826. Bromine gets its name from the Greek bromos meaning stench.
	Bromine consists of a mixture of two isotopes, 79Br and 81Br.
(i)	What is meant by the term isotopes?
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[1]
 
(ii)	Complete the table below to show the atomic structures of the bromine isotopes.
	protons	neutrons	electrons	
79Br				
81Br				
[2]
(iii)	Write the full electronic configuration of a bromine atom.
1s2 .................................................................
[1]
[Total 4 marks]

2.	Calcium and its compounds, have properties typical of Group 2 in the Periodic Table.
	Calcium carbonate, CaCO3, reacts with acids such as nitric acid.
	A student neutralised 2.68 g of CaCO3 with 2.50 mol dm–3 nitric acid, HNO3.
	The equation for this reaction is shown below.
CaCO3(s) + 2HNO3(aq) → Ca(NO3)2(aq) + CO2(g) + H2O(l)
	The student left the solution of calcium nitrate formed to crystallise. Crystals of hydrated calcium nitrate formed containing 30.50% of H2O, by mass.
	Calculate the formula of the hydrated calcium nitrate.

[Total 3 marks]

3.	Rubidium, atomic number 37, was discovered in 1861 by Bunsen and Kirchoff. Rubidium is in Group 1 of the Periodic Table and the element has two natural isotopes, 85Rb and 87Rb.
(a)	Explain the term isotopes.
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[1]

(b)	A sample of rubidium was analysed in a mass spectrometer to produce the mass spectrum below.

(i)	Use this mass spectrum to help you complete the table below.
isotope	percentage	number of	
		protons	neutrons	electrons	
85Rb					
87Rb					
[3]
 
(ii)	Calculate the relative atomic mass of this rubidium sample. Give your answer to three significant figures.

Ar = ................................
[2]

(c)	Which isotope is used as the standard against which the masses of the two rubidium isotopes are measured?
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[1]
[Total 7 marks]

4.	Rubidium forms an ionic compound with silver and iodine. This compound has a potential use in miniaturised batteries because of its high electrical conductivity.
	The empirical formula of this ionic compound can be calculated from its percentage composition by mass: Rb, 7.42%; Ag, 37.48%; I, 55.10%.
(i)	Define the term empirical formula.
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[1]
 
(ii)	Calculate the empirical formula of the compound.

[2]
[Total 3 marks]

5.	Chlorine can be prepared by reacting concentrated hydrochloric acid with manganese(IV) oxide.
	4HCl(aq) + MnO2(s) → Cl2(g) + MnCl2(aq) + 2H2O(l)
(a)	A student reacted 50.0 cm3 of 12.0 mol dm–3 hydrochloric acid with an excess of manganese(IV) oxide.
(i)	Calculate how many moles of HCl were reacted.

answer = ................................ mol
[1]
 
(ii)	Calculate the volume of Cl2(g) produced, in dm3.
Under the experimental conditions, one mole of Cl2(g) occupies 24.0 dm3.

answer = ................................ dm3
[2]
 
(b)	In this reaction, chlorine is oxidised.
	Use oxidation numbers to determine what is reduced.
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[2]
[Total 5 marks]

6.	This question looks at the reaction of sodium with water and with oxygen.
A chemist reacted 0.0500 mol of sodium with water to form 50.0 cm3 of aqueous sodium hydroxide.
	2Na(s) + 2H2O(l) ® 2NaOH(aq) + H2(g)
(i)	What mass of Na was reacted?
mass = ............................... g
[1]
 
(ii)	Calculate the volume of H2, in dm3, that would be produced at room temperature and pressure, r.t.p.
1 mol of gas molecules occupies 24.0 dm3 at r.t.p.
volume = .......................... dm3
[2]
(iii)	Calculate the concentration, in mol dm–3, of NaOH that was formed.
concentration = ................... mol dm–3
[1]
[Total 4 marks]

7.	Sodium reacts with excess oxygen to form sodium peroxide, Na2O2.
Na2O2 is used in laundry bleaches. When added to water a reaction takes place forming an alkaline solution and hydrogen peroxide, H2O2.
(i)	Construct a balanced equation for the formation of sodium peroxide from sodium.
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[1]

(ii)	Construct a balanced equation for the reaction of sodium peroxide with water.
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[1]
(iii)	Draw a ‘dot-and-cross’ diagram for a molecule of H2O2. Show outer electrons only.
[2]
[Total 4 marks]

8.	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.
1s2 ....................................................................................................................
[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]

9.	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]

10.	Magnesium reacts with oxygen to form magnesium oxide.
2Mg(s) + O2(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]

11.	The nitrate ion, NO3–, in Ca(NO3)2 contains both covalent and dative covalent bonds.
(i)	What is the difference between a covalent bond and a dative covalent bond?
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[1]
 
(ii)	Calcium nitrate decomposes on heating to form calcium oxide, oxygen and nitrogen(IV) oxide, NO2.
Construct a balanced equation for this reaction.
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[1]
[Total 2 marks]

12.	Aqueous silver nitrate can be used as a test for halide ions. A student decided to carry out this test on a solution of magnesium chloride. The bottle of magnesium chloride that the student used showed the formula MgCl2.6H2O.
The student dissolved a small amount of MgCl2.6H2O in water and added aqueous silver nitrate to the aqueous solution.
(i)	What is the molar mass of MgCl2.6H2O?
molar mass = ……………… g mol–1
[1]
 
(ii)	What would the student see after adding the aqueous silver nitrate, AgNO3(aq)?
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[1]
(iii)	Write an ionic equation for this reaction. Include state symbols.
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[2]

(iv)	Using aqueous silver nitrate, it is sometimes difficult to distinguish between chloride, bromide and iodide ions.
How can aqueous ammonia be used to distinguish between these three ions?
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[3]
[Total 7 marks]
 
13.	Hydrochloric acid is a strong acid.
	What is meant by the term acid?
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[Total 1 mark]

14.	A fifty pence coin contains nickel alloyed with a metal A.
	Nickel exists as a mixture of three isotopes, nickel-58, nickel-60 and nickel-62.
	Complete the table below to show the atomic structures of the isotopes in metallic nickel.
isotope	protons	neutrons	electrons	
nickel-58				
nickel-60				
nickel-62				
[Total 3 marks]

15.	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]
 
(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]

16.	Metal A can be identified from its relative atomic mass.
	Analysis of a fifty pence coin showed that two isotopes of metal A were present with the following percentage abundances.
isotope	isotope 1	isotope 2	
relative isotopic mass	63.0	65.0	
% abundance	77.2	22.8	
(i)	What analytical method is used to obtain this information?
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[1]

(ii)	Define the term relative atomic mass.
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[3]
 
(iii)	Calculate the relative atomic mass of the sample of metal A.
Give your answer to three significant figures.
answer ...........................
[2]
 
(iv)	Use your answer to (iii) and the Data Sheet to suggest the identify of metal A.
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[1]
[Total 7 marks]

17.	A student carried out two experiments using chlorine gas, Cl2(g).
(a)	In the first experiment, the student bubbled chlorine through 120 cm3 of an aqueous solution of 0.275 mol dm–3 sodium hydroxide, NaOH(aq).
The equation for this reaction is shown below.
Cl2(g) + 2NaOH(aq) ® NaCl(aq) + NaClO(aq) + H2O(l)
Under the reaction conditions, 1 mole of Cl2(g) occupies 24.0 dm3.

(i)	What is meant by the term the mole?
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[1]
 
(ii)	How many moles of NaOH were in the 120 cm3 volume of NaOH(aq)?
answer ....................... mol
[1]
(iii)	Calculate the volume of Cl2(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]

18.	Relative atomic mass, Ar, 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.
Ar ...................................
[2]
[Total 5 marks]

19.	Both calcium carbonate, CaCO3, and calcium oxide, CaO, are white solids.
Dilute hydrochloric acid, HCl, can be used to identify whether a sample of white solid is CaCO3 or CaO.
(i)	Write equations, including state symbols, for the reaction of HCl with CaCO3 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?
CaCO3 .............................................................................................................
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CaO ................................................................................................................
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[1]
[Total 4 marks]

20.	Chemists have developed models for bonding and structure. These models are used to explain different properties of metals and non-metals.
(i)	Draw a labelled diagram to show the currently accepted model for metallic bonding.

[2]
 
(ii)	What feature of this model allows metals to conduct electricity?
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[1]
[Total 3 marks]

21.	The metal magnesium reacts with the non-metal chlorine to form a compound magnesium chloride, MgCl2, which has ionic bonding.
(i)	State what is meant by an ionic bond.
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[1]
 
(ii)	‘Dot-and-cross’ diagrams are used to model which electrons are present in the ion.
	Draw a ‘dot-and-cross’ diagram, including outer electron shells only, to show the ions present in magnesium chloride, MgCl2.

[2]

(iii)	A student finds that solid magnesium chloride and pure water do not conduct electricity. The student dissolved the magnesium chloride in the water and the resulting solution does conduct electricity.
	Explain these observations.
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[3]
[Total 6 marks]

22.	The non-metals chlorine and carbon have very different boiling points. Chlorine is a gas at room temperature but carbon does not boil until well over 4500 °C.
	Explain this difference, in terms of bonding and structure.
	In your answer, you should use appropriate technical terms, spelled correctly.
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[Total 3 marks]

23.	Water forms hydrogen bonds which influences its properties.
	Explain, with a diagram, what is meant by hydrogen bonding and explain two anomalous properties of water resulting from hydrogen bonding.
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[Total 6 marks]

24.	The ions present in Ca(OH)2 are Ca2+ and OH–.
(i)	Complete the electronic configuration of a Ca2+ ion.
1s2 ...................................................................................................................
[1]
 
(ii)	How many moles of ions are in one mole of Ca(OH)2?

moles of ions = ................................
[1]

(iii)	How many moles of electrons are in one mole of OH– ions?

moles of electrons = ................................
[1]
 
(iv)	Draw a ‘dot-and-cross’ diagram of Ca(OH)2. Show outer electron shells only.

[2]
[Total 5 marks]

25.	Compounds with covalent bonding often have polar bonds. Polarity can be explained in terms of electronegativity.
(i)	Explain the term electronegativity.
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[2]

(ii)	Use a suitable example to show how the presence of a polar bond can be explained in terms of electronegativity.
	You may find it useful to draw a diagram in your answer.

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[2]
[Total 4 marks]

26.	The diagram below shows the variation in the boiling points of elements across
Period 3 of the Periodic Table.

(a)	In the table below for the elements Mg, Si and S,
•	complete the structure column using the word giant or simple.
•	complete the bonding column using the word metallic, ionic or covalent.
element	structure	bonding	
Mg			
Si			
S			
[3]
 
(b)	Explain why silicon has a much higher boiling point than phosphorus.
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[2]
 
(c)	Explain why the boiling point increases from sodium to aluminium.
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[2]
[Total 7 marks]

27.	Sodium reacts with chlorine forming the ionic compound sodium chloride, NaCl.
(i)	Write an equation, including state symbols, for this reaction.
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[2]

(ii)	Describe the structure of sodium chloride in the solid state. You may find it useful to draw a diagram.

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[2]
[Total 4 marks]

28.	Successive ionisation energies provide evidence for the arrangement of electrons in atoms. The table below shows the eight successive ionisation energies of oxygen.
ionisation number	1st	2nd	3rd	4th	5th	6th	7th	8th	
ionisation
energy / kJ mol–1	1 314	3 388	5 301	7 469	10 989	13 327	71 337	84 080	
(i)	Define the term first ionisation energy.
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[3]
 
(ii)	Write an equation, with state symbols, to represent the third ionisation energy of oxygen.
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[2]

(iii)	Explain how the information in the table above provides evidence for two electron shells in oxygen.
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[2]
[Total 7 marks]

29.	Electrons are arranged in energy levels.
(a)	An orbital is a region in which an electron may be found.
Draw diagrams to show the shape of an s orbital and of a p orbital.

s orbital	p orbital	
[2]
 
(b)	Complete the table below to show how many electrons completely fill each of the following.
	number of electrons	
a d orbital		
a p sub-shell		
the third shell (n = 3)		
[3]

(c)	The energy diagram below is for the eight electrons in an oxygen atom. The diagram is incomplete as it only shows the two electrons in the 1s level.

	Complete the diagram for the oxygen atom by:
(i)	adding labels for the other sub-shell levels,
[1]
(ii)	adding arrows to show how the other electrons are arranged.
[1]
[Total 7 marks]

30.	Sodium reacts with oxygen to form sodium oxide, Na2O.
Draw a ‘dot-and-cross’ diagram for Na2O. Show outer electrons only.
[Total 2 marks]

31.	In water treatment plants, care must be taken as chlorine can react with nitrogen compounds to form the highly explosive compound, nitrogen trichloride, NCl3. Molecules of NCl3 have a bond angle of 107°.
(i)	Name the shape of an NCl3 molecule.
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[1]

(ii)	Explain why a molecule of NCl3 has this shape and a bond angle of 107°.
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[3]
[Total 4 marks]

32.	In this question, one mark is available for the quality of spelling, punctuation and grammar.
Many physical properties can be explained in terms of bonding and structure. The table below shows the structures and some properties of sodium chloride and graphite in the solid state.
substance	sodium chloride	graphite	
structure			
electrical
conductivity of solid	poor	good	
melting and boiling
point	high	high	
solubility in water	good	insoluble	
Explain these properties in terms of bonding and structure.
[7]
Quality of Written Communication [1]
[Total 8 marks]

33.	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 4.1, describe and explain the trend in first ionisation energies shown by the Period 2 elements, Li–N.
·	Using Table 4.2, 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	1s2 2s1	1s2 2s2	1s2 2s2 2p1	1s2 2s2 2p2	1s2 2s2 2p3	
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]

34.	In their reactions, calcium and strontium each lose electrons to form ions with a 2+ charge. The first and second ionisation energies of calcium and strontium are shown below.
1st ionisation energy
/ kJ mol–1	2nd ionisation energy
/ kJ mol–1	
calcium	590	1145	
strontium	550	1064	
(i)	Write an equation, with state symbols, to represent the second ionisation energy of calcium.
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[2]

(ii)	Why are the second ionisation energies of calcium and strontium greater than their first ionisation energies?
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[1]
 
(iii)	Explain why the first and second ionisation energies of strontium are less than those of calcium.
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[3]
[Total 6 marks]

35.	In this question, one mark is available for the quality of spelling, punctuation and grammar.
Many physical properties can be explained in terms of bonding and structure. The table below show some properties of elements in Period 2 of the Periodic Table.
element	Li	C
(graphite)	N	
electrical conductivity
of solid	good	good	poor	
boiling point / °C	1342	4000	–196	
Explain these properties in terms of bonding and structure.
[11]
Quality of Written Communication [1]
[Total 12 marks]

36.	Limestone contains the ionic compound, CaCO3. Limestone decomposes when it is heated strongly, forming an ionic compound, CaO and a covalent compound, CO2.
		CaCO3(s) ® CaO(s) + CO2(g)
(a)	State what is meant by ionic bonding.
.........................................................................................................................
.........................................................................................................................
[1]

(b)	Draw ‘dot and cross’ diagrams to show the bonding in CaO and CO2. Show outer electron shells only.

	
CaO	CO2	
[3]
 
(c)	Complete the electronic configuration in terms of sub-shells for calcium in CaO.
1s2 ....................................................................................................................
[1]
[Total 5 marks]

37.	The diagram below shows the variation in the first ionisation energies of elements across Period 2 of the Periodic Table.

(i)	Define the term first ionisation energy.
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[3]
 
(ii)	Explain why the first ionisation energies show a general increase across
Period 2.
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[2]
 
(iii)	Explain why the first ionisation energy of B is less than that of Be.
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[2]
[Total 7 marks]

38.	In this question, one mark is available for the quality of spelling, punctuation and grammar.
The halogens chlorine, bromine and iodine each exist as diatomic molecules at room temperature and pressure.
The halogens all have van der Waals’ forces.
·	Explain how van der Waals’ forces are formed.
·	Explain the trend in volatilities of the halogens chlorine, bromine and iodine.
[Total 6 marks]

39.	The first ionisation energies of the elements H to K are shown below. Use this diagram to help with your answers to this question.

(a)	Define the term first ionisation energy.
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[3]
 
(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]

40.	State and explain two anomalous properties of H2O that depend on its intermolecular forces.
[4]
Quality of Written Communication [1]
[Total 5 marks]

41.	This question refers to the elements in the first four periods of the Periodic Table.

	Identify an element from the first four periods that fits each of the following descriptions.
(i)	The element that forms a 2– ion with the same electronic configuration as Ar.
...............................................................……
[1]
(ii)	The element that forms a 3+ ion with ten electrons.
......................................................................
[1]
 
(iii)	An element that forms a compound with fluorine with trigonal planar molecules.
......................................................................
[1]
(iv)	The element that forms a chloride XCl2 with a molar mass of 111.1 g mol–1.
......................................................................
[1]

(v)	The element with the largest atomic radius.
......................................................................
[1]
(vi)	The element with the smallest first ionisation energy.
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[1]
[Total 6 marks]

42.	The Group 7 element bromine was discovered by Balard in 1826. Bromine gets its name from the Greek bromos meaning stench.
	Bromine consists of a mixture of two isotopes, 79Br and 81Br.
	A student added an aqueous solution of sodium iodide to a solution of bromine.
	The colour turned from orange to a deep brown.
	The student then added an aqueous solution of sodium chloride to a solution of bromine.
	The orange colour was unchanged.
 
(i)	Explain these observations.
	In your answer, you should use appropriate technical terms, spelled correctly.
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[3]

(ii)	Write an ionic equation for the reaction that has taken place.
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[1]
[Total 4 marks]

43.	Chlorine is used in the production of safe drinking water throughout the world.
Drinking water is purified by addition of small amounts of chlorine. The reaction that takes place can be represented by the equation below.
Cl2(g) + H2O(l)  2H+(aq) + ClO–(aq) + Cl –(aq)
(a)	Describe a simple test that would confirm the presence of chloride ions in drinking water.
Include an equation in your answer.
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[3]
 
(b)	Chlorine can also be converted into bleach.
How is bleach made from chlorine? Include an equation in your answer.
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[2]
[Total 5 marks]

44.	In this question one mark is available for the quality of spelling, punctuation and grammar.
	Chlorine gas was bubbled through an aqueous solution of bromide ions and also through an aqueous solution of iodide ions. An organic solvent was then added and each mixture was shaken.
•	State what you would see in each case.
•	Write equations for any chemical reactions that take place.
•	State and explain the trend in reactivity shown by these observations.
	(Allow one lined page).
[6]
Quality of Written Communication [1]
[Total 7 marks]

45.	Barium reacts with water in a redox reaction.
Ba(s) + 2H2O(l) ® Ba(OH)2(aq) + H2(g)
(i)	Explain, in terms of electrons, what is meant by oxidation.
.........................................................................................................................
[1]
 
(ii)	Which element has been oxidised in this reaction? Deduce the change in its oxidation number.
element ...........................................................................................................
oxidation number changes from ………… to…………
[2]
[Total 3 marks]

46.	The elements calcium and strontium in Group 2 of the Periodic Table both react with water.
A student reacted 0.20 g of calcium and 0.20 g of strontium separately with 250 cm3 of water. The student measured the volume of gas produced from each reaction.
The student’s results are shown below.
metal	calcium	strontium	
volume of gas / cm3	120	55	
(i)	Name the gas produced.
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[1]
 
(ii)	Write a balanced equation for the reaction of strontium with water.
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[1]
 
(iii)	Explain why the student obtained different volumes of gas by reacting water with the same mass of calcium and strontium.
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[2]
(iv)	Predict the pH of the solutions formed in each of these reactions.
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[1]
[Total 5 marks]

47.	Domestic tap water has been chlorinated.
Chlorine reacts with water as shown below.
Cl2(g) + H2O(l) ® HOCl (aq) + HCl (aq)
(i)	State the oxidation number of chlorine in
Cl2 ...................................................................................................................
HOCl ...............................................................................................................
HCl ..................................................................................................................
[3]
 
(ii)	When carrying out halide tests with aqueous silver nitrate, it is important that distilled or deionised water is used for all solutions, rather than tap water.
Suggest why.
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[1]
[Total 4 marks]

48.	A student prepared an aqueous solution of calcium chloride by reacting calcium with hydrochloric acid. Calcium chloride contains Ca2+ and Cl– ions.
(a)	Complete and balance the following equation for this reaction.
……Ca(s) + …… HCl(aq) ® ……. CaCl2(aq) + …………
[2]

(b)	This is a redox reaction.
Use oxidation states to show that calcium has been oxidised.
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[2]
[Total 4 marks]

49.	Describe and explain the relative reactivity of the halogens chlorine, bromine and iodine in displacement reactions involving halides, using reactions on a test tube scale.
Include equations and observations in your answer.
[5]
Quality of Written Communication [1]
[Total 6 marks]

50.	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]

51.	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]
 
(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]

52.	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]

53.	The reaction of strontium with water is a redox reaction. A student reacted 0.438 g of strontium with 200 cm3 of water.
		Sr(s) + 2H2O(l) ® Sr(OH)2(aq) + H2(g)
(i)	Use oxidation numbers to show that strontium has been oxidised in this reaction.
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[2]
 
(ii)	Calculate how many moles of Sr were reacted.
	Ar: Sr, 87.6
answer ............... mol
[1]
 
(iii)	Calculate the volume, in dm3, of H2(g) produced. You can assume that, under the experimental conditions, 1.00 mol of H2(g) has a volume of 24.0 dm3.
answer .............. dm3
[1]
 
(iv)	Calculate the concentration, in mol dm–3, of the Sr(OH)2 produced.
answer ............... mol dm–3
[1]
[Total 5 marks]

54.	The Group 2 metal strontium, Sr, is very reactive.
Strontium metal is stored under oil and, when exposed to air, the shiny surface of the strontium becomes dull.
Predict, with an equation, what reaction takes place when strontium is exposed to air.
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[Total 2 marks]

55.	An ore of strontium contains strontium carbonate, SrCO3.
To obtain metallic strontium,
·	the SrCO3 is converted into strontium oxide, SrO;
·	SrO is then reduced to produce strontium.
(i)	Suggest how strontium carbonate is converted into strontium oxide.
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[1]
 
(ii)	Aluminium can be used to reduce strontium oxide.
Balance the equation below for this conversion.
............ SrO(s) + ............ Al(s) ® ............ Sr(s) + ............ Al2O3(s)
[1]
 
(iii)	A chemical company receives an order to supply 100 tonnes of strontium. The company needs to work out how much ore to process
The ore typically contains 2% by mass of SrCO3.
	Calculate the mass of ore that the company would need in order to produce 100 tonnes of strontium.
	1 tonne = 106 g
[3]
 
(iv)	Suggest how the company could minimise the environmental impact of strontium production from the ore.
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[1]
[Total 6 marks]

56.	In this question, one mark is available for the quality of written communication.
This question is about the Group 7 elements chlorine, bromine and iodine.
·	Explain why chlorine, bromine and iodine have different physical states at room temperature and pressure.
[4]
·	An aqueous solution of bromine was added to an aqueous solution of chloride ions and also to an aqueous solution of iodide ions.
	State what you would see in each case.
	Include an equation for any chemical reaction that takes place.
	Explain the trend shown by these observations.
[4]
Quality of Written Communication [1]
[Total 9 marks]

57.	When barium metal is added to water, the reaction taking place is much more vigorous than with calcium.
Explain why barium is more reactive than calcium.
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[Total 4 marks]