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Edexcel | Chemistry WCH0 | S 16 5 1 | 1 hour 45 minutes
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21
(a)
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3 Mark s

Chromium is in the d-block of the Periodic Table and it is a transition metal.

 Scandium is also in the d-block of the Periodic Table but it is not a transition metal.

  Explain, by giving any relevant electronic configurations, why scandium is not a 

transition metal.

 

21
(b)
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2 Mark s

 When a few drops of aqueous ammonia are added to an aqueous solution of

chromium(III) ions, a green precipitate of chromium(III) hydroxide is formed.

  Complete the ionic equation for this reaction.  State symbols are not required.

IGNORE square brackets

Rest of equation and balancing

Conditional on correct formula of

chromium(III) hydroxide (1)

IGNORE state symbols even if incorrect

21
(c)
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2 Mark s

Explain, in terms of oxidation numbers of chromium, whether or not each of these

two reactions are redox

 

21
(d) (I)
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2 Mark s

Chromium(III) chloride can exist in aqueous solution as three possible complex ions

with different numbers of free chloride ions.

.There are two possible structures for complex ion Z.

Complete the diagrams below to show the two possible structures for 

complex ion Z.

21
(d) (II)
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2 Mark s

Name the type of bond between the ligands and the chromium(III) ion and

explain how it is formed.

dative(covalent)

ALLOW co-ordinate (covalent/ bonding) (1)

(formed from) the lone pair (of electrons) on

the oxygen / chloride ion / ligand / water (to

the chromium ion) (1)

ALLOW “pair of electrons” for “lone pair”

IGNORE element / molecule / atom

21
(d) (III)
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3 Mark s

The formula of the complex ion present in the solution is found by adding 

aqueous silver nitrate to the solution.  This only reacts with the free chloride ions

to form a precipitate of silver chloride.

 The precipitate is then filtered, washed, dried and weighed.  

 In an experiment, 0.012 mol of one of the forms of chromium(III) chloride was 

used and 3.44 g of silver chloride was formed.

 Deduce the formula of the complex ion.  You must show your working.

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