Chemistry 9701/42 — February/March 2020

Cambridge A-Level · A Level Structured Questions · worked solutions for every part, with the mark scheme

questions

100

marks

120

minutes

Topics Carboxylic Acids and Derivatives · Nitrogen Compounds · Transition Elements · Electrochemistry · Equilibria · Introduction to A Level Organic Chemistry · +9 more

Q1Transition ElementsCarboxylic Acids and DerivativesFree sample

Iron is a transition element in the fourth period. Iron forms compounds containing the ions Fe²⁺ and Fe³⁺.

(a)

(i)

Define the term transition element.

(ii)

Compare the melting point and density of iron with those of calcium, an s-block element in the fourth period.

melting point .......................................................................................................................

density ................................................................................................................................

(iii)

Complete the electronic configuration of an isolated gaseous Fe²⁺ ion.

1s² .................................................................................................................................

(iv)

Aqueous Fe³⁺ ions form coloured complexes.

Explain the origin of the colour in transition element complexes.

(b)

When an excess of $\text{CN}^-(\text{aq})$ ions is added to green $[\text{Fe}(\text{H}_2\text{O})_6]^{2+}(\text{aq})$ ions, yellow $[\text{Fe}(\text{CN})_6]^{4-}$ complex ions are formed.

Heating $[\text{Fe}(\text{CN})_6]^{4-}$ with dilute nitric acid and then neutralising the product with $\text{Na}_2\text{CO}_3(\text{aq})$ produces red crystals, containing the $[\text{Fe}(\text{CN})_5\text{NO}]^{2-}$ complex ion.

NO is a neutral, monodentate ligand.

(i)

State the shape of the $[\text{Fe}(\text{H}_2\text{O})_6]^{2+}(\text{aq})$ complex ion.

(ii)

Write the equation for the reaction between $[\text{Fe}(\text{H}_2\text{O})_6]^{2+}(\text{aq})$ ions and an excess of $\text{CN}^-(\text{aq})$ ions.

(iii)

Deduce the oxidation states of iron in:

$[\text{Fe}(\text{CN})_6]^{4-}$ ................................................ $[\text{Fe}(\text{CN})_5\text{NO}]^{2-}$ . ................................................

(iv)

Define the term monodentate ligand.

(v)

Complete the diagram to show the three-dimensional structure of the $[\text{Fe}(\text{CN})_5\text{NO}]^{2-}$ complex ion.

Fig. 1.1

(vi)

The two complex ions $[\text{Fe}(\text{CN})_6]^{4-}$ and $[\text{Fe}(\text{CN})_5\text{NO}]^{2-}$ are different colours.

Explain why the colours of the two complex ions are different.

(c)

E is a complex ion, $[\text{Fe}(\text{C}_2\text{O}_4)_2\text{Cl}_2]^{4-}$ , containing $\text{Fe}^{2+}$ with a coordination number of 6.

(i)

Define the term coordination number.

(ii)

E shows both optical isomerism and cis-trans isomerism.

One isomer of E is shown. The $\text{C}_2\text{O}_4^{2-}$ ion is represented as

ox symbol

In the boxes, draw three-dimensional diagrams to show:

the trans isomer of E
the optical isomer of E.

Fig. 1.2

(iii)

$[\text{Fe}(\text{C}_2\text{O}_4)_2\text{Cl}_2]^{4-}$ contains ligands which are anions of ethanedioic acid, $\text{HO}_2\text{CCO}_2\text{H}$ .

Complete the table to show any observations for the reactions of $\text{HO}_2\text{CCO}_2\text{H}$ with the named reagents.

Where no change is observed, write ‘none’.

reagent	observations with $\text{HO}_2\text{CCO}_2\text{H}$
warm acidified manganate(VII)
2,4-dinitrophenylhydrazine
warm Tollens’ reagent

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5 more questions

Q2Group 2 · Electrochemistry11M
Q3Electrochemistry · Reaction Kinetics · Chemical Energetics · Equilibria25M
Q4Introduction to A Level Organic Chemistry · Nitrogen Compounds · Hydrocarbons · Analytical Techniques12M
Q5Carboxylic Acids and Derivatives · Hydroxy Compounds · Equilibria · Hydrocarbons · Nitrogen Compounds · Analytical Techniques21M
Q6Organic Synthesis · Carboxylic Acids and Derivatives · Halogen Compounds · Nitrogen Compounds · Polymerisation · Introduction to A Level Organic Chemistry · Transition Elements11M

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