Chemistry 9701/41 — May/June 2020

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

questions

100

marks

120

minutes

Topics Equilibria · Electrochemistry · Transition Elements · Analytical Techniques · Group 2 · Nitrogen Compounds · +6 more

Q1Transition ElementsEquilibriaFree sample

(a)

An aqueous solution of cobalt(II) contains the $[\text{Co}(\text{H}_2\text{O})_6]^{2+}$ complex ion.

(i)

Define the term complex ion.

(ii)

Samples of $[\text{Co}(\text{H}_2\text{O})_6]^{2+}$ are reacted separately with aqueous sodium hydroxide and with an excess of aqueous ammonia.

Give the following information about these reactions.

the reaction of $[\text{Co}(\text{H}_2\text{O})_6]^{2+}$ $[Co (H_{2} O)_{6}]^{2 +}$ with aqueous sodium hydroxide
- colour and state of the cobalt-containing species
- ionic equation
- type of reaction
the reaction of $[\text{Co}(\text{H}_2\text{O})_6]^{2+}$ $[Co (H_{2} O)_{6}]^{2 +}$ with an excess of aqueous ammonia
- colour and state of the cobalt-containing species
- ionic equation
- type of reaction

(b)

When concentrated hydrochloric acid is added to a solution containing $[\text{Co}(\text{H}_2\text{O})_6]^{2+}$ , a blue solution of $[\text{CoCl}_4]^{2-}$ is formed and the following equilibrium is established.

[\text{Co}(\text{H}_2\text{O})_6]^{2+} + 4\text{Cl}^- \rightleftharpoons [\text{CoCl}_4]^{2-} + 6\text{H}_2\text{O}

Use Le Chatelier’s principle to suggest the expected observations when silver nitrate solution is added dropwise to the blue solution of $[\text{CoCl}_4]^{2-}$ . Explain your answer.

(c)

The $[\text{Co}(\text{NH}_3)_3\text{Cl}_3]$ complex shows stereoisomerism.

Complete the three-dimensional diagrams to show the two isomers of $[\text{Co}(\text{NH}_3)_3\text{Cl}_3]$ .

Fig. 1.1

Suggest the type of stereoisomerism.

(d)

Compound X, $\text{C}_6\text{H}_{18}\text{N}_4$ , is a tetradentate ligand.

Fig. 1.2

(i)

Suggest why one molecule of X can form four dative bonds.

(ii)

$\text{C}_6\text{H}_{18}\text{N}_4$ reacts with aqueous cobalt(II) ions, $[\text{Co}(\text{H}_2\text{O})_6]^{2+}$ , in a 1:1 ratio to form a new complex ion.

Construct an equation for this reaction.

The rest of this paper

9 more questions

Q2Group 26M
Q3Electrochemistry7M
Q4Nitrogen Compounds7M
Q5Introduction to A Level Organic Chemistry · Hydrocarbons · Hydroxy Compounds · Analytical Techniques14M
Q6Carboxylic Acids and Derivatives · Equilibria · Analytical Techniques23M
Q7Equilibria · Electrochemistry · Chemical Energetics10M
Q8Equilibria8M
Q9Electrochemistry · Reaction Kinetics7M
Q10Transition Elements5M

Loading the full paper…