An aqueous solution of cobalt(II) contains the [Co(H2O)6]2+ complex ion.

1. (a)(i)Define the term complex ion.[1]
2. (a)(ii)Samples of [Co(H2O)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 [Co(H2O)6]2+ with aqueous sodium hydroxide colour and state of the cobalt-containing species ionic equation type of reaction • the reaction of [Co(H2O)6]2+ with an excess of aqueous ammonia colour and state of the cobalt-containing species ionic equation type of reaction[6]
3. (b)When concentrated hydrochloric acid is added to a solution containing [Co(H2O)6]2+, a blue solution of [CoCl4]²– is formed and the following equilibrium is established. [Co(H2O)6]2+ + 4Cl- ⇌ [CoCl4]2- + 6H2O Use Le Chatelier's principle to suggest the expected observations when silver nitrate solution is added dropwise to the blue solution of [CoCl4]2-. Explain your answer.[2]
4. (c)The [Co(NH3)3Cl3] complex shows stereoisomerism. Complete the three-dimensional diagrams to show the two isomers of [Co(NH3)3Cl3]. Suggest the type of stereoisomerism. [Diagram showing two 'Co' central atoms with bonds for ligands][2]
5. (d)(i)Compound X, C6H18N4, is a tetradentate ligand. [Figure showing structure of Compound X with formula H₂N–CH₂CH₂–NH–CH₂CH₂–NH–CH₂CH₂–NH₂] Suggest why one molecule of X can form four dative bonds.[1]
6. (d)(ii)C6H18N4 reacts with aqueous cobalt(II) ions, [Co(H2O)6]²⁺, in a 1:1 ratio to form a new complex ion. Construct an equation for this reaction.[1]

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