Draw the structure of $\mathbf{Z}$ to show its three-dimensional arrangement. Include the overall charge on the complex ion.

The formation of $\mathbf{Z}$ is an example of the chelate effect. Explain the meaning of the chelate effect with reference to this reaction, explaining why this substitution reaction is thermodynamically highly favourable in terms of entropy and Gibbs free energy.

Part 2: Autocatalysis

Outline how ${Mn}^{2+}$ ions autocatalyse the reaction between ${MnO}_4^{-}$ ions and $C_2{O}_4^{2-}$ ions in acidic solution.

In your answer you should include:

• a description of the curve on a sketch graph showing how the concentration of $C_2{O}_4^{2-}$ ions changes over time (label both axes)
• an explanation of why the initial rate of this reaction is very slow and how the ${Mn}^{2+}$ catalyst provides an alternative route with lower activation energy, including equations for the intermediate steps
• an overall ionic equation for the reaction.

Part 3: Test-tube Reactions

A student adds dilute ammonia solution dropwise until in excess to a solution containing $[Fe(H_{2}O{)}_6{]}^{2+}$ ions. Give the formula of the precipitate that initially forms.

The student then adds sodium carbonate solution to a separate tube containing $[Fe(H_{2}O{)}_6{]}^{3+}$ ions. State two observations the student would make and give an overall ionic equation for this reaction.