Solve the following problem. In your working, be meticulous and double check logic, calculations and assumptions. After arriving at final answers, do a final double check to ensure consistency, correctness and absence of careless mistakes.

Metal containing salt A can be prepared in a simple exchange reaction when the cold, saturated aqueous solutions of the two distinctly colored compounds, B and C are mixed in stoichiometric ratio. 𝟣𝟢.𝟢𝟢 g B in solution mixed with the solution of 𝟣𝟤.𝟪𝟨 g C, and immediately cooled to 𝟤 ∘ C will give 𝟦.𝟫𝟢 g solid A. The yield of A is 32.6 %.
To determine the composition of A, first iodometry is performed. A known mass of A is added to a titration flask, acidified with sulfuric acid, then KI is added in excess and there is a precipitate formation. After a few minutes, sodium citrate solution is added until the solution is free of precipitate. The citrate ions form a strong complex with a metal ion present in the mixture, reversing completely the reaction leading to the precipitate. The resulting mixture is titrated with sodium thiosulfate solution (Titration I via reaction 1). To the blue titrated solution another portion of sulfuric acid (significantly more than the initial amount) is added to protonate the citrate. The previous solid precipitate is formed once again [reaction 2]. The mixture is titrated with the same thiosulfate solution (titration II via reaction 1).
The average volumes for 𝟣𝟢𝟢.𝟢 mg A with 𝟧.𝟢𝟢𝟢 ⋅ 𝟣𝟢−𝟤 mol dm−𝟥 thiosulfate are 𝟧𝟦.𝟣𝟤 cm𝟥 in Titration I and 5.41 cm3 in Titration II.
When the aqueous solution of A is heated, the blue precipitate D can be observed [reaction 3]. Com- pound E can be crystallized from the liquid above D. The low temperature during the synthesis of A is important to avoid contamination by E.

5.1 Write balanced equations for reactions [1] and [2].

The thermal decomposition of A was studied in detail. When pure A is slowly heated, already at around 𝟩𝟧 ∘ C it explodes. When the compound is dispersed in aluminium oxide and the mixture is heated, then the matrix absorbs the excess heat, and the explosion can be avoided. Two decomposition steps can be observed. In the first step (at 𝟨𝟧 ∘ C) in addition to the 14.1 % mass decrease, a two-component solid residue forms [reaction 4]. The components of this residue can be easily separated, as F is well soluble in water, while G does not dissolve at all. The F:G mass ratio is 𝟣.𝟢𝟢 ∶ 𝟤.𝟫𝟩. On further heating, F decomposes without a solid residue [reaction 5]. That means pure G is the final solid decomposition product of A. G contains two other elements in addition to 27.0 wt% oxygen. One of the two components of the gas mixture forming in the first decomposition step can be easily quantitated if it is absorbed in acid solution.
Some hints
• Compound A decomposes without releasing oxygen.
• Compound A contains two different metals.
• Compounds A and B both contain a complex ion.
• C is a well-known compound for any chemistry student. • Compound F does not contain any metal.

Give chemical formulae of A—G. You don’t have to show your calculations, but if your compounds are incorrect you may gain partial marks from correct calculations. Write balanced equations for reactions [3]—[5].