The substance X has been prepared by the following procedures. Copper(II) sulfate pentahydrate (ca 1 — Organic Chemistry Chemistry Question
Preparation of inorganic compound
The substance X has been prepared by the following procedures. Copper(II) sulfate pentahydrate (ca 10 g) was dissolved in a mixture of distilled water (80 cm3) and concentrated sulfuric acid (4 cm3). The solution was boiled with analytical-grade metallic tin (10 g) until the solution became colorless and the deposited copper was covered with a grey coating of tin. The resultant solution was filtered and treated with an ammonia-water solution until the complete precipitation of a product. It was filtered off and washed with water until no odor of ammonia was detectable. The precipitate obtained was added to the nitric acid solution gradually in small portions, with stirring, until the solution was saturated. The suspension was boiled for 2 min, filtered into a warm, insulated flask and allowed to cool slowly. The 1.05 g of crystalline product X was obtained. Under heating X rapidly decomposes with the mass loss of 17.49 %. The residue formed is a binary compound identical with the common mineral of tin. The volatile decomposition products passed over 1.00 g of anhydrous copper(II) sulfate increase its mass by 6.9 %.
Determine the composition of Х.
Model Answer
The common mineral of tin is cassiterite, SnO2. Thus, 1.05 g of Х after decomposition give 0.8664 g of SnO2 that contains 5.738 mmol of tin. Under decomposition 0.069 g (3.833 mmol) of water form. As the ratio n(Sn) : n(H2O) is equal to 1.5 (or 3 : 2), the brutto formula of Х contains 3 equivalents of SnO2, 4 of H and 2 of O (from 2 water molecules). In addition, it also contains nitrogen and probably more oxygen. Their mass is 1.05 – 0.8664 – 0.069 = 0.1146 g and the average molar mass is M = 0.1146 / (0.00383/2) = 60 g mol–1, which corresponds to N2O2. Thus, the formula of X is Sn3O10N2H4, or Sn3O2(NO3)2(H2O)2.
What important instruction has been omitted in the description of the procedure?
Model Answer
All the operations should be performed in an inert atmosphere, because tin(II) hydroxide is oxidized in air.
Predict the structure of the cation in X taking into account that all the metal atoms in it are equivalent.
Model Answer
If all the metal atoms in the cation are equivalent they have the same coordination sphere. So, we may suppose the formula [Sn3(OH)4] 2+, that is a combination of three pyramids linked by joint edges in a cycle (See J.D. Donaldson et al, JCS Dalton Trans, 1995, 2273.):
The pyramidal nonplanar geometry is due to the electron pair on each tin atom.
What particles are formed by addition of an acid or an alkali to the solution of X?
Model Answer
In the acidic solution the hydrated tin(II) ions are formed, in the basic media – the anions [Sn(OH)3] –, [Sn(OH)6] 4– and oligonuclear species such as [Sn2O(OH)4] 2–, [Sn4O(OH)10] 4–.
What happens when a solution of bismuth trichloride in HCl solution is added to the solution of tin chloride? The concentrations of all solutions are 1 mol dm-3. Calculate the equilibrium constant of the reaction. Extract the necessary data from the Latimer diagrams below.
Model Answer
2 BiCl3 + 3 SnCl2 + 6 HCl → 2 Bi + 3 H2SnCl6
E° = 0.317 – 0.15 = 0.167 V,
K = exp(nF E° / RT) = exp(6×96500×0.167 / 8.314×298) = 8.90×10^16