Question

When conc. ${H_{_2}}S{O_4}$is added to hydrated copper [II] sulphate:
(A) white crystals are changed to black powder as water is removed.
(B) brown crystals are changed to black powder as water is removed.
(C) black crystals are changed to white powder as water is removed.
(D) blue crystals are changed to white powder as water is removed.

Answer 1

Conc. sulfuric acid has a very strong affinity for water. It is sometimes used as a drying agent and can be used to dehydrate many compounds. When the acid mixes with water, large amounts of heat are released. To dilute the acid, the acid should be added slowly to cold water with constant stirring. Sulfuric acid reacts with water and forms hydrates with distinct properties.

Complete step by step solution:
First of all, we have to get a basic idea of conc. sulphuric acid and hydrated copper [II] sulphate and the reaction.
Copper sulphate is an inorganic compound. The pentahydrate is the most commonly encountered salt, which is bright blue. Copper sulfate is produced industrially by treating copper metal with hot concentrated sulfuric acid or its oxides with dilute sulfuric acid. Copper sulfate can also be produced by slowly leaching low-grade copper ore in the air; bacteria may be used to hasten the process. Its pentahydrate is the most commonly encountered salt, which is bright blue. The structure of the solid pentahydrate reveals a polymeric structure wherein copper is again octahedral but bound to four water ligands.
Sulfuric acid, also known as oil of vitriol, is a mineral acid composed of the elements sulfur, oxygen and hydrogen. It is a colourless, odourless liquid that is soluble in water and is synthesized in reactions that are highly exothermic. Concentrated sulfuric acid is a weak acid and a poor electrolyte because relatively little of it is dissociated into ions at room temperature. When cold it does not react readily with common metals as iron or copper. When hot it is an oxidizing agent. Hot concentrated sulfuric acid reacts with most metals and with several nonmetals.
The reaction between conc. ${H_{_2}}S{O_4}$and hydrated copper [II] sulphate can be demonstrated by the following chemical equation:
$CuS{O_{_4}}.5{H_2}O + {H_2}S{O_4}(conc.) \to CuS{O_{_4}} + 5{H_2}O$
Conc. sulfuric acid removes water from blue hydrate copper sulphate and convert it to white anhydrous copper sulphate as shown in the above reaction.

Hence, the answer of the above question is (D)- blue crystals are changed to white powder as water is removed.

Note: Don't get confused between concentrated and dilute sulfuric acid. Both their concentration and actions are different. Dilute sulphuric acid is a non-oxidizing acid, though the concentrated one in hot condition acts as an oxidizing agent.