Question

A compound $X$ is heated with ${C_2}{H_5}OH$ and${H_2}S{O_4}$ , the fumes produced burn with green flame. The compound $X$ is?
A: ${H_3}B{O_3}$
B: $N{a_2}{B_4}{O_7}.{H_2}O$
C: ${K_3}B{O_3}$
D: None of the above

Answer 1

Hint: Sulphuric acid acts as a dehydrating agent. Dehydrating agent is a substance that dries or removes water from a material. Dehydration takes place when ethanol is heated with sulphuric acid which is the key step of the reaction.

Complete step by step answer:
When ethanol is heated with concentrated sulphuric acid dehydration takes place. Sulphuric acid acts as a dehydrating agent. Reaction involved is:
${C_2}{H_5}OH + conc.{H_2}S{O_4} \to {C_2}{H_4} + {H_2}O$
The compound $X$ is ${C_2}{H_4}$ . So correct answer is option D i.e., none of the above.

Additional information: Sulphuric acid is also known as oil of vitriol. It is a mineral acid composed of elements of sulphur, oxygen and hydrogen with molecular formula ${H_2}S{O_4}$ it is colorless, odorless and viscous liquid that is soluble in water. Sulphuric acid reacts very vigorously with water in a highly exothermic reaction. If you add water to concentrated sulphuric acid, it can boil and spit and you may get a nasty acid burn.
Properties of sulphuric acid include its acidic nature oxidizing property dehydrating agent. Concentrated sulphuric acid absorbs water and acts as a dehydrating agent. It absorbs water from various substances such as sugar starch paper wood cloth etc.
It is a strong oxidizing agent. Sulphuric acid is used in various industrial processes such as dehydration of ethanol and esterification. In this question we have studied dehydration of ethanol. Sulphuric acid can be used as a dehydrating agent in the contact process as well. It is a common catalyst to manufacture esters.
Dilute sulphuric acid is a non-oxidizing agent but concentrated acid in hot conditions acts as a strong oxidizing agent. It is used in manufacturing of fertilizers, paint pigments, detergents, synthetic fibres, gasoline, explosives, plastic and other chemicals. It is also used as electrolyte in car batteries, in cleaning metals. It is used in refineries such as oil refineries, in crude oil refining it is used as a catalyst.

Note: Understanding the type and steps of reaction is important to identify the missing reactant. One should know the properties of reagent and other chemical compounds such as in this case sulphuric acid is a dehydrating agent.