Question

A student took a sample of a chemical and added acid to it, a gas is released which turned lime water milky. Which of the following option could be the chemical sample taken by the student?

• A. $\text{NaOH}$
• B. $\text{NaCl}$
• C. ${\text{C}}_2{\text{H}}_6$
• D. ${\text{CaCO}}_3$

Answer 1

The correct option is D ${\text{CaCO}}_3$

The chemical sample could be a carbonate or bicarbonate compound. When a metal carbonate reacts with an acid, ${\text{CO}}_2$ gas is released. For example: calcium carbonate on reaction with hydrochloric acid will give calcium chloride, carbon dioxide and water. The reaction involved is:

$2\text{HCl}+{\text{CaCO}}_3\to {\text{CaCl}}_2+{\text{CO}}_2+{\text{H}}_2\text{O}$

The ${\text{CO}}_2$ gas turns lime water ${\text{(Ca(OH)}}_2)$ milky. The reaction occus as follows:

${\text{Ca(OH)}}_2+{\text{CO}}_2\to {\text{CaCO}}_3+{\text{H}}_2\text{O}$

Due to the formation of calcium carbonate compound the lime water turns milky.