Question

When zinc powder is added to the acetic acid ____________.
A.The mixture becomes warm
B.A gas is evolved
C.The colour of the mixture becomes yellow
D.A solid settle at the bottom

Answer 1

Zinc is a metal which occurs in powder form. The reaction of active metal with dilute non-oxyacid salt liberates hydrogen gas and a soluble salt is formed.

Complete step by step answer:
Zinc is an active metal therefore it readily reacts at room temperature. When reacted with acetic acid, hydrogen gas is evolved.
${\text{Zn + 2C}}{{\text{H}}_{\text{3}}}{\text{COOH}} \to {\text{Zn(C}}{{\text{H}}_{\text{3}}}{\text{COO}}{{\text{)}}_{{\text{2 }}}}{\text{ + }}{{\text{H}}_{\text{2}}} \uparrow$
The acetic acid must be in dilute condition which is a non-oxyacid. The reaction of active metal such as zinc with dilute non-oxyacid, acetic acid, hydrogen gas gets liberated and a soluble metal salt is formed. The soluble metal salt is known as zinc acetate. The oxidation salt of zinc is +2 in the soluble salt.
The acetic acid is also known as vinegar. Though the amount of acetic acid in vinegar is small it is more than enough to liberate hydrogen gas when it reacts with zinc powder. Upon addition of vinegar to zinc metal, bubbles can be seen in the reaction due to the liberation of hydrogen gas.
The general reaction can be written as:
${\text{Metal + Dil}}{\text{. Non - Oxyacid}} \to {\text{Salt + Hydrogen}}$

So, the correct option is B.

Note:
Zinc in acetic acid is used in various reduction reactions. Zinc is a post transition metal which like Aluminium does not need any catalysts to react with acetic acid to liberate hydrogen gas. The reduction potential of Zinc ({\text{E^\circ = 0}}{\text{.76 V}}) also depicts that it is a reducing agent.