Question

On reacting \[NaHC{O_3}\] and acetic acid, the gas evolved turns ________.

Answer 1

Hint: Neutralization reaction: It is a chemical reaction in which an acid reacts with a base to form salt and water. The value of resultant \[pH\] varies with the change in strength of an acid or a base. In case of reaction of a weak acid with a weak base, the pH value depends on the respective\[{K_a}\] and \[{K_b}\] values.

Complete answer:
Acetic acid: The molecular formula of the acetic acid is \[C{H_3}COOH\]. The \[{K_a}\]value of acetic acid is \[1.7 \times {10^{ - 5}}\] and we know that lower the \[{K_a}\] value, lesser will be the strength of the acid. So, we can conclude that acetic acid is a weak acid.
Sodium Bicarbonate: Its molecular formula is \[NaHC{O_3}\]. The\[{K_b}\] value of sodium bicarbonate is \[2.4 \times {10^{ - 8}}\] and we know that lower the \[{K_b}\] value, lesser will be the strength of the base. So, we can say that sodium bicarbonate is a weak base.
Therefore, when \[NaHC{O_3}\]reacts with acetic acid, a neutralization reaction takes place and an aqueous salt of sodium acetate is formed along with the evolution of carbon dioxide gas.
The reaction involved in the process proceeds as follows:
\[C{H_3}COOH + NaHC{O_3} \to C{H_3}COONa + {H_2}O + C{O_2} \uparrow \]
The gas evolved in the reaction is carbon dioxide, which is a colourless and odourless gas. It appears as a brisk effervescence, so after the reaction bubbles in the solution can be observed.
Hence, on reacting \[NaHC{O_3}\] and acetic acid i.e., \[C{H_3}COOH\], the gas evolved turns lime water milky.

Note:
The presence of carbon dioxide can also be tested by passing it through lime water. When \[C{O_2}\] gas is passed through the lime water, the formation of solid calcium carbonate takes place due to which the solution turns milky.