Question

When a sample of baking soda was strongly ignited in a crucible, it suffered a loss in weight of $3.1$ g. The mass of baking soda is:

• A. $16.8$ g
• B. $8.4$ g
• C. $11.6$ g
• D. $4.2$ g

Answer 1

The correct option is B $8.4$ g

The reaction is:

$2NaHC{O}_3\to N{a}_{2}C{O}_3+H_{2}O+C{O}_2$.

The loss in weight is due to water and carbon dioxide.

$2$ moles ($2\times 84$ g) of sodium bicarbonate gives $1$ mole ($18$ g) of water and $1$ mole of carbon dioxide ($44$ g).

Thus, decomposition of $168$ g of sodium bicarbonate will result in a loss in weight of $18+44=62$ g.

The loss in weight of 3.1 g corresponds to $\frac{168}{62}\times 3.1=8.4$g of sodium bicarbonate.

Hence, the correct option is $B$