8.4 g of sodium bicarbonate reacts with 20 g of acetic acid to liberate 4.4 g of carbon dioxide gas into the atmosphere. The mass of residue left in the reaction vessel is?

8.4 g of sodium bicarbonate reacts with 20 g of acetic acid to liberate 4.4 g of carbon dioxide gas into the atmosphere. The mass of residue left in the reaction vessel is 24 g.

In this reaction, sodium bicarbonate reacts with acetic acid to produce sodium acetate, carbon dioxide, and water. The reaction equation is as below,
$\mathit{NaHC}{O}_3+C{H}_3\mathit{COOH}\to C{H}_3\mathit{COONa}+C{O}_2+ H_{2}O$

According to the law of conservation of masses,

Total masses of reactants = Total masses of products
Reactants are $8.4 g\mathit{ }\mathit{NaHC}{O}_3\mathit{ and }20 g\mathit{ }C{H}_3\mathit{COOH}$
The total mass of reactants $=28.4g$
Mass of residue                  $=>(28.4 \mathrm{reactants} \mathrm{mass})-(4.4\mathit{g }{\mathit{CO}}_2)$
                                               $=>24.0g\mathit{ }\mathrm{residue} (\mathrm{sodium} \mathrm{acetate} \mathrm{solution})$
The mass of residue is therefore 24 g.