The mass of residue, is
CH3COONa solution, should be
24g of
CH3COONa solution.
In this reaction, sodium bicarbonate reacts with acetic acid to produce sodium acetate, carbon dioxide and water
NaHCO3+CH3COOH⟶CH3COONa+CO2+H2O
According to law of conversation of masses,
total masses of reactants = total masses of products
reactants are 8.4g NaHCO3 and 20g CH3COOH.
total mass of reactants is =28.4g
mass of residue = (28.4g reactants mass) − (4.4g CO2)
= 24.0g residue (sodium acetate solution)
mass of residue is thus 24 grams.