Carbon dioxide obtained during the complete combustion of 8.96 liters of methane is completely absorbed by 300 g of sodium

Carbon dioxide obtained during the complete combustion of 8.96 liters of methane is completely absorbed by 300 g of sodium hydroxide solution containing 6% solute. Determine the mass fraction of salt in the final solution.

CH4 + 2O2 → CO2 + 2H2O
CO2 + 2NaOH → Na2CO3 + H2O
n (CH4) = 8.96 / 22.4 = 0.4 mol
n (CO2) = N (CH4) = 0.4 mol – in excess
n (NaOH) = (300 x 0.06) / 40 = 0.45 mol – deficient
n (Na2CO3) = n (NaOH): 2 = 0.225 mol
m (Na2CO3) = 0.225 x (46 + 12 + 48) = 23.85 g
m (solution) = 300 + 0.4 x 44 = 317.6 g
ω (Na2CO3) = 23.85 / 317.6 x 100% = 7.5%
Answer: the mass fraction of salt (sodium carbonate) in the final solution is 7.5%.