## Chemistry and Chemical Reactivity (9th Edition)

$50.91\%$
Number of moles of NaOH: $11.1\ mL\times 0.121\ M=1.34\ mmol$, same as excess HCl. Total number of moles of HCl: $50.0\ mL\times 0.100\ M=5.00\ mmol$ Number of moles consumed: $5.00-1.34=3.66\ mmol$, same as ammonia. From stoichiometry, the number of moles of ammonium sulfate: $1.83\ mmol$ Mass: $0.00183\ mol\times 132.14\ g/mol=0.242\ g$ Mass percentage: $0.242/0.475\times100\%=50.91\%$