`#AkaShi`
PTHH:
`H_2SO_4+2NaOH->Na_2SO_4+2H_2O`
`->m_{H_2SO_4}=m_{dd}xxC%=200xx9,8%=19,6\ (g)`
`->n_{H_2SO_4}=(19,6)/98=0,2\ (mol)`
`b)`
`->n_{NaOH}=2xxn_{H_2SO_4}=0,2xx2=0,4\ (mol)`
`->V_{NaOH}=(0,4)/(2)=0,2\ (l)=200ml`
`c)`
`->m_{dd\ NaOH}=200xx2,5=300\ (g)`
`->m_{dd\ sau\ pư}=200+300=500\ (g)`
`->n_{Na_2SO_4}=n_{H_2SO_4}=0,2\ (mol)`
`->C%_{Na_2SO_4}=(0,2xx142)/500xx100%=5,56%`