Bài 8 :
Gọi $n_{Na} = a(mol) ; n_{Na_2O} = b(mol)$
Ta có :
$23a + 62b = 23,2$
$n_{NaOH} = a + 2b = 0,8(mol)$
Suy ra a = 0,2 ; b = 0,3
$m_{Na} = 0,2.23 = 4,6(gam)$
Bài 9 :
Gọi $n_{NaOH} = a ; n_{KOH} = b$
$NaOH + HCl \to NaCl + H_2O$
$KOH + HCl \to KCl + H_2O$
Theo PTHH :
$n_{HCl} = a + b = 0,5.1,5 = 0,75(mol)$
$m_{muối} = 58,5a + 74,5b = 49,475(gam)$
Suy ra a = 0,4 ; b = 0,35
Suy ra:
$C_{M_{NaOH}} = \dfrac{0,4}{0,2} = 2M$
$C_{M_{KOH}} = \dfrac{0,35}{0,2} = 1,75M$
Bài 7:
Theo gt ta có: $n_{Zn}=0,2(mol);n_{HCl}=0,5(mol)$
$Zn+2HCl\rightarrow ZnCl_2+H_2$
Ta có: $n_{ZnCl_2}=0,2(mol);n_{H_2}=0,2(mol);n_{HCl/du}=0,1(mol)$
Bảo toàn khối lượng ta có: $m_{dd}=13+182,5-0,2.2=195,1(g)$
$\Rightarrow \%C_{HCl/du}=1,87\%;\%C_{ZnCl_2}=13,94\%$
