Đáp án + Giải thích các bước giải:

1.

$250ml = 0,25l$

$n_{NaOH} = \dfrac{m}{M} = \dfrac{2}{23 + 16 + 1} = \dfrac{2}{40} = 0,05\text{ mol}$

$\Rightarrow C_{MNaOH} = \dfrac{n}{V} = \dfrac{0,05}{0,25} = 0,2M$

2.

$m_{dd} = 5 + 195 = 200g$

$\Rightarrow C\%_{BaCl_2} = \dfrac{m_{ct}}{m_{dd}} . 100\% = \dfrac{5}{200} . 100\% = 2,5\%$

3.

a)

$n_{Zn} = \dfrac{m}{M} = \dfrac{6,5}{65} = 0,1\text{ mol}$

PTHH:
$Zn + 2HCl \longrightarrow ZnCl_2 + H_2 \uparrow$

Theo PTHH:
$n_{HCl} = 2n_{Zn} =2 . 0,1 = 2. 0,1 = 0,2\text{ mol}$
$\Rightarrow m_{HCl} =n . M = 0,2 . (1 + 35,5) = 0,2 . 36,5 = 7,3g$

b) Theo PTHH:
$n_{H_2} = n_{Zn} = 0,1\text{ mol}$
$\Rightarrow V_{H_2} =n . 22,4 = 0,1 . 22,4 = 2,24l$