Đáp án + Giải thích các bước giải:

Bài 1:

a) $\rm H \text{$\rm \mathop{Cl}\limits^{-1}$} + K_2\text{$\rm \mathop{Mn}\limits^{+6}$}O_4 \longrightarrow \mathop{Cl_2}\limits^0 + KCl + \text{$\rm \mathop{Mn}\limits^{+2}$}Cl_2 + H_2O$ 

Chất khử: $\rm HCl$
Chất oxy hoá: $\rm K_2MnO_4$

Quá trình khử: $\rm \mathop{Mn}\limits^{+6} + 4e \longrightarrow \mathop{Mn}\limits^{+2} || \times 1$

Quá trình oxy hoá: $\rm 2\mathop{Cl}\limits^{-1} \longrightarrow \mathop{Cl_2}\limits^0 + 2e || \times 2$

$\Rightarrow \rm K_2MnO_4 + 8HCl \longrightarrow 2Cl_2 + 2KCl + MnCl_2 + 4H_2O$

b) $\rm \text{$\rm \mathop{Fe}\limits^{+2}$}(OH)_2 + H_2\text{$\rm \mathop{S}\limits^{+6}$}O_4 \longrightarrow \text{$\rm \mathop{Fe_2}\limits^{+3}$}(SO_4)_3 + \text{$\rm \mathop{S}\limits^{+4}$}O_2 + H_2O$

Chất khử: $\rm Fe(OH)_2$
Chất oxy hoá: $\rm H_2SO_4$

Quá trình khử: $\rm \mathop{S}\limits^{+6} + 2e \longrightarrow \mathop{S}\limits^{+4} || \times 1$

Quá trình oxy hoá: $\rm \mathop{Fe}\limits^{+2} \longrightarrow \mathop{Fe}\limits^{+3} + e || \times 2$

$\Rightarrow \rm 2Fe(OH)_2 +4H_2SO_4 \longrightarrow Fe_2(SO_4)_3 + SO_2 + 6H_2O$

c) $\rm \mathop{Mg}\limits^0 + H\text{$\rm \mathop{N}\limits^{+5}$}O_3 \longrightarrow \text{$\rm \mathop{Mg}\limits^{+2}$}(NO_3)_2 + \rm \mathop{N_2}\limits^0 + H_2O$

Chất khử: $\rm Mg$
Chất oxy hoá: $\rm HNO_3$

Quá trình khử: $\rm 2\mathop{N}\limits^{+5} + 10e \longrightarrow \mathop{N_2}\limits^0 || \times 1$

Quá trình oxy hoá: $\rm \mathop{Mg}\limits^0 \longrightarrow \mathop{Mg}\limits^{+2} + 2e || \times 5$

$\Rightarrow \rm 5Mg + 12HNO_3 \longrightarrow 5Mg(NO_3)_2 + N_2 + 6H_2O$

d) $\rm \mathop{Al}\limits^0 + H\text{$\rm \mathop{N}\limits^{+5}$}O_3 \longrightarrow \text{$\rm \mathop{Al}\limits^{+3}$}(NO_3)_3 + \text{$\rm \mathop{N}\limits^{-3}$}H_4NO_3 + H_2O$

Chất khử: $\rm Al$
Chất oxy hoá: $\rm HNO_3$

Quá trình khử: $\rm \mathop{N}\limits^{+5} + 8e \longrightarrow \mathop{N}\limits^{-3} || \times 3$

Quá trình oxy hoá: $\rm \mathop{Al}\limits^0 \longrightarrow \mathop{Al}\limits^{+3} + 3e || \times 8$

$\Rightarrow \rm 8Al + 30HNO_3 \longrightarrow 8Al(NO_3)_3 + 3NH_4NO_3 + 9H_2O$

e) $\rm K\text{$\rm \mathop{Mn}\limits^{+7}$}O_4 + \rm H \text{$\rm \mathop{Cl}\limits^{-1}$} \longrightarrow  KCl + \text{$\rm \mathop{Mn}\limits^{+2}$}Cl_2 + \mathop{Cl_2}\limits^0 + H_2O$ 

Chất khử: $\rm HCl$
Chất oxy hoá: $\rm KMnO_4$

Quá trình khử: $\rm \mathop{Mn}\limits^{+7} + 5e \longrightarrow \mathop{Mn}\limits^{+2} || \times 2$

Quá trình oxy hoá: $\rm 2\mathop{Cl}\limits^{-1} \longrightarrow \mathop{Cl_2}\limits^0 + 2e || \times 5$

$\Rightarrow \rm 2KMnO_4 + 16HCl \longrightarrow 2KCl + 2MnCl_2 + 5Cl_2 + 8H_2O$

Bài 2:

$n_{\rm Al}$ $= \dfrac{5,4}{27} = 0,2(\rm mol)$

PTHH:
$\rm 2Al + 3H_2SO_4 \longrightarrow Al_2(SO_4)_3 + 3H_2$

Theo PTHH:

$n_{\rm H_2}$ $= \dfrac{3}{2}n_{\rm Al}$ $= \dfrac{3}{2} . 0,2 = 0,3(\rm mol)$

$\Rightarrow \rm V = V_{H_2}$ $= 0,3 . 22,4 = 6,72(\rm l)$