25 bài tập Phương pháp bảo toàn số mol electron (có lời giải)

Chọn B

Chọn A

Chọn C

a)

b)

${n}_{Fe}\text{= 0{,}25 mol}$

a)

$\overset{0}{Fe}\text{+}{\overset{+1}{\text{H}}}_{2}S{O}_{4}\ \overset{}{\rightarrow }\ \overset{+2}{\text{Fe}}{\text{SO}}_{4}\text{+}{\overset{0}{\text{H}}}_{2}$

$10\overset{+2}{Fe}S{O}_{4}\text{+ 2K}\overset{+7}{\text{Mn}}{\text{O}}_{4}{\text{+ 8H}}_{2}S{O}_{4}\ \overset{}{\rightarrow }\text{5}{\overset{+3}{Fe}}_{2}{{\text{(SO}}_{4}\text{)}}_{3}\text{+ 2}\overset{+2}{\text{Mn}}{\text{SO}}_{4}{\text{+ K}}_{2}S{O}_{4}{\text{+ 8H}}_{2}O$

b) $\overset{BT\text{Fe}}{\rightarrow }{\text{n}}_{FeS{O}_{4}}{\text{= n}}_{Fe}\text{= 0{,}25 mol}$

$\begin{matrix}M{n}^{+7}\text{+ 5e}\overset{}{\rightarrow }{\text{Mn}}^{+2} \\ \text{0{,}05}\leftarrow \text{0{,}25}\end{matrix}||\begin{matrix}\ F{e}^{2+}\ \overset{}{\rightarrow }\ F{e}^{3+}\text{+ 1e} \\ \text{0{,}25}\overset{}{\rightarrow }\text{0{,}25}\end{matrix}$

${n}_{KMn{O}_{4}}{\text{= n}}_{M{n}^{+7}}\text{= 0{,}05 mol}\overset{}{\rightarrow }{\text{V}}_{KMn{O}_{4}}\text{= 50 mL}$

${n}_{Fe{(N{O}_{3})}_{3}}{\text{= 0{,}3 mol; n}}_{N{O}_{2}}\text{= 0{,}1 mol}$

Fe$_{x}$O$_{y}$ + (6x – 2y)HNO$_{3}$ xFe(NO$_{3}$)$_{3}$ + (3x – 2y)NO$_{2}$ + (3x – y)H$_{2}$O

$\overset{PTHH}{\rightarrow }\ \frac{{n}_{Fe{(N{O}_{3})}_{3}}}{{n}_{N{O}_{2}}}\text{=}\frac{x}{3x-2y}=\frac{0{,}3}{0{,}1}\ \Rightarrow \ \frac{x}{y}\text{=}\frac{3}{4}\ \ \overset{}{\rightarrow }{\text{CT oxide: Fe}}_{3}{O}_{4}$

${n}_{{K}_{2}C{r}_{2}{O}_{7}}{\text{= 2.10}}^{-4}\text{mol}$

a) $3{\overset{-2}{C}}_{2}{\text{H}}_{5}{\text{OH + K}}_{2}{\overset{+6}{\text{Cr}}}_{2}{\text{O}}_{7}\text{+ 8}{H}^{+}\ \overset{}{\rightarrow }\text{3}{\overset{-1}{\text{C}}}_{2}{\text{H}}_{4}\text{O + 2}\overset{+3}{Cr}{\text{+ 2K}}^{+}{\text{+ 7H}}_{2}O$

$\begin{matrix}C{r}^{+6}\text{+ 3e}\overset{}{\rightarrow }{\text{Cr}}^{+3} \\ {\text{2.2.10}}^{-4}\ \rightarrow {\text{1{,}2.10}}^{-3}\end{matrix}||\begin{matrix}\ {C}_{2}^{-2}\ \overset{}{\rightarrow }\ {C}_{2}^{-1}\text{+ 2.1e} \\ {\text{6.10}}^{-4}\ \overset{}{\leftarrow }{\text{1{,}2.10}}^{-3}\end{matrix}$

${m}_{{C}_{2}{H}_{5}OH}{\text{= 6.10}}^{-4}.46\text{= 0{,}0276 gam}\ \overset{}{\rightarrow }\text{\%}{m}_{{C}_{2}{H}_{5}OH(25\text{gam})}\text{= 0{,}11\% > 0{,}02\%}$

Vậy người lái xe vi phạm luật giao thông.

${n}_{KMn{O}_{4}}{\text{= 2.10}}^{-3}\text{mol}$

a) $5\overset{+4}{S}{O}_{2}+\text{2}K\overset{+7}{Mn}{O}_{4}+\text{2}{H}_{2}O\ \overset{}{\rightarrow }\text{2}{H}_{2}\overset{+6}{S}{O}_{4}+\ {K}_{2}S{O}_{4}+\overset{+2}{2Mn}S{O}_{4}$

b) $\begin{matrix}M{n}^{+7}\text{+ 5e}\overset{}{\rightarrow }{\text{Mn}}^{+2} \\ {\text{2.10}}^{-3}\ \rightarrow {\text{10}}^{-2}\end{matrix}||\begin{matrix}\ {S}^{+4}\ \overset{}{\rightarrow }\ {S}^{+6}\text{+ 2e} \\ {\text{10}}^{-1}\ \overset{}{\leftarrow }{\text{10}}^{-2}\end{matrix}$

${n}_{S{O}_{2}}{\text{= n}}_{{S}^{+4}}\text{= 0{,}1 mol}\overset{}{\rightarrow }\ {V}_{S{O}_{2}}\text{= 2{,}479 L}$

${n}_{X}\text{= 0{,}1 mol;}\overset{BTKL}{\rightarrow }{\text{m}}_{X}\text{= 8{,}84}-\text{2{,}52 = 6{,}32 gam}$

$\begin{matrix}Mg\ \overset{}{\rightarrow }{\text{Mg}}^{+2}\text{+ 2e} \\ Al\ \overset{}{\rightarrow }{\text{Al}}^{+3}\text{+ 3e}\end{matrix}||\begin{matrix}\ C{l}_{2}\text{(x) + 2.1e (2x)}\overset{}{\rightarrow }\ 2C{l}^{-} \\ \ {O}_{2}\text{(y) + 2.2e (4y)}\overset{}{\rightarrow }\ 2{O}^{-2}\end{matrix}$

a)$\Rightarrow \{\begin{matrix}\overset{{n}_{X}}{\rightarrow }\text{x + y = 0{,}1} \\ \overset{{m}_{X}}{\rightarrow }\text{71x + 32y = 6{,}32}\end{matrix}\ \Rightarrow \{\begin{matrix}\text{x = 0{,}08} \\ \text{y = 0{,}02}\end{matrix}\ \overset{}{\rightarrow }\{\begin{matrix}\%{V}_{C{l}_{2}}\text{= 80\%} \\ \%{V}_{{O}_{2}}\text{= 20\%}\end{matrix}$

b) $\overset{}{\rightarrow }{\text{n}}_{e}\text{= 2x + 4y = 0{,}24 mol}$

a) $4\overset{+2}{Fe}{\overset{-1}{S}}_{2}+\text{11}{\overset{0}{O}}_{2}\ \overset{}{\rightarrow }\text{2}{\overset{+3}{Fe}}_{2}{O}_{3}+\text{8}\overset{+4}{S}{O}_{2}$

b) ${n}_{Fe{S}_{2}}{\text{= 2.10}}^{4}\text{mol}$

$\begin{matrix}Fe{S}_{2}\ \overset{}{\rightarrow }{\text{Fe}}^{+3}{\text{+ 2S}}^{+4}\text{+ 11e} \\ {\text{2.10}}^{4}\ \overset{}{\rightarrow }{\text{2{,}2.10}}^{5}\ \end{matrix}||\begin{matrix}\ {O}_{2}\text{+ 2.2e}\overset{}{\rightarrow }\ 2{O}^{-2} \\ {\text{5{,}5.10}}^{4}\ \leftarrow {\text{2{,}2.10}}^{5}\end{matrix}$

$\Rightarrow {\text{n}}_{kk}{\text{= (100/21).n}}_{{O}_{2}}\ \overset{}{\rightarrow }{\text{V}}_{kk}{\text{= n}}_{kk}\text{.24{,}79 = 6492619 L}$

${n}_{FeS{O}_{4}}{\text{= 2.10}}^{-3}\text{mol}$

a)

$10\overset{+2}{Fe}S{O}_{4}\text{+ 2K}\overset{+7}{\text{Mn}}{\text{O}}_{4}{\text{+ 8H}}_{2}S{O}_{4}\ \overset{}{\rightarrow }\text{5}{\overset{+3}{Fe}}_{2}{{\text{(SO}}_{4}\text{)}}_{3}\text{+ 2}\overset{+2}{\text{Mn}}{\text{SO}}_{4}{\text{+ K}}_{2}S{O}_{4}{\text{+ 8H}}_{2}O$

b) $\begin{matrix}M{n}^{+7}\text{+ 5e}\overset{}{\rightarrow }{\text{Mn}}^{+2} \\ {\text{4.10}}^{-4}\ \leftarrow {\text{2.10}}^{-3}\end{matrix}||\begin{matrix}\ F{e}^{2+}\ \overset{}{\rightarrow }\ F{e}^{3+}\text{+ 1e} \\ {\text{2.10}}^{-3}\ \overset{}{\rightarrow }{\text{2.10}}^{-3}\end{matrix}$

${n}_{KMn{O}_{4}}{\text{= n}}_{M{n}^{+7}}{\text{= 4.10}}^{-4}\text{mol}\overset{}{\rightarrow }{\text{V}}_{KMn{O}_{4}}\text{= 20 mL}$

${n}_{N{H}_{4}Cl{O}_{4}}{\text{= (300/47).10}}^{6}\text{mol}$

$2N{H}_{4}Cl{O}_{4}\ \overset{}{\rightarrow }\ {N}_{2}+\ C{l}_{2}+\text{2}{O}_{2}+\text{4}{H}_{2}O$ (1)

$4Al{\text{+ 3O}}_{2}\ \overset{}{\rightarrow }{\text{2Al}}_{2}{O}_{3}$ (2)

$\overset{PTHH\text{(1)}}{\rightarrow }{\text{n}}_{{O}_{2}}{\text{= n}}_{N{H}_{4}Cl{O}_{4}}$

$\overset{PTHH\text{(2)}}{\rightarrow }{\text{n}}_{Al}{\text{= (4/3)n}}_{{O}_{2}}{\text{= (400/47).10}}^{6}\text{mol}\overset{}{\rightarrow }{\text{m}}_{Al}\text{= 230 (tan)}$

$\overset{PTHH\text{(2)}}{\rightarrow }{\text{n}}_{A{l}_{2}{O}_{3}}{\text{= (2/3)n}}_{{O}_{2}}{\text{= (200/47).10}}^{6}\text{mol}\overset{}{\rightarrow }{\text{m}}_{Al}\text{= 434 (tan)}$

${n}_{{O}_{2}}\text{= 0{,}45 mol}$

a) 2Zn + O$_{2}$ 2ZnO

4Al + 3O$_{2}$ 2Al$_{2}$O$_{3}$

b) $\begin{matrix}Zn\text{(a)}\overset{}{\rightarrow }{\text{Zn}}^{+2}\text{+ 2e (2a)} \\ Al\text{(b)}\overset{}{\rightarrow }{\text{Al}}^{+3}\text{+ 3e (3b)}\end{matrix}||\begin{matrix}\ {O}_{2}\text{+ 2.2e}\overset{}{\rightarrow }\ 2{O}^{-2} \\ \text{0{,}45}\rightarrow \text{1{,}8}\end{matrix}$

$\overset{BTKL}{\rightarrow }{\text{m}}_{oxide}\text{= 30{,}3}-\text{0{,}45.32 = 15{,}9 gam}$

c) $\Rightarrow \{\begin{matrix}\overset{{m}_{kl}}{\rightarrow }\text{65a + 27b = 30{,}3} \\ \overset{BT\text{e}}{\rightarrow }\text{2a + 3b = 1{,}8}\end{matrix}\ \Rightarrow \{\begin{matrix}\text{a = 0{,}3} \\ \text{b = 0{,}4}\end{matrix}\ \overset{}{\rightarrow }\{\begin{matrix}{\text{\%m}}_{Zn}\text{= 64{,}36\%} \\ {\text{\%m}}_{Al}\text{= 35{,}64\%}\end{matrix}$

Chọn B

${n}_{X}\text{= 0{,}35 mol;}\overset{BTKL}{\rightarrow }{\text{m}}_{X}\text{= 30{,}1}-\text{11{,}1 = 19 gam}$

$\begin{matrix}Mg\text{(a)}\overset{}{\rightarrow }{\text{Mg}}^{+2}\text{+ 2e (2a)} \\ Al\text{(b)}\overset{}{\rightarrow }{\text{Al}}^{+3}\text{+ 3e (3b)}\end{matrix}||\begin{matrix}\ C{l}_{2}\text{(x) + 2.1e (2x)}\overset{}{\rightarrow }\ 2C{l}^{-} \\ \ {O}_{2}\text{(y) + 2.2e (4y)}\overset{}{\rightarrow }\ 2{O}^{-2}\end{matrix}$

$\Rightarrow \{\begin{matrix}\overset{{n}_{X}}{\rightarrow }\text{x + y = 0{,}35} \\ \overset{{m}_{X}}{\rightarrow }\text{71x + 32y = 19}\end{matrix}\ \overset{}{\rightarrow }\{\begin{matrix}\text{x = 0{,}2} \\ \text{y = 0{,}15}\end{matrix}$'

$\Rightarrow \{\begin{matrix}\overset{{m}_{Y}}{\rightarrow }\text{24a + 27b = 11{,}1} \\ \overset{BT\text{e}}{\rightarrow }\text{2a + 3b = 0{,}2.2 + 0{,}15.4}\end{matrix}\ \Rightarrow \{\begin{matrix}\text{x = 0{,}35} \\ \text{y = 0{,}1}\end{matrix}\ \overset{}{\rightarrow }{\text{\%m}}_{Al}\text{= 24{,}32\%}$

Chọn A

${n}_{X}\text{= 0{,}25 mol;}\overset{BTKL}{\rightarrow }{\text{m}}_{X}\text{= 23}-\text{7{,}2 = 15{,}8 gam}$

$M\ \overset{}{\rightarrow }{\text{M}}^{+2}\text{+ 2e}||\begin{matrix}\ C{l}_{2}\text{(x) + 2.1e (2x)}\overset{}{\rightarrow }\ 2C{l}^{-} \\ \ {O}_{2}\text{(y) + 2.2e (4y)}\overset{}{\rightarrow }\ 2{O}^{-2}\end{matrix}$

$\Rightarrow \{\begin{matrix}\overset{{n}_{X}}{\rightarrow }\text{x + y = 0{,}25} \\ \overset{{m}_{X}}{\rightarrow }\text{71x + 32y = 15{,}8}\end{matrix}\ \overset{}{\rightarrow }\{\begin{matrix}\text{x = 0{,}2} \\ \text{y = 0{,}05}\end{matrix}$

$\overset{BT\text{e}}{\rightarrow }{\text{2.n}}_{M}\text{= 0{,}2.2 + 0{,}05.4}\Rightarrow {\text{n}}_{M}\text{= 0{,}3}\overset{}{\rightarrow }{\text{M}}_{M}\text{= 24 (Mg)}$

Chọn B

${n}_{{O}_{2}}\text{= 0{,}125 mol;}\overset{BTKL}{\rightarrow }{\text{m}}_{X}\text{= 9{,}1}-\text{0{,}125.32 = 5{,}1 gam}$

$\begin{matrix}Mg\text{(a)}\overset{}{\rightarrow }{\text{Mg}}^{+2}\text{+ 2e (2a)} \\ Al\text{(b)}\overset{}{\rightarrow }{\text{Al}}^{+3}\text{+ 3e (3b)}\end{matrix}||\begin{matrix}\ {O}_{2}\text{+ 2.2e}\overset{}{\rightarrow }\ 2{O}^{-2} \\ \text{0{,}125}\rightarrow \text{0{,}5}\end{matrix}$

$\Rightarrow \{\begin{matrix}\overset{BT\text{e}}{\rightarrow }\text{2a + 3b = 0{,}5} \\ \overset{{m}_{X}}{\rightarrow }\text{24a + 27b = 5{,}1}\end{matrix}\ \Rightarrow \{\begin{matrix}\text{a = 0{,}1} \\ \text{b = 0{,}1}\end{matrix}\ \overset{}{\rightarrow }{\text{m}}_{Mg}\text{= 2{,}4 gam}$

a) $\overset{BTKL}{\rightarrow }{\text{m}}_{C{l}_{2}}\text{= 40{,}3}-\text{11{,}9 = 28{,}4 gam}\Rightarrow \ {\text{n}}_{C{l}_{2}}\text{= 0{,}4 mol}\overset{}{\rightarrow }{\text{V}}_{C{l}_{2}}\text{= 9{,}916 L}$

b) $\begin{matrix}Zn\text{(a)}\overset{}{\rightarrow }{\text{Zn}}^{+2}\text{+ 2e (2a)} \\ Al\text{(b)}\overset{}{\rightarrow }{\text{Al}}^{+3}\text{+ 3e (3b)}\end{matrix}||\begin{matrix}\ C{l}_{2}\text{+ 2.1e}\overset{}{\rightarrow }\ 2C{l}^{-} \\ \text{0{,}4}\rightarrow \text{0{,}8}\end{matrix}$

$\Rightarrow \{\begin{matrix}\overset{BT\text{e}}{\rightarrow }\text{2a + 3b = 0{,}8} \\ \overset{{m}_{kl}}{\rightarrow }\text{65a + 27b = 11{,}9}\end{matrix}\ \Rightarrow \{\begin{matrix}\text{a = 0{,}1} \\ \text{b = 0{,}2}\end{matrix}\ \overset{}{\rightarrow }\{\begin{matrix}\%{m}_{Zn}\text{= 54{,}6\%} \\ {\text{\%m}}_{Al}\text{= 45{,}4\%}\end{matrix}$

a) $\overset{BTKL}{\rightarrow }{\text{m}}_{{O}_{2}}\text{= 30{,}2}-\text{17{,}4 = 12{,}8 gam}\ \Rightarrow {\text{n}}_{{O}_{2}}\text{= 0{,}4 mol}\overset{}{\rightarrow }{\text{V}}_{{O}_{2}}\text{= 9{,}916 L}$

b) $\begin{matrix}Mg\text{(a)}\overset{}{\rightarrow }{\text{Mg}}^{+2}\text{+ 2e (2a)} \\ Al\text{(b)}\overset{}{\rightarrow }{\text{Al}}^{+3}\text{+ 3e (3b)}\end{matrix}||\begin{matrix}\ {O}_{2}\text{+ 2.2e}\overset{}{\rightarrow }\ 2{O}^{2-} \\ \text{0{,}4}\rightarrow \text{1{,}6}\end{matrix}$

$\Rightarrow \{\begin{matrix}\overset{BT\text{e}}{\rightarrow }\text{2a + 3b = 1{,}6} \\ \overset{{m}_{kl}}{\rightarrow }\text{24a + 27b = 17{,}4}\end{matrix}\ \Rightarrow \{\begin{matrix}\text{a = 0{,}5} \\ \text{b = 0{,}2}\end{matrix}\ \overset{}{\rightarrow }\{\begin{matrix}{m}_{Mg}\text{= 12 gam} \\ {\text{m}}_{Al}\text{= 5{,}4 gam}\end{matrix}$

Chọn A

$\begin{matrix}Mg\text{(a)}\overset{}{\rightarrow }{\text{Mg}}^{+2}\text{+ 2e (2a)} \\ Al\text{(b)}\overset{}{\rightarrow }{\text{Al}}^{+3}\text{+ 3e (3b)}\end{matrix}||\begin{matrix}\ 2{H}^{+}\text{+ 2.1e}\overset{}{\rightarrow }{\text{H}}_{2} \\ \text{0{,}15}\leftarrow \text{0{,}075}\end{matrix}$

$\Rightarrow \{\begin{matrix}\overset{BT\text{e}}{\rightarrow }\text{2a + 3b = 0{,}15} \\ \overset{{m}_{kl}}{\rightarrow }\text{24a + 27b = 1{,}5}\end{matrix}\ \Rightarrow \{\begin{matrix}\text{a = 0{,}025} \\ \text{b = 0{,}033}\end{matrix}\ \overset{}{\rightarrow }{\text{m}}_{Mg}\text{= 0{,}6 gam}$

Chọn C

${n}_{{H}_{2}}\text{= 0{,}45 mol}$

$\begin{matrix}\text{Fe (a)}\overset{}{\rightarrow }{\text{Fe}}^{+2}\text{+ 2e (2a)} \\ Al\text{(b)}\overset{}{\rightarrow }{\text{Al}}^{+3}\text{+ 3e (3b)}\end{matrix}||\begin{matrix}\ 2{H}^{+}\text{+ 2.1e}\overset{}{\rightarrow }{\text{H}}_{2} \\ \text{0{,}9}\leftarrow \text{0{,}45}\end{matrix}$

$\Rightarrow \{\begin{matrix}\overset{BT\text{e}}{\rightarrow }\text{2a + 3b = 0{,}9} \\ \overset{{m}_{kl}}{\rightarrow }\text{56a + 27b = 13{,}8}\end{matrix}\ \Rightarrow \{\begin{matrix}\text{a = 0{,}15} \\ \text{b = 0{,}2}\end{matrix}\ \overset{}{\rightarrow }{\text{\%m}}_{Al}\text{= 39{,}13\%}$

Chọn B

$\begin{matrix}\text{Na (a)}\overset{}{\rightarrow }{\text{Na}}^{+}\text{+ 1e (a)} \\ K\text{(b)}\overset{}{\rightarrow }{\text{K}}^{+}\text{+ 1e (b)}\end{matrix}||\begin{matrix}\ 2{H}^{+}\text{+ 2.1e}\overset{}{\rightarrow }{\text{H}}_{2} \\ \text{0{,}015}\leftarrow \text{0{,}0075}\end{matrix}$

$\Rightarrow \{\begin{matrix}\overset{BT\text{e}}{\rightarrow }\text{a + b = 0{,}015} \\ \overset{{m}_{X}}{\rightarrow }\text{23a + 39b = 0{,}425}\end{matrix}\ \ \Rightarrow \{\begin{matrix}\text{a = 0{,}01} \\ \text{b = 0{,}005}\end{matrix}\ \overset{}{\rightarrow }{\text{m}}_{Na}\text{= 0{,}23 gam}$

${n}_{S{O}_{2}}\text{= 0{,}13 mol}$

$2\overset{0}{M}{\text{+ 2nH}}_{2}\overset{+6}{S}{O}_{4}\ \overset{}{\rightarrow }\ {\overset{+n}{\text{M}}}_{2}{(S{O}_{4})}_{n}\text{+ n}\overset{+4}{\text{S}}{\text{O}}_{2}{\text{+ 2nH}}_{2}O$

$\begin{matrix}M\ \overset{}{\rightarrow }{\text{M}}^{+n}\text{+ ne} \\ \text{0{,}26/n}\leftarrow \text{0{,}26}\end{matrix}||\begin{matrix}{\text{S}}^{+6}\text{+ 2e}\overset{}{\rightarrow }{\text{S}}^{+4} \\ \text{0{,}26}\leftarrow \text{0{,}13}\end{matrix}$

$\Rightarrow {\text{M}}_{M}\text{= 9n}\overset{}{\rightarrow }\text{n =3; M = 27 (Al)}$

${n}_{S{O}_{2}}\text{= 0{,}03 mol}$

a) $2\overset{0}{R}{\text{+ 6H}}_{2}\overset{+6}{S}{O}_{4}\ \overset{}{\rightarrow }\ {\overset{+3}{\text{R}}}_{2}{(S{O}_{4})}_{3}\text{+ 3}\overset{+4}{\text{S}}{\text{O}}_{2}{\text{+ 6H}}_{2}O$

b) $\begin{matrix}R\ \overset{}{\rightarrow }{\text{R}}^{+3}\text{+ 3e} \\ \text{0{,}02}\leftarrow \text{0{,}06}\end{matrix}||\begin{matrix}{\text{S}}^{+6}\text{+ 2e}\overset{}{\rightarrow }{\text{S}}^{+4} \\ \text{0{,}06}\leftarrow \text{0{,}03}\end{matrix}$

$\Rightarrow {\text{M}}_{R}\text{= 56}\overset{}{\rightarrow }\text{Fe}$

${n}_{S{O}_{2}}\text{= 0{,}7 mol}$

$\begin{matrix}\text{Cu (a)}\overset{}{\rightarrow }{\text{Cu}}^{+2}\text{+ 2e (2a)} \\ Fe\text{(b)}\overset{}{\rightarrow }{\text{Fe}}^{+3}\text{+ 3e (3b)}\end{matrix}||\begin{matrix}\ {S}^{+6}\text{+ 2e}\overset{}{\rightarrow }\ {S}^{+4} \\ \text{1{,}4}\leftarrow \text{0{,}7}\end{matrix}$

$\Rightarrow \{\begin{matrix}\overset{BT\text{e}}{\rightarrow }\text{2a + 3b = 1{,}4} \\ \overset{{m}_{kl}}{\rightarrow }\text{64a + 56b = 40}\end{matrix}\ \Rightarrow \{\begin{matrix}\text{a = 0{,}52} \\ \text{b = 0{,}12}\end{matrix}\ \overset{}{\rightarrow }\{\begin{matrix}{\text{\%m}}_{Cu}\text{= 83{,}2\%} \\ {\text{\%m}}_{Fe}\text{= 16{,}8\%}\end{matrix}$

a) ${n}_{Mg}{\text{= 3x, n}}_{Al}\text{= 2x}\overset{{m}_{X}}{\rightarrow }\text{24.3x + 27.2x = 12{,}6}\overset{}{\rightarrow }\text{x = 0{,}1 mol}$

$\overset{}{\rightarrow }{\text{\%m}}_{Mg}{\text{= 57{,}14\%; \%m}}_{Al}\text{= 42{,}86\%}$

b) $\begin{matrix}\text{Mg (0{,}3)}\overset{}{\rightarrow }{\text{Mg}}^{+2}\text{+ 2e (0{,}6)} \\ Fe\text{(0{,}2)}\overset{}{\rightarrow }{\text{Fe}}^{+3}\text{+ 3e (0{,}6)}\end{matrix}||\begin{matrix}\ {S}^{+6}\text{+ 2e}\overset{}{\rightarrow }\ {S}^{+4} \\ \text{1{,}2}\rightarrow \text{0{,}6}\end{matrix}$

${n}_{S{O}_{2}}{\text{= n}}_{{S}^{+4}}\text{= 0{,}6 mol}\overset{}{\rightarrow }{\text{V}}_{S{O}_{2}}\text{= 14{,}874 L}$