Answer to Question #318643 in General Chemistry for Austine

Question

7. Use the oxidation number method to balance the following equations:

 a) Al_(s) + H₂SO_{4 (aq)} Al₂(SO₄)_{3 (aq)} + H_{2 (g)}

b) PbS_(s) + O_2(g) PbO _(s) + SO_{2 (g)}

Answer 1

a.$Al^0 -3e \rightarrow Al^{+3}$

$2H^+ +2e\rightarrow H_2^0$

Coefficient for Al =2

Coefficient for H₂ =3

$2Al(s) + 3H_2SO_4 (aq) \rightarrow Al_2(SO_4)_3 (aq) +3 H_2 (g)$

b.$S^{-2} -6e \rightarrow S{+4}$

$O_2^0 +4e \rightarrow 2O^{-2}$

Coefficient for S =2(4/2)

Coefficient for O₂=3(6/2)

$2PbS(s) + 3O2(g) \rightarrow 2PbO (s) + 2SO2 (g)$