No 14,15 dengan cara

≈ STOIKIOMETRI ≈

[14]

Diketahui :
V H2 = 6,72 L (STP)
% Al = 90%
% Cu = 10%

Ditanya :
m campuran = ....?

Reaksi :
6 HCl + 2 Al ===> 3 H2 + 2 AlCl3
HCl + Cu ≠≠≠> tidak ada reaksi

n H2 = V / 22,4 L/mol
= 6,72 L / 22,4 L/mol
= 0,3 mol

n Al = (koef. Al / koef. H2) × n H2
= ⅔ × 0,3 mol
= 0,2 mol

m Al = Ar Al × n Al
= 27 × 0,2 mol
= 5,4 gram

m campuran = ( 100% / % Al ) × m Al
= ( 100% / 90% ) × 5,4 gram
= 6 gram (B)

[15]

Diketahui :
% H2O = 14,25 %
m Pb(C2H3O2)2 . x H2O = 8 gram

Ditanya :
x = ....?

m H2O = % H2O × m Pb(C2H3O2)2 . x H2O
= 14,25% × 8 gram
= 1,14 gram

Mr H2O = 2 Ar H + Ar O
= 2(1) + 16
= 18

n H2O = m H2O / Mr H2O
= 1,14 gram / 18
= 0,0633 mol

% Pb(C2H3O2)2 = 100% - % H2O
= 100% - 14,25%
= 85,75%

m Pb(C2H3O2)2 = % Pb(C2H3O2)2 × m Pb(C2H3O2)2 . x H2O
= 85,75% × 8 gram
= 6,86 gram

Mr Pb(C2H3O2)2 = Ar Pb + 4 Ar C + 6 Ar H + 4 Ar O
= 207 + 4(12) + 6(1) + 4(16)
= 325

n Pb(C2H3O2)2 = m Pb(C2H3O2)2 / Mr Pb(C2H3O2)2
= 6,86 gram / 325
= 0,0211 mol

n H2O : n Pb(C2H3O2)2 = 0,0633 mol : 0,0211 mol = 3 : 1
x = 3 (A)