Diketahui:

Ar Mg = 24 gram/mol

Mr HNO₃ = (1 × Ar H) + (1 × Ar N) + (3 × Ar O)

Mr HNO₃ = (1 × 1) + (1 × 14) + (3 × 16) = 63 gram/mol

Massa Mg = 4,8 gram

Mol Mg = Massa / Mr

Mol Mg = (4,8 gram) / (24 gram/mol)

Mol Mg = 0,2 mol

Penyetaraan Persamaan Reaksi:

  Mg    +    2 HNO₃     ⇒     Mg(NO₃)₂    +     H₂

Penyelesaian:

a. Massa HNO₃ yang diperlukan

"Perbandingan mol sama dengan koefisien"

   Mg    +    2 HNO₃     ⇒     Mg(NO₃)₂    +     H₂

0,2 mol       0,4 mol              0,2 mol          0,2 mol

Massa HNO₃ = mol × Mr

Massa HNO₃ = (0,4 mol) × (63 gram/mol)

Massa HNO₃ = 25,2 gram

b. Massa Mg(NO₃)₂ yang dihasilkan

Mr Mg(NO₃)₂ = (1 × Ar Mg) + [(1 × Ar N) + (3 × Ar O)] × 2

Mr Mg(NO₃)₂ = (1 × 24) + [(1 × 14) + (3 × 16)] × 2

Mr Mg(NO₃)₂ = 148 gram/mol

Massa Mg(NO₃)₂ = mol × Mr

Massa Mg(NO₃)₂ = (0,2 mol) × (148 gram/mol)

Massa Mg(NO₃)₂ = 29,6 gram

c. Volume gas H₂ (P = 0,82 atm dan T = 27°C = 300 K)

P × V = n × R × T

V = (n × R × T) / P

V = [ (0,2 mol) × (0,082 atm.L/mol.K) ] × (300 K) / (0,82 atm)

V = 6 liter