Относительные молекулярные массы веществ:

SO₃
S = 32.06 g/mol
O = 16.00 g/mol
SO₃ = 32.06 + 16.00*3 = 32.06 + 48.00 = 80.06 g/mol

P₂O₅
P = 30.97 g/mol
O = 16.00 g/mol
P₂O₅ = 30.972 + 16.005 = 61.94 + 80.00 = 141.94 g/mol

H₂SO₃
H = 1.01 g/mol
S = 32.06 g/mol
O = 16.00 g/mol
H₂SO₃ = 1.012 + 32.06 + 16.003 = 2.02 + 32.06 + 48.00 = 82.08 g/mol

CaCO₃
Ca = 40.08 g/mol
C = 12.01 g/mol
O = 16.00 g/mol
CaCO₃ = 40.08 + 12.01 + 16.00*3 = 40.08 + 12.01 + 48.00 = 100.09 g/mol

Fe(OH)₃
Fe = 55.85 g/mol
O = 16.00 g/mol
H = 1.01 g/mol
Fe(OH)₃ = 55.85 + 16.003 + 1.013 = 55.85 + 48.00 + 3.03 = 106.88 g/mol

O₂
O = 16.00 g/mol
O₂ = 16.00*2 = 32.00 g/mol

Cl₂
Cl = 35.45 g/mol
Cl₂ = 35.45*2 = 70.90 g/mol