Answer is: mass of the mixture is 24,47 g.
1) N(Na₂SO₄) = 3,5·10²².
n(Na₂SO₄) = 3,5·10²² ÷ 6·10²³ 1/mol.
n(Na₂SO₄) = 0,058 mol.
m(Na₂SO₄) = 0,058 mol · 142 g/mol.
m(Na₂SO₄) = 8,24 g.
2) n(H₂O) = 0,500 mol.
m(H₂O) = 0,5 mol · 18 g/mol.
m(H₂O) = 9 g.
3) m(total) = 8,24 g + 9 g + 7,23 g.
m(total) = 24,47 g.
n - amount of substance.
