Question

Assuming complete dissociation calculate the freezing point of asolution prepared by dissolving 6g of na2so4 10h20

Answer 1

The complete reaction will be according to the equation - 

Na₂SO₄ → 2Na⁺ + SO₄

So, three particles have been formed after complete dissociation.

The molar mass of Na₂SO₄.10H₂O will be = 46 + 32 + 64 + (10 x 18) = 322

The weight of water Wa = 0.1 kg = 100 g

The weight of the solute (Glauber's salt) Wb = 6.0 g

Kf = 1.86 k kg. mol⁻¹

i (Vont Hof factor) = 3

According to the relation, DTf = kf / MB x 1WB/WA x 1000 x i

= 1.86 / 322 x 6.0 / 100 x 1000 x 3 = 1.039 K

So, the freezing point will be calculated as = 273 - 1.039 K = 271.96 K