What is the freezing point of each solution?

Question

a)1.40mol Na2SO4 in 1750 g H2O

Are these the right steps?

1.40mol Na2SO4 / 1.75kg = .8m

3 * 1.86 degrees C * .8m = 4.46 degrees C

4.46 degrees C - 1.86 degrees C = 2.6 degrees C

Answer 1

a)1.40mol Na2SO4 in 1750 g H2O

Are these the right steps?

1.40mol Na2SO4 / 1.75kg = .8m

3 * 1.86 degrees C * .8m = 4.46 degrees C
OK to here. The next step is wrong.

4.46 degrees C - 1.86 degrees C = 2.6 degrees C
Why is it wrong? The normal freezing point of water is zero C; therefore, the freezing point of this solution is 4.46 degrees lower than that OR 0-4.46 = -4.46^o C.