boiling point

Question

How much Magnesium chloride would you need to put in 555 g of water to raise the boiling point by 11 o C

Answer 1

As with your previous question, you use ∆T = imK to solve this problem.

∆T = change in temperature = 11ºC

i = van't Hoff factor = 3 for MgCl₂

m = molality = ?

K = boiling point constant for water = 0.52ºC/m

11 = (3)(m)(0.52)

m = 7.05 moles/kg

Since the problem states that you have 555 g of water, and assuming a density of 1g/ml, that equates to 0.555 kg water.

7.05 moles/kg x 0.555 kg = 3.91 moles MgCl₂

3.91 moles MgCl₂ x 95.2 g/mole = 373 g MgCl₂ needed