chemisty 2 question 2

Question

how many moles of sodium chloride should be added to 0.875 kg of water to produce a solution that boils at 103.00 celcius? assume ideal van't Hoff behavior is observed.

Answer 1

∆T = imK

∆T = change in boiling point = 3º

i = van't Hoff factor = 2 (Na+ and Cl-, i.e 2 particles)

m = molality = moles NaCl/kg water = ?

K = boiling point constant for H2O = 0.512

3 = (2)(m)(0.512)

m = 2.93 moles / kg

2.93 mol / kg x 0.875 kg = 2.56 mol NaCl needed