I have the correct answer (29.7 torr) however I am having issues figuring out ho

Question

I have the correct answer (29.7 torr) however I am having issues figuring out how the answer was found (my answers when I try to attempt to solve the problem are way off). Can anyone please help me with the process? If possible, please show work/formula

This question has two parts (10 pts) (a) Consider the freezing point of 0.01m KCl(aq), t(KC), compared with that of 0.01 m Ca(NO 2a), t(Ca(NO3)z. Which of the following is true (circle one only)? (b) If 97.2 g of KCI, M-74.6 g/mol; electrolyte), are added to 658 mL of water (assume density of water-1.00 g/mL), determine the vapor pressure of the resulting solution 30°C. The vapor pressure of pure water at 30°C is 31.8 torr torr

Explanation / Answer

(a) dTf = i.Kf.m

with Kf and m being the same, the freezing point lowering will depend upon the Van't Hoff factor

As, KCl has i = 2 (K+ and Cl-) as, compared to

Ca(NO3)2, i = 3 (1Ca2+ and 2NO3-)

dTf would be higher for Ca(NO3)2, so Tf the actual freezing point would be lower then KCl

thus,

(i) Tf(KCl) > Tf(Ca(NO3)2)

(b) find moles of KCl

moles = 97.2 g/74.6 g/mol

   = 1.30 mols

moles of water = 658/18 [with density = 1, volume = mass]

= 36.55 mols

total moles = 1.30 + 36.55 = 37.85 mols

mole fraction of water = 36.55/37.85 = 0.96

vapor pressure of solution = 0.96 x 31.8 = 30.53 torr

So, I am getting 30.53 torr as vapor pressure of solution with the values given.

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