(#45) determine the freezing point of a solution that contains 62.8 g of urea di

Question

(#45) determine the freezing point of a solution that contains 62.8 g of urea dissolved in 275 g of water Due vapor pressure of a solution at 25that contains 85.3 g of n (C10H8) in 540 g of benzene (C6H6). The vapor pressure of benzene at 25°C is 74.6 tor A) 74.6 toff. B) 68.0 torr. C) 54.9 torr D) 7.52 torr. E) 22.4 toff Answer: B aphthale 45) Determine the freezing point of a solution that contains 62.8 g of urea (CH4N20) dissolved in 275 g of water (Kf= 1.86°C/m). A) -7.07°C B) -4.82°C C) -13.1°C D) -3.01°C E)-9.12°C Answer: A 46) The boiling point elevation of an aqueous sucrose solution is found to be 0.39°C. Wha mass of sucrose (molar mass- 342.30 g/mol) would be needed to dissolve in 500.0 g of water? Kb (water) = 0.512°C/m. A) 261 g sucrose B) 528 g sucrose C) 762 g sucrose D) 223 g sucrose F 130 Sucrose

Explanation / Answer

DTf = i*kf*m

DTf = T0-Tf = 0-x

DTf = i*Kf*m

i = vanthoff factor of urea = 1

Kf = frreezing point constant of water = 1.86 C/m

molality(m) = (w/M)*(1000/Wt)

w = 62.8 g

M = molarmass of urea = 60 g/mol

Wt = wt of water = 275 g

molality(m)= (62.8/60)*(1000/275)

(0-x) = 1*1.86*(62.8/60)*(1000/275)

x =freezing point of solution = -7.08 C

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