# KEY CH12 worksheet

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```					CHEM162                                                                                KEY CH12 worksheet

1) An aqueous solution of hydrochloric acid is 11.8 M and has a density of 1.190 g/mL. Calculate its:
(a) mass percent
(b) molality
(c) mole fraction
Hint: for these problems, assume 1L solution . . . In 1 L solution, there are 11.8 moles HCl

2) Calculate the vapor pressure lowering of a solution of 2.00 g aspirin (C9H8O4, i=1) in 50.0 g methanol
(CH3OH) at 21.2°C. Pure methanol has a vapor pressure of 101 torr at this temperature

∆P = XP˚i

P˚ = 101 torr

i=1

∆P = 7.06  101 torr  1 = 0.713 torr
CHEM162                                                                                 KEY CH12 worksheet

3) What is the boiling point of the solution when you add 1.00 kg of ethylene glycol (C 2H6O2, i=1) to 4450 g

∆Tbp = Kbpmi

Kbp = 0.512°C/m

i=1

∆Tbp = 0.512°C/m  3.62 m  1 = 1.85°C

Tbp(soln) = Tbp(solvent) + ∆Tbp = 100.00°C + 1.85°C = 101.85°C

4) What is the minimum concentration (molality) of an aqueous ethylene glycol (K f.p.= 1.86°C/m, i = 1)
solution that will protect a car’s cooling system from freezing at -18.0°C?

∆Tfp = Kfpmi

∆Tfp = Tfp(solvent) – Tfp(solution) = 0.0°C – (-18.0°C) = 18.0°C

Kbp = 1.86°C/m

i=1

molality > 9.68 m

Would you need a more or less concentrated solution of ethylene glycol if acetic acid
(Kf.p.= 3.90°C/m, i = 1) were used as the solvent?

molality > 4.62 m            LESS CONCENTRATED

5) What is the osmotic pressure of blood if a 0.30 M aqueous solution of sucrose (C 12H22O11, i=1) that is at
37˚C has approximately the same osmotic pressure?

 = MRTi

```
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