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


∆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
of water (Kb.p.= 0.512°C/m, b.p. = 100.00°C) in your car radiator?

∆Tbp = Kbpmi

         Kbp = 0.512°C/m


∆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


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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