192 11 · SOLUTIONS AND SOLUBILITY
11.1.Which of the following are true?
(i) Water is more soluble in hexane than hexane is soluble in
water.
(ii)Long-chained organic molecules are usually more soluble
in water than shorter-chained molecules.
(iii)The osmotic pressure of a solution depends upon the
molecular mass of the solute.
(iv)The hydrophobic end of a molecule is attracted to water
molecules.
(v)An aerosol is defined as a dispersion of a solid in a gas.
11.2.Use Table 11.2 to find out whether the following pairs of
liquids are immiscible or miscible, in each case explaining your
answer by considering the intermolecular forces involved:
(i)Propan-2-ol and water.
(ii)Propanone and methyl benzene.
(The molecular formulae are listed in Table 11.1.)
11.3.The solubility of sodium chloride (in grams NaCl per
100 g solvent) at 25C in three solvents (A, B and C) is (A)
36.1 g, (B) 1.3 g and (C) 0.1 g. Which solvent is likely to be the
least polar? Explain your answer.
11.4.Ks(CaCO 3 )8.7 10 ^9 mol^2 dm^6 at 25C.
(i)Calculate(a)the molar solubility and (b)the solubility in
gdm^3 of solution, of calcium carbonate at 25C.
(ii)A test-tube containing 2.0 10 ^5 g of calcium chloride in
10.0 cm^3 of aqueous solution was added to 10.0 cm^3 of 2.0
10 ^5 mol dm^3 sodium carbonate solution at 25C. Will cal-
cium carbonate precipitate?
11.5.A saturated solution of calcium oxalate (Ca(C 2 O 4 )) was
found to contain 4.47 10 ^5 mol dm^3 of calcium ion at
25 C. What is the solubility product of calcium oxalate at this
temperature? (The oxalate ion is C 2 O 42 .)
11.6.The distribution of a drug between the oil octanol and
water is sometimes used to mimic the absorption of drugs
from the aqueous solution in the stomach into the (lipid)
stomach wall. If the Kd(octanol/water) for a drug is 1000 at
25 C, and the concentration of drug in the stomach (i.e. the
aqueous layer) is 0.01 mg dm^3 , estimate the equilibrium con-
centration of drug in the stomach wall.
11.7.The solubility of chlorine gas at 0C and an air pressure
of 1 atm is about 4.6 m^3 of gas per cubic metre of water.
Assuming no subsequent reaction, estimate the concentration
of dissolved gas (in mol dm^3 ) in a saturated solution under
these conditions. (The molar volume of an ideal gas at 0C and
1 atm pressure is 22.4 dm^3 .)11.8.The solubility of oxygen gas in water at a pressure of
1 atm is 14.6 and 7.6 mg dm^3 at 0C and 30C, respectively.
Show that these concentrations correspond to about 10
and 6 cm^3 of dissolved oxygen gas per dm^3 of water. (Take the
molar volume of oxygen as 22.4 dm^3 at 0C and as 24.9 dm^3 at
30 C.)11.9.(i)Calculate the osmotic pressure at exactly 25C pro-
duced by a 0.0050 mol dm^3 aqueous solution of a protein sep-
arated from pure water by a semipermeable membrane.(ii)Use the equation PVnRTto calculate the gas pressure
exerted by a sample of gas of concentration 0.0050 mol dm^3
at exactly 25C. Compare your answer with that obtained in
(i).11.10.(i)5.0 g of polystyrene was dissolved in exactly 200 cm^3
methyl benzene (toluene) and its osmotic pressure measured
(against pure methyl benzene) as 0.0175 atm at 25C. Calculate
the average molecular mass of the polystyrene polymer.(ii)Calculate the osmotic pressure (against pure water) of a
solution of a polypeptide of average molecular mass 100 000 u,
which contains 0.100 g of polypeptide dissolved in 1.00 dm^3 of
water at 20C.11.11.Light from a torch is spread out when passed through
soapy water – why? Could the particles causing this effect be fil-
tered off with standard laboratory filter paper?11.12.The shell of an egg is mainly calcium carbonate, and is
easily dissolved by soaking the egg in vinegar. If a raw egg is left
in a jar of vinegar for 3 days, it swells up. If the egg is now
placed in syrup (concentrated sugar solution) it shrinks.
Explain these observations.Revision questions
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