Dr. C. Rogers --- Chem 206 GENERAL CHEMISTRY II --- EXTRA PROBLEMS
PROPERTIES OF SOLUTIONS
p. 1
(Ch.13-14 K&T)
#1. Which of the following pairs of liquids should be miscible? Explain using molecular structures
and a discussion of intermolecular interactions, including illustrations of hydrogen bonding where
appropriate.
(a) Water and butane (CH3CH2CH2CH3)
(b) Benzene (C6H6) and carbon tetrachloride
(c) Water and acetone (CH3COCH3)
#2. Silver ion has an average concentration of 28 ppb (parts per billion) in U.S. water supplies.
(a) What is the molality of silver ion in this water?
(b) If you wanted 1.0102 g of silver and could recover it chemically from water supplies, what
volume of water (in L) would you have to treat? Assume the density of the water is
1.0g/mL.
#3. Which aqueous solution is expected to have the lower freezing point? Explain in words and
with calculations.
(a) 0.20 m KBr or
(b) 0.12 m NH4NO3
0.30 m sugar
or 0.10 m Na2CO3
#4. The solubility of ethylene (C2H4) in water at 20 ºC and 0.300 atm pressure is 1.27×10-4 molal.
(a) Calculate the Henry’s law constant for this gas in units of molality/torr.
(b) How many grams of ethylene would dissolve in 1.00 kg of water at 20 ºC if the pressure of
ethylene above the water is 500 torr?
#5. Assume that blood is isotonic with (i.e, exerts same pressure as…) a 0.16 M NaCl solution in
water, and use a van’t Hoff factor (i ) of 1.9 for NaCl.
(a) Estimate the osmotic pressure of human blood at 37°C.
(b) Some people are (legitimately) concerned about their dietary sodium intake for health
reasons. Using your understanding of colligative properties, think about the possible
effects of combining a severely salt-restricted diet with drinking demineralized bottled water
(dissolved minerals < 10 ppm) as your main source of fluids.
#6. If an egg is placed in dilute acetic acid (vinegar), the acid reacts with the calcium carbonate of
the shell but the membrane around the egg remains intact. Explain this first phenomenon, and
then explain the following observations:
(a) If the egg, without its shell, is placed in pure water, the egg swells.
(b) If the egg is placed in a solution with a high solute concentration (e.g., a mixture of equal
volumes of water and corn syrup), it shrivels dramatically.
Dr. C. Rogers --- Chem 206 GENERAL CHEMISTRY II --- CONTEXTUAL PROBLEMS
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#7. Consider a 10m-tall maple tree growing at an altitude where the atmospheric pressure is 0.98
atm (this could be somewhere in Quebec…).
(a) What must be the total molality of solutes if the sap rises to the very top of the tree by
osmotic pressure (at 20°C)? Note that the pressure exerted by a 1 mm column of water is
considerably less than 1 mm of Hg; conversion factor 1 mm Hg = 13.6 mm H2O. Some
simplifying assumptions: assume the groundwater outside the tree is pure water and that
the density of the sap is 1.0 g/mL.
(b) If the only solute in the sap is sucrose, C12H22O11, what is its percentage by mass in the
sap? (Of course, other flavourful compounds are also present in small quantities...mmm…maple syrup….)
#8. A sample of seawater freezes at –2.01 ºC. What temperature would the same sample boil at?
Assume that NaCl is the only solute (it isn’t of course…also present are K+, Li+, Br-, I-, fish urine (NH3) and all
sorts of other stuff); also assume that our solute is behaving in an ideal way (ideal van’t Hoff factor, i ).
#9. Butylated hydroxyanisole (BHA) is used as an antioxidant in margarine and other fats and
oils; it prevents oxidation and prolongs the shelf life of the food. What is the molar mass of BHA?
Not too hard to find out via a simple experiment --- let’s say you went into the lab and found that
0.640 g of the compound dissolved in 25.0 g of chloroform produced a solution whose boiling point
was 62.22 °C. Hint: you’ll need to look up the normal boiling point of chloroform to answer this….
#10. A newly synthesized compound containing only boron and fluorine is 22.1% boron by mass.
Dissolving 0.146g of the compound in 10.0g of benzene gives a solution with a vapour pressure of
94.16 mm Hg at 25°C (note: the vapour pressure of pure benzene at this temperature is 95.26 mm
Hg) In a separate experiment, it is found that the compound does not have a dipole moment.
(a) What is the molecular formula for the compound?
(b) Draw a Lewis structure for the molecule, and suggest a possible molecular geometry. Give
the bond angles in the molecule and the hybridization of the boron atom.