8/3/2019 206 Extra Problems-properties of Solutions

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Dr. C. Rogers --- Chem 206 GENERAL CHEMISTRY II --- EXTRA PROBLEMS p. 1

PROPERTIES OF SOLUTIONS (Ch.13-14 K&T)

#1. Which of the following pairs of liquids should be miscible? Explain using molecular structuresand a discussion of intermolecular interactions, including illustrations of hydrogen bonding whereappropriate.

(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, whatvolume of water (in L) would you have to treat? Assume the density of the water is1.0g/mL.

#3. Which aqueous solution is expected to have the lower freezing point? Explain in words andwith calculations.

(a) 0.20m KBr or 0.30m sugar

(b) 0.12m NH4NO3 or 0.10 m Na2CO3

#4. The solubility of ethylene (C2H4) in water at 20 C and 0.300 atm pressure is 1.2710 -4 molal.(a) Calculate the Henrys 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 C if the pressure ofethylene 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 inwater, and use a vant Hoff factor (i) of 1.9 for NaCl.

(a) Estimate the osmotic pressure of human blood at 37C.(b) Some people are (legitimately) concerned about their dietary sodium intake for health

reasons. Using your understanding of colligative properties, think about the possibleeffects 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 ofthe shell but the membrane around the egg remains intact. Explain this first phenomenon, andthen 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.

8/3/2019 206 Extra Problems-properties of Solutions

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Dr. C. Rogers --- Chem 206 GENERAL CHEMISTRY II --- CONTEXTUAL PROBLEMS

#7. Consider a 10m-tall maple tree growing at an altitude where the atmospheric pressure is 0.98atm (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 byosmotic pressure (at 20C)? Note that the pressure exerted by a 1 mm column of water isconsiderably less than 1 mm of Hg; conversion factor 1 mm Hg = 13.6 mm H2O. Somesimplifying assumptions: assume the groundwater outside the tree is pure water and thatthe 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 thesap? (Of course, other flavourful compounds are also present in small quantities...mmmmaple syrup.)

#8. A sample of seawater freezes at 2.01 C. What temperature would the same sample boil at?Assume that NaCl is the only solute (it isnt of coursealso 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 vant Hoff factor, i ).

#9. Butylated hydroxyanisole (BHA) is used as an antioxidant in margarine and other fats andoils; 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 --- lets say you went into the lab and found that0.640 g of the compound dissolved in 25.0 g of chloroform produced a solution whose boiling pointwas 62.22 C. Hint: youll 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 of94.16 mm Hg at 25C (note: the vapour pressure of pure benzene at this temperature is 95.26 mmHg) 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.

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