Section 8.5: Solubility and Saturation
Tutorial 1 Practice, page 395
1. (a) A solution of potassium nitrate, KNO3, is unsaturated at 60 g/100 g water, H2O, because
the saturation point of potassium nitrate is 64 g/100 g H2O at 40 ºC.
(b) The saturation point of potassium nitrate at 20 ºC is 32 g/100 g water. The mass of solute that
would crystallize is equal to the difference.
60 g/100 g H2O – 32 g/100 g H2O = 28 g/100 g H2O
2. From the curve, we can determine that the saturation point of sodium hydrogen carbonate,
NaHCO3, at 30 ºC is approximately 12 g/100 g water. The mass required to saturate a solution
containing 10 g/100 g water is equal to the difference.
12 g/100 g H2O – 10 g/100 g H2O = 2 g/100 g H2O
3. From the curve, we can determine that 50 g of ammonium chloride, NH4Cl, becomes saturated
at 50 ºC.
Mini Investigation: Making a Supersaturated Solution, page 396
!" Na2S2O3(l) + 5 H2O(g)
A. Na2S2O3 i 5H2O(s) !heat
B. The reaction was a decomposition reaction of the sodium thiosulfate pentahydrate solid into
sodium thiosulfate liquid and water vapour.
C. (i) Prior to the addition of the seed crystal, the mixture in the test tube was saturated.
(ii) After the addition of the seed crystal, the mixture became supersaturated.
Section 8.5 Questions, page 397
1. (a) The bottle of pop left on the counter becomes flat first because its surroundings are
warmer. Gases such as carbon dioxide are generally less soluble at higher temperatures.
2. The three solutions can be distinguished by adding more solute to each. In the unsaturated
solution, the additional solute dissolves. In the saturated solution, the solute remains unchanged,
while in the supersaturated solution, the addition of more solute will cause more dissolved solute
to precipitate from the solution.
3. Increasing temperature increases the solubility of sucrose, but decreases the solubility of
carbon dioxide.
4. (a) Storing honey in the refrigerator may speed up the process of crystallization because the
solubility of sugar decreases as the temperature of the honey decreases.
(b) The warmth of the water causes the sugar crystals in the honey to dissolve.
(c) If you pour clear liquid honey into a jar that contains a few sugar crystals, the sugar crystals
may cause more sugar from the honey to crystallize.
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Chapter 8: Water and Solutions
8.5-1
5. (a)
(b) The trend in the solubility of calcium hydroxide is opposite to the solubility trend observed in
Figure 4. The solubility of calcium hydroxide decreases as temperature increases.
(c) The predicted solubility of calcium hydroxide at 100 ºC is 0.08 g/100 g water. This is
obtained by extending the curved line that fits the points.
(d) The solubility of calcium hydroxide at 25 ºC is 0.16 g/100 g H2O. The solubility of calcium
hydroxide at 50 ºC is 0.12 g/100 g water.
(e) The solubility is 0.15 g/100 g water at 27 ºC.
(f) The solution is unsaturated because it lies below the plotted line. The addition of 0.5 g/100 g
water of solute will make the solution saturated. This is taken from the value on the fitted curve
of 0.19 g/100 g water at 0 ºC.
(g) From the curve, we can see that 0.60 g of calcium hydroxide dissolved in 500 mL of water
corresponds to 0.12 g/100 g water. This solution is unsaturated since the point (40 °C,
0.12 g/100 g water) lies below the plotted line.
6. (a) A mass of 25 g of potassium chlorate, KClO3, should dissolve in 100 g of water at 60 °C
because 25 g/100 g water is the saturation point of potassium chlorate.
(b) The least soluble substance at 20 °C is potassium chlorate because 7 g/100 g water. The most
soluble substance at 20 °C is ammonium chloride, NH4Cl, because 37 g/100 g water, which is
only slightly above sodium chloride, NaCl.
(c) The solubility of potassium nitrate is most affected by temperature (steepest slope).
(d) The saturation point of potassium nitrate at 50 ºC is 85 g/100 g water and at 20 ºC is
32 g/100 g water. The mass of solute that would crystallize is equal to the difference.
85 g/100 g H2O – 32 g/100 g H2O = 53 g/100 g H2O
(e) The solubilities of potassium nitrate and ammonium chloride are equal at 24 ºC where the
two solubility curves cross.
7. Deforestation at the shore of a river leads to the water in the river being subjected to more
direct sunlight. This warms the water in the river, which may result in thermal pollution.
8. As scuba divers ascend, the pressure of the water acting on their bodies decreases. As a result,
dissolved gases in the blood and other body fluids become less soluble and leave the solution in
which they are dissolved. This can increase the pressure within blood vessels, which may cause
some to burst.
9. The solubility of gases decreases as the temperature increases. Since boiled water contains less
dissolved gases than water at room temperature, ice cubes made from boiled water contain less
dissolved gases. Ice cubes made from boiled distilled water contain fewer dissolved substances
that may make the ice cube cloudy than ice cubes made from distilled water at room temperature.
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Chapter 8: Water and Solutions
8.5-2
10. (a) The solubility of a gas in a water decreases as the temperature of solution increases.
(b) Two important dissolved gases in aquatic ecosystems are oxygen and carbon dioxide. Most
forms of aquatic life require oxygen to conduct cellular respiration. Many aquatic plants require
carbon dioxide to conduct photosynthesis.
(c) Global warming could effect the environment of aquatic organisms. An increase in global
temperatures may decrease the solubility of dissolved gases in water. This could decrease the
concentration of oxygen and carbon dioxide in water. However, any decrease in carbon dioxide
concentrations will likely be offset by an increase in the atmospheric concentration of carbon
dioxide. As the quantity of carbon dioxide in the atmosphere increases, more will dissolve in
water.
11. Gout is a form of arthritis. Symptoms of gout include red and swollen joints. Some of these
symptoms are caused by bone erosion from the accumulation of uric acid in the joints. One of the
main causes of uric acid accumulation is the inefficiency of the kidneys to keep uric acid
concentrations under control. Some lifestyle and dietary changes can help reduce uric acid
concentrations. These include reducing the consumption of meat, seafood, and alcohol.
Consuming vitamin C and avoiding obesity also helps. A number of medications are also used to
treat gout.
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Chapter 8: Water and Solutions
8.5-3