1) Explain why three teaspoons of sugar will completely dissolve in a serving of hot tea, but will not dissolve in an equally sized serving of iced tea.
Due to the different temperatures, the solubility, or maximum quantity of a substance that will dissolve in a certain quantity of water at a specified temperature, for hot tea is higher than the solubility of iced tea. This is why three teaspoons of sugar will completely dissolve in a serving of hot tea, but not in an equally sized serving of iced tea.
2) What is the maximum mass of potassium chloride (KCl) that will dissolve in 100g water at 70°C?
The maximum mass of KCl that will dissolve in 100g water at 70°C is 48g.
3) If the solubility of sugar (sucrose) in water is 2.0g/mL at room temperature, what is the maximum mass of sugar that will dissolve in
a. 100mL water?
b. 355mL (12 oz) water?
c. 946mL (1 qt) water?
a. 200g.
b. 710g.
c. 1,892g.
4) Rank the substances in Figure 1.33 (page 54) from most soluble to least soluble at
a. 20°C.
b. 80°C.
a. NaCl (sodium chloride), KCl (potassium chloride), KNO3 (potassium nitrate).
b. KNO3 (potassium nitrate), KCl (potassium chloride), NaCl (sodium chloride).
5) Distinguish between the terms saturated and unsaturated.
Saturated means that too much of a substance has been added into a solvent for it to be able to dissolve into it, and therefore it settles at the bottom of the container; no amount stirring will make the crystals dissolve into the liquid. A saturated solution, however, is a solution in which the solvent contains as much dissolved solute as it normally can at that temperature. On the other hand, an unsaturated solution is a solution that contains less dissolved solute than the amount the solvent can normally hold at that temperature.
6) Using the graph on page 54, answer these questions about the solubility of potassium nitrate, KNO3:
a. What maximum mass of KNO3 can dissolve into 100g water if the water temperature is 20°C?
b. At 30°C, 55g KNO3 is dissolved in 100g water. Is this solution saturated, unsaturated, or supersaturated?
c. A saturated solution of KNO3 is formed in 100.0g water at 75°C. If some solute precipitates as the saturated solution cools to 40°C, what mass (in grams) of solid KNO3 should form?
a. 30g KNO3 can dissolve into 100g water if the water temperature is 20°C.
b. This solution is supersaturated.
c. 60g of solid KNO3 should form.
7) You are given a solution of KNO3 of unknown concentration. What will happen when you add a crystal of KNO3 if the solution is
a. unsaturated?
b. supersaturated?
c. saturated?
a. The solution would either become saturated or remain unsaturated (depending on how many crystals are needed for it to become saturated)
b. The one crystal would cause the other extra solute crystals to appear and settle. This would make the solution rebalanced.
c. The extra crystal would settle to the bottom of the container as a precipitate, since the solvent would have contained as many solutes as it could hold.
8) A 35-g sample of ethanol us dissolved in 115g water. What is the percent concentration of the ethanol, expressed as percent ethanol by mass?
115g water
35 x 1.15 = 40.25
1.15 x 40.25g = 46.2875g
46.2875/115 = 0.4025
The percent concentration of the ethanol, expressed as percent ethanol by mass, is 40.25%
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