Unit test: Solutions and solubility
By: Narjis Fatima, Jiwei Li, Tatiana Vrabie
MULTIPLE CHOICE [K/U] (10 marks) Choose any 10 questions.
Circle the most suitable answer for the following questions (each question – 1 mark):
1. What is a solute?
a) solution that contain water
b) a substance that is dissolved in a solvent
c) greatest amount in a solution
d) a homogeneous mixture
2. Anti freeze liquids are mixed with water in car radiators to form solutions with low freezing points, what type of solution is this?
a) solid dissolved in liquid
b) liquid dissolved in gas
c) liquid dissolved in liquid
d) liquid dissolved in solid
e) a& d
3. To make up a solution with a specific volume, chemist use a piece of special glassware called ______?
a) a beaker
b) a wash bottle
c) a volumetric flask
d) a container
4. What rule should be followed when diluting concentrated acids
a) is to add water to acid
b) is to add acid to water
c) a & b
5. What is the symbol of molar concentration?
a) M
b) C
c) m
d) c
e) V
6. What is Solubility?
a) property of solution
b) the concentration of solution at given temperature
c) property of solute
d) the concentration of saturated solution at given temperature
e) a and b
f) b and c
g) a and d
7. What factors affect solubility?
a) size of crystals
b) pressure
c) shaking
d temperature
e) a and b
f) b and d
g) c and d
8. How solubility of gasses depends on temperature?
a) increase with temperature
b) decrease with temperature
c) doesn’t depend on temperature
d) prediction is not reliable
9. How solubility of solids depends on temperature?
a) increase with temperature
b) decrease with temperature
c) doesn’t depend on temperature
d) prediction is not reliable
10. How solubility of liquids depends on temperature?
a) increase with temperature
b) decrease with temperature
c) doesn’t depend on temperature
d) prediction is not reliable
11. A compound that ionizes in water to form hydroxide ions is
a. / an acid / d. / both a and bb. / a salt / e. / both b and c
c. / a base
12. Which of the following is the correct dissociation reaction for calcium hydroxide?
a. / Ca(OH)2(s) ® Ca2+(aq) + 2OH–(aq)b. / CaOH(s) ® Ca+(aq) + OH–(aq)
c. / Ca(OH)2(s) ® 2Ca2+(aq) + OH–(aq)
d. / Ca(OH)3(s) ® Ca3+(aq) + 3OH–(aq)
e. / Ca(OH)2(s) ® 2 Ca2+(aq) + 2OH–(aq)
13. Nitric acid is classified as a strong acid because
a. / it has high electrical conductivityb. / it ionizes about 50%
c. / ionizes more than 99%
d. / both a and c
e. / it has a higher concentration than other acids
14. A dilute solution of a strong acid can be more dangerous than a concentrated solution of a weak acid because
a. / there are still more H+(aq) ions in the dilute strong acidb. / there are more molecules in the strong acid
c. / the amount of H+(aq) ions is the same for both
d. / the strong acid contains chloride ions
e. / the weak acid has fewer molecules than the strong acid
15. Which of the following is NOT a strong base?
a. / NaOH(aq) / d. / CsOH(aq)b. / KOH(aq) / e. / Mg(OH)2(aq)
c. / LiOH(aq)
SHORT ANSWERS: (10 marks) choose 5 questions
Give a short answer in 2-3 sentences to the following situational questions. (2 marks for each question).
1. Give three examples of aqueous solutions: one with a solid solute , one with a liquid solute, and one with a gas solute? [T/I]
2. Name two pieces of glassware that are used by chemists to prepare a solution with a known concentration? [C]
3. When you open a can of pop, which is more likely to fizz and spray: a can at room temperature or a cold can from refrigerator? Explain why using your understanding of gas solubility. [App]
4. Some Industries, particularly electric power generating stations, get rid of waste water by releasing it into a nearby lake or river. Use your knowledge of solubility and temperature to describe why this thermal pollution is detrimental to most fish. [App]
5. How does dilution affect the pH of (a) acidic solutions? (b) basic solutions? [C]
6. List three empirical properties for acids and three empirical properties for bases. [K/U]
ESSAY QUESTIONS: (5 marks), choose one question.
1. Describe the technique used by the chemist and non-scientist use for grinding solids and how the factor like “surface area” effects the rate of dissolving? [T/I, C] (8 marks)
2. Describe how discovered Ernest Solvay the chemical technology is related to solubility. [C]
(8 marks)
PROBLEM BASED QUESTIONS: (25 marks) choose any problems to get 24-26 points.
1. How would you prepare 400 mL of a 3.5 % (m/v) solution of sodium acetate? [K/U] (4 marks)
2. Gasoline sold in Ontario must contain at least 5.0% v/v ethanol. How much ethanol is a driver likely to get when buying 30 L of gasoline? [K/U] (5 marks)
3. Water is added to 100mL of 0.15 mol/L sodium nitrate NaNO3, to make 700 mL of diluted solution. Calculate the molar concentration of the diluted solution. [T/I] (6 marks)
4. The task is to obtain silver from of 0.015 M solution of AgNO3. Given is 0.4 g of metal Cu. Would all silver in 1000 ml of 0.015 M solution of AgNO3 precipitate with given amount of Cu. If not, how much silver will remains in solution and how many gram of Cu should we add to obtain all silver from 1L of given solution? [T/I] (8 marks)
5. Calculate amount (in g) of precipitate formed in reaction of 100 ml 0.1 M solution of Ca(NO3)2 salt with 3.0 g Na2SO4. [K/U] (4 marks)
6. Design a chemical procedure to identify presence of Ca2+ and/or Cu+ .in a solution. Draw chart-flow and write down appropriate chemical reactions. [T/I] (8 marks)
7. A swimming pool has a pH of 7.5. Calculate the hydrogen ion concentration in the pool. [K/U] (4 marks)
8. Coffee has a pH of 5.0 and grapefruit juice has a pH of 3.0. Calculate the hydrogen ion concentration for both drinks and determine how many times more concentrated the hydrogen ion is in the juice compared to the coffee. [App] (6 marks)
Answer key
Multiple choices
1. B
2. C
3. C
4. B
5. D
6. G
7. F
8. B
9. A
10. D
11. C
12. A
13. D
14. A
15. E
Short answers:
1. The three examples of aqueous solutions are, solid solute: sugar in water liquid solute: alcohol in water and gas solute: carbon dioxide in water.
2. A volumetric flask and a volumetric pipette, or graduated pipette , can be used to prepare a solution with a known concentration.
3. A can of pop at room temperature is more likely to fizz and spray at opening then a can from refrigerator. Water at higher temperature can keep less dissolved gasses and they go out, because solubility of gasses decreases with temperature.
4. Waste water usually is at higher temperature than ambient water, furthermore organic compound in waste water undergo bacterial fermentation, which is exothermic process. High temperature decreases the concentration of oxygen in the lake, because solubility of gasses decreases with temperature. Low oxygen concentration causes respiratory problems for fish.
5. (a) Diluting acidic solutions decreases the hydrogen ion concentration. This increases the pH and makes these solutions less acidic.
(b) Diluting basic solutions decreases the pH and makes these solutions less basic.
6. Acids
-tastes sour
-turns blue litmus red
-reacts with active metals to produce hydrogen gas
Bases
-tastes bitter
-feels slippery
-has a pH higher than 7
-neutralizes acids
Essay answers:
1. Cooks, bakers, laboratory technicians, chemical engineers and others who work with solutions apply a variety of techniques and instruments to increase the rate of dissolving.
The rate of dissolving is a measure of how quickly a solute dissolves in a solvent. The factors that affect the rate of dissolving are agitation/mixing, temperature and surface area.
Grinding increase the surface area and by that the rate of dissolving.
The higher is surface area of a solute, the higher is the amount of solute that is in direct contact with the solvent, and thereby the frequency of collisions with the solvent molecules is bigger, making the solute to dissolve more rapidly.
For grinding solids may be used mortar and pestle, grinder and other techniques.
2. Following issues should be addressed in the essay:
· Process was designed for production of baking soda NaHCO3 and washing soda Na2CO3
· The major discovery was
o Reaction
NH4HCO3(aq) + NaCl(aq) →NH4Cl(aq) + NaHCO3 (s)
· Solubility of NaHCO3 (sodium hydrogen carbonate) is considerably lower than NH4Cl (ammonium chloride)
· Difference in solubility was used to separate baking soda by crystallization.
Problem based questions:
1. Measure 14 g of the solute and dissolve in water, add water to bring the total volume of the solution to 400mL.
2. v/v= volume of solute /volume of solution X100%
1.5L
3. 0.02 mol/L
4.
2 AgNO3 + Cu → Cu(NO3)2 + Ag
0.2725 g of Ag+ will remain in solution
To precipitate it all Ag + we need 0.48 g of Cu or 0.08 g more than it is given
5. Amount of precipitate formed in given reaction is 1.36 g.
6. Analysis: Use solubility chart (Nelson Chemistry 11, 2002, p.324) to determine which anions selectively precipitate only one of these cations.
Solution: Cl- makes low solubility salt (precipitate) with Cu+ and SO42- with Ca2+, so we can use soluble salt such as NaCl and Na2SO4 for qualitative analysis.
Cl- + Cu+ → CuCl (s)
SO42- + Ca2+ → CaSO4 (s)
7.
The hydrogen ion concentration of the swimming pool is 3.2 x 10–8 mol/L.
8.
coffee / grapefruit juiceThe hydrogen ion concentration is 100´ greater in grapefruit juice than it is in coffee.
Therefore, grapefruit juice is 100 more acidic than coffee.
References:
1. Clancy, C., Doram, T., Hiembecker, B., Mazza, M., McNulty, P., Mustoe, F. (2011). Chemistry 11. Whitby, Ontario: McGraw-Hill Ryerson
2. Jenkins, F., van Kessel, H., Davies, L., Lantz, O., Thomas, P. & Tompkins, D. (2002). Nelson chemistry 11. Toronto, Ontario: Nelson Thomson Learning.