Chemistry I-Honors

Chemistry I-Honors Solutions / Colligative Properties Practice Test - Answer Key

1. A Which of the following substances (all at 1.0-molal) would have the lowest freezing point?

A) Na3PO4; B) C12H22O11 (sucrose); C) C6H12O6 (glucose); D) HCl; E) NH3

2. C If the pressure is increased over a solution in which a solid is dissolved in a liquid, what happens to the solubility of the solid? A) increases; B) decreases; C) no change; D) need to know the entropy of the solution.

3. D Which colligative property is based on mole fraction? A) freezing point depression; B) boiling point elevation; C) osmotic pressure; D) vapor pressure lowering; E) plasmolysis.

4. Alloy A solid dissolved in another solid is called a solid solution. What is the more common term for this type of solution if the solids are metals?

5. A Of the following, which has the smallest particle size difference? A) true solution; B) suspension; C) colloids; D) gels; E) dust particles in air.

6. E A student is studying three different solutions. Solution A was formed by dissolving 0.50 moles of NaCl in 200. grams of water. Solution B was formed by dissolving 2.60 moles of NaCl in 800. grams of water. Solution C was formed by dissolving 1.50 moles of NaCl in 500. grams of water. Which of the following statements is true? A) all three solutions are isotonic; B) A is hypertonic to C; C) A is hypertonic to B; D) B is hypotonic to C; E) B is hypertonic to A.

7. G Which of the following is a weak electrolyte?

A) sodium iodide; B) ammonium hydroxide; C) perchloric acid; D) glucose (C6H12O6); E) cesium hydroxide; F) hydrofluoric acid; G) both B and F.

8. D Which of the following types of mixtures exhibit the Tyndall effect? A) true solutions and suspensions; B) true solutions and colloids; C) only true solutions; D) only colloids; E) only suspensions; F) all three types.

9. D What is primarily responsible for the high solubility of ammonia in water? A) dispersion forces; B) ionic bonds; C) covalent bonds; D) hydrogen bonds; E) London forces.

10. A Which of the following substances dissolves most readily in water?

A) Na3PO4; B) CaCO3; C) C6H14 (hexane); D) methane (CH4); E) gasoline (C8H18)

11. A In general, as the temperature of a solution composed of a gas in a liquid in decreased, the solubility of the gas: A) increases; B) decreases; C) remains the same. -2-

12. A In general, as the pressure over a solution composed of a gas dissolved in a liquid in increased, the solubility of the solid: A) increases; B) decreases; C) remains the same.

13. B When a leucocyte (a white blood cell), which contains a 5% saline solution (a saline solution contains 5% sodium chloride dissolved in 95% water) is placed into a 20% saline solution, which process occurs? A) plasmolysis; B) crenation; C) inspidation; D) Tyndall effect; E) hygroscopic.

14. D Which of the following are miscible combinations?

A) baking soda (a basic salt) in benzene (C6H6); B) acetic acid (vinegar) and gasoline;

C) gasoline (nonpolar molecule) and water; D) methanol (CH3OH) and water.

15. B & D Which of the following factors determine the solubility of a substance? A) agitation (stirring); B) adjusting the temperature; C) crushing the substance to a powder; D) nature of the intermolecular forces; E) all of the above.

16. E Which of the following is not classified as a strong electrolyte?

A) NaCl; B) HClO4; C) Ba(OH)2; D) NaOH; E) Fe(OH)3;

F) H2SO4; G) only A, D, and F are strong electrolytes.

Essays:

1. Briefly explain how the change in entropy (S) can determine whether or not a temperature increase can affect the solubility of a solid being dissolved in a liquid solvent, such as water.

2. Why must a substance must be nonvolatile for the boiling point of an aqueous solution of this substance to have a higher boiling point?

3. If the molarity of an aqueous solution is known, what other property of the substance must be known in order to determine the molality of the solution? How does the magnitude of the value of molality compare to the value of the molarity of the same substance?

4. Why does a 2.00-molal aqueous solution of glucose (C6H12O6) have the same freezing point as a 2.00-

molal solution of sucrose (C12H22O11), even though the M.Wt. of sucrose is much greater?

5. Eight types of colloidal dispersions were listed in class. Give four types and give one example for each. -3-

1. 2.15 m What is the molality of a solution of a nonelectrolyte if 4.000 grams, when dissolved in 200.0 ml of water causes the freezing point to be -4.00oC?

4.00oC = (1.86oC/m)(m), then m = 2.15

(Note: 4.000 grams and 200.0 ml are not important!)

2. 4.05 atm. What is osmotic pressure (in atm.) if 0.0200 moles of potassium carbonate ( a strong electrolyte) is dissolved in enough water to produce 350.0 ml of solution? The temperature is 15oC.

 = iMRT = 3(0.0200 mol / 0.3500 liters)(0.0821)(288 K) = 4.05 atm

3. 101.78oC What is the boiling point of an aqueous solution if 56.0 grams of a nonvolatile nonelectrolyte (MW = 80.7 g/mole) is dissolved in 200.0 grams of water?

o o t = kbm = (0.512 C/m)[(56.0 g / 80.7 g/mol) / 0.200 kg] = 1.776 C

B. Pt = 101.78oC

4. 1.08 x 104 g/mol What is the molecular weight of an organic solute if 3.72 grams of this compound, when dissolved in water, produced an osmotic pressure of 79.8 mm Hg? The volume of the solution is 95.0 ml and the temperature is 80.0oC.

MW = gRT / V = [(3.72 g)(0.0821)(353 K)] / [(79.8 mm / 760)(0.0950 liter)]

MW = 10808 = 1.08 x 104 g/mol

5.______A pure solvent exerts a vapor pressure of 625 torr at 40.0oC. When carbon tetrachloride is added to 0.250 moles of the pure solvent, the vapor pressure of the resulting solution is only 588 torr. How many moles of carbon tetrachloride were added?

6.______What is the normality of a solution of a 2.50 M solution of potassium chromate if the chromium in the chromate ion is reduced to pure chromium metal? -4-

7.______What is the normality of a cesium hydroxide solution if 42.00 ml of this basic solution is required to neutralize 28.80 ml of a 0.383 M solution of phosphoric acid?

Consider the following information when answering the next 4 questions: The "ammonium hydroxide" solution of commercial use is actually a solution of ammonia gas - NH3 - in water. A concentrated solution contains 21.25% NH3 by weight. The density of this solution is 0.8995 g/ml at 20.0oC.

8.______What is the molarity of this solution?

9.______What is the molality of this solution?

10.______What is the mole fraction of ammonia in the solution?

11.______What is the osmotic pressure (in atm.) of this solution?

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12.______What is the molal freezing point depression constant (kf) for pure cyclohexane if the following data is known: the freezing point of pure C6H12 is 6.55oC. This solvent's molecular weight is 84.0 g/mole. When 5.00 grams of a nonvolatile, nonelectrolyte (MW = 282 g/mole) is added to 100.0 grams of this solvent, the freezing point of the resulting solution is 3.00oC. -5-

Consider the following data for this next set of questions:

An 0.844-molal aqueous solution of hydrosulfuric acid (a weak acid) has a freezing point of -2.23oC.

13.______What should have been the freezing point of this solution if H2S had been a nonvolatile, nonelectrolyte?

14.______What is the van't Hoff factor (i) for this solution?

15.______What is the percent dissociation () of this acid?

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16.______What is the molarity of a solution of sulfuric acid if 30.0 ml of this acid solution are required to neutralize 55.4 ml of a 2.006 N solution of aluminum hydroxide?

17.______What is the molecular weight of a nonvolatile, nonelectrolyte, if 3.000 grams of this substance, when dissolved into 26.00 grams of water drops the freezing point to -2.45oC?

18.______What is the molarity of a solution of potassium oxalate, given that the density of the solution is 1.25 g/ml and the solution is known to be 28.85% by weight of the solute?

19.______What is the molality of the above solution, assuming the same conditions? -6-

20.______How many grams of glucose (MW = 180.0 g/mole) must be dissolved into water to make a 450.0 ml of a solution that exerts an osmotic pressure of 45.0 torr?

21.______What is the boiling point of a 3.00-molal aqueous solution if a weak electrolyte is

known to dissociate only 34.3%? The formula for the weak electrolyte is A3B.

22.______What is the value for the molal freezing point depression constant - kf - given the following data: A pure solvent normally freezes at 45.0oC. It has a molecular weight of 387 g/mole. When 5.00 grams of a nonvolatile, nonelectrolyte are added to 250.0 grams of the solvent, the freezing point of the solution drops to 38.7oC. The molecular weight of the solute is 144 g/mole.

23.______How many equivalents are there in 40.00 ml of a 2.50 M solution of aluminum nitrate if the aluminum cation is reduced to aluminm metal?

24.______What is the percent dissociation of calcium iodate if 0.200 moles of this solute, when dissolved in 200.0 grams of water, causes the freezing point to drop 2.80oC? -7-

25.______How many grams of ferric hydroxide must be dissolved in water in order to make 300.0 ml of a 0.120 N solution?

26.______How many liters of water must be used in order to dilute 3.00 liters of a 7.50 M solution of phosphoric acid in order to produce a solution that is 0.500 M?

27.______What is the boiling point of a solution in which 4.00 moles of sodium phosphate (a strong electrolyte) is dissolved in 975 grams of water?