UNIT 8 – SELF-TEST

Matching

Column A                                           Column B

1.  saturated solution                a.  solubility product constant

2.  colligative properties            b.  the maximum amount of substance that can be dissolved at a given temperature

3.  solute                                  c. concentration of a solution as measured by the ratio of moles of solute per liter of solution

4.  molarity                              d.  dissolving medium

5.  unsaturated solution            e.  equilibrium constant

6.  solvent                                ab.  contains less solute than can theoretically be dissolved

7.  Keq                                    ac. dissolved substance

8. chemical equilibrium               ad.  contains more solute than can theoretically be held at a given temperature

9.  supersaturated solution            ae.  depends upon the number of particles the solute yields in solution

10. Ksp                                      bc.  a chemical system with reversible reactions

Part II:  Multiple Choice with explanation: Indicate the correct answer and write a sentence to explain your choice.

  1. Which of the following is not an electrolyte?  (a) cane sugar(aq)  (b) HCl(aq)       (c) KCl(aq)  (d) (NH4)2SO4(aq)

  2. An electric current is conducted by:  (a) a solution of NaCl.  (b) a sugar solution.  (c) methane gas.  (d) none of the above

  3. If the temperature on an aqueous gas solution increases, the solubility of the gas:  (a) goes down.  (b) goes up.  (c) is unaffected.  (d) can’t be determined.

  4. Increasing the temperature of a solution will generally:  (a) increase the rate at which a soluble solid solute dissolves.  (b) increase the amount of soluble solid solute that dissolves.  (c) both a and b  (d) neither a nor b

  5. An ionic compound has a solubility of 30. g per 100. mL of water at room temperature.  A solution containing 70. g of the compound in 250. mL of water at the same temperature is:  (a) saturated.  (b) supersaturated.  (c) unsaturated.          (d) a suspension.

  6. If more solvent is added to a solution the: (a) molarity decreases.  (b) solution will be less dilute.  (c) mole ratio of solute to solvent increases.  (d) all of the above

  7. What is the molarity of a 200. mL solution in which 0.20 mol of sodium bromide is dissolved?  (a) 0.20 M  (b) 1.0 M  (c) 0.0010 M  (d) 40. M

  8. Which of the following is not a colligative property of a solution?  (a) boiling point elevation  (b) solubility  (c) vapor pressure lowering  (d) freezing point depression

  9. If one mole of each of these soluble solids is added to the same amount of water, which solution has the highest boiling point?  (a) Al2(SO4)3  (b) Mg(C2H3O2)2   (c) C6H12O6  (d) CuCl2

  10. If the pressure of a gas above a liquid is decreased (at constant temperature), the solubility of the gas in the liquid:  (a) remains unchanged.  (b) increases.            (c) decreases.  (d) would change but in an unpredictable direction.

  11. Supersaturated solutions are characterized by  (a) being super hot.  (b) having great stability.  (c) having a larger amount of solute than can be dissolved at the current temperature and pressure.  (d) being able to exist only at very low temperatures.

  12. The maximum quantity of a substance that will dissolve in a given amount of solvent is called the substance’s:  (a) molarity.  (b) saturation level.  (c) solubility.  (d) molality.

  13. An aqueous solution is a solution in which solvent?  (a) alcohol.  (b) water.  (c) any ionic solvent.  (d) any polar solvent.

  14. From what type of solution will a precipitate form?  (a) a saturated solution.  (b) an unsaturated solution.  (c) a supersaturated solution  (d) none of the above

  15. A precipitation reaction is an example of a:  (a) double replacement reaction.  (b) single replacement reaction.  (c) synthesis reaction.  (d) decomposition reaction.

  16. In the reaction A+(aq) + B-(aq) + C+(aq) + D-(aq) à AD(s) + B-(aq) + C+(aq), which of the ions are spectator ions?  (a) B- and C+ only  (b) D- and A+ only  (c) all the ions  (d) none of the ions

Problems and Short Answers:

  1. Calculate the molarity of a solution prepared by mixing 2.45 g of CH3CH2OH in enough water to make 335 mL of solution.

  2. What volume of solution would be required to dissolve 0.213 kg of AlCl3 to yield a concentration of 1.50 M?  

  3. How many moles of ClO4- are present in 75.0 mL of 1.70 x 10-2M Al(ClO4)3 solution?  

  4. If 2.35 g of Pb(NO3)2 dissolved in water react stoichiometrically according to the balanced equation with NaI in a solution with a total volume of 23.5 mL, what was the concentration (molarity) of the NaI solution before the reaction occurred?

                                Pb(NO3)2 (aq)  +  2 NaI(aq)  à  PbI2(s)  +  2 NaNO3(aq)  

  5. If 0.0410 mol of solid MnS reacts stoichiometrically according to the balanced equation in a reaction solution with 810. mL of aqueous HCl, what molarity (M) of HCl is required?
    MnS(s)  +  2HCl(aq)      à  H2S(g)  +  MnCl2(aq)  

  6. What mass of sucrose, C12H22O11, is needed to make 300. mL of 0.50 M solution?  

  7. A ground water sample contains the hazardous ion, CrO42-.  A 100. L sample of water is tested for CrO42-.  Cu(NO3)2 (aq) is added until the copper (II) chromate precipitate stops forming.  After separation the mass of the pure dry precipitate is 0.313 g.  Determine the original molarity of CrO42- in the sample.  

  8. Explain why crushed salt dissolves faster in water than large lumps of rock salt.  

  9. Write a balanced chemical equation for each of the following:  (a) the dissolution of potassium carbonate (K2CO3).  (b) the precipitation of lead (II) bromide (PbBr2) from its ions.  (c) silver sulfate (Ag2SO4) in equilibrium with its ions.  

  10. Write a complete ionic equation and a net ionic equation for what occurs when a saturated solution of potassium sulfide is mixed with a saturated solution of chromium(III) nitrate, given that the sulfides of all transition metals are only slightly soluble and that all nitrates are soluble.

Chapter 18 – SELF-TEST QUESTIONS

1)      Classify each of these statements as always true (AT), sometimes true (ST), or never true (NT).

  1. The concentrations of reactants and products in a system at dynamic equilibrium are always changing.

  2. A change in the pressure on a system can cause a shift in the equilibrium position.

  3. For a chemical equilibrium to be established, the chemical reaction must be irreversible.

  4. The Keq for a certain reaction was 2 x 10-7.  For this reaction at equilibrium, the concentration of the reactants is greater than the concentration of the products.

  5. The term “common ion effect” refers to the lowering of the solubility of a substance by the addition of a common ion.

2)      Calculate Keq for this reaction:  2SO3(g)  à  2SO2(g)  +  O2(g), if the equilibrium concentrations are:  [SO2] = 0.42 M, [O2] = 0.21 M, [SO3] = 0.072 M.

3)      At 25oC, the following reaction has an equilibrium constant of 9.0 x 10-4.  Find the concentration of A(g) in moles per liter, when the concentration of B(g) is 0.030 mol/L and the concentration of C(g) is 0.060 mol/L.  
                                                A(g)  ßà  B(g)  +  2C(g)

4)      Explain how the equilibrium position of this reaction is affected by the following changes:
                                4HCl(g)  +  O2(g)  ßà  2Cl2(g)  +  2H2O(g)

a)      add Cl2

b)      remove O2

c)      increase pressure

d)      use a catalyst

5)      At a certain temperature, an equilibrium is established for this reaction in a 3.0 L container:   
Cl2(g)  +  Br2(g)  ßà  2BrCl(g).  Given 0.85 mol Cl2, 0.85 mol Br2, and 0.30 mol BrCl, what is Keq?

6)      Aluminum hydroxide has a Ksp of 3.0 x 10-34.  Calculate the equilibrium concentrations of aluminum and hydroxide ions.

7)      Explain what happens when HCl is added to a saturated solution of AgCl?

8)      The solubility of SrCrO4 in water is 1.2 grams per liter of solution.  Calculate Ksp.

9)      Will a precipitate form when 0.00070 mol Na2CO3 is mixed with 0.0015 mol Ba(OH)2 in 1.00 liter of solution?  Assume that these two salts both dissolve completely.  (The Ksp for BaCO3 is 5.0 x 10-9.)

CHECK YOUR ANSWERS