GRADE 12 DEPARTMENTAL EXAMINATION

CHEMISTRY 30, JUNE 2002

SECTION I: Multiple-Choice Questions

ANSWER THE FOLLOWING 30 QUESTIONS ON THE COMPUTER SHEET ENTITLED "STUDENT EXAMINATION FORM."

1. The strength of a solution of NaNO 3 (aq) is listed as 5.0 g •L-1 . The concentration of this solution can also be expressed as

A. 0.029 mol .14-1 B. 0.059 mol .14-1 C. 0.50 mol .L-1 D. 5.0 mol .L-1

2. The following steps are used to prepare a 250 mL solution of NaCl.

1. Measure 100 mL of distilled water into a 250 mL volumetric flask.

2. Dissolve the solid NaC1 in the distilled water. 3. Accurately weigh the desired amount of solid NaCl. 4. Top up the solution to the 250 mL etched line with distilled

water.

The correct order of the steps is

A. 4, 2, 3, 1 B. 3, 1, 4, 2 C. 2, 3, 1, 4 D. 3, 1, 2, 4

3. Which positive ion will form a compound with low solubility in water when combined with 011 - ?

A. Cu' B. K+ C. H+ D. NH4+

GRADE 12 DEPARTMENTAL EXAMINATION

CHEMISTRY 30, JUNE 2002

SECTION I: Multiple-Choice Questions

ANSWER THE FOLLOWING 30 QUESTIONS ON THE COMPUTER SHEET ENTITLED "STUDENT EXAMINATION FORM."

1. The strength of a solution of NaNO 3 (aq) is listed as 5.0 g • L-1 . The concentration of this solution can also be expressed as

A. 0.029 mol .L-1 B. 0.059 mol .L-1 C. 0.50 mol D. 5.0 mol

2. The following steps are used to prepare a 250 mL solution of NaCl.

1. Measure 100 mL of distilled water into a 250 mL volumetric flask.

2. Dissolve the solid NaC1 in the distilled water. 3. Accurately weigh the desired amount of solid NaCl. 4. Top up the solution to the 250 mL etched line with distilled

water.

The correct order of the steps is

A. 4, 2, 3, 1 B. 3, 1, 4, 2 C. 2, 3, 1, 4 D. 3, 1, 2, 4

3. Which positive ion will form a compound with low solubility in water when combined with OH- ?

A. Cu' B. K+ C. 11+ D. NH4+

I. II. III.

3B+X2 +31.1 kJ -.4133)(2 A 2 + 4B 2AB 2 + 42.5 kJ X2 + Y2 2XY = —40.9 kJ

= +22.6 kJ Iv. C 4 +5G2 2C2G5

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4. A sample of polluted water contains 5.0 ppm of Pb +2 (aq) ions. What is the concentration of Pb'(aq) in mol .L-1?

A. 5.0x10 3 mol B. 2.4x10 5 mol C. 5.0x10 -3 mol •L-1 D. 2.4x10 -5 mol .L-1

5. Choose the one pair of salts whose aqueous solutions would, upon mixing, create a precipitate. Assume all ion concentrations are above 0.1 mol

A. CaCl 2 , CuSO4 B. Li 2SO 4 , KNO3 C. NaNO3 , MgBr2 D. Na 2 SO4 , (NH4 )2S

Use the following information to answer question 6.

6. Which of the above reactions is(are) endothermic?

A. II only B. III only C. I and IV only D. II and III only

7. MgO(s) and CO(g) are produced from their elements according to the following equations.

Mg(s) + —1

02 (g) —> MgO(s) 2

AH° = —602 kJ • mor l MgO

1 C(s)+

2— 02 (g) —> CO(g) AH° = —110 kJ • morl CO

The AH° for the reaction Mg0(s)+ C(s) —› Mg(s) + CO(g) is

A. —712 kJ • mol' Mg.

B. — 492 kJ • morl Mg.

C. +492 kJ • mol' Mg. D. +712 kJ • mol -1 Mg.

8. Using bond enthalpies, an estimated AH° for the reaction,

H H H H \ / I I C=C (g)+H—H(g) --. H—C—C—H(g)

/ \ I I H H H H

would be

A. {C=C+2H—C+H—H}—{2C—H+C—C} B. {C = C+ 4H —C+ H —11}— {6C —H+ C —C} C. {C=C+H—C+H—H}—{C—H+C—C} D. {2C-H+C—C}—{C=C+4H—C+H—H}

9. Consider the following reaction.

4 HNO3 (aq) + 5 N 2 H4 (t) —> 7 N 2 (g) +12 H 2 0(g) zH = —2462.0 kJ

Which statement is correct for the indicated reaction?

A. 205.2 kJ are absorbed per mole of H 2 0(g) used.

B. 351.7 kJ are absorbed per mole of N 2 (g) formed.

C. 615.5 kJ are released per mole of HNO 3 (aq) used.

D. 492.4 kJ are released per mole of N 2H4 (g) formed.

10. Which of the following does NOT affect the rate of a chemical reaction?

A. AH of the reaction B. Use of a catalyst C. Temperature of the reacting system D. Concentration of the reactants

11. Scientists have proposed that the burning of methane involves the following four-step reaction pathway.

1 CH4 (g)+ —

202 (g) --> CH3OH(t)

1 CH3 OH(t) + —

2 O2 (g) —> CH 2 0(g)+ H20(g)

1 CH 2 0(g)+ —

202 (g) —> HCOOH(g)

1 HCOOH(g) +

2— 02 (g) --> CO 2 (g) + H20(g)

CH,(g)+ 2 02 (g) -p CO2 (g) + 2 H20(g)

Which of the following is NOT an intermediate?

A. CH3OH(2)

B. CH20(g) C. HCOOH(g) D. CO 2 (g)

Reaction II Eal Eat

Number of Particles

Reaction I

Number of Particles

Kinetic Energy Kinetic Energy

Reaction III Ea3

Number of Particles

Reaction IV Ea4

Number of Particles

Kinetic Energy Kinetic Energy

5

12. Consider the following identical kinetic energy distribution curves for four different reactions. The reactions are occurring at the same temperature. Ea represents activation energy.

The reaction occurring most rapidly is probably

A. Reaction I. B. Reaction II. C. Reaction III. D. Reaction IV.

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40

100

Diagram I

Diagram II

Diagram III Diagram IV

13. In each of the following potential energy diagrams, the horizontal axis is the reaction coordinate and the vertical axis represents potential energy in kJ. Which potential energy diagram best describes a forward reaction which has an activation energy of 40 kJ and a net energy change (reaction enthalpy) of —100 kJ ?

A. Diagram I B. Diagram II C. Diagram III D. Diagram IV

14. A flask contains the following chemicals at equilibrium.

A(s) + B(g) + heat <=> C(s)

If the volume of the flask is decreased by means of a piston, the equilibrium will shift to

A. lower the [C(s)]. B. reduce the moles of B(g). C. produce more heat. D. liquify the A(s).

15. Consider the equilibrium system S 8 (s) + 8 02 (g) <=> 8 SO2 (g). What effect will the addition of solid sulphur, S 8 (s), have on the system?

A. There will be no change. B. More S0 2 (g) will be produced. C. Less 0 2 (g) will be produced. D. The pressure will decrease.

16. For the reaction A(g) + B(s) 4 C(g), the value for the K eq is 20.0. The

value for the Keq of the reverse reaction, C(g) <=> A(g) + B(s), is

A. 20.0 B. 2.00 C. 0.0500 D. impossible to determine from the information given.

17. In an equilibrium system, the condition that must be "equal" is

A. concentrations of reactants = concentrations of products.

B. amount of products being removed from the system = amount of reactants being added to the system.

C. value of Keq at 20 °C = value of Keq at 150 °C.

D. rate of forward reaction = rate of reverse reaction.

18. Three acid-base indicators were used to test an unknown solution. The following observations were made.

Indicator Colour in Solution methyl red yellow phenol red yellow alizarin yellow yellow

The approximate pH of the solution is

A. 5.0 - 5.6 B. 6.0 - 6.6 C. 8.0 - 8.6 D. 10.0 - 10.6

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19. Nitric acid (HNO 3 ) is a strong acid. Which of the following statements concerning nitric acid is NOT true?

A. A 1 M solution of nitric acid has an [111 of 1 M. B. A 6 M solution of nitric acid will conduct an electric current better

than a 1 M solution. C. Even a very dilute solution of nitric acid has an [11 + ] greater than

M. D. Nitric acid will turn pink litmus paper blue.

20. H3X(aq) represents a polyprotic acid. The strongest acid in its dissociation series is

A. H3X(aq) B. H2X-(aq) C. HX-2(aq) D. X-3(aq)

21. Which of the following is a polyprotic acid?

A. HCO3- B. HC1 C. H2SO4 D. HC104

22. A solution has a pH = 9. The [OW] of the solution is

A. 1 x 10" mol B. 1x10 -9 mol C. 1x10-' mol D. 1x10 -5 mol .L-1

23. In the reaction represented by the equation H2S03 +1120 <=> H30+ + HS03- , the Bronsted-Lowry acids are

A. H2S03 and H30+ B. H2O and H30+

C. H2S03 and HS03-

D. -1120 and HS03-

24. Which generalization about the Standard Electrode Potential Table is valid?

A. Metallic ions and non-metallic ions are generally reducing agents. B. Metallic ions and non-metallic elements are generally oxidizing

agents. C. Metallic elements and non-metallic elements are generally reducing

agents. D. Metallic elements and non-metallic ions are generally oxidizing

agents.

25. In which change are electrons gained?

A. Ca'(aq) to Ca(s) B. 2 C1 - (aq) to C12(g) C. Fe+2 (aq) to Fe' (aq) D. NaCl(s) to Na + (aq) and (aq)

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Ni

HC1

I

Ni

Pb(Cl)2

Ni

AlC13

Ni

AuC13

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26. Into each of the following 1.0 mol solutions, a nickel metal strip was inserted.

IV

In which solution would NO REACTION occur?

A. I B. II C. III D. IV

27. In an experiment, strips of metals A, B, and D were placed in 1.0 M solutions of A', B' , and D' ions. The following results were observed.

A(s) B(s) D(s) A' (aq) no reaction no reaction no reaction

B' (aq) deposit of B(s) on strip

no reaction no reaction

D' (aq) deposit of D(s) on strip

deposit of D(s) on strip

no reaction

The ions, listed in order of decreasing effectiveness in competition for electrons, are

A. D' , , A' B. B +2 A +2

C. B',D', A' D. A', D',

28. Balance the following equation, using the half-reaction method.

Cr2 07 -2

+ NO(g) Cr' + NO3 + H2O

When the equation is balanced, the coefficients of the equation are

A. 1, 14, 2, 2, 3, 3 B. -.1, 6, 2, 2, 2, 3 C. 1, 5, 3, 6, 2, 7 D. 1, 14, 3, 2, 3, 8

29. Which of the following is the best oxidizing agent at standard conditions?

A. K+(aq) B. r(aq) C. Au(s) D. C12(g)

30. Steel pipelines can be protected against corrosion by burying a zinc cable which is attached to the pipeline. How does protection occur?

A. No corrosion will occur because the steel will be galvanized. B. Only zinc will corrode because it has a lower reduction potential. C. Only zinc will corrode because it will be reduced instead of steel. D. No corrosion will occur because the metals are not connected by a

salt bridge.

100 10 20 30 40 50 60 70 80 90

Solubility Curves for Selected Solutes 1500

1400

1300

1200

1100

1000

900

800

700

600

500

400

300

200

100

0o

2

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SECTION II: Short-Answer Questions (Compulsory)

ANSWER ALL OF THE QUESTIONS IN THIS SECTION. ANSWER IN THE SPACES PROVIDED IN THE EXAMINATION BOOKLET. SHOW ALL YOUR WORK. MARKS WILL BE GIVEN FOR FORMULAS, CALCULATIONS, AND UNITS. ALL ANSWERS MUST BE WRITTEN IN INK.

1. Solubility charts, like the one shown below, are a convenient way to represent the solubility-temperature relationships of several substances in a condensed format.

Temperature (°C)

a. With the aid of the solubility chart above, determine the solubility, in g • L-1 , of the following:

i. KNO3 at 45 °C

ii. NaC1 at 60 °C

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b. Based on the solubility chart, at what temperature would you expect 500 g of the following solutes to form saturated solutions in 1 L of H20 ?

i. HC1

KNO3

c. What characteristic do HC1 and SO 2 have in common that would result in their solubilities decreasing with an increase in temperature?

d. A student was asked to prepare a stock solution using 3.72 g of Ba(NO3 )2 (s) dissolved in enough distilled water to make 175 mL of solution. What would be the concentration of the solution?

e. The student was also asked to prepare a solution for an experiment which required 125 mL of 0.0920 M NaCl. What volume of 0.484 M NaCl stock solution would be needed to prepare the new solution?

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When concentrated sulfuric acid is added to water, a great deal of energy is released. A student collected the following data in an experiment to determine the molar heat of solution of sulfuric acid.

volume of concentrated sulfuric acid total mass of solution initial temperature final temperature specific heat capacity of solution

used = 6.75 = 179.90 g =10.0 °C = 14.9 °C = 4.18 J • g' • °C-1

a. Using the data collected, determine the quantity of heat involved in the dissolving of the acid.

b. Calculate the molar heat of solution (AH) for the acid in kJ • mor l . The concentration of the acid is 18 M.

c. If the student used 13.5 mL of acid instead of 6.75 mL, how would this affect the value of All? Explain your answer.

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Experienced skiers and hikers often carry chemical "hot packs" with them in case of an emergency. These hot packs are known to contain powdered iron and activated carbon. When the plastic packaging is removed, oxygen from the air is allowed to combine with the iron causing the following exothermic reaction to begin.

4 Fe(s) + 3 02 (g) —> 2 Fe 203 (s) All = —1652 kJ

a. Identify two factors which would increase the rate of reaction within the "hot pack."

i.

11.

b. For the two rate factors identified in part a., use the collision theory to account for their effect.

i.

c. Activated carbon is present within the hot pack, however it is not part of the overall chemical equation.

i. Explain the significance of the carbon.

ii. If carbon was eliminated from the "hot pack," what would happen to the overall rate of reaction?

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14.00

10.00

0.00 1.00 2.00 3.00 4.00 5.00 6.00 7.00 8.00 9.00

- COC12(g) - CO(g)

• - C12(g) • 12.00

• 8.00

441.4 6.00 ,))

4.00

2.00

0 ❑

A 1.1,---. 11. no, wrAil riari,...„ isimpmwini.-_--ii r mow

A A A

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The equilibrium system, COC1 2 (g) <=> CO(g)+ C1 2 (g) + heat, was established in a closed container. The following graph illustrates changes in the equilibrium as a result of changes to the system.

Time (min)

a. i. What stress was applied at time = 3.00 min?

ii. What is the effect on the concentration of the other two substances as a result of the stress?

b. A different stress was applied to the system at time = 6.00 min. State one possible stress that could have been applied and indicate whether it was an increase or a decrease.

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c. What feature of the graph indicates that equilibrium has been reached?

d. ' Write the Keq expression for this equilibrium.

e. Calculate Keq given the following equilibrium data:

[C0C1 2 (g)]= 0.78 mol [CO(g)] = 0.56 mol [C1 2 (g)]= 0.94 mol

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. Boric acid, H 3 B03 (aq), is used as a flame retardant. A student titrated this acid against 0.350 M LiOH. The following data were collected.

Trial #1 Trial #2 Trial #3 H3B03 LiOH H3B03 LiOH H3B03 LiOH

Final Volume (mL) 16.00 27.60 33.00 54.64 49.00 82.84

Initial Volume (mL) 0.0 0.0 16.00 27.60 33.00 54.64

Volume Used (mL)

a. Complete the last row in the table above.

b. Write a balanced neutralization equation for the reaction.

c. Calculate the [H 3B03 (aq)] for each trial.

d. What is the average concentration of boric acid?

e. In a different experiment, HC1 was used instead of H 3B03 . A student found the [HC1(aq)] to be 0.785 M. If the actual [HC1(aq)] was 0.825 M, what was the student's experimental error?

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. The following diagram represents an Al(s) Al' 3(aq)

Al metal Pt metal

C12(g) C1-(aq) cell.

a. i. Write the half-reaction occurring at the anode.

ii. Write the half-reaction occurring at the cathode.

iii. Write the net ionic equation for the cell.

iv. Calculate the potential difference of the cell.

b. Is this an electrolytic or electrochemical cell? How can you tell?

c. Why is one electrode made of platinum (Pt) metal?

d. What happens to the mass of the Al(s) as the reaction proceeds?

e. Is the charge on the Al(s) electrode negative or positive?