CHEM 217 Study Guide - Midterm Guide: Reversible Reaction, Bayerischer Rundfunk, Equilibrium Constant

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Sample Midterm Examination

The midterm examination is two (2) hours long. In the actual

examination you would not be allowed consult your books or notes;

however, you would be able to use a calculator. We strongly recommend

that you sit this examination as if you were writing it in an invigilated

setting. You will get a much better idea of your degree of preparedness

for the actual examination.

Part A: Short-answer Questions (1 mark each)

1. In the chemical reaction A + B → 2C, the rate of decrease in [A] was

measured to be 2.0 Ms-1. What was the rate of increase in [C]?

2. A given reaction was found to follow first order kinetics, with a rate

constant k = 8.3 × 10-2 s-1. What is the half–life of this reaction?

3. If the reaction between atomic chlorine with ozone,

Cl + O3 → ClO + O2, is an elementary reaction, what is the rate law

for this reaction?

4. In a study of the effects of temperature on the rate of reaction

Cl + O3 → ClO + O2, the following equation for the rate constant was

found:

−

−−

=

260

32 1 1

(1.75 10 ) T

k M s e

What is the activation energy for the reaction Cl + O3 → ClO + O2, in

units kJ/mol?

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5. For the equilibrium reaction N2(g) + 3H2(g)  2NH3(g), write the

expression for Kc.

6. For the equilibrium reaction N2(g) + 3H2(g)  2NH3(g), write the

expression for Kp in terms of Kc.

7. For the reversible reaction 2A + B  2C, the equilibrium constant

Kc = 1.85. If a mixture of A, B, and C has concentrations [A] = 0.40 M,

[B] = 0.40 M, and [C] = 0.30 M, will the reaction mixture shift to the

left (to reactants) or the right (to the product)?

8. A 1.0 L vessel was initially filled with pure NOBr(g) to a pressure of

4.0 atm. The final partial pressure of NOBr was 2.5 atm after the

following equilibrium was established: 2NOBr(g)  2NO(g) + Br2(g).

What is the value of Kp?

9. What is the pH of 0.25 M formic acid (Ka = 1.8 × 10-4)?

10. What is the percent ionization of 0.25 M formic acid?

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11. The pKa of the amino acid glycine is 2.35. What is the Kb of the

conjugate base of glycine?

12. What is the pH of a 1.0 M glycine solution?

13. What is the pH range of a buffered solution composed of equal

molar concentrations of acetic acid and acetate? (Ka = 1.8 × 10-5)

14. What is the pH of a solution composed of 0.40 M acetic acid and 0.20 M

sodium acetate?

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Related Questions

1. The following data were collected at 20 ^oC for the reaction of bromphenol blue, HBPB^2-, and hydroxide ions, OH^-, shown in the equation below

HBPB^2- + OH^- <---> BPB^3- + H₂O

a)What is the rate equation for the reaction?

Determination	[HBPB^2-]₀, M	[OH^-]_o, M	Rate, M/sec
1	7.22 x 10^-6	1.00	9.627 x10^-9
2	7.22 x 10^-6	0.25	2.490 x10^-9
3	3.63 x 10^-6	1.00	4.750 x10^-

The reaction was run three times with different initial concentrations of the reactants yielding the following rates:

b)Determine the reaction order with respect to HBPB^2-

c)Determine the reaction order with respect to OH^-

d)Calculate the rate constant for this reaction at 20 ^oC

e)What is the ârate lawâ for this reaction?

f)What other information do you need to calculate the activation energy for this reaction?

2. Why is it better to transfer one group of solutions into one flask and a second group into a second flask and then mix them, instead of pipetting the solutions sequentially into the same flask?

3. What will be the concentration of [I^-] in the reaction flask after mixing (See Run #6): 1.0 ml starch + 2.0 mL 1.2 x10^-2 M Na₂S₂O₃ + 4.0 mL 0.20 M KI + 4.0 mL 0.20 M KNO₃ + 4.0 mL 0.20 M (NH₄)₂S₂O₈ + 4.0 mL 0.20 M (NH₄)₂SO₄ ?

4. What will be the concentration of [S₂O₈^2-] in the same reaction mixture as above?

Procedure Part A:

Oxone reaction: Dissolve 0.40 g Oxone Â® in 2.0 mL of water by

shaking vigorously, but carefully, in a sealed vial. (SAFETY: Be sure that the flask is

sealed well. Oxone Â® solution is strongly oxidizing and should not come into contact

with skin.) Dissolve 50 ?L of cyclohexene in 2.0 mL of acetone in a small Erlenmeyer

flask. Cool the cyclohexene solution in an icebath, then add the oxone solution dropwise

over 5 minutes with swirling in the icebath. Remove the Erlenmeyer flask from the

icebath and allow the reaction to sit for at least 15 minutes. (This is a good point to begin

the permanganate reaction.) After 15-30 minutes, add about 0.1 mL of conc. HCl to the

reaction dropwise with swirling. Allow the reaction to sit for about 10 minutes, swirling

occasionally.

Procedure Part B:

Potassium permanganate reaction: Dissolve 100 mg of KMnO4 in

4.0 mL of 0.1 M NaOH solution in a small Erlenmeyer flask. Cool the KMnO4 solution

in an icebath. Dissolve 50 ?L of cyclohexene in 2.0 mL of t-butanol in a separate

container. Quickly add the cyclohexene solution into the potassium permanganate. Swirl

the flask in the icebath for 3-5 minutes. Remove the Erlenmeyer flask from the icebath

and allow to sit for 10 minutes.

Procedure Part C:

Thin Layer Chromatography: Obtain a TLC plate. Mark the plate

with four marks, two for each reaction mixture. Spot the crude reaction mixtures lightly.

It may be hard to spot the KMnO4 slurry, but keep trying, you may find it easier if you

use a slightly wider capillary for this one. Allow the plate to dry for a couple of minutes,

or use a heat gun to gently dry the aqueous spots. Develop the plate in a chamber with

ethyl acetate as the eluent. Remove it from the chamber and mark the solvent front. Stain

the plate using anisaldehyde stain, and heat the plate gently to develop the spots. The cis

isomer should stain red, and have an Rf value of ~0.37, the trans isomer should stain blue,

and have an Rf value of ~0.31.

Questions

1. Draw a sketch of the TLC analysis for both reactions.

2. Calculate the Rf of both products formed.

3. Using you text and any other information you can find predict the products of the

4. reactions you performed.

5. Are these reactions stereoselective, stereopsecific or do they give mixtures?

CHEM 217 Study Guide - Midterm Guide: Reversible Reaction, Bayerischer Rundfunk, Equilibrium Constant

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