Exam 1 Worksheet

Exam 1 Worksheet

Exam 1 Worksheet ? Chemistry 104

Chapter 13 ? Solutions

1. Vinegar is 5.0% by mass (in water). If the density of vinegar is 1.006 gmL?1, what is the concentration in units of molarity and molality?

2. Stainless steel sinks can increase the concentration of chromium ions in water. If the allowed concentration of chromium in waste water is 0.0875 ppm, what mass (in mg) of chromium is in 1000 L of water? What volume of water contains 1.00 g of chromium?

3. Determine the concentrations in units of molarity, molality, and percent by mass for each of the solutions. Assume the density of water to be 1.00 gmL?1. a. 12.5 g of potassium nitrate in 250 mL of water (the final volume of the solution is 250 mL) b. 45.0 mL of ethanol (density 0.789 gmL?1) and 45.0 mL of water (assume the volumes are additive). This is 100 proof alcohol (which is sold %v/v). c. A solution of potassium hydroxide made with a 1:3 ratio (by mass) of solute to water. The density of the solution is 1.29 gmL?1 d. A solution of ammonium sulfate with 117 g of the solute dissolved per liter of solution made. The density of the solution is 1.06 gmL?1. e. Phosphoric acid which 85.0% by mass with a density of 1.689 gmL?1. f. Ammonia which is 29.89% by mass with a density of 0.8960 gmL?1.

4. You have a 35 g of potassium nitrate at 80oC in 100 g of water which you cool to 20oC, what mass of potassium nitrate will precipitate out of solution? (Use Figure 13.3, in your textbook.)

5. What additional mass of sodium nitrate is soluble in 150 g of a saturated solution at 70oC versus 30oC? (Hint: For this question, consider the mass of NaNO3 in 100 g H2O (also then, what is the mass of the solution) at 70oC compared to the mass of NaNO3 in a solution with a total mass of 150 g ? the connection between what is presented in the figure and what is asked here.)

6. What is the relationship between the solubility of gases and temperature? Why should you not boil water (and then cool it) if you are going to use it in a fish bowl?

7. The Henry's law constant for the solubility of oxygen in water is 3.30?10?4 Matm?1 at 12oC and 2.85?10?4 Matm?1 at 22oC. Air is 21% (by volume) of oxygen. a. What mass of oxygen can be dissolved in 1000 L of water at 12oC at an air pressure of 1 atm? b. What mass of oxygen can be dissolved in 1000 L of water at 22oC at the same pressure as part a?

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Exam 1 Worksheet

c. If the partial pressure of oxygen (at 22oC) is increased to 0.80 atm, how does the solubility of oxygen in water change?

d. If the partial pressure of oxygen (at 22oC) is increased to 0.80 atm, what volume of oxygen can be dissolved in 1000 L of water?

8. What is the relationship between pressure and the solubility of gases?

9. Using Table 5.2 (and assume the density of water is 1.00 gmL?1), what is the vapor pressure of the solutions? a. 58.5 g of sugar (C12H22O11) dissolved in 500 mL of water at 35oC. b. 58.5 g of glucose (C6H12O6) dissolved in 500 mL of water at 35oC. c. 58.5 g of sugar (C12H22O11) dissolved in 500 mL of water at 55oC. d. 58.5 g of glucose (C6H12O6) dissolved in 500 mL of water at 55oC.

10. The vapor pressure of pure ethanol at 45oC is 155 mmHg. The density of ethanol is 0.79 gmL?1 and the density of water is 1.0 gmL?1. Using Table 5.2 (in your textbook), what is the vapor pressure of ethanol and water in the solutions listed? a. 100 mL containing equal masses of ethanol and water. b. 100 mL containing equal volumes of ethanol and water. c. 100 mL containing equal molar amounts of ethanol and water.

11. What is the boiling point and freezing point of the solutions? (Use Table 13.3 for measured van't Hoff factor if given, otherwise use the calculated value.) a. 58.5 g of sugar (C12H22O11) dissolved in 500 mL of water. b. 58.5 g of glucose (C6H12O6) dissolved in 500 mL of water. c. 22.5 g of potassium nitrate in 250 mL of water. d. 22.5 g of sodium nitrate in 250 mL of water. e. 58.5 g of sugar (C12H22O11) dissolved in 500 mL of ethanol. f. 58.5 g of glucose (C6H12O6) dissolved in 500 mL of ethanol.

12. A compound contains 42.9% carbon, 2.4% hydrogen, 16.6% nitrogen, and 38.1% oxygen. The addition of 3.16 g of this compound to 75.0 mL of cyclohexane (density = 0.779 gmL?1) gives a solution with a freezing point at 0.0oC. What is the molecular formula and molar mass of the solute?

13. A 50.0 mL solution is prepared by dissolving 225 mg of a protein in water. The solution has an osmotic pressure of 4.18 mmHg at 25oC. What is the molar mass of the protein?

14. The molar mass of a type of hemoglobin was determined by osmotic pressure of 4.60 mmHg for a solution at 20oC containing 3.27 g of hemoglobin in 0.200 L of solution. What is the molar mass of hemoglobin?

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Exam 1 Worksheet

Chapter 14 ? Kinetics

1. Give the expressions for the rate in terms of change of concentration over change in time for the reactions listed:

a. H2 g Br2 g 2HBr g

b. 2NOBr g 2NO g Br2 g

c. N2 g 3H2 g 2NH3 g

2. The change in concentrations and time for one substance is given for each reaction in number 1. What is the reaction rate? What is the change in concentration for all other species for the same time period?

Reaction A B C

Substance HBr(g) NOBr H2

[A]0 0 M 2.0?103 M 5.0?102 M

[A]t 1.5?103 M 1.6?103 M 1.5?103 M

time 2.0 min 5.0 sec 25 sec

Which reaction has the fastest rate? Which reaction has the slowest rate?

3. Determine the reaction order with respect to each reactant, reaction order overall, the

rate expression, and evaluate the rate constant for the following initial rates versus

initial concentrations.

Exp 1

Exp 2

Exp 3

[A], M 1.0 ? 104

1.0 ? 104

8.0 ? 104

[B], M 4.0 ? 104

8.0 ? 104

8.0 ? 104

Rate, Mh-1

0.15

0.15

9.6

a. What plot would yield a straight line when evaluating the time versus the

reactant concentration?

b. Is this reaction relatively slow or fast?

c. Select the slow mechanistic step from the reaction mechanism below.

A D C

CBF

2A D d. Give the overall reaction.

4. Determine the reaction order with respect to each reactant, reaction order overall, the

rate expression, and evaluate the rate constant for the following initial rates versus

initial concentrations.

Exp 1

Exp 2

Exp 3

[C], M 2.0 ? 104

2.0 ? 104

4.0 ? 104

[D], M 4.0 ? 104

8.0 ? 104

8.0 ? 104

Rate, Ms-1

1.05

2.10

4.20

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Exam 1 Worksheet

a. What plot would yield a straight line when evaluating the time versus the reactant concentration?

b. Is this reaction relatively slow or fast? c. Select the slow mechanistic step from the reaction mechanism below.

CA D A B CD E d. Give the overall reaction.

5. Determine the half life of a substance that has 45.0 kg initially and after 14 days only 1.975 g remains. (Assume first order decay) a. Determine how much of a 12.0 g sample will remain after 12 hours. b. Determine the rate constant. c. Determine the time it takes for one metric ton (1 ? 106 g) to be reduced to 1.0 g.

6. Determine the half life of a substance that has 2.000 g initially and after 14 days only 1.975 g remains. (Assume first order decay) a. Determine how much of a 12.0 g sample will remain after 12 years. b. Determine the rate constant. c. Determine the time it takes for one metric ton (1 ? 106 g) to be reduced to 1.0 g.

7. Determine the amount of substance after 1 year if the sample was initially 757 g and has a half life of 4.5 days.

8. Determine the amount of substance after 1 year if the sample was initially 757 g and has a half life of 4.5 months.

9. Determine the amount of substance after 10 years if the sample was initially 757 g and has a half life of 4.5 days.

10. Determine the amount of substance after 10 years if the sample was initially 757 g and has a half life of 4.5 months.

11. Determine the amount of time it would take for a substance with a half life of 3500 years to reduce to 10% of the initial amount.

12. Determine the amount of time it would take for a substance with a half life of 3500 years to reduce to 1.0% of the initial amount.

13. Determine the amount of time it would take for a substance with a half life of 3500 years to reduce to 0.10% of the initial amount.

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Exam 1 Worksheet

14. For the second-order decomposition of acetaldehyde, the rate constant at 700 K increases by an order of magnitude when the temperature increases by only 10%. What is the activation energy for this reaction?

15. For the same reaction, would the rate be higher or lower at a lower temperature? Plot the Maxwell-Boltzmann distribution of gases showing the fraction of molecules greater than the activation energy at these two temperatures to support your conclusion.

16. The activation energy for the first order reaction of the isomerization of methyl isocyanide to acetonitrile is 160 kJmol1 and the frequency factor is 3.98?1013 s1, what is the rate constant at 375 K?

17. The activation energy for the first order reaction of the decomposition of ethyl iodide to ethylene and hydrogen iodide is 209 kJmol1. If the rate constant at 550 K is 1.28?103 hr1, what is the rate constant at 450 K? At what temperature is the rate constant 2.00?102 hr1?

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