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AP Chemistry Scoring Guide

Unit 8 Progress Check: MCQ

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1.

Pure water autoionizes as shown in the equation above. Based on this information, which of thefollowing is correct?

AThe autoionization equilibrium for pure water favors the formation of reactants at compared to

.

BThe autoionization equilibrium for pure water produces the same amount of ions at and

.

C At , for pure water.

D At , for pure water.

2. at Based on the information above, which of the following is true for a sample of pure water at ?

A

B

C

D

3. The endothermic autoionization of pure water is represented by the chemical equation shownabove. The of pure water is measured to be 7.00 at and 6.02 at . Which of thefollowing statements best explains these observations?




A At the higher temperature water dissociates less, , and the water becomes basic.

B At the higher temperature water dissociates less, , and the water remains neutral.

C At the higher temperature water dissociates more, , and the water becomes acidic.

D At the higher temperature water dissociates more, , and the water remains neutral.

4. Which of the following gives the best estimate for the of a solution at?

A because is a strong acid.

B because is a weak acid.

C because is a weak base.

D because is a strong base.

5. Which of the following gives the best estimate for the of a solution at?




A because is a strong acid.

B because is a strong acid.

C because is a strong base.

D because is a strong base.

6. Which of the following is the correct mathematical relationship to use to calculate the of a aqueous solution?

A

B

C

D

7. at Initial

Percent Ionization Equilibrium

0.150 3.4%

0.100 4.2%

0.0500 5.8%The equilibrium for the acid ionization of is represented by the equation above and thetable gives the percent ionization for at different initial concentrations of the weak acid at

. Based on the information, which of the following is true for a aqueous solution of?




AIt has a larger percent ionization, a lower , and a lower than a solution does.

BIt has a larger percent ionization, a lower , and a higher than a solution does.

CIt has a lower percent ionization, a larger , and a higher than a solution does.

DIt has a lower percent ionization, a larger , and a higher than a solution.

8.

The reaction between and water is represented above. A solution that is initially in has a of 11.28. Which of the following correctly predicts the of a solution for which

, and why?

AThe will be lower than 11.28 because decreasing the initial concentration of increases theequilibrium concentration of the conjugate acid .

BThe will be lower than 11.28 because the equilibrium concentration of ions decreaseswhen the initial concentration of the base decreases.

CThe will be higher than 11.28 because decreasing the initial concentration of decreasesthe equilibrium concentration of the conjugate acid .

DThe will be higher than 11.28 because the equilibrium concentration of ions increaseswhen the initial concentration of the base decreases.

9. The acid ionization equilibrium for at is shown above. A aqueous solution ofthis acid has a of about 4.2. If a solution with an initial concentration of of isallowed to reach equilibrium at the same temperature, which of the following correctly predicts its

, and why?




AThe will be higher than 4.2 because increasing the concentration of the weak acid decreasesthe percent ionization.

BThe will be higher than 4.2 because, for weak acid solutions, the is directly proportional tothe initial concentration of the weak acid.

CThe will be lower than 4.2 because increasing the concentration of the weak acid producesmore to establish equilibrium.

DThe will be lower than 4.2 because the of the weak acid is inversely proportional to the initialconcentration of the weak acid.

10. The weak acid has a of 4.76. A solution is prepared by mixing of and of . Which of the following can be used to

calculate the of the solution?

A

B

C

D

11. Which of the following provides the correct mathematical expression to calculate the of asolution made by mixing of and of at ?




A

B

C

D

12. Substance

9.25

A buffer solution is formed by mixing equal volumes of and ,which reduces the concentration of both solutions by one half. Based on the data given in thetable, which of the following gives the of the buffer solution?

A

B

C

D




13.

The versus volume data for the titration of with is plottedon the graph above. Based on the data, which of the following species is present in the greatestconcentration after of has been added to the solution of ?

A

B

C

D




14.

A solution of the weak acid potassium hydrogen phthalate ( ) is titrated with. Based on the titration curve shown in the graph above, the of is

closest to which of the following?

A 3.6

B 5.4

C 8.8

D 11.8




15.

A sample of was titrated with . Based on the resulting titrationcurve shown above, what was the approximate concentration of in the sample?

A

B

C

D




16. Name Structure

Acid 1

Acid 2

The table above provides information on two weak acids. Which of the following explains the difference in their acidstrength?




A Acid 1 is a stronger acid because it has more acidic hydrogen atoms than acid 2.

B Acid 1 is a stronger acid because it can make more hydrogen bonds than acid 2.

CAcid 2 is a stronger acid because it is a larger, more polarizable molecule with strongerintermolecular forces than acid 1.

DAcid 2 is a stronger acid because it has a more stable conjugate base than acid 1 due to the greaternumber of electronegative atoms.

17.

Acid

The equilibrium reactions for diprotic oxoacids with a general formula are represented bythe equations above. The acid ionization constants for and are provided in thetable. Which of the following best explains the difference in strength for these two acids?




A is weaker because has a smaller positive formal charge than , resulting in a decrease

in its ability to transfer an to .

B is weaker because has a smaller positive formal charge than , resulting in a

decrease in its ability to transfer an to .

C is weaker because is more electronegative than , resulting in more stable conjugate

bases and than those for .

D is weaker because is less electronegative than , resulting in less stable conjugate

bases and than those for .

18.

Lewis diagrams of the weak bases and are shown above. Based on these diagrams,which of the following predictions of their relative base strength is correct, and why?

A is a stronger base than because more than one resonance structure exists for its

conjugate acid , making it more stable than .

B is a stronger base than because of the greater electronegativity of compared with .

C is a weaker base than because of the greater electronegativity of compared with .

D is a weaker base than because more than one resonance structure exists for its

conjugate acid , making it more stable than .




19.

A student measures the of a buffer solution made with and , as shownabove. The of is 7.40 at . Based on this information, which of the following bestcompares the relative concentrations of and in the buffer solution?

A

B

C

D It is not possible to compare the concentrations without knowing the of .




20.

is a weak acid with a value of 3.5. The graph above shows the results of a titration ofan aqueous solution of with . Based on the results, the concentration of

is greater than the concentration of at which of the following values?

A 2.0

B 3.0

C 3.5

D 4.0




21.

The weak acid ionization equilibrium for is represented by the equation above. Astudent measures the of using a probe and a meter in the experimentalsetup shown. Based on the information given, which of the following is true?

A since the of the weak acid is less than .

B since the of the weak acid is greater than the of the

solution.

C since the for is less than .

D since the for is less than the for .




22.

The acid equilibrium for and the base equilibrium for arerepresented above. One liter of a buffer solution with is made by mixing

and . If of is added tothe buffer, which of the following is most likely the resulting , and why?

AThe will be much less than 4.85, because the buffer will respond to the addition of byproducing more .

BThe will be much greater than 4.85, because there is a large increase in the concentration of theweak base, .

CThe will be slightly less than 4.85, because the addition of reduces the autoionization of

.

DThe will be slightly greater than 4.85, because some will react with the addedbases, resulting in a slight decrease in .

23. A buffer solution that is in both and has a . A student saysthat if a very small amount of is added to the buffer, the will decrease by a verysmall amount. Which of the following best supports the student’s claim?

A will accept a proton from to produce more and .

B will accept a proton from to produce more and .

C will donate a proton to to produce more and .

D will donate a proton to to produce more and .

24.The equilibrium representing the acid dissociation of is shown above. A buffer solutionis prepared by adding of to of . Assuming the changein volume is negligible, which of the following expressions will give the of the resulting buffer at

?




A

B

C

D

25. To prepare a buffer solution for an experiment, a student measured out of (molarmass ) and added it to of . However, in the process of adding the

to the , the student spilled some of the onto the bench top. As aresult, only about of was actually added to the . Which of thefollowing best describes how the buffer capacity of the solution is affected as a result of the spill?

AThe solution has a greater buffer capacity for the addition of base than for acid, because

.

BThe solution has a greater buffer capacity for the addition of base than for acid, because

.

CThe solution has a greater buffer capacity for the addition of acid than for base, because

.

DThe solution has a greater buffer capacity for the addition of acid than for base, because

.

26. The acid ionization equilibrium for is represented by the equation above. A mixture of

of and of will produce a buffer solution with a. If the solution was mislabeled and was instead of , which of the

following would be true?




AThe of the resulting solution would still be 4.87 because buffer solutions regulate changes in regardless of how much is added.

BThe of the resulting solution would be somewhat higher than 4.87 because adding that is10 times more concentrated makes the concentration of the conjugate base 10 times larger.

CThe of the resulting solution would be much higher than 4.87 because the weak acid would becompletely neutralized by the larger amount of added.

DThe of the resulting solution would still be 4.87 because the solution contains a large volume ofthe weak acid to react with the and maintain the same .

27.

Sample Solution Composition

1 buffer solution 3.26


3 buffer solution and one drop of 3.03


5 buffer solution 3.25The acid ionization equilibrium for is represented by the equation above. A buffersolution is prepared by mixing of and of . To testthe buffer capacity, the is measured and recorded in the table for four samples of the buffer andone sample of a mixture of the buffer and . Which of the following best helps explain why the

of sample 4 is lower than the pH of the other samples containing only buffer solution?

APrior to measuring the of sample 4, some water evaporated, resulting in an increase in theconcentration of in the sample.

BAfter measuring the of the more acidic sample 3, the probe was not rinsed and wiped,resulting in the neutralization of a very small amount of the conjugate base in sample 4.

CPrior to measuring the of sample 4, the room temperature dropped suddenly, resulting in anincrease in the for .

DThe volume used to measure the of sample 4 was less than , resulting in a decrease inthe concentration of .




Buffer solutions containing Na2CO3 and NaHCO3 range in pH from 10.0 to 11.0. The chemical equationbelow represents the equilibrium between CO32−and H2O, and the table lists the composition of fourdifferent buffer solutions at 25°C.

CO32−(aq)+H2O(l)⇄HCO3−(aq)+OH−(aq)Kb=2.1×10−4at25°C

Buffer [NaHCO3] [Na2CO3] pH

1 0.150 0.100 ?

2 0.200 0.200 10.32

3 0.100 0.100 10.32

4 0.100 0.200 ?

28. Which of the following chemical equilibrium equations best shows what happens in the buffersolutions to minimize the change in when a small amount of a strong base is added?

A

B

C

D

29. Which of the following mathematical expressions can be used to determine the approximate ofbuffer 1 ?



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A

B

C

D

30. Which mathematical expression can be used to explain why buffer 2 and buffer 3 have the same?

A

B

C

D

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Unit 8 Progress Check: MCQ - supertallteacher.weebly.com · Unit 8 Progress Check: MCQ A.... in print beyond your school’s participation in the program is prohibited.?