AP CHEM-Unit 8 Test - Assessment

1.

Multiple Choice

30 sec

1 pt

The stronger the acid, the stronger its conjugate base.

True

False

2.

Multiple Choice

30 sec

1 pt

CCl₃COOH is a weaker acid than CH₃COOH.

True

False

3.

Multiple Choice

3 mins

1 pt

The term K_a for NH₄⁺ refers to which equation?

NH₄⁺(aq) + H₂O(l) ⇌ NH₃(aq) + H₃O⁺(aq)

NH₄⁺(aq) + OH^-(l) ⇌ NH₃(aq) + H₂O(l)

NH₃(aq) + H₂O(l) ⇌ NH₃(aq) + OH^-(aq)

NH₃(aq) + H₃O⁺(aq) ⇌ NH₄⁺(aq) + OH^-(aq)

4.

Multiple Choice

5 mins

1 pt

Which solution has the lowest concentration of hydroxide ions?

pH = 3.21

pH = 12.59

pH = 9.82

pH = 7.00

5.

Multiple Choice

2 mins

1 pt

What is the conjugate acid of NH₃?

NH₄⁺

NH₃⁺

NH₂^-

NH₃

6.

Multiple Choice

5 mins

1 pt

HF(aq) + H₂O(l) ⇌ H₃O⁺(aq) + F^-(aq)

Which of the following shows what would happen to the % ionization of HF when, in two separate

experiments, 1.0 mL of distilled water and 1.0 mL of 1.0 M KF are added to a 10. mL sample of 1.0 M HF(aq)?

A

B

C

D

7.

Multiple Choice

5 mins

1 pt

Which of the following aqueous solutions has the lowest [H⁺]?

a 1.0 x 10⁻³ M solution of NaOH

a 1.0 x 10⁻⁴ M solution of HNO3

pure water

a solution with a pOH of 10.0

8.

Multiple Choice

3 mins

1 pt

Values of pK_w at various temperatures are listed in

the table. Based on the information, which of the following statements is true?

The dissociation of water is an exothermic process.

The pH of pure water is 7.00 at any temperature.

As the temperature increases, the pH of pure water increases

As the temperature increases, the pH of pure water decreases.

9.

Multiple Choice

2 mins

1 pt

Which of the following indicators would be the best choice for determining the endpoint in this titration?

methyl orange (pH range: 2.1-3.6)

methyl red (pH range: 4.2-6.5)

thymol blue (pH range: 8.0-9.6)

alizarin yellow (pH range: 10.0-12.0)

10.

Multiple Choice

3 mins

1 pt

A solution is prepared by adding 1.0 M HC₂H₃O₂ to 1.0 M NaC₂H₃O₂. The solution's pH is measured to be 4.73. After 3 drops of 1.0 M HCl are added to the solution, the pH of the solution is still 4.73. Which equation accounts for the fact that acid was added but there was no detectable change in pH?

H₃O⁺(aq) + OH^–(aq) → 2 H₂O(l)

H₃O⁺(aq) + Cl^–(aq) → HCl(g) + H₂O(l)

H₃O⁺(aq) + C₂H₃O₂^–(aq) → HC₂H₃O₂(aq) + H₂O(l)

H₃O⁺(aq) + HC₂H₃O₂(aq) → H₂C₂H₃O₂⁺(aq) + H₂O(l)

11.

Multiple Choice

3 mins

1 pt

A solution contains equimolar amounts of HOCl and NaOCl and has a pH of 7.5. Then KOH is added to this solution. Which of the following most accurately identifies the species present in greater concentration and the pH of the solution after KOH is added?

HOCl; pH < 7.5

HOCl; pH > 7.5

OCl^-; pH < 7.5

OCl^-; pH > 7.5

12.

Multiple Choice

3 mins

1 pt

A sample of a weak acid, HA, is titrated, with 0.100 M NaOH added. Which of the following is the best particulate representation of the species (other than H₂O) that are present in significant concentrations in the solution at point U in the titration?

13.

Fill in the Blank

3 mins

1 pt

Which particle diagram best represents the acid with the least stable conjugate base?

14.

Fill in the Blank

2 mins

1 pt

On the basis of the pH curve, the pKa value of the acid used in the titration is closest to

15.

Fill in the Blank

10 mins

1 pt

A 0.070 M base solution eventually reaches a pOH of 5.00, what is the percent ionization?

16.

Fill in the Blank

10 mins

1 pt

Benzoic acid, C₆H₅COOH, is 1.0 % ionized in a 0.010 M aqueous solution according the equation: C₆H₅COOH(aq) ⇌ H⁺(aq) + C₆H₅COO^-(aq)

What is the value of K_a for aqueous benzoic acid?

17.

Open Ended

5 mins

1 pt

Which curve represents the titration of a weak base? Include 2 reasons.

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18.

Open Ended

5 mins

1 pt

Buffers were created using a weak acid, HA, (pKa = 3.20) and LiA.

Buffer X = 1.00 M of HA + 0.50 M of LiA.

Buffer Y = 0.50 M of HA + 1.00 M of LiA.

Buffer Z = 2.00 M of HA and 4.00 M of LiA.

Which buffer will be best at resisting a change to the pH when a base is added? Justify your answer.

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19.

Open Ended

5 mins

1 pt

Based on the data, which species is dominant at a pH of 5? The acid or the conjugate base? Explain your reasoning.

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20.

Open Ended

15 mins

1 pt

A solution contains 150.0 g of Ba(OH)₂ in 12.5 L of solution. Calculate the pH of the solution.

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21.

Open Ended

15 mins

1 pt

The pOH of 50.0 mL of a solution of H₂SO₄ is 12.44. How many moles of H₂SO₄ are in the solution?

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22.

Open Ended

10 mins

1 pt

At 50°C the K_wof pure water is 5.476 x 10^-14. Calculate the H₃O⁺ concentration.

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23.

Open Ended

10 mins

1 pt

A 50.0 mL sample of a weak acid is titrated with 0.10 M NaOH. What is the concentration of the weak acid?

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24.

Open Ended

15 mins

1 pt

What is the concentration of acetic acid, HC₂H₃O₂, in a buffer solution with a pH of 5.293. The solution contains 0.530 M C₂H₃O₂^-. Acetic acid has a K_a of 1.80 x 10^-5.

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25.

Open Ended

10 mins

1 pt

You heated a sample of pure water and measured that the pH was 6.767. What is the concentration of the hydroxide ion?

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26.

Open Ended

15 mins

1 pt

Calculate the pH of a solution that is composed of 90.0 mL of 0.345 M NaOH and 50.0 mL of 0.123 M lactic acid, HC₃H₅O₃. (K_a of lactic acid = 1.38x10^-4)

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27.

Open Ended

15 mins

1 pt

What is the hydronium ion concentration of a solution formed from 150.0 mL of 0.200 M NH₃ and 150.0 mL of 0.200 M HCl? (K_b for NH₃ is 1.80x10^-5)

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