U N I T T E S T P R A C T I C E

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1 Aubrey High School AP Chemistry Name 4 Acid Base Solutions Period Date U N I T T E S T P R A C T I C E Part 1 Multiple Choice You should allocate 30 minutes to finish this portion of the test. No calculator should be used. A periodic table and data table will be provided. Select the answer that best responds to each question. 1. Consider the equilibrium, HF(aq) H 2(l) H 3 (aq) F (aq). Which pair of substances makes up a conjugate acid-base pair? (A) H 2 and F (B) H 2 and H 3 (C) H 3 and F (D) HF and H 2 2. A solution of NH 3(aq) and H 2(l) turns universal indicator blue (basic). In this situation, which of the following statements is true? (A) H 2 is a base because it accepts a proton from NH 3. (B) H 2 is amphoteric because it both accepts and donates a proton. (C) H 2 is an acid because it donates a proton to NH 3. (D) NH 3 is a base because it donates a proton to H Methylamine, CH 3NH 2, is a weak base. When it reacts with water, the products include: (A) CH 3NH (B) CH 3NH 3 (C) H 3 (D) NH 4 5. At 0ºC, K w = What is the ph of a glass of pure ice water at 0ºC? (A) 8.0 (B) 7.5 (C) 7.0 (D) Milk of Magnesia, magnesium hydroxide, has low solubility in water and is used to neutralize excess stomach acid, hydrochloric acid. Which equation correctly represents the net reaction when milk of magnesia reaches the stomach? (A) H (aq) H (aq) H 2(l) (B) Mg(H) 2(s) 2H(aq) 2H 2(l) Mg 2(s) (C) Mg 2 (aq) 2 (aq) Mg 2(s) (D) Mg(H) 2(s) 2H (aq) 2H 2(l) Mg 2 (aq) 7. Which one of the following substances is not amphoteric/amphiprotic? (A) C 6H 5NH 2 (B) H 2 (C) HC 3 (D) NH 4 4. A 10.0 ml sample of a M H solution was obtained. What is the ph of the solution if 90.0 ml of water was added to the solution? (A) 1.0 (B) 2.0 (C) 3.0 (D) 4.0

2 M solutions with two different substances were prepared, and are represented by these particulate drawings: M of which of the following would have the lowest ph? (A) Chloroacetic acid, K a = (B) 3-chlorobenzoic acid, K a = (C) Benzoic acid, K a = (D) Ascorbic acid, K a = The representation on the right best illustrates which of the following substances? (A) HF(aq) (B) NaH(aq) (C) H 2S(aq) (D) NH 3(aq) 9. A 0.10 M sample of a weak base was placed in water. The ph of the solution was 11.0, when tested. What is the value of the K b for the base? (A) (B) (C) (D) How do the amounts of these species compare when solid NaN 2 is added to water? K a of HN 2 = f the following salts, which one forms a 0.1 M solution with the lowest ph? (A) KBr (B) KC 2H 3 2 (C) NaN 2 (D) NH Carbonic acid, H 2C 3, is a diprotic acid. Which equation correctly shows the dissociation of carbonic acid s second proton? (A) H 2C 3(aq) 2H (aq) C 2 3 (aq) (B) H 2C 3(aq) H 2(g) C 2(g) 2 (C) HC 3 H 2(l) H 3 (aq) C 3 (aq) (D) HC 3 (aq) H 2(l) H 2C 3(aq) H (aq) 15. Consider the following acids: H 3, H 4, HI 3, HI 2 When listed from weakest to strongest, the order would be: (A) H 3 < H 4 < HI 2 < HI 3 (B) H 4 < H 3 < HI 3 < HI 2 (A) H < HN 2 < H < N 2 < Na (C) HI 2 < H 3 < HI 3 < H 4 (B) H < HN 2 = H < N 2 < Na (D) HI 2 < HI 3 < H 3 < H 4 (C) HN 2 < H < H < N 2 = Na (D) HN 2 < H = H < N 2 = Na 11. Suppose we have a 0.10 M HF solution. Which of the following, when added, would result in the lowest [F ]? (A) Nothing else added (B) mol H (C) mol KF (D) mol KH

3 Part 2 Free Response You should allocate 30 minutes to finish this portion of the test. You may use a scientific calculator. A periodic table and data table will be provided. Respond to each part of the questions completely. Be sure to show your work clearly for questions that involve calculations. 16. Methylamine, CH 3NH 2, is a weak base, and has a base ionization constant, K b, of at 25 C a. Consider the ionization of methylamine when dissolved in water. i. Write the chemical equation for this process. ii. Identify a Brønsted-Lowry conjugate acid-base pair in this reaction. iii. A sample of methylamine has a ph of What is the molar concentration of methylamine in this sample? b mol KH was added to 1.00 L of a M CH 3NH 2 solution. What is the ph of this solution? c g of methylammonium chloride, CH 3NH 3, was dissolved in water to prepare a ml solution. i. Write the net ionic equation for this process. ii. Find the value of the acid ionization constant, K a, of the methylammonium ion, CH 3NH 3. iii. Calculate the ph of this solution.

4 17. Consider the following acids: Acetic acid CH 3CH H H C C H H Chloroacetic acid CH 2CH H C C H H Dichloroacetic acid CH 2CH C C H H Trichloroacetic acid C 3CH C C H pk a = 4.76 pk a = 2.86 pk a = 1.35 pk a = 0.66 a. Which is the strongest among the four acids? Justify your answer quantitatively. b. Provide a reason using the molecular structure to explain why the acid in part a. is the strongest. c. Consider the salts NaCH 3C and NaC 3C. If mol of each were used to make a 1.00 L solution, which would have the lower ph? Explain.

5 South Pasadena AP Chemistry Name 4 Acid Base Solutions Period Date U N I T T E S T B L U E P R I N T Part 1: Multiple Choice Format: 15 questions, four answer choices: (A)-(D) Expected time: 30 minutes Allowed resources: Periodic Table, Equations and Constants. No calculators. Q Lesson Topic bjective Bronsted-Lowry Identify the acids, bases, conjugate acids, and conjugate bases in Bronsted- Lowry acid-base reaction Types of Identify whether a substance is an acid or base or neither, write its conjugate acid/base, and write its dissociation equation Types of Identify carboxylic acids as organic acids, and amines as organic bases and write their dissociation equations ph of Solutions Calculate the ph, ph, [H ], and [H ] of a solution and determine whether it s acidic or basic. Recall properties of acids and bases, including the behavior of indicators (i.e. universal indicator, litmus, phenolphthalein, and cabbage juice) ph of Solutions Show the effects of how the value of K w of a solution changes with temperature Arrhenius Write the neutralization equation for the reaction between an Arrhenius acid and base Amphiprotic Show how a substance is amphiprotic/amphoteric. Substances Strong Acid/Base Describe a strong acid or strong base solution Weak Acid/Base Describe a weak acid or weak base solution using its K a or K b Acidic/basic salt or Find the K b of a conjugate base given the K a of a weak acid (or v/v). Conjugate Acid/Base Describe an acidic or basic salt dissolved in solution Common Ion Effect Describe a solution with a weak acid and its conjugate base (or v/v). Describe a solution with a strong acid and weak acid (or v/v) Strength of Compare the strength of acids by comparing K a or K b values Acidic/Basic Salts Determine whether a salt is acidic or basic using K a and K b values Polyprotic Acids Write the dissociation equations for a polyprotic acid Strength of Acids based on Molecular Structure Compare the strength of acids by looking at its molecular structure. Part 2: Free Response Format: o 1 long question (5-8 parts) o 1 short questions (2-4 parts) Expected time: 30 minutes Allowed resources: Periodic Table, Equations and Constants, and scientific calculators. Topics: Any