Problem 1. What is the ph of a 291mL sample of 2.993M benzoic acid (C 6 H 5 COOH) (K a =6.4x10-5 )?

Transcription

1 Problem 1 What is the ph of a 291mL sample of 2.993M benzoic acid (C 6 H 5 COOH) (K a =6.4x10-5 )?

2 Problem 2 A 489mL sample of M HNO 3 is mixed with 427mL sample of NaOH (which has a ph of 14.06). What is the ph of the resulting solution?

3 The K a values at 25 o C for a series of acids is given: 1.8 x x x x x 10-2 Which of the following acids has a K a = 1.4 x 10-3? Problem 3

4 Problem 4 Consider a solution containing 0.45M HCN and 0.69M NaCN for the next two questions. The K a for HCN = 6.2 x What is the ph of this solution?

5 Problem 5 Consider a solution containing 0.45M HCN and 0.69M NaCN for the next two questions. The K a for HCN = 6.2 x Now calculate the ph of this solution after 0.25 mol of NaOH is added to 1.00L of the solution. Assume that the volume does not change.

6 Problem 6 Consider a 7.3 x M solution of HCl at 285 K. What is the ph of the solution?

7 Problem 7 For the following reaction, K < 1 at room temperature. HOCl (aq) + HCO 3 - (aq) H 2 CO 3 (aq) + OCl - (aq) Which of the following statements is true? A) H 2 CO 3 is a stronger acid than HOCl. B) HOCl is a stronger acid than H 2 CO 3. C) OCl - is a stronger acid than HOCl. D) HCO - 3 is stronger base than OCl -. E) More information is needed.

8 Problem 8 What is the ph of a solution that results from adding mol Ca(OH) 2 (s) to 1.37L of a buffer comprised of 0.21M HF and 0.21M NaF?

9 Problem 9 A 0.251L solution of 1.89M sulfurous acid (K a1 = 1.5x10-2 and K a2 = 1.0x10-7 ) is titrated with 1.25M NaOH. What will the ph of the solution be when L of the NaOH has been added?

10 Problem 9 A 0.251L solution of 1.89M sulfurous acid (K a1 = 1.5x10-2 and K a2 = 1.0x10-7 ) is titrated with 1.25M NaOH. What will the ph of the solution be when L of the NaOH has been added?

11 Problem 10 The titration of 1.00L of a 1.00M solution of the triprotic acid, H 3 A, with 1.00M NaOH is shown below. It is not drawn to scale. What is the ph at D? H 3 A + H 2 O H 3 O + + H 2 A - K a1 =3.29x10-3 H 2 A - + H 2 O H 3 O + + HA 2- K a2 =6.43x10-7 HA 2- + H 2 O H 3 O + + A 3- K a3 =4.25x10-10

12 Problem 11 The titration of 1.00L of a 1.00M solution of the triprotic acid, H 3 A, with 1.00M NaOH is shown below. It is not drawn to scale. What is the ph at C? H 3 A + H 2 O H 3 O + + H 2 A - K a1 =3.29x10-3 H 2 A - + H 2 O H 3 O + + HA 2- K a2 =6.43x10-7 HA 2- + H 2 O H 3 O + + A 3- K a3 =4.25x10-10

13 Problem 12 Consider a 0.35M solution of each of the following salts in distilled water. Will the solution be acidic, neutral, or basic? You may need to reference a table of K a and K b Tables values.. NH 4 OBr: BaClO 4 : RbCH 3 COO: (CH 3 CH 2 ) 3 NHNO 2 :

14 Problem 13 How many of the following are true? 1. The buffer with the greatest buffering capacity for a phenol/sodium phenolate buffer system will have a ph of A buffer resists ph change when base is added by converting hydroxide ions to hydronium ions.. 3. A buffered system can be formed by combining a weak acid/conjugate base pair in solution. 4. A buffer is formed when you add HCl to NH A buffer is formed when you add HCl to CH 3 COOH.

15 Problem 14 Which of the following solutions will produce a buffer with ph near 10.50? L of 0.50M HSO 4 - (K a = 1.0x10-7 ) L of 0.25M KOH L 0.50M H 2 NNH 2 (K b = 3.0x10-6 ) L 0.25M HI L 1.00M H 3 BO 3 (K a = 5.8x10-10 ) L 2.50M HBr L of 0.50M HONH 2 (K b = 1.1x10-8 ) L of 0.050M HNO L 1.00M CH 3 NH 2 (K b = 4.4x10-4 ) L 0.25M HI.

16 Problem 15 The next three problems deal with the titration of 145mL of 1.35M methylamine CH 3 NH 2 (K b = 4.4 x 10-4 ) with 0.25M HCl. Water will be a major species throughout the titration. The chemical species, in addition to water, that can be found in this reaction mixture during the titration are: I. H + II. OH - III. Cl - IV. CH 3 NH 2 V. CH 3 NH 3 + What is the ph at equivalence point?

17 Problem 15 The next three problems deal with the titration of 145mL of 1.35M methylamine CH 3 NH 2 (K b = 4.4 x 10-4 ) with 0.25M HCl. Water will be a major species throughout the titration. The chemical species, in addition to water, that can be found in this reaction mixture during the titration are: I. H + II. OH - III. Cl - IV. CH 3 NH 2 V. CH 3 NH 3 + What is the ph at equivalence point?

18 Problem 16 The next three problems deal with the titration of 145mL of 1.35M methylamine CH 3 NH 2 (K b = 4.4 x 10-4 ) with 0.25M HCl. Water will be a major species throughout the titration. The chemical species, in addition to water, that can be found in this reaction mixture during the titration are: I. H + II. OH - III. Cl - IV. CH 3 NH 2 V. CH 3 NH 3 + How many ml of HCl will need to be added to reach ph=10.64?

19 Problem 17 The next three problems deal with the titration of 145mL of 1.35M methylamine CH 3 NH 2 (K b = 4.4 x 10-4 ) with 0.25M HCl. Water will be a major species throughout the titration. The chemical species, in addition to water, that can be found in this reaction mixture during the titration are: I. H + II. OH - III. Cl - IV. CH 3 NH 2 V. CH 3 NH 3 + What are the major species when 783mL of HCl has been added?

20 Problem 18 A 0.613M solution of a weak acid has a ph of at 309K. What is the K a of the weak acid?

21 Consider the following titration curve: Problem 19 How many of the following are true? 1. The ph at point B is pk a1. 2. The ph at point E will be the average of pk a1 and pk a2. 3. To the right of point F [A 3- ] > [HA 2- ]. 4. HA 2- will be a major species at point E. Which is based on the following reactions: H 3 A H + + H 2 A - H 2 A - H + + HA 2- HA 2- H + + A 3-5. The second dissociation of H + will play a large role in the ph level at point E.