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CHM 112
Section 1

Homework Assignment #15
Due March 6, 2006 by 8:05 a.m.

Practice (not to be turned in): Problems 15.46, 15.50, 15.51, 15.53, 15.133

Consider a solution of the acid corresponding to the last digit of your Student ID Number. The initial concentration of the acid is equal to the seventh and eighth digits of your Student ID Number divided by 1000. Find the pH. You can find equilibrium constants from the Table of Acid Ionization Constants. Write the equilibrium reaction that your answer is based on and show all of your work.

0) Bromoacetic acid

1) Chloroacetic acid

2) Chlorous acid

3) Cyanic acid

4) Dichloroacetic acid

5) Fluoroacetic acid

6) Hydrogen sulfate ion

7) Hydrogen selenate ion

8) Iodic acid

9) Trichloroacetic acid



Answers:

Reactions used:

0) Bromoacetic acid

BrCH2COOH(aq) + H2O(l) H3O+(aq) + BrCH2COO(aq)

1) Chloroacetic acid

ClCH2COOH(aq) + H2O(l) H3O+(aq)+ ClCH2COO(aq)

2) Chlorous acid

HClO2(aq) + H2O(l) H3O+(aq) + HClO2(aq)

3) Cyanic acid

HOCN(aq) + H2O(l) H3O+(aq) + OCN(aq)

4) Dichloroacetic acid

CHCl2COOH(aq) + H2O(l) H3O+(aq) + CHCl2COO(aq)

5) Fluoroacetic acid

FCH2COOH(aq) + H2O(l) H3O+(aq) + FCH2COO(aq)

6) Hydrogen sulfate ion

HSO4(aq) + H2O(l) H3O+(aq) + SO42–(aq)

7) Hydrogen selenate ion

HSeO4(aq) + H2O(l) H3O+(aq) + SeO42–(aq)

8) Iodic acid

HIO3(aq) + H2O(l) H3O+(aq) + IO3(aq)

9) Trichloroacetic acid

CCl3COOH(aq) + H2O(l) H3O+(aq) + CCl3COO(aq)

To find the pH, use the usual methodology:

 
HA(aq)
+
H2O(l)
H3O+(aq)
+
A(aq)
 
Initial
[HA]ini
     
0
 
0
Change
– x
     
+ x
 
+ x
Equilibrium
[HA]ini – x
     
x
 
x

In nearly all cases, the initial concentration is too low to use the approximations, so:

This equation is solved using the quadratic formula. The positive root for x gives the hydronium ion concentration. The pH is found from the definition pH = –log[H3O+].

Most of the initial concentrations and Ka values had two significant figures, so the H3O+ concentration generally has two significant figures and the pH has two places past the decimal.

Specific Answers:

Student ID Number

[HA]ini

Ka

[H3O+]e

pH

100006330

0.033

1.3×10–3

5.9×10–3

2.23

100008852

0.085

1.1×10–2

2.6×10–2

1.59

100009388

0.038

1.6×10–1

3.2×10–2

1.50

100010785

0.078

2.6×10–3

1.3×10–2

1.89

100017560

0.056

1.3×10–3

7.9×10–3

2.10

100046288

0.028

1.6×10–1

2.4×10–2

1.61

100064823

0.082

3.5×10–4

5.2×10–3

2.29

100077590

0.059

1.3×10–3

8.1×10–3

2.09

100105142

0.014

1.1×10–2

8.1×10–3

2.09

100143544

0.054

5.5×10–2

3.4×10–2

1.47

100148294

0.029

5.5×10–2

2.1×10–2

1.68

100160251

0.025

1.4×10–3

5.3×10–3

2.28

100164496

0.049

1.1×10–2

1.8×10–2

1.74

100168422

0.042

1.1×10–2

1.7×10–2

1.78

100170841

0.084

1.4×10–3

1.0×10–2

1.99

100173015

0.001

2.6×10–3

7.7×10–4

3.11

100173826

0.082

1.1×10–2

2.5×10–2

1.60

100173947

0.094

2.2×10–2

3.6×10–2

1.45

100175807

0.080

2.2×10–2

3.2×10–2

1.49

100176275

0.027

2.6×10–3

7.2×10–3

2.14

100180084

0.008

5.5×10–2

7.1×10–3

2.15

100180208

0.020

1.6×10–1

1.8×10–2

1.75

100187549

0.054

3.0×10–1

4.7×10–2

1.33

100188349

0.034

3.0×10–1

3.1×10–2

1.51

100192352

0.035

1.1×10–2

1.5×10–2

1.83

100193608

0.060

1.6×10–1

4.6×10–2

1.33

100193957

0.095

2.2×10–2

3.6×10–2

1.44

100194186

0.018

1.1×10–2

9.6×10–3

2.02

100194417

0.041

2.2×10–2

2.1×10–2

1.68

100195646

0.064

1.1×10–2

2.2×10–2

1.67

100196467

0.046

2.2×10–2

2.3×10–2

1.64

100197351

0.035

1.4×10–3

6.3×10–3

2.20

100197396

0.039

1.1×10–2

1.6×10–2

1.80

100200053

0.005

3.5×10–4

1.2×10–3

2.94

100201157

0.015

2.2×10–2

1.0×10–2

1.99

100203271

0.027

1.4×10–3

5.5×10–3

2.26

100205446

0.044

1.1×10–2

1.7×10–2

1.77

100205601

0.060

1.4×10–3

8.5×10–3

2.07

100207237

0.023

2.2×10–2

1.4×10–2

1.85

100210253

0.025

3.5×10–4

2.8×10–3

2.55

100210303

0.030

3.5×10–4

3.1×10–3

2.51

100212014

0.001

5.5×10–2

9.8×10–4

3.01

100212080

0.008

1.3×10–3

2.6×10–3

2.58

100212092

0.009

1.1×10–2

5.9×10–3

2.23

100212152

0.015

1.1×10–2

8.5×10–3

2.07

100212510

0.051

1.3×10–3

7.5×10–3

2.12

100213402

0.040

1.1×10–2

1.6×10–2

1.79

100214888

0.088

1.6×10–1

6.3×10–2

1.20

100215062

0.006

1.1×10–2

4.3×10–3

2.37

100215125

0.012

2.6×10–3

4.4×10–3

2.35

100215264

0.026

5.5×10–2

1.9×10–2

1.72

100215471

0.047

1.4×10–3

7.4×10–3

2.13

100216695

0.069

2.6×10–3

1.2×10–2

1.92

100216822

0.082

1.1×10–2

2.5×10–2

1.60

100217841

0.084

1.4×10–3

1.0×10–2

1.99

100218709

0.070

3.0×10–1

5.9×10–2

1.23

100218865

0.086

2.6×10–3

1.4×10–2

1.86

100218867

0.086

2.2×10–2

3.4×10–2

1.47

100218981

0.098

1.4×10–3

1.1×10–2

1.96

100219014

0.001

5.5×10–2

9.8×10–4

3.01

100219019

0.001

3.0×10–1

1.0×10–3

3.00

100219138

0.013

1.6×10–1

1.2×10–2

1.92

100219323

0.032

3.5×10–4

3.2×10–3

2.50

100219636

0.063

1.1×10–2

2.1×10–2

1.67

100219715

0.071

2.6×10–3

1.2×10–2

1.91

100219950

0.095

1.3×10–3

1.0×10–2

1.98

100220082

0.008

1.1×10–2

5.4×10–3

2.27

100220712

0.071

1.1×10–2

2.3×10–2

1.64

100220848

0.084

1.6×10–1

6.1×10–2

1.22

100220947

0.094

2.2×10–2

3.6×10–2

1.45

100221065

0.006

2.6×10–3

2.9×10–3

2.54

100221836

0.083

1.1×10–2

2.5×10–2

1.60

100222238

0.023

1.6×10–1

2.0×10–2

1.69

100222876

0.087

1.1×10–2

2.6×10–2

1.59

100223382

0.038

1.1×10–2

1.6×10–2

1.80

100223879

0.087

3.0×10–1

7.0×10–2

1.15

100224279

0.027

3.0×10–1

2.5×10–2

1.60

100224930

0.093

1.3×10–3

1.0×10–2

1.98

100226239

0.023

3.0×10–1

2.1×10–2

1.67

100229080

0.008

1.3×10–3

2.6×10–3

2.58

100229858

0.085

1.6×10–1

6.1×10–2

1.21

100243524

0.052

5.5×10–2

3.3×10–2

1.49