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CHM 112
Section 1

Homework Assignment #22
Due April 3, 2006 by 8:05 a.m.

Practice (not to be turned in): 16.43, 16.47, 16.51, 16.96, 16.103

Calculate the molar solubility of:

1. Silver nitrite in an X molar solution of silver nitrate where X = the sixth and seventh digits of your Student ID Number divided by 1000.

2. Calcium hydroxide in a buffered solution with a pH = 13.00 + Y where Y = the last two digits of your Student ID Number divided by 100. (If your Student ID Number is 100123456, then the pH = 13.56.)



Answers:

1. Silver nitrite: AgNO2

 

AgNO3(aq)

Ag+(aq)

+

NO3(aq)

 

AgNO2(s)

Ag+(aq)

+

NO2(aq)

 

Ksp = [Ag+]e[NO2]e = 6.0×10–4

Initial

 

 

X

 

0

Change

 

 

+ x

 

+ x

Equilibrium

 

 

X + x

 

x

Since Ksp is fairly large and X is also pretty large (relatively speaking), no approximation should be made (although this is a close call in many cases).

6.0×10–4 = [X + x]x

x2 + Xx – 6.0×10–4 = 0

x = [–X + (X2 + 4×6.0×10–4)½]/2

x is the molar solubility of silver nitrite in the silver nitrate solution.



2. Calcium hydroxide: Ca(OH)2

The pH gives the hydroxide ion concentration in the solution:

pOH = 14.00 – pH (assuming 25 °C) so pOH = 14.00 – 13.Y = 1.00 – Y

Then, [OH ] = 10pOH = 10(1.00 – Y)

 

Ca(OH)2(s)

Ca2+(aq)

+

2 OH(aq)

 

Ksp = [Ca2+]e[OH]e2 = 5.5×10–6

Initial

 

 

0

 

10(1.00 – Y)

Change

 

 

+ x

 

+ 2x

Equilibrium

 

 

x

 

10–(1.00 – Y) + 2x


Since this is a buffered solution, 10–(1.00 – Y) + 2x = 10–(1.00 – Y). Then x = 5.5×10–6/ (10–(1.00 – Y))2, where (in this case) x is the molar solubility of calcium hydroxide.


Specific answers:


Student ID Number

X

[AgNO2]e
M

pH

[Ca(OH)2]e
M

100006330

0.063

0.0084

13.30

1.4×10–4

100008852

0.088

0.0064

13.52

5.0×10–5

100009388

0.093

0.0061

13.88

9.6×10–6

100010785

0.007

0.02

13.85

1.1×10–5

100017560

0.075

0.0073

13.60

3.5×10–5

100046288

0.062

0.0085

13.88

9.6×10–6

100064823

0.048

0.010

13.23

1.9×10–4

100077590

0.075

0.0073

13.90

8.7×10–6

100105142

0.051

0.0099

13.42

7.9×10–5

100143544

0.035

0.013

13.44

7.3×10–5

100148294

0.082

0.0068

13.94

7.3×10–6

100160251

0.002

0.02

13.51

5.3×10–5

100164496

0.044

0.011

13.96

6.6×10–6

100168422

0.084

0.0066

13.22

2.0×10–4

100170841

0.008

0.02

13.41

8.3×10–5

100173015

0.030

0.014

13.15

2.8×10–4

100173826

0.038

0.012

13.26

1.7×10–4

100173947

0.039

0.012

13.47

6.3×10–5

100175807

0.058

0.0090

13.07

4.0×10–4

100176275

0.062

0.0085

13.75

1.7×10–5

100180084

0.000

0.024

13.84

1.1×10–5

100180208

0.002

0.02

13.08

3.8×10–4

100187549

0.075

0.0073

13.49

5.8×10–5

100188349

0.083

0.0067

13.49

5.8×10–5

100192352

0.023

0.016

13.52

5.0×10–5

100193608

0.036

0.012

13.08

3.8×10–4

100193957

0.039

0.012

13.57

4.0×10–5

100194186

0.041

0.011

13.86

1.0×10–5

100194417

0.044

0.011

13.17

2.5×10–4

100195646

0.056

0.0092

13.46

6.6×10–5

100196467

0.064

0.0083

13.67

2.5×10–5

100197351

0.073

0.0075

13.51

5.3×10–5

100197396

0.073

0.0075

13.96

6.6×10–6

100200053

0.000

0.024

13.53

4.8×10–5

100201157

0.011

0.020

13.57

4.0×10–5

100203271

0.032

0.013

13.71

2.1×10–5

100205446

0.054

0.0095

13.46

6.6×10–5

100205601

0.056

0.0092

13.01

5.3×10–4

100207237

0.072

0.0075

13.37

1.0×10–4

100210253

0.002

0.02

13.53

4.8×10–5

100210303

0.003

0.02

13.03

4.8×10–4

100212014

0.020

0.016

13.14

2.9×10–4

100212080

0.020

0.016

13.80

1.4×10–5

100212092

0.020

0.016

13.92

7.9×10–6

100212152

0.021

0.016

13.52

5.0×10–5

100212510

0.025

0.015

13.10

3.5×10–4

100213402

0.034

0.013

13.02

5.0×10–4

100214888

0.048

0.010

13.88

9.6×10–6

100215062

0.050

0.010

13.62

3.2×10–5

100215125

0.051

0.0099

13.25

1.7×10–4

100215264

0.052

0.0097

13.64

2.9×10–5

100215471

0.054

0.0095

13.71

2.1×10–5

100216695

0.066

0.0081

13.95

6.9×10–6

100216822

0.068

0.0079

13.22

2.0×10–4

100217841

0.078

0.0071

13.41

8.3×10–5

100218709

0.087

0.0064

13.09

3.6×10–4

100218865

0.088

0.0064

13.65

2.8×10–5

100218867

0.088

0.0064

13.67

2.5×10–5

100218981

0.089

0.0063

13.81

1.3×10–5

100219014

0.090

0.0062

13.14

2.9×10–4

100219019

0.090

0.0062

13.19

2.3×10–4

100219138

0.091

0.0062

13.38

9.6×10–5

100219323

0.093

0.0061

13.23

1.9×10–4

100219636

0.096

0.0059

13.36

1.0×10–4

100219715

0.097

0.0058

13.15

2.8×10–4

100219950

0.099

0.0057

13.50

5.5×10–5

100220082

0.000

0.024

13.82

1.3×10–5

100220712

0.007

0.02

13.12

3.2×10–4

100220848

0.008

0.02

13.48

6.0×10–5

100220947

0.009

0.02

13.47

6.3×10–5

100221065

0.010

0.020

13.65

2.8×10–5

100221836

0.018

0.017

13.36

1.0×10–4

100222238

0.022

0.016

13.38

9.6×10–5

100222876

0.028

0.014

13.76

1.7×10–5

100223382

0.033

0.013

13.82

1.3×10–5

100223879

0.038

0.012

13.79

1.4×10–5

100224279

0.042

0.011

13.79

1.4×10–5

100224930

0.049

0.010

13.30

1.4×10–4

100226239

0.062

0.0085

13.39

9.1×10–5

100229080

0.090

0.0062

13.80

1.4×10–5

100229858

0.098

0.0058

13.58

3.8×10–5

100243524

0.035

0.013

13.24

1.8×10–4