CHM 112L Info Page

Dr. Krueger's web page for all things CHM 112-lecture related is here.

 

The main LAB information page (with spreadsheets, etc.) is here

 

Answers to recitation worksheets throughout the semester:

Answers to Week 2 exercise:

Assume 100 g of solution so it contains 2.000 g of CaCl2 and 98.00 g H2O (2.000 mass%)

Molar mass of CaCl2 is 110.984 g/mol

M = 0.1832 mol/L

X = 3.302E-03

%w/v = 2.033

m = 0.1839 mol/kg

 

Answers to Week 3 exercise (rate laws and equilibrium constant)

1.  a. 2

b. 1

c. rate = k[NO]2[O2]

d.  k = 7.06 x 103 M-2 s-1

e.  rate = 0.0565 M s-1

2.  a.    no

b. i)  K = [Cr(OH)4-]/[Cr3+][OH-]4

ii)  K = [Ag(NH3)2+][ Cl-]/[ NH3]2

iii)  K = [Fe3+]/[H3O+]3

 

Answers to Week 4 Exercises (integrated rate law and Le Chatelier’s principle)

1. a.  0.0514 M            b.  89.7% reacted                    c.  36.6 min

2. a., b. and c. – shifts R,  d. and e. no shift,  f. shifts L

 

Answers to Week 5 exercises, Calculating equilibrium concentrations

1. (a) MgF2(s)   Mg2+(aq) + 2F-(aq)

(b) Ksp = [Mg2+][F-]2

(c) Ksp = 3.02 ´ 10-11 (since [Mg2+] = 4.0432 ´ 10-3 M and [F-] = 8.64 ´ 10-5 M (given))

2. a. Q = 1, reaction proceeds in reverse direction to reach equilibrium

b.  [CO]eq = [H2O]eq = 0.123 M, [CO2]eq = [H2]eq = 0.077 M

3.  Use quadratic equation to solve.  [NO2]eq = [SO2]eq = 0.0281 M

 

Answers to Week 6 exercises, Bronsted-Lowry acids and bases

1.  Identify the Bronsted-Lowry acid and base in the following reactions. Predict the products and identify the conjugate acid and conjugate base.

a.  F-(aq)  +  HCO3-(aq)        HF(aq)  +  CO32-(aq)

b.  NH4+(aq)  +  CN-(aq)      NH3(aq)  +  HCN(aq)

c.  NO2-(aq)  +  H2PO4-(aq)    HNO2(aq)  +  HPO42-(aq)

d.  HC2H3O2(aq)  +  OH-(aq)    C2H3O2-(aq)  +  H2O(l))

2.  [H3O+] = 6.49 x 10-3 M                  pH = 2.19

6.49% dissociated

[NO2-] = 6.49 x 10-3 M

[HNO2] = 0.094 M

[OH-] = 1.54 x 10-12 M

 

Answers to Week 7 exercise, Acids and Bases

1. a. 12.18       b.  8.82            c.  0.96            d.  8.60            e.  1.50

 

Solutions to Week 9 exercises, buffers and solubility equilibria

1. a. pH = 9.00            b.  pH = 8.93  H3O+  +  NH3  à  H2O  +  NH4+

2.  a. OH-  +  HOCl  à  H2O  +  OCl-            b.  pH = 7.59              

c.  [HOCl] = 0.18 M, [OCl-] = 0.25 M

3.  a.  7.32 x 10-4 M     b.  6.28 x 10-7 M

 

 

Solutions to Week 10 exercises, Free energy, enthalpy and entropy

1.  a.  117.2 J K-1        b.  -211.0 kJ, exothermic        c.  -246.0 kJ, H2O2 will decompose

2.  a.  -43.0 kJ              b.  -35.3 kJ, spontaneous

3.  7 x 10-6

 

Answers to Week 12 exercises

Galvanic cells and cell potentials

1.  H2O2

2.  Al

3.  Eox = -0.34 V

4.  Ered = -0.83 V

5.  Ecell = -1.17 V, reaction will not occur under standard conditions (nonspontaneous)

6.  With water, Ecell = -0.07 V, with H+, Ecell = 0.76 V

 

Electrolytic cells and electrolysis

1.  1.54 g Al

2.  Anode (oxidation)  2H2O(l) → O2(g)  +  4H+(aq)  +  4e-             

Cathode (reduction) Cu2+(aq)  +  2e-    Cu(s)

Cell reaction:  2Cu2+(aq)  +  2H2O(l) → 2Cu(s) + O2(g)  +  4H+(aq) 

Ecell = -0.89 V

 

 

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