Activity: Chemical Equilibrium and Acid-Base
Reading: Kenkel (p 99 -113, Chp6 and Chp8), Harris (p120 Harris 8th Ed) or any General Chem Text
http://en.wikipedia.org/wiki/Le_Chatelier%27s_principle
____ / _20_ Score
Name (last)____________________(KEY)____________________
Follow the following directions: For numerical calculations, show your complete work in a separate piece of paper, box your
answer, and then write answer in this worksheet.
i.
Consider the following system at equilibrium:
2CH4(g) + C(s) + O2(g)  2H2CO (g) ΔH = - 135.2 Kcal
Complete the following table. Indicate changes in moles and concentrations by entering I, D, N, or ? in the table.
(I = increase, D = decrease, N = no change, ? = insufficient information to determine)
Direction of shift, left, right or no
Change in number of
Change in molar
Change or stress imposed on
change to re-establish, equilibrium
moles
concentration
the system at equilibrium
(After stress has been imposed)
CH4
C
O2 H2CO C H4
C
O2 H2CO
a) Add C
No Change (NC)
Chg
Temp
NC
NC
NC
NC
NC
NC
NC
NC
NC
b) Remove CH4
Left
I
I
I
D
I
NC
I
D
D
c) Add H2CO
Left
I
I
I
D
I
NC
I
D
D
d) Increase O2 pressure
Right
D
D
D
I
D
NC
D
I
I
e) Decrease volume of reaction
vessel
Right
D
D
D
I
D
NC
D
I
I
f)
Increase temperature
Left
I
I
I
D
I
NC
I
D
D
g)
Add catalyst
NC
NC
NC
NC
NC
NC
NC
NC
NC
h)
2.0 mol of O2 & H2CO are
added at the same time
I
I
I
D
I
NC
I
D
D
ii. For the reaction:
No Change (NC)
Left
H2 (g) + l2 (g)  2 HI (g),
Keq = 0.170, at 500.0 K.
a) What concentration of l2 (g) will be in equilibrium with H2 = 0.040 M, Hl = 0.150 M?
iii. The solubility of CaCO3 at 25°C is 6.90 •10-5 M. The reaction is:
a) Calculate the concentration of Ca+2 and CO3-2 at equilibrium.
___3.31___(Answer)
CaCO3 (s)  Ca+2(aq) + CO3-2(aq)
_____6.90•10-5________ Ca+2
______6.90•10-5______ CO3-2 (Answer)
b) Calculate the equilibrium constant for the dissolution reaction. (This equilibrium constant is also known as the solubility product.)
________4.76•10-9________ Ksp (Answer)
iv.
The value of Kc = 2.20•10-10 for the equilibrium: COCl2 (g)  CO(g) + Cl2 g)
If the concentration of Cl2 at equilibrium = 4.80•10-6M,
a) what are the equilibrium concentration of the other two substances?
[CO] eq = ____4.80•10-6____(Answer)
[COCL2]eq = ____0.105____(Answer)
b) what was the initial conc. of COCl2 ?
[COCL2]o = ___0.105____(Answer)
1
v. A 0.400 M HClO solution was found to have an H+ concentration of 1.10•10-4M.
The reaction is: HClO (aq)  H+(aq)
a) Calculate the equilibrium constant for the ionization reaction (also known as the acid dissociation constant, Ka).
+ ClO-(aq)
_3.03•108_(Answer)
b) Calculate the ratio ( Δ[HClO] / [HClO] initial)* 100 . This value is also known as the percent ionization (α).
____0.0275%___(Answer)
vi.
At 1285°C the equilibrium constant for the reaction: Br2(g)  2 Br (g) is Kc = 1.04•10-3.
A 0.200-L vessel contains an equilibrium mixture of the gases has 0.245g Br2 (g), what is the mass of Br (g) in the vessel?
__0.04077 g__(Answer)
vii. Hydrosulfuric acid is a diprotic acid. Its two stages of ionization is shown below:
H2S (aq)  H+ + HS-(aq)
Kal 5.70 • 10-8
HS- (aq)  H+ + S2-(aq)
Ka2 = 1.00 • 10-9
a) Calculate the concentration of HS- ion in a 0.222 M H2S solution
b) determine the pH of the solution.
pH = ___3.95____(Answer)
-2
c) determine the S concentration.
[S2-] = _____1.00•10-9____(Answer)
[HS-] =___1.13•10-4___(Answer)
viii. Methyl red is a common acid-base indicator. It has a Ka equal to 6.3•10-6. Its un-dissociated form is red and its anionic form is
yellow. a) What color would a methyl red solution have at pH = 7.00 ? Show your calculations and explain your answers (in words).
Hint: Determine the concentration ratio of methyl red and its conjugate.
[Mr] / [HMr] = 63, The solution is Yellow (Undissociated form)
ix.
Rank the following in order of increasing pOH and justify: 0.10M solutions of chloroacetic acid, carbonic acid and citric acid
Write out the order instead of placing 1, 2 ...
Carbonic
pOH =
x.
10.324
Citric
Chloracetic
11.936
12.067
Rank the following in order of increasing pKa and justify: 0.10 M Mandelic acid, 0.20 M Maleic acid, 0.40M Malonic acid.
Write out the order instead of placing 1, 2 ...
pOH =
Maleic
Malonic
Mandelic
1.87
2.84
3.41
xi.
Consider the titration of 20.00 mL of 0.250 M HF solution with 0.250 M KOH. Calculate the pH.after: 0.00, 5.00, 10.00, 19.00,
20.00 and 25.00 mL of base have been added. Sketch and label the titration curve for this problem.
Your answer here
Vol KOH
pH
0.00-mL
1.885
5.00-mL
2.69
10.00-mL
3.167
19.00-mL
4.446
20.00-mL
8.148
14
12
10
8
6
4
2
0
2
0
5
10
15
20
25
30
35
40
45
50
25.00-mL
12.444