CEM 142 LATEST 2026 TEST PAPER QUESTIONS AND SOLUTIONS SCORED

CEM 142 LATEST 2026 TEST PAPER QUESTIONS AND
SOLUTIONS SCORED A+
✔✔A+B--><-- C+D K=200 @ 298K
At equilibrium there are
A. More products
B. More reactants
C. Equal amounts
D. It depends - ✔✔- A
*If K s large (>1) there are more products than reactants (but not the form of K may be a
little different depending on the coefficients.)

✔✔A+B--><--C+D K=200 @ 298 K
What is he value of K at 400K?
A. > 200
B. < 200
C. 200
D. It depends - ✔✔- D
*K is temperature dependent - how it changed depends on the enthalpy change (as we
will see).

✔✔K is expressed with either concentrations (Kc) or partial pressures (Kp). That is
either for solutions or gases BUT for __________ and __________ ______________
the concentration does not change and therefore we do not need to put these terms in
the expression for K. - ✔✔-Solids.
-Pure Liquids.

✔✔For CaCO3(s) --><-- CaO(s) + CO2
K=?
A. [CaO][CO2] / [CaCO3]
B. [CaCO3] / [CaO][CO2]
C. [CO2]
D. It depends - ✔✔- C

✔✔Acid Dissociation Constant Ka:
HA + H2O --><-- H3O+ + A-
Ka = [H3O+][A-] / [HA]
Ka can be used to quantify acid strength. Do you expect a strong acid to have a large or
small Ka?
A. Large Ka
B. Small Ka
C. I dont know - ✔✔- A
*Large Ka -strong acid.
*Small Ka- weak acid.

,✔✔Which is the strongest acid?
A. HF, Ka = 7.2X10^-4
B. CH3COOH, Ka = 1.76X10^-5
C. H2CO3 (Carbonic) 1st, Ka = 4.3X10^-7
D. NH4Cl, Ka = 5.6X10^-10. - ✔✔- A

✔✔pKa formula: - ✔✔-pKa = -logKa

✔✔Large Ka means __________pKa (strong acid)
Small Ka means __________ pKa (weak acid) - ✔✔-Small.
-Large.

✔✔Which is the strongest acid ?
Which is the weakest acid?
A. H2O
B. NH3
C. CH4
Which acid would you expect to have the largest pKa?
Which acid would you expect to have the smallest pKa? - ✔✔-A
-C
-C
-A

✔✔Acid-Base Equilibria:
Here is an acid base reaction:
CH3COOH +NH3 --><-- CH3COO- +NH4+
pKa CH3COOH = 4.8
pKa NH4+ = 9.24
On which side does the equilibrium lie? Why?
A. Left
B. Right
C. In the middle
D. Impossible to tell - ✔✔-B

✔✔If a 0.10M solution of an acid has a pH of 4.3, what is the Ka and the pKa?
Ka:
A. 2.5X10^-8
B. 5.0X10^-5
C. 2.5X10^-9
D. 2.0X10^-4
pKa:
A. 3.69
B. 8.6
C. 4.30
D. 7.60 - ✔✔- A

, -D

✔✔What is the pH of a 0.10 M solution of an acid with a pKa of 8.4?
1. Find Ka (10^-pKa)
2. Write down the expression for Ka
Ka = [H3O+][A] / [HA]
3. Assume [H3O+] = [A-] = "x"
Assume [HA] = 0.1 M (since x < 5%)
Ka = x^2 /0.1
4. Solve for x = [H3O+]
5. pH = -log [H3O+] - ✔✔

✔✔K tell us ....?
Large K means...?
Small K means...? - ✔✔-Where the equilibrium position is for a reaction.
-More products.
-More reactants.

✔✔K forward = __________reverse? - ✔✔-1/K reverse.

✔✔So the value of K tells us in which direction a reaction will proceed if we know
something about the initial conditions. But we also know another factor that will tell us
something about...? - ✔✔-Whether a reaction will go...

✔✔What factor tells us about the direction change?
A. Delta H
B. Delta S system
C. Delta G
D. All of the them - ✔✔- C

✔✔Delta G and K both indicate the direction change. What is Delta G at equilibrium?
A. (+)
B. (-)
C. 0
D. It depends - ✔✔- C

✔✔Imagine we have a reaction A--><--B where K =1.
If we start with an initial concentration of A=1.0M:
*What will the equilibrium [A]? (0.5M)
*What will be the equilibrium [B] (0.5M) WHY?

A. 1.0M
B. 0
C. 0.5M - ✔✔- C