Exam 3 Practice Questions given by Prof. K
Unit 12 (solutions, molarity, solubility rule and molecular and net ionic
reactions.)
1. A 45 g sampleofsodium sulfate isdissolved in 1.50 L ofsolution.
Whatisthemolarityofthesolution? (Answer – 0.21 M)
2. What is the concentration of carbonate ions in a 0.125 M Al2(CO3)3 solution?(Answer –
0.375 M)
3. A student prepared a stock solution by dissolving 10.0 g of KOH in enough water to
make 150. mL of solution. She then took 15.0 mL of the stock solution and diluted it with
enough water to make 65.0 mL of a final solution. What is the concentration of KOH for
the final solution? (Answer – 0.274 M, seethesolution in Unit 12 iClicker file in
theSapling)
4. Give the complete ionic equation for the reaction that occurs when aqueous solutions of
lithium sulfide and copper (II) nitrate are mixed. (Answer - 2Li+ + S2- + Cu2+ + 2NO3- ----- 2Li+ + 2NO3- + CuS)
5. Give the net ionic equation for the reaction that occurs when aqueous solutions of lithium
sulfide and copper (II) nitrate are mixed. (Answer - S2- + Cu2+ ------ CuS(s))
6. A 56.0 mLaliquot of a 1.70 Msolution is diluted to a total volume of 218 mL. A
109 mLportion of that solution is diluted by adding 117 mL of water. What is the final
concentration? Assume the volumes are additive. (Answer - 0.211 M)
7. A 67.0 mLaliquot of a 0.500 M stock solution must be diluted to 0.100 M. Assuming the
volumes are additive, how much water should be added. (Answer - 268mL)
Unit 13 (Definition of, expression for k and manipulation of k)
1. Derive equilibrium expressions (Kc and Kp) for the following equation
a)
b)
c)
d)
4NO(g) + 6H2O(g) ⇌ 4NH3(g) + 5O2(g)(Answer–[NH3]4× [O2]5/[NO]4 × [H2O]6)
7NH3(g) + 7HCl(g) ⇌ 7NH4Cl(s)? (Answer - 1/[NH3]7 × [HCl]7)
heat + C(s) + CO2(g) ⇌ 2CO(g)(Answer –PCO2/PCO2)
3CaCO3(s) ⇌ 3CaO(s) + 3CO2(g)?(Answer –Kp = PCO23 or Kc = [CO2]3)
2. Meaning of K: K>1, K = 1, and K<1 (Answer – K>1 means concentration of products
are higher that of reactants; K=1 means concentration of products are equal to that
of reactants; K<1 means concentration of products are lower that of reactants)
3. Based on the concentration vs time plot below, what can be said of the equilibrium
constant for the reaction 2NO2(g) ⇌N2O4(g)? (Draw a figure) (Answer – K<1)
4. Consider the equilibrium reaction: N2(g) + 3H2(g) ⇌ 2NH3(g). At equilibrium at a
certain temperature, the concentrations of NH3(g), H2(g) and N2(g) are 0.980 M, 1.53 M
and 0.510 M, respectively. Calculate the value of Kc for this reaction. (Answer – 0.53)
5. As written, the reaction 2N2(g) + O2(g) ⇌ 2N2O(g) has a K value of K1. What is the
value of K2 for the reaction written as 4N2O(g) ⇌ 4N2(g) + 2O2(g) ? (Answer K2 =
(1/K1)½)
6. Given the following information:
OI¯ + H2O ⇌ HOI + OH¯
K1 = 5 x 10-4
H2O ⇌ ½H3O+ + ½OH¯ K2 = 1 x 10-7
What is the value of K for the rxnHOI + H2O ⇌ OI¯ + H3O+? (Answer K2 = 2 x 10-11, see the
solution in iCliker presentation uploaded in the Sapling)
7. Given the following information:
N2(g) + O2⇌ 2NO
N2 + ½O ⇌ N2O(g)
K1 = 4.1 x 10-31
K2 = 2.4 x 10-18
What is the value of Knew for the rxn N2O(g) + ½O ⇌2NO? (Answer Knew = 1.7 x 10-13, see the
solution in iCliker presentation uploaded in the Sapling)
Unit 14 (Relationship between Q and K, LeChatelier’s Principle (Effects of T,
P/V, Concentration, inert gas and catalyst on the equilibrium)
1. Consider the following reaction at a fixed temperature :
2SO3(g) ⇌ 2SO2(g) + O2(g)
Kc = 3.3 x 10-3
If you put 0.28 mol of SO3, 0.050 mol of SO2, and 0.080 mol of O2 into a 4.50 L container what
happens to the reaction? (Q = 5.7 x 10-4, Q < Kcand therefore reaction will proceed forward.)
2. Consider the following reaction at a fixed temperature :
2SO3(g) ⇌ 2SO2(g) + O2(g)
K = 3.3 x 10-3
If you put 0.44 atm of SO3, 0.32 atm of SO2, and 0.16 atmof O2 into sealed container, what
happens to the reaction? (Q = 0.085, Q > K and therefore the reaction will proceed backward)
3. Consider the following reaction at a 100oC:
SO2Cl2(g) ⇌ SO2(g) + Cl2(g)
Kc = 0.078
0.35 moles of SO2, 0.25 moles of SO2Cl2, and 0.80 moles of Cl2 are combined in an evacuated
5.0 L flask and heated to 100oC. What is Q before the reaction begins? Which direction will the
reaction proceed in order to establish equilibrium? (Answer - Q = 0.224, Q > Kc, and therefore
reaction will proceed backward.)
4. Consider this system at equilibrium.
A(aq)↽−−⇀B(aq)Δ𝐻=−350 kJ/mol
What can be said about Q and K immediately after an increase in temperature? (Answer - K will
decrease and Q will increase)
5. Consider the reaction C(s) + O2(g) ⇌ CO2(g) at equilibrium.If I add C(s), the reaction
6.
7.
8.
9.
10.
will shift neither left nor right, and if I reduce the size of the reaction flask, the reaction
will shift neither left nor right.
Consider the endothermic reaction C(s) + CO2(g) ⇌ 2CO(g).If such a system at
equilibrium is heated, equilibrium will shift to the right and the value of K increase.
Consider the exothermic reaction 2CO(g) ⇌ C(s) + CO2(g).If such a system at
equilibrium is heated, equilibrium will shift to the left and the value of K decrease.
Consider an endothermic reaction C(s) + CO2(g) ⇌ 2CO(g).If such a system at
equilibrium is heated and compressed at the same time, what happens to the equilibrium
position? (It cannot be decided because heating will shift the reaction to the right,
but the increased pressure will shift the reaction to the left. We do not know which
one will win)
Consider the exothermic reaction at equilibrium:2 SO2(g) + O2(g) - 2 SO3(If a catalyst
is added to the reaction, the equilibrium will:(no shift in either direction as catalyst has
on the equilibrium)
Consider the exothermic reaction at equilibrium:2SO2(g) + O2(g) ⇌ 2SO3(g). If 3
moles of argon is added to the reaction, what will happen to the equilibrium point?(Not
shift in either direction because inert gas has no effect on the equilibrium.)
Unit 15 Acids and bases
1. What are Arhenius and Bronsted Acids and Bases?
2. What are strong acids and strong bases, weak acids and weak bases? (See the list in
the uploaded iCliker presentation in the Sapling)
3. What are conjugate acids and bases in the following reactions?
a)
b)
c)
d)
e)
HSO4¯ (acid)+ H2O (base)⇌ SO42-(conjugate base) + H3O+(conjugateacid)
NH3(base)+ H2O(acid)⇌ NH4+(conjugateacid)+ OH-(conjugate base)
H2PO4-(base)+ H2O (acid)⇌ H3PO4(conjugateacid)+ OH-(conjugate base)
CO32-(base) + H3O+(acid)⇌ HCO3¯(conjugateacid) + H2O (conjugate base)
HA(aq)(acid) + H2O(l)(base)⇌ H3O+(aq)(conjugateacid) + A-(aq)(conjugate
base)
4. What is the relationship between Ka and acid strength? (The higher is the value of
Ka, the strongest is the acid)
5. What is the relationship between Ka and temperature (The value of Ka increases
with the increase of temperature)
6. Understand the concept of Ka1, Ka2 and Ka3(H2SO4 has Ka1 and Ka2 because it is
diprotic whereas H3PO4 has Ka1, Ka2 and Ka3 because it is triprotic and HCl has
onlu Ka1 because it is monoprotic acid)
7. Understand the relationship between Ka1 and Kb1 (Kw = Ka1 × Kb1)
Unit 16 (pH and pOH)
1. Relation between pH and H+ and pH and pOH (pH = -log[H+]; 14 = pH + pOH)
2. What is the pOH of 0.05 M solution of LiOH? (pOH of LiOH= 1.3)
3. What can you say about pH of 0.088M HF and HCl? ((pH = 1.1 is for HCl because
it is strong acid, but it will be more than 1 because HF is a weak acid)
4. The diagrams represent aqueous solutions of three acids (HX, HY, and HZ) withwater
molecules omitted for clarity. Rank these acids from lowest pH to highestpH.
(Answer: HX, HY, HZ)
5. Relationship between H+/OH-and Kw(Kw = [H+][OH-])
6. What is the pH of 0.01 M solution of LiOH at 25oC? (Answer pH = 12)
7. Calculate the concentration of hydronium ions in a 0.044 M KOH solution at 100oC
(Kw at 100 oC = 5.43×10-13) (Answer 1.2×10-11 M)
8. What is the pOH of 0.001 M solution of HBr at 25oC? (Answer pOH = 11)
9. What is kb for Na2CO3. Given the following table.
(Answer 1.79 x 10-4)