Acids & Bases
Acids, Bases, and pH
Equilibrium, Ka, Kb, and buffers
Redox Reactions and Galvanic Cells
100
What is a bronsted acid? What is a bronsted base?
Bronsted acids are proton donors (lose one H+)
- Bronsted bases are proton acceptors (gain one H+)
100
What are the conversions between [H3O+], [OH-], pH, and pOH? Draw them out.
100
Which of the following could be used to prepare a buffer, assuming the solutions were combined in roughly equimolar amounts?
a. NaOH and NaCl
b. HF and KF
c. HBr and HCl
b. HF and KF; This is a weak acid-conjugate base pair, so it can be a buffer.
a. would not be a buffer because NaOH is a strong base.
c. would not be a buffer because both HBr and HCl are strong acids.
100
Which substance is the oxidizing agent in the following reaction?
Ca(s) + Zn2+(aq) → Ca2+(aq) + Zn(s)
Zn2+(aq)
200
What is an arrhenius acid? What is an arrhenius base?
Arrhenius acids form hydronium (H3O+) ions in solution
Arrhenius bases form hydroxide (OH-) ions in solution
200
Air-saturated water has a hydronium ion concentration of 2.0×10−6 M. Calculate the pH of the solution.
pH = -log[H3O+]
pH = -log[2x10-6M]
pH = 5.70
200
C8H10N4O2 is a weak base. What is the value of Kb for C8H10N4O2 if a solution at equilibrium has
[C8H10N4O2] = 0.050 M, [C8H10N4O2H+] = 5.0x10−3 M, and [OH−] = 2.5x10−3 M?
Kb = ([OH-][HB+])/[B]
Kb= ((2.5x10−3)(5.0x10−3))/0.050
Kb = 2.5x10-4
200
In which one of the following molecules does sulfur have the smallest oxidation number?
a) SO3
b) S2O32-
c) SO42-
d) SO2
b) S2O32-
300
What is the conjugate base of the acid HBr?
Br-
300
Blood has a pH of 7.3. What is the hydronium ion concentration of whole blood?
[H3O+]=10-pH
[H3O+]=10-7.3
[H3O+]= 5x10-8M
300
At equilibrium, a solution contains [CH3CO2H] = 0.0787 M and [H3O+]=0.00118M, [CH3CO2−]=0.00118M. What is the value of Ka?
CH3CO2H(aq) + H2O(l) ⇌ H3O+(aq) + CH3CO2−(aq)
Ka = ([H3O+][A-])/[HA]
Ka = (0.00118)2/(0.0787)
Ka = 1.77x10-5
300
What is E°red for the reaction
Al(s) + 3 Ag+(aq) → 3Ag(s) + Al3+(aq)?
Standard reduction potential for
Al3+(aq) + 3e- → Al (s) = -1.66 V E°cell = +2.46 V
Ecell = Eox + Ered
+2.46 = +1.66 + Ered
Ered = 0.8V
400
Identify the bronsted acid, base, and two conjugate pairs for the following reaction:
HCl (aq) + NH3 (aq) → NH4+ (aq) + Cl- (aq)
HCl (aq) + NH3 (aq) → NH4+ (aq) + Cl- (aq)
acid base conj. acid conj. base
400
Sea water has a hydronium ion concentration of 6.33x10-9. What is the hydroxide ion concentration?
[OH-] = Kw/[H3O+]
[OH-] = 1x10-14/6.33x10-9
[OH-] = 1.58x10-6
400
What is the pH of a 0.534M solution of formic HCO2H?
HCO2H(aq) + H2O(l) ⇌ H3O+(aq) + HCO2−(aq) Ka=1.8×10−4
R HCO2H H3O+ HCO2-
I 0.534 0 0
C -x +x +x
E 0.534-x x x
Ka = x2/(0.534-x) *assume x is small
Ka = x2/0.534
1.8×10−4 = x2/0.534
0.534 x (1.8×10−4) = x2 *square root both sides*
x = 9.8x10-3 M = [H3O+]
pH = -log[9.8x10-3 M] = 2.01
400
A galvanic cell is run for 240 seconds at a current of 15 amps. How many moles of electrons are produced?
15A x 240sec = 3600C
3600C x (1mol e-/96485C) = 0.037 moles e-
500
Name the formula for at least 3 of the 6 strong acids.
H2SO4 So
HI I
HBr Brought
HNO3 No
HCl Clean
HClO4 Clothes
500
If moist soil has a hydroxide concentration of 3.19x10-5, what is the pH?
There are two ways to solve this.
a) [OH-] -> pOH -> pH
b) [OH-] -> [H3O+] -> pH
Either method is fine. The answer should be:
pH = 9.5
500
Calculate the pH of an acetate buffer that is a mixture with 0.10 M acetic acid and 0.10 M sodium acetate.
Ka = 1.8x10-5
R CH3CO2H H3O+ CH3CO2-
I
C
E
R CH3CO2H H3O+ CH3CO2-
I 0.10 0 0.10
C -x +x +x
E 0.10-x x 0.10+x
Ka = [H3O+][CH3CO2-]/[CH3CO2H]
1.8x10-5 = (x)(.10+x)/(.10-x) *assume x is small
1.8x10-5 = (x)(.10)/(.10)
x = 1.8x10-5 = [H3O+]
pH = -log[1.8x10-5] = 4.74
500
Balance the following redox reaction in basic solution:
MnO4- + C2O4-2 → Mn+2 + CO2
