Equilibrium concepts
Acid/base concepts
Conjugate pairs
pH
Problem solving
100
If reaction quotient Q is greater than K, in which direction will the reaction proceed to reach equilibrium?
The reaction will proceed to the left until Q = K.
100
What is the definition of an Arrhenius acid?
An Arrhenius acid forms H3O+ in water.
100
Identify the Bronsted-Lowry acid/base conjugate pairs in the following reaction:
HSO4- (aq) + H2O (l) ⇌ OH- (aq) + H2SO4 (aq)
HSO4- (base) and H2SO4 (acid) are a conjugate pair, H2O (acid) and OH- (base) are a pair.
100
A solution with a high pOH will be: (acidic/neutral/basic)
Acidic
100
Rank the following acids from strongest to weakest:
HF: Ka= 6.8x10-4
HCN: pKa= 9.20
HC2H3O2: pKa = 4.75
HCO3- : Ka = 1.5x10^-6
HF> HC2H3O2 >HCO3->HCN
200
According to Le Chatelier’s principle, if heat is added to a system with an exothermic reaction, in which direction will the reaction shift?
The reaction will shift to the left to consume the heat added.
200
What is the definition of a Bronstead-Lowry Acid?
A Bronstead-Lowry acid donates a proton.
200
Given the Ka value for a weak acid, how would the Kb value for its conjugate base be calculated?
Kb = Kw / Ka Kw = 1.0 x 10-14
200
The following pictures represent aqueous solutions of binary acid HA (water molecules have been omitted for clarity). In each figure, 7 molecules of HA are originally present. Arrange in order of increasing acid strength.
D < A < C < B
200
A weak acid with a concentration of 0.250M has a pH of 4.51 at equilibrium. What is the Ka of the acid?
3.84x10^-9
300
According to Le Chatelier’s principle, which way will a reaction involving gases shift when pressure is decreased?
The reaction will shift to the side with a higher number of moles of gas.
300
Write a balanced equation for the dissociation of the Bronsted-Lowry acid HCO3- in water:
HCO3- (aq) + H2O (l) ⇌ CO32- (aq) + H3O+ (aq)
300
Consider acids 1 and 2. If acid 2 is stronger than acid 1, is the conjugate base of acid 2 stronger or weaker than the conjugate base of acid 1?
The conjugate base of acid 2 is weaker than that of acid 1.
300
What is the trend of binary acid strength on the periodic table?
Acid strength increases down a group and across a period.
300
What is the equilibrium concentration of H3O+ if the initial concentration of a weak acid HA is 0.100 M? Ka = 1.8 x 10-5
[H3O+] = 1.3 x 10-3 M
400
In what situation can the small x approximation be used?/What is the ‘threshold’?
When a dissociation is small relative to initial concentration, threshold of x < 5%
400
How is [H+] calculated from pH?
[H+] = 10-pH
400
Write an acid/base reaction for a fully reacted H2SO4(aq) in water.
H2SO4(aq) +H2O(l) --> H3O+ (aq) + HSO4(aq)
HSO4(aq) +H2O(l) --> H3O+ (aq) + SO4 (aq)
400
A weak monoprotic acid has molar mass = 204.2 g/mol and Ka = 3.91 x 10-6. Calculate the pH of the solution when 0.60 g of the acid is dissociated 50.0 mL of water.
pH = 3.32
500
Consider two reactions, 1 and 2, with equilibrium constants of Ka1 and Ka2. What is the equilibrium constant for a reaction that is the net result of reversing reaction 1, doubling reaction 2, and adding them together?
((K_(a2))^2)/K_(a1)
500
How is [OH-] calculated from pH?
Can either calculate the pOH from pH and then raise ten to that or calculate the concentration of H+ and then calculate based on the ionization constant of water.
500
Consider the following Bronsted-Lowry acids: HCl, H2SO4, HNO3, CH3COOH (acetic acid), and HBr. Which acid’s conjugate base will produce the highest concentration of OH- ions in water?
CH3COOH
500
What is the pH of a 0.040 M Ca(OH)2 solution at 25 ᵒC?
pH = 12.90
500
What mass of benzoic acid, C6H5COOH, needs to be dissolved in 350.0 mL of water to produce a solution with a pH of 2.85? Ka = 6.3 x 10-5
1.39 g C6H5COOH