pH Problems
Determine the pH of a 0.30 M solution of HF (Ka = 6.8 × 10⁻⁴)
pH= 1.86
What is the effective pH range of a buffer?
What is the Bronsted-Lowry definition of an acid?
Acids donate H+ ions
What is the Bronsted-Lowry definition of a base?
Substances that accept H+ protons.
How do you find Kb if given Ka?
Kb = Kw / Ka
Determine the pH of a 0.65 M solution of HCO₂K. The value of Ka for HCOOH is 1.8 × 10⁻⁴.
pH=8.78
Determine the pH of a buffer that is 0.95 M HBrO and 0.68 M KBrO. The value of pKa for HBrO is 8.68.
pH=8.53
Do acids have a high pH or a low pH?
Low pH
How do you know that NO2- is a weak base?
NO2- has the ability to accept a proton and form the conjugate acid HNO2 making it a base.
What is the Henderson-Hasselbalch equation?
pH=pKa + log(base/acid)
Aspirin (acetylsalicylic acid, HC₉H₇O₄) has a value of Ka equal to 3.3 × 10⁻⁴. What is the pH after 652 mg of aspirin is dissolved in a solution of 237 mL?
pH=2.68
A buffer contains significant amounts of CH3COOH and CH3COO-. Write 2 equations for how this buffer would neutralize added HBr and NaOH.
CH3COOH(aq) + NaOH(aq) → NaCH3COO(aq) + H2O(l)
CH3COO-(aq) + HBr(aq) → CH3COOH(aq) + Br-
If an acid completely dissociates, is it strong or weak?
Which of the following is a Bronsted-Lowry base?
a) H2CO3
b) HF
c) C9H7N
d) NH4+
c) C9H7N
How do you find pKa if given Ka?
pKa = -log(Ka)
What is the pH of a 0.320 M solution of Ca(NO₂)₂ (Ka of HNO₂ is 4.5 × 10⁻⁴)?
8.58
Determine the resulting pH when 0.0015 mol of solid Ba(OH)₂ is added to a 0.350 L buffer containing 0.110 M weak acid, HA, and 0.220 M of its conjugate base, A⁻. The value of Ka for HA is 3.2 × 10⁻⁹.
pH = 8.85
For oxyacids, the more electronegative the Y is, the ___ the acid (weaker or stronger).
Y--O--H
Which of the following is a weak base?
a) NH3
b) C6H5COOH
c) HCN
d) Ba(OH)2
a) NH3
How do you find pKa if given Kb?
Divide Kw by Kb to solve for Ka then do -log(Ka).
A diprotic acid, H₂A, has Ka1 = 3.4 × 10⁻⁴ and Ka2 = 6.7 × 10⁻⁹. What is the pH of a 0.18 M solution of H₂A?
pH=2.11
Calculate the pH when 60.0 mL of 0.200 M HBr is mixed with 30.0 mL of 0.400 M CH₃NH₂ (Kb = 4.4 × 10⁻⁴).
pH=5.76
Which of the following is a weak acid and why?
a) KClO
b) HBrO
c) HClO4
d) CH3NH2
b) HBrO
It is an acid because it donates an H+ proton unlike CH3NH2 and KClO which accept protons. It is weak because it only partially dissociates unlike HClO4 which fully dissociates.
Would HC9H7O4 function as an acid or base? If acid, what is the conjugate base? If base, what is the conjugate acid?
HC9H7O4 is a weak acid. Its conjugate base is C9H7O4-.
How do you validate x is small when using the Henderson-Hasselbalch equation?
After you solve for the pH, solve for [H3O+] concentration by raising 10 to the power of (-pH). Divide [H3O+] by its coefficient in the chemical equation to find x. Then do
(x/concentration) x 100. x is small is valid if the answer is less than 5%.