Worksheet: Dissociation Constants and pH

In this worksheet, we will practice converting between the pH or pOH of a solution and the dissociation constants of dissolved acids and bases.

Q1:

Aniline is an amine that is used to manufacture dyes. It is isolated as aniline hydrochloride, [ C H N H ] C l 6 5 3 + – , a salt prepared by the reaction of the weak base aniline and hydrochloric acid. What is the pH of a 0.233 M solution of aniline hydrochloride, to 3 significant figures? 𝐾 b of aniline is 4 . 3 × 1 0 . − 1 0

  • A2.14
  • B3.01
  • C1.99
  • D2.63
  • E5.76

Q2:

Formic acid, H C O H 2 , is the irritant that triggers the body’s reaction to ant stings.

What is the concentration of hydronium ions in a 0.534 M solution of formic acid? Take 𝐾 = 1 . 8 × 1 0 a − 4 .

  • A 1 . 8 × 1 0 − 4 M
  • B 9 . 6 × 1 0 − 5 M
  • C 5 . 0 × 1 0 − 4 M
  • D 9 . 8 × 1 0 − 3 M
  • E 6 . 0 × 1 0 − 5 M

Q3:

What is the pH of a 0.25 M solution of trimethylamine, a weak base?

Take 𝐾 = 6 . 3 × 1 0 b − 5 .

Q4:

What is the concentration of hydroxide ions in a 0.0325 M solution of ammonia, a weak base with a 𝐾 b of 1 . 7 6 × 1 0   ?

  • A 1 . 1 2 × 1 0   M
  • B 6 . 1 0 × 1 0   M
  • C 9 . 3 4 × 1 0   M
  • D 7 . 5 6 × 1 0   M
  • E 6 . 6 2 × 1 0   M

Q5:

The pH of a 0.0516 M solution of nitrous acid ( H N O 2 ) is 2.34. Calculate the 𝐾 a of nitrous acid to 2 significant figures.

  • A 4 . 6 × 1 0  
  • B 2 . 1 × 1 0  
  • C 4 . 7 × 1 0  
  • D 4 . 4 × 1 0  
  • E 4 . 0 × 1 0  

Q6:

The pH of a solution of household ammonia, a 0.950 M solution of N H , 3 is 11.612. What is 𝐾 b for N H , 3 to 2 significant figures?

  • A 5 . 6 × 1 0 
  • B 1 . 7 × 1 0  
  • C 4 . 3 × 1 0  
  • D 1 . 8 × 1 0  

Q7:

Sodium bisulfate ( N a H S O 4 ) is used in some househould cleaners because it contains the H S O 4 – ion, which is weakly acidic: The 𝐾 a of H S O 4 – is 1 . 2 × 1 0 − 2 . Calculate to 2 decimal places the pH of a H S O 4 – solution with a concentration of 0.50 M.

Q8:

Caffeine, a weak base, has a 𝐾 b value of 2 . 5 × 1 0 − 4 . Calculate to 1 decimal place the pH of a 0.010 M aqueous caffeine solution.

Q9:

The 𝐾 a of H C N is 4 . 9 × 1 0 − 1 0 . Calculate to 1 decimal place the pH of a 0.083 M solution of C N – .

Q10:

Aluminum chloride dissolves completely to produce the hydrated aluminum ion [ A l ( H O ) ] 2 6 3 + , which behaves as a monoprotic acid. The 𝐾 a of [ A l ( H O ) ] 2 6 3 + is 1 . 4 × 1 0 − 5 . Calculate to 2 decimal places the pH of a 0.10 M solution of aluminum chloride.

Q11:

The pH of a 0.15 M solution of H S O 4 – is 1.43. What is 𝐾 a for H S O 4 – from these data?

  • A 8 . 9 × 1 0 − 5
  • B 2 . 3 × 1 0 − 2
  • C 1 . 6 × 1 0 − 4
  • D 1 . 2 × 1 0 − 2
  • E 3 . 6 × 1 0 − 6

Q12:

The pH of a solution of household ammonia, a 0.950 M solution of N H 3 , is 11.612. What is 𝐾 b for N H 3 from these data?

  • A 5 . 0 5 × 1 0  
  • B 3 . 1 6 × 1 0  
  • C 3 . 5 8 × 1 0  
  • D 1 . 7 7 × 1 0  
  • E0.950

Q13:

White vinegar is a 5.00% by mass solution of acetic acid in water. If the density of white vinegar is 1.007 g/mL, what is the pH at 2 5 ∘ C ? The 𝐾 a of acetic acid is 1 . 8 × 1 0 − 5 .

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