18.2 Calculations Involving Acids & Bases

Question 1

Marks: 1

The table shows the pK_a and K_a values for four acids

Acid	pK_a	*K_a*
Butanoic Acid	-	1.51 x 10^-5
Nitrous acid	3.1	-
Lactic acid	3.4	-
Phenol	-	1 x 10^-10

Which of the following is the correct order of increasing strength of the acids

Phenol < butanoic acid < lactic acid < nitrous acid
Nitrous acid < lactic acid < butanoic acid < phenol
Nitrous acid < butanoic acid < phenol < lactic acid
Phenol < lactic acid < butanoic acid < nitrous acid

Key Concepts

Acid & Base Dissociation Constants

Question 2

Marks: 1

Which of the following statements is correct?

As temperature increases, the pH value of pure water decreases
As temperature decreases, the pH value of pure water decreases
The pH of water is unaffected by temperature
Pure water is not neutral

Key Concepts

Relating Kw to Ka

Question 3

Marks: 1

Which of the following statements about conjugate acid and base pairs are correct?

If an acid has a pK_a value of 4, its conjugate base will have a pK_b value of 10

II.

K_a + K_b = K_w

III.

The conjugate base for ethanoic acid is CH₃COO^-

I and II only
I and III only
II and III only
I, II and III

Key Concepts

Acid & Base Calculations

Question 4

Marks: 1

What is the correct expression to use to determine the pH of butanoic acid with concentration of 0.75 mol dm^-3?

The K_a of butanoic acid at 298 K is 1.51 x 10^-5 mol dm^-3

-log₁₀ ( $1.51 \times 10^{- 5} \times 0.75$ )
-log₁₀ $\sqrt{(1.51 \times 10^{- 5} \times 0.75)}$
-log₁₀0.75
$\frac{0.75}{1.51 \times 10^{- 5}}$

Key Concepts

Acid & Base Calculations

Question 5

Marks: 1

What is the correct expression for the base dissociation constant, K_b, for propylamine?

K_b = $\frac{[C H_{3} C H_{2} C H_{2} N {H_{3}}^{+}] [O H^{-}]}{[C H_{3} C H_{2} C H_{2} N H_{2}]}$
K_b = $\frac{[C H_{3} C H_{2} C H_{2} N {H_{3}}^{+}] [H_{2} O]}{[C H_{3} C H_{2} C H_{2} N H_{2}]}$
K_b = $\frac{[C H_{3} C H_{2} C H_{2} N {H_{3}}^{+}] [O H^{-}]}{[C H_{3} C H_{2} C H_{2} N H_{2}] [H_{2} O]}$
K_b = $[C H_{3} C H_{2} C H_{2} N {H_{3}}^{+}] [O H^{-}]$

Key Concepts

Acid & Base Dissociation Constants

DP IB Chemistry: HL

Topic Questions

18.2 Calculations Involving Acids & Bases

Question 1

Key Concepts

Question 2

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Question 3

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Question 4

Key Concepts

Question 5

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