Chapter 9: Q11P (page 208)

A $0.0450 M$ solution of benzoic acid has a pH of $2.78$ . Calculate ${pK}_{a}$ for this acid

Short Answer

Expert verified

The ${pK}_{a}$ for benzoic acid is $= 4.20$

Step by step solution

Define pKa

${pK}_{a}$ is the number that describes the acidity of a particular molecule. The formula to find the ${pK}_{a}$ is

${pK}_{a} = - {logK}_{a}$

Reaction of dissociation

$C_{6} H_{5} {CO}_{2} H \overset{}{⇌} C_{6} H_{5} {CO}_{2}^{-} + H^{+} [C_{6} H_{5} {CO}_{2} H] = F - 10^{- 2.78} [C_{6} H_{5} {CO}_{2}^{-}] = [H^{+}] = 10^{- 278}$

Calculating the Ka of benzoic acid

$K_{a} = \frac{[C_{6} H_{5} {CO}_{2}^{-}] [H^{+}]}{[C_{6} H_{5} {CO}_{2} H]} K_{a} = \frac{{(10^{- 2.78})}^{2}}{0.0450 - 10^{- 2.78}} = 6.35 \times 10^{- 5}$

Calculating pKa of benzoic acid

Substituting the value of $K_{a}$ in the formula ${pK}_{a}$ we get

${pK}_{a} = - {logK}_{a} = - \log (6.35 \times 10^{- 5}) = 4.20$

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A $0.0450 M$ solution of benzoic acid has a pH of $2.78$ . Calculate ${pK}_{a}$ for this acid

Short Answer

Step by step solution

Define pKa

Reaction of dissociation

Calculating the Ka of benzoic acid

Calculating pKa of benzoic acid

One App. One Place for Learning.

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A 0.0450Msolution of benzoic acid has a pH of2.78. CalculatepKafor this acid

Short Answer

Step by step solution

Define pKa

Reaction of dissociation

Calculating the Ka of benzoic acid

Calculating pKa of benzoic acid

One App. One Place for Learning.

Most popular questions from this chapter

Recommended explanations on Chemistry Textbooks

Inorganic Chemistry

Organic Chemistry

The Earths Atmosphere

Chemistry Branches

Making Measurements

Nuclear Chemistry

Study anywhere. Anytime. Across all devices.

A $0.0450 M$ solution of benzoic acid has a pH of $2.78$ . Calculate ${pK}_{a}$ for this acid