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This quiz contains 10 questions from a mix of 1 subtopics.

What is the correct equation for the dissociation constant (Ka) of a weak acid (HA)?

Ka ​=[A−][H+][HA]​
Ka ​=[H+][A−][HA]​
Ka ​=[H+][A−][HA]​
Ka ​=[HA][H+][A−]​

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What does a larger Ka value indicate?

lower dissociation of HA

greater dissociation of HA

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What does a smaller pKa value indicate?

stronger acid

weaker acid

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A acid partially dissociates in aqueous solution.

weak

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Which situation would cause the approximation [H+]equilIbrium ≈ [A-]equilibrium to break down when calculating Ka for a weak acid?

when the concentration of the weak acid is very high

when the concentration of the weak acid is very low

when the concentration of the conjugate base is very high

when the pH of the solution is less than 6

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When does the approximation [HA]equilibrium ≈ [HA]undissociated break down when calculating Ka for a weak acid?

when the concentration of the conjugate base becomes significant

when the concentration of hydrogen ions becomes significant

when the concentration of the weak acid becomes significant

when the pH of the solution is less than 7

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Which type of weak acids would the approximation [HA]equilibrium ≈ [HA]undissociated not be justified for?

weak acids with small Ka values

weak acids with large Ka values

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How can the pKa of a weak acid be calculated using the Ka expression?

pKa ​=Ka​1​
pKa ​=−log10​Ka​
pKa ​=log10​Ka​
pKa ​=√Ka​​

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Calculate the pH of a 0.0250 mol dm-3 solution of ethanoic acid.

Ka for ethanoic acid = 1.80 x 10-5 mol dm-3

Give your answer to 2 decimal places.

3.17

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The pH of a 0.055 mol dm-3 solution of propanoic acid is 3.08. 

Calculate the Ka of propanoic acid.

1.51 x 10-2 mol dm-3

1.26 x 10-5 mol dm-3

6.92 x 10-7 mol dm-3

8.31 x 10-4 mol dm-3

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