Acids, bases and buffers

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Question 12
Medium

This question is about acids and bases found in the laboratory and home.

a.

Propanoic acid, CH3CH2COOH\text{CH}_3\text{CH}_2\text{COOH}CH3​CH2​COOH, is a weak monoprotic acid.

A student carries out an experiment to determine the pKa\text{p}K_apKa​ value of CH3CH2COOH\text{CH}_3\text{CH}_2\text{COOH}CH3​CH2​COOH.

  • The concentration of CH3CH2COOH\text{CH}_3\text{CH}_2\text{COOH}CH3​CH2​COOH is 0.750 mol dm-3.
  • The pH of the solution is 2.47.

Write the expression for the acid dissociation constant, KaK_aKa​, of CH3CH2COOH\text{CH}_3\text{CH}_2\text{COOH}CH3​CH2​COOH.

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b.

Calculate the pKa\text{p}K_apKa​ value of CH3CH2COOH\text{CH}_3\text{CH}_2\text{COOH}CH3​CH2​COOH. Give your answer to two decimal places.

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c.

Determine the percentage dissociation of propanoic acid in the solution. Give your answer to three significant figures.

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d.

Many solid drain cleaners are based on potassium hydroxide, KOH\text{KOH}KOH.

  • A student dissolves 1.45 g of a solid cleaner in water and makes up the solution to 200.0 cm3.
  • The student measures the pH of this solution as 13.05.

Determine the percentage, by mass, of KOH\text{KOH}KOH in the solid cleaner. Give your answer to three significant figures. [Kw=1.00×10−14 mol2 dm−6K_w = 1.00\times 10^{-14} \text{ mol}^2\text{ dm}^{-6}Kw​=1.00×10−14 mol2 dm−6 at 298 K, molar mass of KOH=56.11 g mol−1\text{KOH} = 56.11\text{ g mol}^{-1}KOH=56.11 g mol−1]

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e.

Potassium nitrite, KNO2\text{KNO}_2KNO2​, is a salt containing the nitrite ion, NO2−\text{NO}_2^-NO2−​. The skeletal structure is shown below:

O=N−O− \text{O}=\text{N}-\text{O}^- O=N−O−

Draw the 'dot-and-cross' diagram for the nitrite ion. Show outer electrons only and use different symbols for electrons from N and O, and any 'extra' electrons.

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Acids, bases and buffers Questions

  1. A Level
  2. /Chemistry
  3. /Acids, bases and buffers