A student investigates how pH measurements can be used to distinguish between the strength of acids and bases (not just their concentration). They prepare four 0.10 mol L\(^{-1}\) aqueous solutions at 25 \(^\circ\)C using deionised water: hydrochloric acid (HCl), ethanoic acid (CH\(_3\)COOH), sodium hydroxide (NaOH) and aqueous ammonia (NH\(_3\)(aq)).
They calibrate a pH probe and record the following pH values:
| Solution (0.10 mol L\(^{-1}\)) | Measured pH |
|---|---|
| HCl(aq) | 1.00 |
| CH\(_3\)COOH(aq) | 2.87 |
| NaOH(aq) | 13.00 |
| NH\(_3\)(aq) | 11.13 |
The student also repeats the measurements after diluting each solution tenfold with deionised water to make 0.010 mol L\(^{-1}\) solutions. The following pH values are obtained:
| Solution (0.010 mol L\(^{-1}\)) | Measured pH |
|---|---|
| HCl(aq) | 2.00 |
| CH\(_3\)COOH(aq) | 3.37 |
| NaOH(aq) | 12.00 |
| NH\(_3\)(aq) | 10.63 |
Using your results from the 0.10 mol L\(^{-1}\) solutions, determine the approximate percentage ionisation of CH\(_3\)COOH and of NH\(_3\) in water. Use Brønsted–Lowry reasoning to explain what these percentages indicate about the strength of these acid/base solutions compared with HCl and NaOH.
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Create Free Account Log inThis is a free HSC HSC Chemistry practice question worth 6 marks, testing your understanding of Changing acid and base models. It falls under Properties of Acids and Bases in Module 6: Module 6: Acid/Base Reactions. Submit your answer above to receive instant AI-powered marking and personalised feedback.
Students analyse how and why the definitions of both an acid and a base have changed over time, and how the current definitions characterise the many chemical reactions of acids. Acids react in particular ways to a variety of substances. These reactions follow a pattern that students identify and explore in detail. Acids and bases, and their reactions, are used extensively in everyday life and in the human body. The chemistry of acids and bases contributes to industrial contexts and the environment. Therefore, it is essential that the degree of acidity in these situations is continually monitored. By investigating the qualitative and quantitative properties of acids and bases, students learn to appreciate the importance of factors such as pH and indicators.
Inquiry question: What is an acid and what is a base?
explore the changes in definitions and models of an acid and a base over time to explain the limitations of each model, including but not limited to: - Arrhenius' theory - Brønsted–Lowry theory (ACSCH064, ACSCH067)
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