AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
The pH scale and neutralisation: Acids produce hydrogen ions (H⁺) in aqueous solutions.
Acids produce hydrogen ions, H⁺, when dissolved in water.
- 4 key terms
Study notes
From the checked teaching notes for this specification point.
The idea
Acids produce hydrogen ions, H⁺, when dissolved in water. In aqueous solution, an acid releases H⁺ ions, which are responsible for acidic properties such as low pH, reaction with metals to form hydrogen, and neutralisation by bases. For example, hydrochloric acid in water forms H⁺ and Cl⁻ ions; the H⁺ ions make the solution acidic. The concentration of H⁺ ions determines pH: higher H⁺ concentration gives lower pH. Strong acids ionise completely, while weak acids ionise partially, but both produce H⁺ in aqueous solution. This idea explains why acids only show acidic behaviour when water is present.
What earns the marks
- Acids produce hydrogen ions, H⁺, when dissolved in water.
- The H⁺ ion is responsible for acidic properties, including low pH and neutralisation.
- In aqueous solution, an acid ionises or dissociates to release H⁺ ions.
- The concentration of H⁺ ions determines the pH of the solution.
- Strong acids ionise completely in water, while weak acids ionise partially, but both produce H⁺ ions.
Common mistakes and how to put them right
Writing H⁺ as H+ or H plus.
Put it right: Use the correct ion symbol H⁺.
Confusing strong and concentrated.
Put it right: Use the terms precisely.
Exam tips
- Define an acid as a source of H⁺ ions in aqueous solution, and link this to acidic properties.
- Use the formula H⁺ correctly in equations and explanations, including state symbols where appropriate.
- When comparing strong and weak acids, refer to the extent of ionisation and the concentration of H⁺ ions.
Try the lesson
The start of the The pH scale and neutralisation: Acids produce hydrogen ions (H⁺) in aqueous solutions. lesson, made from checked teaching notes for this specification point.
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Which ion is produced by all acids when they are dissolved in water to form an aqueous solution?
Listen
Acids produce hydrogen ions, H⁺, when dissolved in water. In aqueous solution, an acid releases H⁺ ions, which are responsible for acidic properties such as low pH, reaction with metals to form hydrogen, and neutralisation by bases. For example, hydrochloric acid in water forms H⁺ and Cl⁻ ions; the H⁺ ions make the solution acidic. The concentration of H⁺ ions determines pH: higher H⁺ concentration gives lower pH. Strong acids ionise completely, while weak acids ionise partially, but both produce H⁺ in aqueous solution. This idea explains why acids only show acidic behaviour when water is present. A strong answer earns marks for these points. Acids produce hydrogen ions, H⁺, when dissolved in water. The H⁺ ion is responsible for acidic properties, including low pH and neutralisation. In aqueous solution, an acid ionises or dissociates to release H⁺ ions. The concentration of H⁺ ions determines the pH of the solution. A common slip: Writing H⁺ as H+ or H plus: the charge must be shown as a superscript, H⁺. Instead, use the correct ion symbol H⁺. Exam tip: Define an acid as a source of H⁺ ions in aqueous solution, and link this to acidic properties.
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Key words
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Acids
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pH
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Strong acids
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Neutralisation
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See every definition
- Acids
- Substances that produce hydrogen ions, H⁺, when dissolved in water, and only show acidic behaviour when water is present.
- pH
- A measure determined by the concentration of H⁺ ions, where a higher H⁺ concentration gives a lower pH.
- Strong acids
- Acids that ionise completely in water, while weak acids ionise partially, but both produce H⁺ ions.
- Neutralisation
- An acidic property for which the H⁺ ion is responsible, alongside low pH, and which involves reaction with bases.
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