CC3.1Acids, alkalis, neutralisation and the pH scale; titrations and indicators; strong vs weak acids (HT)

Notes

pH 0–14: pH < 7 = acidic; pH 7 = neutral; pH > 7 = alkaline.

Acids release H⁺ ions in solution. Alkalis release OH⁻ ions in solution.

Neutralisation: acid + alkali → salt + water $$H^+(aq) + OH^-(aq) \to H_2O(l)$$

Strong acid (e.g. HCl, H₂SO₄, HNO₃): completely dissociates in water → high [H⁺].
Weak acid (e.g. ethanoic acid, citric acid): partially dissociates → lower [H⁺] at same concentration.

A strong acid of the same concentration as a weak acid has a lower pH (more H⁺ ions).

Acid + metal → salt + hydrogen Acid + metal oxide → salt + water Acid + metal carbonate → salt + water + carbon dioxide

Salt name: metal + acid-derived name (hydrochloric → chloride; sulfuric → sulfate; nitric → nitrate).

Used to find the exact volume of one solution needed to neutralise another. Indicator (e.g. phenolphthalein or methyl orange) shows the endpoint.

AI-generated · claude-opus-4-7 · v3-edexcel-combined-science

Try each before peeking at the worked solution.

Question 14 marks
Neutralisation calculation
(4 marks) 25.0 cm³ of NaOH solution is neutralised by 20.0 cm³ of 0.10 mol/L HCl.

(a) Calculate the moles of HCl used. (1 mark)
(b) Write the equation for this reaction. (1 mark)
(c) Calculate the concentration of the NaOH solution. (2 marks)
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AI-generated · claude-opus-4-7 · v3-edexcel-combined-science
Question 23 marks
Strong vs weak acid
(3 marks) Explain why 0.1 mol/L hydrochloric acid has a lower pH than 0.1 mol/L ethanoic acid.
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AI-generated · claude-opus-4-7 · v3-edexcel-combined-science

CC3.1 — Acids, alkalis, pH and neutralisation

5-card SR deck for Edexcel Combined Science topic CC3.1

5 cards · spaced repetition (SM-2)