Eduqas GCSE Chemistry
Eduqas GCSE Chemistry 7 Chemistry of Acids Exam Questions
Free Eduqas GCSE Chemistry revision for 7 Chemistry of Acids: what you need to know, common mistakes and exam-style questions with answers. Covers reactions of acids, pH, neutralisation, strong and weak acids, making salts, titration, concentration and tests for sulfate and carbonate ions.
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About Eduqas GCSE Chemistry 7 Chemistry of Acids
Chemistry of acids covers how acids react and how they are used to make salts. In Eduqas GCSE Chemistry you learn the reactions of acids with metals, metal oxides, hydroxides and carbonates, the pH scale and indicators, neutralisation as H+ + OH- → H2O, and the difference between strong and weak acids. You prepare a soluble salt from an insoluble base or carbonate (SP7A) and carry out an acid-alkali titration (SP7B), then use the results to calculate concentration in mol/dm3. Tests for sulfate and carbonate ions are also included. Examiners often ask for salt preparation methods, word and symbol equations, and titration calculations.
What you need to know
- Reactions of acids Acid + metal → salt + hydrogen. Acid + metal oxide or hydroxide → salt + water. Acid + metal carbonate → salt + water + carbon dioxide. Hydrochloric acid makes chlorides, sulfuric acid makes sulfates and nitric acid makes nitrates.
- pH and neutralisation Acids produce H+ ions in water and alkalis produce OH- ions. pH below 7 is acidic, 7 neutral, above 7 alkaline; universal indicator or a pH probe measures it. Neutralisation: H+(aq) + OH-(aq) → H2O(l).
- Strong and weak acids Strong acids (hydrochloric, sulfuric, nitric) are fully ionised in water; weak acids (ethanoic, citric, carbonic) are partially ionised. Concentration is the amount of acid per volume, which is different from strength.
- SP7A: making a soluble salt Add excess insoluble base or carbonate to warm acid until no more reacts, filter off the excess, heat the filtrate to evaporate some water, then leave to crystallise and dry the crystals.
- SP7B: titration Use a pipette to add a known volume of alkali to a conical flask with indicator. Add acid from a burette, swirling, until the indicator changes colour. Repeat until results are concordant and calculate a mean titre.
- Concentration and ion tests Concentration (mol/dm3) = moles / volume in dm3; divide cm3 by 1000. Sulfate: add dilute hydrochloric acid then barium chloride, white precipitate. Carbonate: add acid, fizzing, gas turns limewater milky.
Common mistakes in 7 Chemistry of Acids
- Confusing strong with concentrated. Strong means fully ionised; concentrated means a large amount of acid in a given volume.
- Forgetting to convert cm3 to dm3 in concentration calculations. Divide by 1000 before using concentration = moles / volume.
- Leaving out water as a product when an acid reacts with a carbonate. The products are salt, water and carbon dioxide.
- Adding insoluble base until the acid is just used up. Add the base in excess so all the acid reacts, then filter off the excess.
- Including the rough titration in the mean. Use only concordant results, usually within 0.10 cm3 of each other.
Try three 7 Chemistry of Acids exam-style questions
1. 25.0 cm3 of 0.100 mol/dm3 sodium hydroxide was neutralised by 20.0 cm3 of hydrochloric acid. NaOH + HCl → NaCl + H2O. Calculate the concentration of the acid. (3 marks)
Show the mark scheme answer
Moles NaOH = 0.100 x 25.0 / 1000 = 0.00250 mol; moles HCl = 0.00250 mol (1:1); concentration = 0.00250 / 0.0200 = 0.125 mol/dm3.
2. Describe how to make pure dry crystals of copper(II) sulfate from copper(II) oxide and dilute sulfuric acid. (4 marks)
Show the mark scheme answer
Warm the acid and add copper(II) oxide until in excess / no more dissolves; filter to remove excess copper(II) oxide; heat filtrate to evaporate some water then leave to crystallise; pat crystals dry with filter paper.
3. Write the ionic equation for neutralisation, including state symbols. (2 marks)
Show the mark scheme answer
H+(aq) + OH-(aq); → H2O(l).
7 Chemistry of Acids FAQs
What does Eduqas GCSE Chemistry 7 Chemistry of Acids cover?
It covers reactions of acids, pH, neutralisation, strong and weak acids, making soluble salts, acid-alkali titrations and concentration calculations, and tests for sulfate and carbonate ions.
Which paper is 7 Chemistry of Acids examined in?
It is examined in Component 1: Concepts in Chemistry (2 hours 15 minutes, 120 marks). Component 2: Applications in Chemistry can also test it through practical contexts and an unseen article.
What do I need to know about titrations for Eduqas GCSE Chemistry 7 Chemistry of Acids?
Know the apparatus (pipette, burette, conical flask, indicator), how to read the burette to 0.05 cm3, what concordant results are, and how to use the mole ratio and concentration = moles / volume to find an unknown concentration.
