AQA · Chemistry · 8462
GCSE Chemistry (AQA): Strong Acids & Weak Acids
Topic 4 — Chemical Changes. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Strong Acids & Weak Acids | pH & Concentration of Hydrogen Ions (2027/28 exams)"; each card deep-links to the moment in the video it came from. Lesson 4.03 of Cognito's AQA GCSE Combined Science (Trilogy) and Chemistry course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-c_4.03.
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By what factor does hydrogen ion concentration change for each decrease of one on the pH scale?
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It increases by a factor of 10.
What does pH measure?
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The concentration of hydrogen ions in a solution — the higher the H+ concentration, the lower the pH.
In the dissociation of a weak acid, which side does the equilibrium lie on?
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The left — at equilibrium there are far more undissociated acid molecules than dissociated ones.
Name three examples of weak acids.
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Ethanoic acid, citric acid and carbonic acid.
What subatomic particle is a hydrogen ion (H+) equivalent to?
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A proton — it is a hydrogen atom that has lost its single electron.
How many times higher is the hydrogen ion concentration at pH 3 than at pH 5?
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100 times higher (10 × 10).
Name three examples of strong acids.
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Hydrochloric acid, nitric acid and sulfuric acid.
The ionisation of a weak acid is ?, so an equilibrium exists between its undissociated and dissociated forms.
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reversible
What defines a strong acid?
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It ionises completely in aqueous solution, so all acid particles dissociate to release hydrogen ions.
Why must a weak acid be very concentrated to reach a low pH?
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Only a small proportion of its particles ionise, so a lot of acid is needed to release enough hydrogen ions.
What is the difference between acid strength and acid concentration?
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Strength is the proportion of acid molecules that ionise in water; concentration is the amount of acid per unit volume.
What is an acid?
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A substance that forms aqueous solutions with a pH of less than 7, because it ionises to release hydrogen ions.
At the same concentration, why does a strong acid have a lower pH than a weak acid?
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A higher proportion of the strong acid's molecules dissociate, giving a greater hydrogen ion concentration.
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