Lesson T5.1.2

T5.1.2 The pH scale and indicators Quiz: KS3 Chemistry, Unit 5

20 questions

Written by Revision Ninja · Last reviewed 11 October 2026

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Lesson T5.1.2, The pH scale and indicators: 20 multiple choice questions for the KS3 Chemistry (National Curriculum), Unit 5: Acids and alkalis, written with Revision Ninja.

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The 20 questions

  1. What does the pH scale measure?

    • How hot a solution becomes when mixed
    • How acidic or alkaline a solution is
    • How many dissolved solids a solution contains
    • How heavy a solution is

  2. What is the pH of a neutral solution at 25 °C?

    • 7
    • 14
    • 0
    • 1

  3. Which pH value shows a strongly acidic solution?

    • 13
    • 1
    • 10
    • 7

  4. Which pH value shows an alkaline solution?

    • 3
    • 7
    • 5
    • 11

  5. Which indicator turns red in acid and blue in alkali?

    • Litmus
    • Universal indicator, which turns green
    • Limewater
    • Phenolphthalein

  6. What colour is phenolphthalein in an alkali?

    • Yellow
    • Green
    • Colourless
    • Pink

  7. Which natural substance can be used as an indicator?

    • Red cabbage juice
    • Distilled water
    • Sugar syrup
    • Tap water

  8. What does universal indicator show?

    • Only whether a solution is acid or alkali
    • A range of colours that match a pH value
    • Only the mass of a solution
    • Only the temperature of a solution

  9. A solution has pH 3. Compared with a solution of pH 5, which is correct?

    • It is a stronger acid, because a lower pH means more acidic
    • It is equally acidic, because both are acids
    • It is neutral, because pH 3 is neutral
    • It is a weaker acid, because a lower pH means less acidic

  10. A lemon juice turns universal indicator red. What is its approximate pH?

    • About 2
    • About 7
    • About 11
    • About 14

  11. Which description of an indicator is correct?

    • A solid that dissolves into a solution to make it acidic when it is added
    • A substance that changes colour depending on whether a solution is acidic or alkaline
    • A metal that reacts with dilute acids to produce hydrogen gas and a metal salt solution
    • A salt that is always neutral in water and so does not change colour at any pH

  12. Why does a larger number on the pH scale mean a more alkaline solution?

    • Because the solution has fewer hydrogen ions
    • Because the solution is heavier
    • Because the solution has more hydrogen ions
    • Because the solution contains more salt

  13. Which pH would a solution of sodium hydroxide most likely have?

    • 5
    • 7
    • 13
    • 2

  14. Which pH would a solution of vinegar most likely have?

    • 12
    • 10
    • 7
    • 3

  15. Why does pH paper change colour when it is dipped into a solution?

    • The paper is heated by the solution and then burns, changing its colour
    • The paper dissolves into the solution and the dissolved paper changes colour
    • The paper reacts with oxygen gas dissolved in the solution and turns colour
    • The indicator dye in the paper reacts with hydrogen ions or hydroxide ions

  16. A solution's pH falls from 9 to 4. What happens to the hydrogen ions?

    • They become zero
    • They decrease in number
    • They stay exactly the same
    • They increase in number

  17. Why does adding an alkali to an acid make the pH rise towards 7?

    • The alkali removes water from the acid so the solution becomes more concentrated
    • The alkali turns the acid into a gas that escapes from the solution quickly
    • The alkali adds more hydrogen ions to the acid so the acid becomes weaker
    • The alkali removes hydrogen ions from the acid as they neutralise each other

  18. A student tests a mixture with universal indicator and it turns orange. Which pH is most likely?

    • About 13
    • About 7
    • About 10
    • About 3 to 4

  19. Which pair correctly describes an acidic and an alkaline solution?

    • Acidic: pH 7, turns litmus purple; alkaline: pH 7, turns litmus purple
    • Acidic: pH 12, turns litmus blue; alkaline: pH 2, turns litmus red
    • Acidic: pH 2, turns litmus blue; alkaline: pH 12, turns litmus red
    • Acidic: pH 2, turns litmus red; alkaline: pH 12, turns litmus blue

  20. Why is a pH meter more accurate than indicator paper for measuring pH?

    • It changes the pH of the solution to exactly 7
    • It gives a precise numerical reading rather than a colour match
    • It only works for solids, not liquids
    • It works without needing to dip anything into the solution

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