Acids, Alkalis & pH · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Acids, Alkalis, and the pH Scale

Science · Matter & Materials · ages 12-13
Name ______________________   Date ____________

  1. What pH number counts as exactly neutral, neither acid nor alkali?

    • 0
    • 7
    • 14

  2. Lemon juice tastes sour and has a pH of about 2. What kind of substance is lemon juice?

    • An acid
    • An alkali
    • Neutral

  3. A liquid with lots of hydrogen ions (H⁺) floating in it is more acidic.

    Circle one:   True   False

  4. Bicarbonate of soda dissolved in water has a pH of about 9. Is this solution acidic, alkaline, or neutral?

    01234567891011121314
    • Acidic, because 9 is a small number
    • Alkaline, because 9 is above 7
    • Neutral, because 9 is close to 7

  5. A student dips universal indicator paper into a mystery liquid and it turns deep red. What does the colour tell you?

    • The liquid is a strong acid
    • The liquid is a strong alkali
    • The liquid is neutral

  6. An acid has a pH of 3. Its matching alkali sits the same distance above neutral (7) as the acid sits below it. What is the alkali's pH?

    Answer: ______________

  7. A student slowly adds alkali to an acid until universal indicator shows green, pH 7. What has happened to the mixture?

    • It has turned into a stronger acid
    • It has turned into bleach
    • It has become neutral, acid and alkali balancing out

  8. Priya dips blue litmus paper into vinegar and it turns red. She says this means vinegar is neutral. What is wrong with her thinking?

    • Red litmus paper actually shows an acid, not a neutral liquid
    • Litmus paper cannot be used on vinegar
    • Blue litmus paper always stays blue
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Acids, Alkalis, and the pH Scale W1-mt_AN2kJE6I0s-s1

  1. 7 · 0 and 14 are the extreme ends of the scale. 7 sits in the middle and is neutral.
  2. An acid · A pH of 2 is far below 7, and lemon juice is one of the most common acids in a kitchen.
  3. True · The more H⁺ ions a liquid has, the more acidic it is and the lower its pH number.
  4. Alkaline, because 9 is above 7 · Any pH above 7 is alkaline, and bicarbonate of soda solution sits at about 9.
  5. The liquid is a strong acid · Universal indicator turns red at the acidic end of the scale, so deep red means a strong acid.
  6. 11 · 3 is 4 steps below 7. Adding 4 steps above 7 gives a pH of 11.
  7. It has become neutral, acid and alkali balancing out · Green at pH 7 shows the acid and alkali have balanced each other out, leaving a neutral mixture.
  8. Red litmus paper actually shows an acid, not a neutral liquid · Litmus turning red is the acid signal. A neutral liquid would leave blue litmus paper unchanged.
Worksheet · LightMySky