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Lesson 9 of 10

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Seven quick questions, one for each lesson. Use the table if you get stuck.

Acids, Bases and Salts — what each reading tells you
IdeaRemember
The shelf againBlue turning red names an acid. Red turning blue names a base. Neither strip moving names a neutral substance.
What acids shareEvery acid frees H⁺ ions in water. A base that dissolves in water frees OH⁻ ions.
Metals and carbonatesA dilute acid with a reactive metal gives a salt and hydrogen. An acid with a carbonate gives a salt, water and carbon dioxide.
The pH scaleUsually, pH runs from 0 to 14. Below 7 is acidic, 7 is neutral, above 7 is basic. A lower pH means more H⁺.
Living windowsA living thing keeps its own narrow pH window. One reading can be fine in one place. It can be trouble in another.
NeutralisationAn acid and a base give a salt and water. The same two solutions always neutralise in the same ratio.
Crystals with waterHeat drives the crystal's held water out and leaves a different substance. Adding water brings the first substance back.

A liquid leaves the blue strip blue. It turns the red strip blue. What is it?

  • Neutral — the blue strip did not change
  • A base — the red strip turned blue
  • An acid — a blue strip that stays blue means acid

Glucose has hydrogen in its formula. Why is it not an acid?

  • It frees no H⁺ ions in water
  • It has too little hydrogen
  • It does not dissolve in water

Baking soda fizzes in dilute acid. The gas is tested. Which gas is it?

  • Hydrogen — it burns with a pop
  • Oxygen — it makes a glowing splint burn brighter
  • Carbon dioxide — it turns lime water milky

Solution P has pH 2. Solution Q has pH 5. Which has more H⁺ ions?

  • Q — 5 is the bigger number
  • Both — they are both acidic, so equal
  • P — a lower pH means more H⁺

After sweets, a mouth reads pH 5.2. What can happen?

  • Enamel starts to wear — the pH is below 5.5
  • Nothing — it is still close to neutral
  • The mouth turns basic — bacteria make a base

6 mL of acid neutralises 9 mL of a base. How much acid neutralises 18 mL of that base?

  • 6 mL — it is the same acid, so the same volume
  • 12 mL — double the base needs double the acid
  • 9 mL — the acid matches the base

Blue crystals turn white on heating. Water turns them blue again. What did the heat drive out?

  • Loose dampness from outside
  • Some of the blue colour, a dye added to it
  • Water of crystallisation, built into the crystal

Chapter 2 is in your Class 10 book, Science. It is Acids, Bases and Salts. It goes further into each idea.

Next comes Metals and Non-metals. It opens with the same shelf.

Reveal every answer to finish this lesson.