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Chemical Changes

Acids, alkalis and the pH scale

  • 3 things to know
  • Paper 1

Overview

The hydrogen ions released by acids and hydroxide ions released by alkalis, the ions in sodium hydroxide and sulfuric acid solutions, and the pH values of acidic, neutral and alkaline solutions.

What you need to know

Answer each one before you reveal it.

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Key term

Which ion do all acids release when they dissolve in water?

Key term

Which ion is released into solution when an alkali dissolves in water?

Key term

Name the ion responsible for the acidic behaviour of a solution of hydrochloric acid.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Which ion do all acids release when they dissolve in water?

    Model answer

    Acids release hydrogen ions, H⁺, into the solution.

  2. 2

    Which ion is released into solution when an alkali dissolves in water?

    Model answer

    An alkali releases hydroxide ions, OH⁻, into the solution.

  3. 3

    Name the ion responsible for the acidic behaviour of a solution of hydrochloric acid.

    Model answer

    The hydrogen ion, H⁺, is responsible for its acidic behaviour.

  4. 4

    Name the two ions formed when sodium hydroxide dissolves in water.

    Model answer

    It forms sodium ions, Na⁺, and hydroxide ions, OH⁻.

  5. 5

    Explain why hydrogen chloride only behaves as an acid once it has dissolved in water.

    Model answer

    Only in solution does it release hydrogen ions, and these ions are what make a solution acidic.

  6. 6

    Name the two ions present in an aqueous solution of sulfuric acid.

    Model answer

    Hydrogen ions, H⁺, and sulfate ions, SO₄²⁻, are present.

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Key Concepts in Chemistry
States of Matter and Mixtures
Chemical Changes
Extracting Metals and Equilibria

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A holds the acid.
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AChlorine is a pale green gas at room temperature.
BBromine is a red-brown liquid at room temperature.
CIodine is a dark grey solid at room temperature.

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