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1. Acid reactions with metals

Acids react with metals to produce a salt and hydrogen.

acid + metal → salt + hydrogen

Example:

hydrochloric acid + magnesium → magnesium chloride + hydrogen

2HCl(aq) + Mg(s) → MgCl₂(aq) + H₂(g)

Observations: grey solid magnesium disappears, colourless solution produced, heat released, bubbles.

The hydrogen in these reactions can be tested. The test for hydrogen is:

• apply a lighted splint
• a popping sound results

2. Acid reactions with bases - neutralisation

Acids react with bases to form a salt and water.

acid + base → salt + water

Example:

sulfuric acid + copper(II) oxide → copper(II) sulfate + water

H₂SO₄(aq) + CuO(s) → CuSO₄(aq) + H₂O(l)

Observations: black solid copper(II) oxide disappears, blue solution produced.

3. Acid reactions with carbonates and hydrogencarbonates

Acids react with metal carbonates and hydrogencarbonates in the same way. These reactions produce salt, water and carbon dioxide.

acid + carbonate → salt + water + carbon dioxide

or

acid + hydrogencarbonate → salt + water + carbon dioxide

Example - carbonate:

hydrochloric acid + copper(II) carbonate → copper(II) chloride + water + carbon dioxide

2HCl(aq) + CuCO₃(s) → CuCl₂(aq) + H₂O(l) + CO₂(g)

Observations: green solid copper(II) carbonate disappears, blue solution produced, heat released, bubbles.

Example - hydrogencarbonate:

hydrochloric acid + sodium hydrogencarbonate → sodium chloride + water + carbon dioxide

HCl(aq) + NaHCO₃ (s) → NaCl(aq) + H₂O(l) + CO₂(g)

Observations: solid white sodium hydrogencarbonate disappears, colourless solution produced, bubbles.

The carbon dioxide gas produced in these reactions can be tested. The test for carbon dioxide is:

• bubble gas into colourless limewater (calcium hydroxide solution)
• the solution will change from colourless to milky if the gas is carbon dioxide