Acids produce H+ ions in aqueous solution.
HCl → H⁺ + Cl⁻
Acid solutions have pH values less than 7. The lower the pH, the stronger the acid.
Strong Acids
A strong acid is one, which can completely dissociate its H+ ions in water. This means that it can give off the greatest number of hydrogen ions when placed in solution.
e.g. HCl, H₂SO₄
Weak Acids
A weak acid is one, which does not completely dissociate its H+ ions in water. This means that it does not give off many hydrogen ions when placed in solution.
e.g. ethanoic acid, citric acid
ACID REACTIONS
Acid + Metals
Acids react with a metal to form a salt and hydrogen gas. This is a redox reaction.
Acid + Metal → Salt + Hydrogen gas
E.g. 2HCl + Fe → FeCl₂ + H₂
Hydrogen’s oxidation number in HCl = +I
Hydrogen’s oxidation number in H₂ = 0
Since Hydrogen gains electrons, it is reduced.
Iron’s oxidation number in Fe = 0
Iron’s oxidation number in FeCl₂ = +2
Since Iron loses electrons, it is oxidised.
Since reduction and oxidation occurs at the same time, this reaction is a redox reaction.
Acid + Metal oxides
Acids react with a metal oxides to form a salt and water.
Acid + Metal Oxide → Salt + Water
E.g. 2HCl + CaO -> CaCl₂ + H₂O
Acid + Alkali
Acids react with alkali to form a salt and water.
Acid + Alkali → Salt + Water
E.g. HCl + NaOH -> NaCl + H₂O
This is a neutralisation reaction.
Acid + Carbonate
Acids react with carbontes to form a salt, water and carbon dioxide.
Acid + Carbonate → Salt + Water + Carbon dioxide
E.g. 2HCl + CaCO₃ -> CaCl₂ + H₂O + CO₂
