From lemon juice to antacid tablets, acids and bases are everywhere. Learn how they behave and how salts are made.
An acid gives hydronium ions (H₃O⁺) in water, and an alkali gives hydroxide ions (OH⁻). The basicity of an acid is the number of hydrogen ions it can give per molecule, and the acidity of a base is the number of hydroxide ions it can give. Indicators and the pH scale show whether a solution is acidic, neutral or alkaline.
What is the basicity of H₂SO₄ and of H₃PO₄?
H₂SO₄ is dibasic (basicity 2) and H₃PO₄ is tribasic (basicity 3)
What colour does methyl orange show in an alkali, and phenolphthalein?
Methyl orange is yellow in an alkali, and phenolphthalein turns pink
What is the pH of a neutral solution, and how does pH differ for an acid and an alkali?
A neutral solution has pH 7; an acid has pH below 7 and an alkali has pH above 7
A salt is formed when the hydrogen of an acid is replaced by a metal or ammonium ion. A normal salt (Na₂SO₄) has all of its replaceable hydrogen replaced, and an acid salt (NaHSO₄) still has some left. Salts can be made by direct combination, displacement, neutralisation or precipitation.
Write the equation for neutralisation of sulphuric acid by sodium hydroxide to give a normal salt.
H₂SO₄ + 2NaOH → Na₂SO₄ + 2H₂O
Which method is used to prepare insoluble AgCl from AgNO₃ and NaCl?
Precipitation (double decomposition): AgNO₃ + NaCl → AgCl + NaNO₃
What happens when blue copper sulphate crystals, CuSO₄·5H₂O, are heated?
They lose their water of crystallisation and turn white, giving anhydrous CuSO₄
1. Define an acid in terms of the ions it produces in water.
2. What is the basicity of H₂SO₄?
3. What colour does methyl orange turn in an alkali?
4. What is the pH of a neutral solution?
5. Name the products of the reaction between NaOH and HCl.
6. Give an example of an acid salt.
7. Name the method used to prepare AgCl from AgNO₃ and NaCl solutions.
8. What happens when hydrated copper sulphate is heated?
9. How does a base differ from an alkali?
10. Why is H₂SO₄ called a dibasic acid?