Answers section

Answers to Questions 5.3.3

1. Substance	Observation when a few drops of 2M sulphuric (VI) acid is added to the substance	Equation of the reaction
   Blue litmus solution		xxxxxxxx
   Zinc granules	Bubbles of a colourless, odourless gas that extinguishes a burning wooden splint with a pop sound. A colourless solution is formed	Zn(s) + H2SO4(aq) → ZnSO4(aq) + H2(g)
   2M sodium hydroxide solution	A colourless solution with no observable effect on litmus paper if both the substance and acid are completely reacted	2NaOH(aq) + H2SO4(aq) → Na2SO4(aq) + H2O(l)
   Iron (II) oxide	The black solid oxide dissolves to form a pale green solution.	FeO(s) + H2SO4(aq) → FeSO4(aq) + H2O(l)
   Copper (II) carbonate powder	Effervescence, occurs; a colourless, odourless gas that turns wet blue litmus pink and lime water cloudy is forms. A blue solution is formed	CuCO3(s) + H2SO4(aq) → CuSO4(aq) + H2O(l) + CO2(g)
   Sodium hydrogencarbonate	Vigorous effervescence, occurs; a colourless, odourless gas that turns wet blue litmus pink and forms a white precipitate with calcium hydroxide solution is produced.	2NaHCO3(aq) + H2SO4(aq) → Na2SO4(aq) + 2H2O(l) + 2CO2(g)
   Potassium sulphite	Effervescence, occurs; a colourless gas with a pungent smell, and which turns blue litmus red then bleaches it is formed.	K2SO3(aq) + H2SO4(aq)→ K2SO4(aq) + 2H2O(l) + SO2(g)



2. In dilute solutions, sulphuric acid is completely dissociated into ions; so it has a high concencentration of H⁺ and is therefore strong. But concentrated (VI) acid exists as undissociated molecules (H₂SO₄(l)), with virtually no hydrogen ions; so it is weak.