6.4 - Chemical Properties of Acids and Alkalis

Chemical Properties of Acids

Reaction	General products / Example
Acid + base	Salt + water; $2HN{\mathrm{O}}_3(\mathrm{aq})+\mathrm{CuO}(\mathrm{s})\to \mathrm{Cu}(\mathrm{N}{\mathrm{O}}_3{)}_2(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$
Acid + reactive metal	Salt + hydrogen; ${\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4(\mathrm{aq})+\mathrm{Zn}(\mathrm{s})\to \mathrm{ZnS}{\mathrm{O}}_4(\mathrm{aq})+{\mathrm{H}}_2(\mathrm{g})$
Acid + metal carbonate	Salt + water + carbon dioxide; $2HCl(\mathrm{aq})+\mathrm{CaC}{\mathrm{O}}_3(\mathrm{s})\to \mathrm{CaC}{\mathrm{l}}_2(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})+\mathrm{C}{\mathrm{O}}_2(\mathrm{g})$

Reaction observations:

• Acid + base: Warm sulphuric acid; add copper(II) oxide until excess; filter; concentrate the blue copper(II) sulphate filtrate; cool, filter, rinse and dry the crystals.
• Acid + reactive metal: Add zinc to hydrochloric acid. Hydrogen gives a pop with a lighted splinter. Add zinc to excess, filter, concentrate, cool, filter, rinse and dry the zinc chloride crystals.
• Acid + metal carbonate: React marble chips with nitric acid. Effervescence occurs; the gas turns limewater cloudy, confirming $\mathrm{C}{\mathrm{O}}_2$; calcium nitrate remains in solution.

Chemical Properties of Alkalis

Reaction	General products / Example
Alkali + acid	Salt + water; $2KOH(\mathrm{aq})+{\mathrm{H}}_2\mathrm{S}{\mathrm{O}}_4(\mathrm{aq})\to {\mathrm{K}}_2\mathrm{S}{\mathrm{O}}_4(\mathrm{aq})+2{\mathrm{H}}_2\mathrm{O}(\mathrm{l})$
Alkali + ammonium salt, heated	Salt + water + ammonia; $\mathrm{KOH}(\mathrm{aq})+\mathrm{N}{\mathrm{H}}_4\mathrm{Cl}(\mathrm{aq})\to \mathrm{KCl}(\mathrm{aq})+{\mathrm{H}}_2\mathrm{O}(\mathrm{l})+\mathrm{N}{\mathrm{H}}_3(\mathrm{g})$
Alkali + metal ion	Insoluble metal hydroxide + alkali cation; $2NaOH(\mathrm{aq})+\mathrm{M}{\mathrm{g}}^{2+}(\mathrm{aq})\to \mathrm{Mg}(\mathrm{OH}{)}_2(\mathrm{s})+2N{\mathrm{a}}^{+}(\mathrm{aq})$

Reaction observations:

• React sodium hydroxide with benzoic acid, filter excess acid and evaporate the filtrate to obtain salt crystals.
• Heat sodium hydroxide with ammonium chloride; ammonia turns moist red litmus blue.
• Add sodium hydroxide to copper(II) sulphate; a blue insoluble copper(II) hydroxide precipitate forms.