5. IMPORTANT REACTIONS OF

COMMON BASES - ALKALIS

e.g. sodium hydroxide and ammonia

Doc Brown's Chemistry  GCSE/IGCSE/O level Science–Chemistry Revision Notes

pH scale of acidity and alkalinity, acids, bases–alkalis, salts and neutralisation

Part 5. Some important reactions of Bases (alkali = soluble base)

Part 5 Apart from the reactions with acids, this section also covers in detail other reactions of bases (acid reactions are covered in Part 4) with other chemicals e.g. the reaction of the alkali sodium hydroxide with ammonium salts, carbon dioxide and metals salts to give hydroxide precipitates. Word and symbol equations are given for the reaction of the base sodium hydroxide with ammonium salts. Word and symbol equations are given for the formation of metal hydroxide precipitates when sodium hydroxide is added to solutions of soluble metal salts.

 These revision notes on the reactions of soluble bases (alkalis) and insoluble bases should prove useful for the new AQA chemistry, Edexcel chemistry & OCR chemistry GCSE (9–1, 9-5 & 5-1) science courses.

GCSE/IGCSE Acids & Alkalis revision notes sub–index: Index of all pH, Acids, Alkalis, Salts Notes 1. Examples of everyday acids, alkalis, salts, pH of solution, hazard warning signs : 2. pH scale, indicators, ionic theory of acids–alkali neutralisation : 4. Reactions of acids with metals/oxides/hydroxides/carbonates, neutralisation reactions : 5. Reactions of bases–alkalis like ammonia & sodium hydroxide : 6. Four methods of making salts : 7. Changes in pH in a neutralisation, choice and use of indicators : 8. Important formulae of compounds, salt solubility and water of crystallisation : 10. More on Acid–Base Theory and Weak and Strong Acids

See also Advanced Level Chemistry Students Acid–Base Revision Notes – use index

5. Some important reactions of Bases (alkali = soluble base)

Bases, both soluble and insoluble, react with acids to form salts. Such base may be metal oxides, metal hydroxides, metal carbonates and ammonia. Alkalis (soluble bases) include soluble metal hydroxides, soluble metal carbonates and ammonia.

  • Neutralisation of bases with acids is dealt with Part 4, so Part 5 mainly concentrates on other reactions of bases.

    • BUT a few examples wouldn't go amiss here e.g

      • (soluble base) potassium hydroxide + hydrobromic acid ==> potassium bromide + water

        • KOH(aq) + HBr(aq) ==> KBr(aq) + H2O(l)

      • (insoluble base) magnesium hydroxide + hydrochloric acid ==> magnesium chloride + water

        • Mg(OH)2(s) + 2HCl(aq) ==> MgCl2(aq) + 2H2O(l)

      • (soluble, alkali) ammonia + nitric acid ==> ammonium nitrate

        • NH3 + HNO3 ==> NH4NO3

          • NH3(aq) + HNO3(aq) ==> NH4NO3(aq)

          Similarly ...

          ammonia + hydrochloric acid ==> ammonium chloride

          • NH3 + HCl ==> NH4Cl

            • NH3(aq) + HCl(aq) ==> NH4Cl(aq)

          and

          ammonia + sulphuric acid ==> ammonium sulphate

          • 2NH3 + H2SO4 ==> (NH4)2SO4

            • 2NH3(aq) + H2SO4(aq) ==> (NH4)2SO4(aq)

      • (insoluble base) zinc oxide + hydrochloric acid ==> zinc chloride + water

        • ZnO(s) + 2HCl(aq) ==> ZnCl2(aq) + H2O(l)

      • (insoluble) calcium carbonate + hydrochloric acid ==> calcium chloride + water + carbon dioxide

        • CaCO3(s) + 2HCl(aq) ==> CaCl2(aq)+ H2O(l) + CO2(g)

      • (soluble) sodium carbonate + hydrochloric acid ==> sodium chloride + water + carbon dioxide

        • Na2CO3(s) + 2HCl(aq) ==> 2NaCl(aq) + H2O(l) + CO2(g)

      • (slightly soluble) sodium hydrogencarbonate + hydrochloric acid ==> sodium chloride + water + carbon dioxide

        • NaHCO3(s) + HCl(aq) ==> NaCl(aq) + H2O(l) + CO2(g)

  • Reaction of sodium hydroxide with ammonium salts

  • Ammonium salts are decomposed when mixed with a strong base e.g. the alkali sodium hydroxide produces ammonia gas  ...

    • (i) sodium hydroxide + ammonium chloride ==> sodium chloride + water + ammonia

      • NaOH(aq) + NH4Cl(aq) ==> NaCl(aq) + H2O(l) + NH3(g)

    • (ii) sodium hydroxide + ammonium nitrate ==> sodium nitrate + water + ammonia

      • NaOH(aq) + NH4NO3(aq) ==> NaNO3(aq) + H2O(l) + NH3(g)

    • (iii) sodium hydroxide + ammonium sulfate ==> sodium sulfate + water + ammonia

      • 2NaOH(aq) + (NH4)2SO4(aq) ==> Na2SO4(aq) + 2H2O(l) + 2NH3(g)

    • The ammonia is readily detected by its pungent odour (strong smell) and by turning damp red litmus blue.

    • The ionic equation for all three reactions is:

      • NH4+(aq) + OH(aq) ==> H2O(l) + NH3(g)

    • This reaction can be used to prepare ammonia gas and as a simple chemical test for an ammonium salt.

  • Use of limestone and lime to control soil acidity is dealt with in the 1st section on the Extra Industrial Chemistry page.

  • Alkali's (soluble bases) are used to produce the insoluble hydroxide precipitates of many metal ions from their soluble salt solutions.

    • (aq) indicates soluble, (s) indicates insoluble - precipitate formed e.g.

    • sodium hydroxide + copper(II) sulphate ==> sodium sulphate + copper(II) hydroxide

    • 2NaOH(aq) + CuSO4(aq) ==> Na2SO4(aq) + Cu(OH)2(s) a blue precipitate

    • ionically: Cu2+(aq) + 2OH(aq) ==>  Cu(OH)2(s) 

    • This reaction can be used as a simple test to help identify certain metal ions.

  • Aqueous solutions of alkalis like sodium hydroxide ('caustic soda') and calcium hydroxide ('limewater') react with the acidic gas carbon dioxide to form carbonate compounds if the gas is bubbled into their solutions.

    • There are two possible reactions with sodium hydroxide and carbon dioxide

    • (i) sodium hydroxide + carbon dioxide ==> sodium hydrogen carbonate + water

      • NaOH(aq) + CO2(g)  ==> NaHCO3(aq)

    • (ii) sodium hydroxide + carbon dioxide ==> sodium carbonate + water

      • 2NaOH(aq) + CO2(g)  ==> Na2CO3(aq) + H2O(l)

      • This reaction can be used to remove carbon dioxide gas from a mixture of gases.

    • The reaction with 'limewater' is ...

    • calcium hydroxide + carbon dioxide ==> calcium carbonate + water

      • Ca(OH)2(aq) + CO2(g) ==> CaCO3(s) + H2O(l)

      • The formation of the white precipitate of calcium carbonate is used as a test for the gas carbon dioxide.

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describe with equations the reactions of ammonia with acids, describe with equations the reactions of sodium hydroxide with acids, describe with equations the reaction of sodium hydroxide with ammonium salts keywords formula equations: NaOH(aq) + NH4Cl(aq) ==> NaCl(aq) + H2O(l) + NH3(g) * NaOH(aq) + NH4NO3(aq) ==> NaNO3(aq) + H2O(l) + NH3(g) * 2NaOH(aq) + (NH4)2SO4(aq) ==> Na2SO4(aq) + 2H2O(l) + 2NH3(g) * NH4+(aq) + OH–(aq) ==> H2O(l) + NH3(g) * 2NaOH(aq) + CuSO4(aq) ==> Na2SO4(aq) + Cu(OH)2(s) * NaOH(aq) + CO2(g) ==> NaHCO3(aq) * 2NaOH(aq) + CO2 (g) ==> Na2CO3(aq) + H2O(l) * Ca(OH)2(aq) + CO2(g) ==> CaCO3(s) + H2O(l) * NaOH + NH4Cl ==> NaCl + H2O + NH3 * NaOH + NH4NO3 ==> NaNO3 + H2O + NH3 * 2NaOH + (NH4)2SO4 ==> Na2SO4 + 2H2O + 2NH3 * NH4+ + OH– ==> H2O + NH3 * 2NaOH + CuSO4 ==> Na2SO4 + Cu(OH)2 * NaOH + CO2 ==> NaHCO3 * 2NaOH + CO2 ==> Na2CO3 + H2O * Ca(OH)2 + CO2 ==> CaCO3 + H2O  Revision KS4 Science GCSE/IGCSE/O level Chemistry Information Study Notes for revising for AQA GCSE Science, Edexcel Science Chemistry IGCSE Chemistry & OCR 21st Century Science Chemistry, OCR Gateway Science Chemistry, WJEC gcse science chemistry CCEA/CEA gcse science chemistry (revise science chemistry courses equal to US grade 8, grade 9 grade 10. Revision notes on acids, bases, alkalis, salts, solution pH word equations balanced symbol equations science chemistry courses revision guides gcse chemistry revision free detailed notes on reactions of bases and alkalis with acids to help revise igcse chemistry igcse chemistry revision notes on reactions of bases and alkalis with acids O level chemistry revision free detailed notes on reactions of bases and alkalis with acids to help revise gcse chemistry free detailed notes on reactions of bases and alkalis with acids to help revise O level chemistry free online website to help revise reactions of bases and alkalis with acids for gcse chemistry  free online website to help revise reactions of bases and alkalis with acids for igcse chemistry free online website to help revise O level reactions of bases and alkalis with acids chemistry how to succeed in questions on reactions of bases and alkalis with acids for gcse chemistry how to succeed at igcse chemistry how to succeed at O level chemistry a good website for free questions on reactions of bases and alkalis with acids to help to pass gcse chemistry questions on reactions of bases and alkalis with acids a good website for free help to pass igcse chemistry with revision notes on reactions of bases and alkalis with acids a good website for free help to pass O level chemistry

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