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Doc Brown's Chemistry  GCSE/IGCSE Science-Chemistry Revision Notes

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

Part 4. Some important REACTIONS of important ACIDS

The reactions of acids with metals, oxides, hydroxides, carbonates and hydrogencarbonates are described and lots of examples of word and symbol equations.

Part 4 Describes and explains the reactions of common acids like hydrochloric acid, sulfuric acid and nitric acid with moderately reactive metals, metal oxides, metal hydroxides,\metal carbonates and aqueous ammonia solution. What is formed in these reactions? Are the products of these reactions of any use?

EQUATION NOTE: The equations are often written three times: (i) word equation, (ii) balanced symbol equation without state symbols, and, (iii) with the state symbols (g), (l), (s) or (aq) to give the complete balanced symbol equation.

GCSE/IGCSE Sub-index: (c) doc b Index of all pH, Acids, Alkalis, Salts Notes 1. Examples of acid-alkali chemistry : 2. pH scale, indicators, ionic theory of acids-alkali neutralisation : 3. pH examples of acid, neutral or alkaline solutions : 4. Acid reactions with metals/oxides/hydroxides/carbonates and neutralisation reactions : 5. Reactions of bases-alkalis like sodium hydroxide : 6. Four methods of making salts : 7. Changes in pH in a neutralisation : 8. Important formulae, salt solubility and water of crystallisation : 9. Further examples of word/symbol equations for salt preparations : 10. More on Acid-Base Theory and Weak and Strong Acids

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

4. Some important reactions of Acids

  • Acids are neutralised by reaction with metals, oxides, hydroxides or carbonates to form salts and other products.

  • Apart from metals (which is an electron loss/gain redox reaction), the other reactants listed above are considered as bases (meaning they react by accepting a proton from an acid). Water soluble bases are known as alkalis.

  • The reaction between acids and bases like oxides, hydroxides and carbonates are called neutralisation reactions.

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REACTION OF ACIDS WITH METALS

  • General word equation: metal + acid ==> a salt + hydrogen

  • e.g. the grey-silvery solid zinc dissolves with effervescence to evolve hydrogen gas and leave a colourless solution of the salt zinc chloride.

    • zinc + hydrochloric acid ==> zinc chloride + hydrogen

    • Zn + 2HCl ==> ZnCl2 + H2

      • Zn(s) + 2HCl(aq) ==> ZnCl2(aq) + H2(g)

    • Its the same equation for many other Group 2 and Transition metals e.g. Mg, Ca and Fe, Co, Ni

      • instead of zinc/Zn in the word/symbol equations

    • Note that hydrochloric acid gives a chloride salt.

    • methods of gas preparation - apparatus, chemicals and equation (c) doc bmethods of gas preparation - apparatus, chemicals and equation (c) doc b

    • Illustrated above are two ways in which the zinc - hydrochloric reaction can be used to prepare a sample of hydrogen gas.

  • A strip of magnesium ribbon dissolves with effervescence to evolve hydrogen gas and leave a colourless solution of the salt magnesium sulphate.

    • magnesium + sulphuric acid ==> magnesium sulphate + hydrogen

    • Mg + H2SO4 ==> MgSO4 + H2

      • Mg(s) + H2SO4(aq) ==> MgSO4(aq) + H2(g)

        •

    • Note that sulphuric/sulfuric gives a sulphate/sulfate salt

    • Similarly ...

    • zinc + sulphuric acid ==> zinc sulphate + hydrogen

    • Zn + H2SO4 ==> ZnSO4 + H2

      • Zn(s) + H2SO4(aq) ==> ZnSO4(aq) + H2(g)

      •

    • Instead of Mg or Zn, you can have Fe

  • (c) doc bYou can test the gas given off with lit splint and the sound of a squeaky pop confirms it to be hydrogen gas AND therefore the original solid was a metal.

    • 2H2 + O2 ==> 2H2O + heat energy!

      • 2H2(g) + O2(g) ==> 2H2O(l)

    • You might see the condensed water on side of test tube when doing this test.

  • Note that nitric acid (HNO3) doesn't usually form hydrogen with a metal, instead you get nasty brown fumes of nitrogen dioxide! but you still get the metal nitrate salt ....

    • so in general ....

    • metal + nitric acid ==> metal nitrate salt + water + nitrogen oxides

  • The reaction of metals with acids is a REDOX reaction and NOT an acid-base reaction.

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REACTION OF ACIDS WITH BASES - basic oxides and hydroxides

These may be alkalis (soluble bases) or water insoluble bases

  • The general word equation for this classic 'neutralisation' reaction is

  • alkali (soluble base ) + acid ==> salt + water

  • metal hydroxide + acid ==> a salt + water

    • e.g.

    • sodium hydroxide + hydrochloric acid ==> sodium chloride + water

    • NaOH + HCl ==> NaCl + H2O

      • NaOH(aq) + HCl(aq) ==> NaCl(aq) + H2O(l)

      •

    • All solutions involved are colourless but the reaction can be monitored using universal indicator or a pH meter.

    • Soluble bases i.e. here, soluble oxides or hydroxides, are called alkalis.

    • soluble salt preparation from soluble base-acid neutralisation

    • This neutralisation reaction is used in salt preparations (see method (a)

  • top sub-indexor  sodium hydroxide + sulphuric acid ==> sodium sulphate + water

    • 2NaOH + H2SO4 ==> Na2SO4 + 2H2O

      • 2NaOH(aq) + H2SO4(aq) ==> Na2SO4(aq) + 2H2O(l)

    • Its the same equation for any Group 1 Alkali Metal hydroxide e.g. LiOH, KOH etc.

      •

    • e.g.

    • potassium hydroxide + nitric acid ==> potassium nitrate + water

    • KOH + HNO3 ==> KNO3 + 2H2O

      • KOH(aq) + HNO3(aq) ==> KNO3(aq) + 2H2O(l)

  • insoluble base + acid ==> salt + water

    • (note: oxides that react with acids to form salts are known as 'basic oxides')

      •

    • e.g. metal oxide + acid ==> salt* + water

    • Black copper (ii) oxide dissolves in colourless sulfuric acid to give a blue solution of copper(II) sulfate from which the salt can be crystallised.

    • copper(II) oxide + sulphuric acid ==> copper(II) sulphate + water

    • CuO + H2SO4 ==> CuSO4 + H2O

      • CuO(s) + H2SO4(aq) ==> CuSO4(aq) + H2O(l)

        •

    • Note that insoluble bases, like these insoluble oxides, although reacting with acids to form salts, are NOT alkalis.

    • Instead of copper/Cu, you can have magnesium/Mg, zinc/Zn or nickel/Ni in the word/symbol equations.

    • soluble salt preparation from insoluble base-acid neutralisationsoluble salt preparation from insoluble base-acid neutralisation

    • This neutralisation reaction is used in salt preparations (see method b)

    • Apart from copper compounds, all solutions involved here are colourless and all the salts form colourless crystal if the solution is carefully evaporated to cause crystallisation.

  • calcium hydroxide + hydrochloric acid ==> calcium chloride + water

    • Ca(OH)2 + 2HCl ==> CaCl2 + 2H2O

      • Ca(OH)2(s) + 2HCl(aq) ==> CaCl2(aq) + 2H2O(l)

  • See also extra examples

  • Apart from copper compounds, all solutions involved here are colourless and all the salts form colourless crystal if the solution is carefully evaporated to cause crystallisation.

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REACTION OF ACIDS WITH CARBONATES or HYDROGEN CARBONATES

  • Contrary to what some textbooks may say, but often do not point out, all carbonates are bases and react with acids to form salts, the difference in reaction with alkalis or insoluble bases is that carbon dioxide gas is evolved.

  • On adding a solid carbonate or hydrogencarbonate to an acid you see effervescence from carbon dioxide gas and the general word equation is ...

    • metal carbonate or hydrogencarbonate + acid ==> a salt + water + carbon dioxide

    • e.g. the white solid calcium carbonate (limestone) dissolves in dilute hydrochloric acid to form a colourless solution of calcium chloride and colourless carbon dioxide gas.

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

      • CaCO3 + 2HCl ==> CaCl2 + H2O + CO2

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

      • methods of gas preparation - apparatus, chemicals and equation (c) doc b  methods of gas preparation - apparatus, chemicals and equation (c) doc b

        •

      • Illustrated above are two ways in which the limestone chips (calcium carbonate) - hydrochloric acid reaction can be used to prepare a sample of carbon dioxide gas.

    • soluble salt preparation from insoluble base-acid neutralisationsoluble salt preparation from insoluble base-acid neutralisation

    • This neutralisation reaction is used in salt preparations (see method b)

    • Apart from copper compounds, all solutions involved here are colourless and all the salts form colourless crystal if the solution is carefully evaporated to cause crystallisation.

      •

  • top sub-indexThe dark turquoise-green solid copper(II) carbonate dissolves in hydrochloric acid to form a greeny-blue solution of copper(II) chloride and effervescence from the carbon dioxide formed.

    • copper(II) carbonate + hydrochloric acid ==> Copper(II) chloride + water + carbon dioxide

      • CuCO3 + 2HCl ==> CuCl2 + H2O + CO2

        • CuCO3(s) + 2HCl(aq) ==> CuCl2(aq) + H2O(l) + CO2(g)

          •

      • and with sulphuric acid a blue solution of copper(II) sulphate is formed.

    • copper(II) carbonate + sulphuric acid ==> Copper(II) sulphate + water + carbon dioxide

      • CuCO3 + H2SO4 ==> CuSO4 + H2O + CO2

        • CuCO3(s) + H2SO4(aq) ==> CuSO4(aq) + H2O(l) + CO2(g)

  • Similarly, but forming colourless solutions from white solid carbonates  ...

    • magnesium carbonate + hydrochloric acid ==> magnesium chloride + water + carbon dioxide

      • MgCO3 + 2HCl ==> MgCl2 + H2O + CO2

        • MgCO3(s) + 2HCl(aq) ==> MgCl2(aq) + H2O(l) + CO2(g)

          •

    • or calcium carbonate + nitric acid ==> calcium nitrate + water + carbon dioxide

      • CaCO3 + 2HNO3 ==> Ca(NO3)2 + H2O + CO2

        • CaCO3(s) + 2HNO3(aq) ==> Ca(NO3)2(aq) + H2O(l) + CO2(g)

    • Its the same equation for many other Group 2 and Transition metals e.g. Mg, Sr and Co, Ni, Cu

      • Test for carbon dioxide gas - it gives a white precipitate of calcium carbonate (cloudiness) when bubbled into limewater (calcium hydroxide solution).

      • Ca(OH)2 + CO2 ==> CaCO3 + H2O

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

    • (c) doc bNote: Using sulphuric acid and calcium carbonate you don't get much of a fizz! because the calcium sulphate salt formed, is not very soluble, and coats the remaining calcium carbonate inhibiting the reaction! This will happen with any reaction between an acid and a water insoluble reactant which forms an insoluble solid product!

  • magnesium carbonate + sulphuric acid ==> magnesium sulphate + water + carbon dioxide

    • MgCO3 + H2SO4 ==> MgSO4 + H2O + CO2

      • MgCO3(s) + H2SO4(aq) ==> MgSO4(aq) + H2O(l) + CO2(g)

        •

  • AND six equations for sodium carbonate and sodium hydrogencarbonate, in each case the white solid of the hydrogencarbonate dissolves to give a colourless solution of the colourless salt with the evolution of carbon dioxide gas e.g....

    • sodium hydrogencarbonate + hydrochloric acid ==> sodium chloride + water + carbon dioxide

      • NaHCO3 + HCl ==> NaCl + H2O + CO2

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

          •

    • sodium hydrogencarbonate + nitric acid ==> sodium nitrate + water + carbon dioxide

      • NaHCO3 + HNO3 ==> NaNO3 + H2O + CO2

        • NaHCO3(s) + HNO3(aq) ==> NaNO3(aq) + H2O(l) + CO2(g)

    • top sub-indexsodium carbonate + hydrochloric acid ==> sodium chloride + water + carbon dioxide

      • Na2CO3 + 2HCl ==> 2NaCl + H2O + CO2

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

    • sodium hydrogencarbonate + sulphuric acid ==> sodium sulphate + water + carbon dioxide

      • 2NaHCO3 + H2SO4 ==> Na2SO4 + 2H2O + 2CO2

        • 2NaHCO3(s) + H2SO4(aq) ==> Na2SO4(aq) + 2H2O(l) + 2CO2(g)

    • sodium carbonate + sulfuric acid ==> sodium sulfate + water + carbon dioxide

      • Na2CO3 + H2SO4 ==> Na2SO4 + H2O + CO2

        • Na2CO3(s) + H2SO4(aq) ==> Na2SO4(aq) + H2O(l) + CO2(g)

    • sodium carbonate + nitric acid ==> sodium nitrate + water + carbon dioxide

      • Na2CO3 + 2HNO3 ==> 2NaNO3 + H2O + CO2

        • Na2CO3(s) + 2HNO3(aq) ==> 2NaNO3(aq) + H2O(l) + CO2(g)

  • test for CO2You can test the gas given off with limewater and the formation of a white precipitate confirms it to be carbon dioxide AND therefore the original solid was a carbonate or hydrogencarbonate.

  • For more reactions of acids and carbonates see Limestone Chemistry page

 

REACTIONS OF ACIDS WITH AMMONIA

  • Ammonia gas is very soluble in water to form an alkaline solution that can be neutralised by acids to form ammonium salts. All solutions involved here are colourless and all the salts form colourless crystal if the solution is carefully evaporated to cause crystallisation.

  • ammonia + acid ==> ammonium salt

    • Note that no water is formed and see also note (c) below.

    • e.g. (i) ammonia + hydrochloric acid ==> ammonium chloride

      • NH3 + HCl ==> NH4Cl

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

          •

    • or (ii) ammonia + nitric acid ==> ammonium nitrate

      • NH3 + HNO3 ==> NH4NO3

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

    • or (iii) ammonia + sulphuric acid ==> ammonium sulphate

      • 2NH3 + H2SO4 ==> (NH4)2SO4

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

  • NOTE that

    • (a) NH3 is used in equations, NOT NH4OH which doesn't exist!

    • (b) All these ammonium salts are colourless crystalline solids - formed if the water is carefully evaporated salt preparations (see method a)

    • (c) Reactions (ii) and (iii) are used to make fertiliser salts - see ammonia chemistry and uses.

  • -

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NOTE (a): As already mentioned, and to summarise, the name of the particular salt formed depends on (i) the metal name, which becomes the first part of salt name, and (ii) the acid e.g. H2SO4 sulphuric acid on neutralisation makes a ... sulphate; HCl hydrochloric acid makes a ... chloride;  HNO3 nitric acid makes a ... nitrate etc.

NOTE (b): There is a list of compound formulae and their solubility in section 8. The first part of the salt name is ammonium derived from ammonia (with metals or their compounds the metal retains its original name), but the second part of the salt name is always derived from the acid as in NOTE (a) above.

NOTE (c): Ammonia is an alkaline gas that is very soluble in water. It is a weak alkali or soluble base and is readily neutralised by acids in solution to form ammonium salts which can be crystallised on evaporating the resulting solution. Sometimes the equations are written with the 'fictitious' 'ammonium hydroxide'

e.g. NH4OH(aq) + HCl(aq) ==> NH4Cl(aq) + H2O(l)

but this is not considered to be a correct representation of this neutralisation reaction these days.

NOTE (d): There are more equations in section 9. and an extensive structured question on acid reaction equations.

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keywords equations: Zn + 2HCl ==> ZnCl2 + H2 * Mg + H2SO4 ==> MgSO4 + H2 * NaOH + HCl ==> NaCl + H2O * 2NaOH + H2SO4 ==> Na2SO4 + 2H2O * NaOH + HNO3 ==> NaNO3 + 2H2O * CuO + H2SO4 ==> CuSO4 + H2O * Ca(OH)2 + 2HCl ==> CaCl2 + 2H2O * CaCO3 + 2HNO3 ==> Ca(NO3)2 + H2O + CO2  * MgCO3 + H2SO4 ==> MgSO4 + H2O + CO2  * NaHCO3 + HNO3 ==> NaNO3 + H2O + MgCO3 + 2HCl ==> MgCl2 + H2O + CO2  * MgCO3 + 2HCl ==> MgCl2 + H2O + CO2  * CuCO3 + H2SO4 ==> CuSO4 + H2O + CO2  * NaHCO3 + HCl ==> NaCl + H2O + CO2 * NaHCO3 + HNO3 ==> NaNO3 + H2O + CO2 * NH3 + HCl ==> NH4Cl * NH3 + HNO3 ==> NH4NO3 * 2NH3 + H2SO4 ==> (NH4)2SO4 * NOT NH4OH * Zn + 2HCl ==> ZnCl2 + H2 * Mg + H2SO4 ==> MgSO4 + H2 * NaOH + HCl ==> NaCl + H2O * 2NaOH + H2SO4 ==> Na2SO4 + 2H2O * NaOH + HNO3 ==> NaNO3 + 2H2O * CuO + H2SO4 ==> CuSO4 + H2O * Ca (OH)2 + 2HCl ==> CaCl2 + 2H2O * CaCO3 + 2HNO3 ==> Ca(NO3)2 + H2O + CO2 * MgCO3 + H2SO4 ==> MgSO4 + H2O + CO2 * NaHCO3 + HNO3 ==> NaNO3 + H2O + MgCO3 + 2HCl ==> MgCl2 + H2O + CO2 * MgCO3 + 2HCl ==> MgCl2 + H2O + CO2 * CuCO3 + H2SO4 ==> CuSO4 + H2O + CO2 * NaHCO3 + HCl ==> NaCl + H2O + CO2 * NaHCO3 + HNO3 ==> NaNO3 + H2O + CO2 * NH3 + HCl ==> NH4Cl * NH3 + HNO3 ==> NH4NO3 * 2NH3 + H2SO4 ==> (NH4)2SO4 * NOT NH4OH * Zn + H2SO4 ==> ZnSO4 + H2 * CuCO3 + H2SO4 ==> CuSO4 + H2O + CO2  * NaHCO3 + HCl ==> NaCl + H2O + CO2 * NaHCO3 + HNO3 ==> NaNO3 + H2O + CO2 * Na2CO3 + 2HCl ==> 2NaCl + H2O + CO2 * 2NaHCO3 + H2SO4 ==> Na2SO4 + 2H2O + 2CO2 * Na2CO3 + H2SO4 ==> Na2SO4 + H2O + CO2 * Na2CO3 + 2HNO3 ==> 2NaNO3 + H2O + CO2 * Zn + H2SO4 ==> ZnSO4 + H2 * CuCO3 + H2SO4 ==> CuSO4 + H2O + CO2 * NaHCO3 + HCl ==> NaCl + H2O + CO2 * NaHCO3 + HNO3 ==> NaNO3 + H2O + CO2 * Na2CO3 + 2HCl ==> 2NaCl + H2O + CO2 * 2NaHCO3 + H2SO4 ==> Na2SO4 + 2H2O + 2CO2 * Na2CO3 + H2SO4 ==> Na2SO4 + H2O + CO2 * Na2CO3 + 2HNO3 ==> 2NaNO3 + H2O + CO2 *

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