Neutralisation and ionic compounds

Neutralisation and Ionic Equations

Key Definitions

  • Neutralisation Reaction: A chemical reaction in which an acid and a base react to form water and a salt.

  • Acids: Substances that release hydrogen ions (H+) when dissolved in water.

  • Alkalis: Substances that release hydroxide ions (OH-) when dissolved in water.

  • Salt: A substance formed from the neutralisation reaction between an acid and a base.

Common Ions Produced from Acids and Their Salts

  1. Acids and Their Common Salts:

    • Nitric Acid → makes Nitrate Salts

    • Hydrochloric Acid → makes Chloride Salts

    • Sulphuric Acid → makes Sulphate Salts

Acids in Water

  • Acids are completely soluble in water and dissociate into ions:

    • The dissociation examples are:

    • Hydrochloric Acid:
      ext{HCl (aq)}
      ightarrow ext{H}^+ (aq) + ext{Cl}^- (aq)

    • Nitric Acid:
      ext{HNO}3 (aq) ightarrow ext{H}^+ (aq) + ext{NO}3^- (aq)

    • Sulphuric Acid:
      ext{H}2 ext{SO}4 (aq)
      ightarrow 2 ext{H}^+ (aq) + ext{SO}_4^{2-} (aq)

  • Definition: Acids release H+ ions in solution.

Alkalis in Water

  • Alkalis are alkaline chemicals that are soluble and dissociate into ions:

    • The dissociation examples are:

    • Sodium Hydroxide:
      ext{NaOH (aq)}
      ightarrow ext{Na}^+ (aq) + ext{OH}^- (aq)

    • Calcium Hydroxide:
      ext{Ca(OH)}_2 (aq)
      ightarrow ext{Ca}^{2+} (aq) + 2 ext{OH}^- (aq)

    • Ammonia:
      ext{NH}3 (aq) + ext{H}2 ext{O} (l)
      ightarrow ext{NH}_4^+ (aq) + ext{OH}^- (aq)

  • Definition: Alkalis release OH- ions in solution.

General Neutralisation Reactions

  1. Acid + Metal Hydroxide → Salt + Water

  2. Acid + Metal Oxide → Salt + Water

  3. Acid + Metal Carbonate → Salt + Water + Carbon Dioxide

  4. Acid + Metal → Salt + Hydrogen

Identification of Spectator Ions

  • Spectator ions are ions that do not participate in the actual chemical reaction but are present in the solution. In ionic equations, they are removed.

Solubility of Salts

Soluble Salts:

  • Sodium, potassium, ammonium salts: All soluble

  • Nitrates: All soluble

  • Chlorides: Mostly soluble (except Silver Chloride and Lead Chloride)

  • Sulphates: Mostly soluble (except Lead Sulphate, Barium Sulphate, Calcium Sulphate)

Insoluble Salts:

  • Carbonates: Mostly insoluble (except Sodium, Potassium, Ammonium Carbonates)

  • Hydroxides: Mostly insoluble (except Sodium, Potassium, Ammonium Hydroxides)

Ionic Formulae and Dissociation Examples

  • For the following chemicals:

    1. Hydrochloric Acid (HCl) → ext{H}^+ (aq) + ext{Cl}^- (aq)

    2. Nitric Acid (HNO3) → ext{H}^+ (aq) + ext{NO}_3^- (aq)

    3. Sulphuric Acid (H₂SO₄) → 2 ext{H}^+ (aq) + ext{SO}_4^{2-} (aq)

    4. Sodium Hydroxide (NaOH) → ext{Na}^+ (aq) + ext{OH}^- (aq)

    5. Calcium Hydroxide (Ca(OH)₂) → ext{Ca}^{2+} (aq) + 2 ext{OH}^- (aq)

    6. Sodium Chloride (NaCl) → ext{Na}^+ (aq) + ext{Cl}^- (aq)

Ionic Equations for Neutralisation

  • Full Ionic Equation of Hydrochloric Acid and Sodium Hydroxide:

    • ext{HCl (aq)} + ext{NaOH (aq)}
      ightarrow ext{NaCl (aq)} + ext{H}_2 ext{O (l)}

    • Full ionic equation:
      ext{H}^+ + ext{Cl}^- + ext{Na}^+ + ext{OH}^-
      ightarrow ext{Na}^+ + ext{Cl}^- + ext{H}_2 ext{O}

    • Ionic Equation (spectator ions removed):
      ext{H}^+ + ext{OH}^-
      ightarrow ext{H}_2 ext{O}

Writing Ionic Equations for Reactions

  • Task Examples: Write ionic equations for the following:

    1. ext{HNO}3 (aq) + ext{NaOH (aq)} ightarrow ext{NaNO}3 (aq) + ext{H}_2 ext{O (l)}

    2. 2 ext{HCl (aq)} + ext{Ca(OH)}2 (aq) ightarrow ext{CaCl}2 (aq) + 2 ext{H}_2 ext{O (l)}

    3. ext{H}2 ext{SO}4 (aq) + 2 ext{KOH (aq)}
      ightarrow ext{K}2 ext{SO}4 (aq) + 2 ext{H}_2 ext{O (l)}

Important Notes on Ionic Equations

  • The ionic equation for the neutralisation of an acid and alkali to make a soluble salt is always ext{H}^+ + ext{OH}^-
    ightarrow ext{H}_2 ext{O}

  • If using an insoluble base, the ions are not treated as separate species.

Methods for Making Salts

1. Making a Soluble Salt from an Insoluble Base:

  • Procedure:

    1. Choose the appropriate acid and base (metal oxide or carbonate).

    2. Mix acid in a beaker.

    3. Add an excess of base and stir to react completely.

    4. Filter the mixture to remove undissolved base.

    5. Evaporate water from the solution to crystallise the salt.

2. Making a Soluble Salt from a Soluble Base (Alkali):

  • Procedure:

    1. Fill a burette with acid to create the titre.

    2. Measure 25 cm³ of alkali in a conical flask.

    3. Add an indicator.

    4. Add acid slowly while swirling until neutralisation is complete.

    5. Record the titre volume, repeat for concordant results.

    6. Calculate mean titre and repeat without indicator.

    7. Evaporate resulting solution to crystallise the salt.

3. Making an Insoluble Salt:

  • An insoluble salt can be recovered via filtration only using acid and alkaline reactions.

  • Care should be taken to wash the salt after filtering.

Conclusion

  • Understanding how to construct ionic equations and the various methods for making salts from neutralisation reactions is crucial for grasping the concepts of acid-base chemistry. This knowledge is applicable in laboratory settings involving chemical synthesis and practical applications in various fields of chemistry.