Ionic equations

Double replacement reactions and other reactions of ions in aqueous solution are usually represented by that are known as “net ionic equations”. To write a net ionic equation, one firstly writes an equation in which all strong electrolytes are shown as dissociated ions in solution (without steps, of course). For example:

1. Formation of slightly soluble substance:

CuSO₄ + 2NaOH = Cu(OH)₂¯ + Na₂SO₄

Cu²⁺ + SO₄^2- + 2Na⁺ + 2OH^- = Cu(OH)₂¯ + 2Na⁺ + SO₄^2- -

this is a complete ionic equation.

Cu²⁺ + 2OH^- = Cu(OH)₂¯ - this is net ionic equation.

2. Formation of weak electrolyte:

a) HCl + KOH = KCl + H₂O,

H⁺ + Cl^- +K⁺ + OH^- = K⁺ + Cl^- + H₂O,

H⁺ + OH^- = H₂O.

b) СH₃COONa + HCl = CH₃COOH + NaCl,

CH₃COO^- + Na⁺ + H⁺ + Cl^- = CH₃COOH + Na⁺ + Cl^-,

CH₃COO^- + H⁺ = CH₃COOH.

3. Formation of gas:

а) K₂CO₃ + 2HNO₃ = 2KNO₃ + CO₂­ + H₂O,

2K⁺+ CO₃^2- + 2H⁺ + 2NO₃^- = 2K⁺ + 2NO₃^- + CO₂­ + H₂O,

CO₃^2- + 2H⁺ = CO₂­ + H₂O.

b) FeS + 2HCl = FeCl₂ + H₂S­.

Iron (II) Sulfide is slightly soluble and Hydrogen Sulfide is a weak electrolyte (gas). Therefore:

FeS + 2H⁺ + 2Cl^- = Fe²⁺+ 2Cl^- + H₂S­,

FeS + 2H⁺ = Fe²⁺+ H₂S­.

Interactions in the solutions of electrolytes are realized completely if in the result the following will be formed:

а) weak electrolyte;

б) sediments;

в) gases.

PRACTICE PROBLEMS

1. Write the dissociation equation for the ions of the following compounds:

H₂SO₄, HClO₄, Ca(OH)₂, AlCl₃, Fe₂(SO₄)₃, K₂CO₃, Bi(NO₃)₃, Na₂HPO₄, NH₄HCO₃, Co(NO₃)₃.

2. Write molecular, complete and net ionic equations:

Ø BaCl₂ + Fe₂(SO₄)₃ →

Ø Cu(NO₃)₂ + Na₂CO₃ →

Ø Na₂SiO₃ + H₂SO₄ →

Ø FeCl₃ + KOH →

Ø H₃PO₄ + Ba(OH)₂ →

Ø Cu(OH)₂ + HCl →

Ø Na₂HPO₄ + CaCl₂ →

3. Which of two reactions does proceed in the solution up to the end and why? Draw the corresponding molecular, complete and net ionic equations:

Ø Calcium Chloride + Magnesium Nitrate →

Ø Sodium Carbonate + Zinc Chloride →

Ø Lithium Sulfate + Potassium hydroxide →

Ø Iron (II) Sulfate + Sodium hydroxide →

Ø Iron (III) hydroxide + Nitric Acid →

4. Draw molecular equations of the reactions between substances interacted in aqueous solution according to the following scheme:

Ø Ba²⁺ + SO₄^2- → BaSO₄;

Ø Fe(OH)₃ + 3H⁺ → Fe³⁺ + 3H₂O;

Ø CaCO₃ + 2H⁺ → Ca²⁺ + CO₂ + H₂O;

Ø 3Mg²⁺ + 2PO₄^3- → Mg₃(PO₄)₂;

Ø Ca²⁺ + 2 F^- → CaF₂.

Date: 2015-01-12; view: 839