Chemical Equations: Tests for Anions - Chp 6

Reactant

starting substances that react to form the product

Product

the substances formed as a result of a reaction

The Law of Conservation of Mass

states that the total mass of the products of a chemical reaction is the same as the total mass of the reactants

The Law of Conservation of Matter

states that in any chemical reaction, matter is neither created nor destroyed but merely changes from one form to another

Anion: Chloride TOI

Test - add a few drops of AgNO₃ solution to a solution of the solid
Observation - a white precipitate is formed which is soluble in dilute ammonia solution
Inference - Ag⁺ + Cl⁻ -> AgCl↓

Anion: Sulfate or Sulfite TOI

1. Test - add BaCl₂ solution to a solution of the solid
   Observation - a white precipitate is formed
   Inference

   - Ba²⁺ + SO₄ ²⁻ → BaSO₄↓

   - Ba²⁺ + SO₃ ²⁻ → BaSO₃↓

2. Test - distinguishing test, add dilute HCl
   Observation

   - if precipitate remains → sulfate

   - if precipitate dissolves → sulfite
   Inference

   - SO₃ ²⁻ + 2H⁺ → SO₂ + H₂O

   - BaSO₄ + HCl → no reaction

Precipitate

an insoluble solid that emerges from a liquid solution

Reagents

substances which cause a chemical reaction to take place

Anion: Carbonate or Hydrogen-carbonate TOI

1. Test - Add dilute HCl to the solution of the solid
   Observation - Fizzing is observed. The gas (CO₂) is given off which turns limewater milky
   Inference - CO₃ ²⁻ + 2H⁺ → CO₂ + H₂O

• HCO₃ ⁻ + H⁺ → CO₂ + H₂O
• Ca(OH)₂ + CO₂ → CaCO₃↓ + H₂O

1. Test - Distinguishing test. Add MgSO₄ to a fresh solution of the solid
   Observation - White precipitate forms → Carbonate

• No precipitate forms → Hydrogen-carbonate, boiling will give a precipitate
  Inference - Mg²⁺ + CO₃ ²⁻ → MgCO₃↓

• Mg²⁺ + 2HCO₃⁻ → Mg(HCO₃)₂

• Mg(HCO₃)₂ → MgCO₃↓ + CO₂ + H₂O

Anion: Nitrate TOI

Test - Brown ring test. Add freshly prepared FeSO₄ solution to a solution of the solid. Add concentrated sulfuric acid
Observation - A brown ring is formed at the junction of the two liquids → nitrate ion is present
Inference - Brown ring is due to the presence of nitrate

Anion: Phosphate TOI

Test - Ammonium molybdate is added to a solution of the solid. Concentrated nitric acid is added, the solution is warmed.
Observation - a yellow precipitate is formed
Inference - Phosphate ions are present