Part 3 - Qualitative analysis of simple inorganic salt - Anion tests 2

Qualitative analysis of simple inorganic salt - Anion test

1. Salt with dil.H₂SO₄ and MnO₂: 

A small amount of the salt is warmed with dil.H₂SO₄ and cooled. To this, solid MnO₂ is added slowly.

Observation    : Brisk effervescence

Inference         : Presence of Oxalate

Explanation    : Oxalate group reacts with MnO₂ in the presence of H₂SO₄ and gives CO₂. The release of CO₂ is observed as effervescence.

Effervescence - Oxalate

Observation    : No brisk effervescence

Inference         : Absence of Oxalate

2. Salt with con.H₂SO₄ in cold condition:

To a small amount of the salt, con. H₂SO₄ is added. The following observations may occur.

Observation    : Immediate brown vapors

Inference         : Presence of Bromide

Explanation    : Bromide salts react with con.H₂SO₄ and gives hydrogen bromide (HBr) gas. The release of HBr is observed as brown fumes.

2a. Brown vapor - Bromide

Observation    : Violet vapors

Inference         : Presence of Iodide

Explanation    : Iodide salts react with con.H₂SO₄ to give hydrogen iodide (HI) gas. The release of HI is observed as violet fumes.

2b. Violet vapor - Iodide

Observation    : Colorless vapors

Inference         : Presence of Chloride

Explanation    : Chloride salts react with con.H₂SO₄ to give hydrogen chloride (HCl) gas. The release of HCl is observed as colorless gas.

This colorless gas is giving dense fumes with glass rod dipped in ammonium hydroxide (NH₄OH).

2c. Colorless gas gives dense fumes with glass rod dipped in NH₄OH - Chloride

Observation    : No characteristic change

Inference         : Absence of Bromide, Iodide, and Chloride

3. Salt with con.H₂SO₄ in hot condition:

To a small amount of the salt, con. H₂SO₄ is added. The solution is heated and the following observations may occur.

Observation    : Colorless gas gives a white deposit on a wet glass rod and oily appearance on the sides of the test tube.  

Inference         : Presence of Fluoride

Explanation    : Fluoride salts react with con.H₂SO₄ and gives hydrogen Fluoride (HF) gas. The release of HF is observed as colorless gas.

This HF (colorlesss gas) reacts with SiO2 (glass rod) and produces silicon tetrafluoride (SiF4) and also hydrofluorosilicic acid (H2SiF6). As a result of these products, white deposit and oily drop appearance are observed in this experiment.

    

3a. Colorless gas gives a white deposit on a wet glass rod - Fluoride

Observation    : Brown fumes  

Inference         : Presence of Nitrate

Explanation    : Nitrate salts react with con.H₂SO₄ and gives Nitric acid (HNO3). Nitric acid on heating decomposed to give the brown vapor (NO2).

3b. Brown vapor - Nitrate

Observation    : No characteristic change 

Inference         : Absence of Fluoride and Nitrate