Salt Analysis-2

What is Salt Analysis?

The salt analysis involves qualitative analysis of different qualitative analysis present in a given inorganic salt. This is also called systematic qualitative analysis. These salts are separated into different ions by conducting a series of experiments in the inorganic laboratory conditions to confirm the absence or presence of the ions. 

The aim of this experiment is to identify the anion and cation present in the given unknown salt.

Apparatus and chemicals required for this experiment will be Burner, Dry test tubes, Test tube holder, Droppers, Glass rod, Beaker, Watch glass containing salt, Concentrated sulphuric acid, Concentrated nitric acid, Acetic acid, Dilute sulphuric acid, Dilute nitric acid.

Dilute hydrochloric acid, Ammonium hydroxide solution, Sodium hydroxide solution, Silver nitrate solution, Lead acetate solution, Dimethylglyoxime solution, Aqua regia, Hydrogen sulphide gas (Kipp’s apparatus)

Manganese dioxide solid, Potassium dichromate, Red litmus paper, Distilled water,  Ammonium chloride solid. 

Procedure

The procedure followed for this experiment will be: 

• First record the preliminary analysis of the given salt: colour and dry heating test. 
• To perform the dry heating test, take a clean, dry test tube with 0.1 g of salt and heat it under the flame. Observe any characteristic colour change. 

Anions

• Group 1: Take a small amount of salt in a test tube and add dil. H₂SO₄ solution. Warm the solution. If no reaction occurs, then move to group 2 anions. 
• Group 2: Take a small amount of salt in a test tube and add conc. H₂SO₄ solution. If no reaction occurs, then move to individual tests for SO₄^2- and PO₄^3-. 
• Perform the confirmatory test for the group that gave a positive test. 

Confirmatory tests (Observe and record the characteristic results):

• Salt + conc. H₂SO₄ solution + heat

Colourless gas + a glass rod dipped in NH₄OH

• Salt + MnO₂ + conc. H₂SO₄ solution

• Salt + water + silver nitrate 

Precipitate + NH₄OH solution. 

• Salt + K₂Cr₂O₇ + conc. H₂SO₄ solution + heat 

Dark red vapours + NaOH solution

Yellow solution + acetic acid + lead acetate solution

Cations: 

• Group zero: Take 0.1 g of salt and add 1-2 mL of NaOH solution and heat it. Observe the smell of ammonia. 
• Prepare the original solution of the given salt by testing solubility in the following sequence: distilled water (room temperature and warm), dil. HCl (room temperature and warm), conc. HCl (heat), dil. HNO₃ and 3:1 ratio of conc. HCl and conc HNO₃. 
• Group 1: Add dil. HCl to a small amount of the original solution. If a white precipitate is obtained, perform the confirmatory test for Pb²⁺. 
• Group 2: To the above solution, add water and pass H₂S gas through it. If a precipitate is formed, perform the confirmatory tests for group 2 cations. 
• Group 3: Take the original solution and heat it with a few drops of HNO₃ solution. Cool the solution and add NH₄Cl solid and NH₄OH until it smells of ammonia. The formation of a precipitate indicates the presence of group 3 ions.
• Group 4: Take the above solution and pass hydrogen sulphide (H₂S) gas through it. If a flesh-coloured or black-coloured, or white precipitate is formed, it indicates the presence of group 4 cations.  

1. Confirmatory test for group 4 cations: (Observe and record the characteristic results)

• Black precipitate + aqua regia + heat

Divide the clear solution into 2 parts.

Clear solution 1 + NH₄OH + DMG solution

Thus, it can be concluded that the given salt is NiCl₂.

FAQs on Salt Analysis