Salt Analysis-1

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. 

This experiment aims to identify the anion and cation present in the given unknown salt

Here, we will find the unknown cation and anion present in the given inorganic salt. Let us take a look at salt analysis in a virtual lab.

Procedure

Preliminary test for cations:

• Flame test, take a platinum loop with a small amount of salt and bring it close to the flame. Observe the colour.  
• Dry heating test, take a clean, dry test tube with 0.1 g of the salt and heat it under the flame. Observe any characteristic colour change.

Preliminary test for anions:

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

Confirmatory test for chloride ion:

• Salt + conc. H₂SO₄ 
• Colourless gas + a glass rod dipped in NH₄OH
• Salt + MnO₂ + conc. H₂SO₄ solution
• Salt + water + dilute nitric acid + silver nitrate solution
• Precipitate + NH₄OH solution
• Salt + K₂Cr₂O₇ + conc. H₂SO₄ solution + heat
• Dark red vapours + NaOH solution
• Solution + acetic acid + lead acetate solution

Cations: 

• Group 0: Mix 0.1g salt with NaOH, heat, and detect the ammonia smell. 
• Create the original solution by testing solubility in water, HCl, and 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: Heat the original solution with HNO₃ solution. Cool the solution and add NH₄Cl solid and NH₄OH until it smells of ammonia. The formation of a reddish-brown or gelatinous white precipitate indicates the presence of Fe³⁺ or Al³⁺ ions. 

Confirmatory test for group 3 cations:

• Precipitate (from group identification test) + dil. HCl ? clear solution
• Divide the clear solution into 2 parts.
• Clear solution 1 + potassium ferrocyanide ? Prussian blue precipitate
• Clear solution 2 + potassium thiocyanate ?  Blood-red colouration

FAQs on Salt Analysis