Salt Analysis-3

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 detect the presence of one cation and one anion from the given salt. 

The apparatus and chemicals required for this experiment are: 

Watch glass containing salt, Platinum loop, Burner, Dry test tubes, Test tube holder, Droppers, Starch paper, Beaker, Spatula, Distilled water (wash bottle), Dilute sulphuric acid, Concentrated hydrochloric acid, Concentrated sulphuric acid, Chloroform solution, Dilute hydrochloric acid, Chlorine water, Dilute nitric acid, Silver nitrate solution, Ammonium hydroxide solution, Sodium hydroxide solution, Concentrated nitric acid, Ammonium carbonate solution, Dilute acetic acid, Potassium chromate solution, Ammonium chloride solid, Manganese dioxide solid

Hydrogen sulphide gas (Kipp’s apparatus)

The procedure followed for this experiment is: 

• First, record the preliminary analysis of the given salt: colour, dry heating test and flame test. 
• To perform the dry heating test, take a clean and dry test tube with 0.1 g of the salt and heat it over a flame. Observe any characteristic colour change. 
• To perform the flame test, take a platinum loop with a small amount of the salt and bring it close to the flame. Observe and record the colour. 

Anions: 

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

Tests for iodide ions (observe and record the results): 

Tests for iodide ions 

Salt(s) + conc. H₂SO₄ solution + Heat 

• Violet vapours + starch paper: Paper turns blue-black
• Salt + MnO₂ + conc. H₂SO₄ solution: Dense violet vapours

• Salt + water + CHCl₃ + dil. HCl + chlorine water: The organic layer turns violet

• Salt + water + dil. HNO₃ + silver nitrate: Yellow precipitate
• Precipitate + NH₄OH solution: Insoluble

Cations: 

• Group 0: Take 0.1 g of the 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 its 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 hydrogen sulphide (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 H₂S gas through it. If a flesh-coloured, black-coloured, or white precipitate is formed, it indicates the presence of group 4 cations.  
• Group 5: Take the original solution and add solid NH₄Cl and NH₄OH followed by (NH₄)₂CO₃. The formation of a white precipitate indicates the presence of group 5 ions. 

Confirmatory test for group 5 cations 

White precipitate + dilute acetic acid + boil ? precipitate dissolves

Divide the solution into three parts

Solution 1 + potassium chromate: Yellow precipitate formed confirms Ba²⁺  

Flame test with the group 5 precipitate:  An apple-green coloured flame further confirms the presence of Ba²⁺ ions. 

FAQs on Salt Analysis