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What is Salt Analysis?
The salt analysis involves qualitative analysis of different qualitative analyses 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
Procedure
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.
The procedure followed for this experiment will be:
- First, record the given salt’s preliminary analysis: 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.
- Perform the confirmatory test for the group that gave a positive test.
Confirmatory Test for Nitrate Ion
- Salt + water + FeSO4 + decant ? clear solution
- Add H2SO4 dropwise through the walls of the test tube; the formation of a brown ring at the junction of solutions confirms the presence of nitrate ions in the salt.
Clear solution + H2SO4 (dropwise through the walls of the test tube) ? Brown ring
Cations
- Group zero: Take 0.1 g of salt, add 1-2 mL of NaOH solution and heat it. Observe the smell of ammonia.
- Prepare the original solution of the given salt and test solubility.
- 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+.
Confirmatory test for group 1 cations:
- White precipitate (formed during Group 1 analysis) + distilled water + heat: A clear solution
- Divide the solution into three parts.
- Solution ‘1’ + potassium iodide (KI): Yellow precipitate of lead iodide
- Solution ‘2’ + potassium chromate (K2CrO4): Yellow precipitate of lead chromate, soluble in sodium hydroxide and insoluble in ammonium acetate solution
- Solution ‘3’ + ethanol + dil. H2SO4: White precipitate soluble in ammonium acetate solution
Hence, the given inorganic salt is Pb(NO3)2.
FAQs on Salt Analysis
What is the purpose of performing a flame test in salt analysis?
Answer: It is used to identify the presence of certain metal ions based on the characteristic colour they emit when heated in a flame. Each metal ion emits a unique colour due to the energy transitions of its electrons. This helps in identifying the cation present in a salt sample.
What type of bonding is present in inorganic salts?
Answer: The bond that exists in the inorganic salts is ionic.
Describe the basic principle of salt analysis.
Answer: The main principles that are involved in salt analysis are solubility and ionic products. The ionic product should always be greater than the solubility product for a precipitate to be formed in a reaction.
What is the preliminary test for group 1 cation?
Answer:
White precipitate (formed during Group 1 analysis) + distilled water + heat: A clear solution
Divide the solution into three parts.
1) Solution ‘1’ + potassium iodide (KI): Yellow precipitate of lead iodide
2) Solution ‘2’ + potassium chromate (K2CrO4): Yellow precipitate of lead chromate, soluble in sodium hydroxide and insoluble in ammonium acetate solution
3) Solution ‘3’ + ethanol + dil. H2SO4: White precipitate soluble in ammonium acetate solution
What is the confirmatory test for nitrate ions?
1) When the salt reacts with FeSO4 , a clear solution is obtained.
Salt + water + FeSO4 + decant ? clear solution
2) Add H2SO4 dropwise through the walls of the test tube, the formation of a brown ring at the junction of solutions confirms the presence of nitrate ions in the salt.
Clear solution + H2SO4 (dropwise through the walls of the test tube) ? Brown ring
JEE Main