What is the use of sodium carbonate extract in salt analysis?
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The preparation of sodium carbonate extract affords a convenient method for bringing the anions of the mixture into solution which were otherwise insoluble with caution of salt. It removes the basic radical (usually coloured) which interferes in the usual tests of some of the acidic radicals.
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The preparation of sodium carbonate extract affords a convenient method for bringing the anions of the mixture into solution which were otherwise insoluble with caution of salt. It removes the basic radical (usually coloured) which interferes in the usual tests of some of the acidic radicals.
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Sodium Carbonate extract:
If the given salt mixture is partly soluble or insoluble in water then sodium carbonate extract is prepared for analysis. Preparation of soda extract is a three step process.
Step 1 Dissolution: Take 1-2g of salt mixture and 5-6g anhydrous sodium carbonate, and add 10ml water to dissolve them. Heat it for 15 minutes and filter. Wash the residue with water and add washings to the filtrate.
Step 2- Acidification: Now acidify the filtrate with 8M nitric acid (HNO3) and boil gently to expel CO2(g) and allow it to cool.
Step 3- Neutralization: Add 2M ammonia solution to make it just alkaline, stir the solution while adding ammonia. Now boil gently to remove excess of ammonia. Allow it to cool.
This is called as neutralized soda extract which we will use for the analysis of anions. On boiling with sodium carbonate, metal cations form metal carbonates that can be removed as precipitates and anions remain in solution in the company of sodium ions.
Since there is no systematic scheme for the analysis of anions, you have to analyze each of them separately. In the given mixture first try to find out which group of anion is present then try specific tests to confirm it. Take a small amount of given mixture in a test tube and add 2ml dilute sulphuric acid and observe it, if there is no effervescence or bubbles then heat the solution and note the observation. Sign of any reaction with dilute sulphuric acid indicates the presence of dilute acid group anions. Preliminary observation can narrow down your search of anion, so observe very carefully.
Observation
Inference
Brisk effervescence and emission of colorless gas
Carbonate (CO3 2-) or Hydrogen carbonate (HCO3 -) may be present.
Colorless gas with rotten egg like smell
Sulphide (S2-) may be present.
Colorless gas with a smell of burning sulphur
Sulphite (SO32-) or Thiosulphate (S2O32-) may be present.
Colorless gas with vinegar like smell
Acetate (CH3COO-) may be present.
Colorless gas with odor of bitter almond
Cyanide (CN-) may be present.
Light brown gas
Nitrite (NO2-) may be present.
Greenish coloured gas with suffocating smell of chlorine
Hypochlorite (OCl-) may be present.
If the given salt mixture is partly soluble or insoluble in water then sodium carbonate extract is prepared for analysis. Preparation of soda extract is a three step process.
Step 1 Dissolution: Take 1-2g of salt mixture and 5-6g anhydrous sodium carbonate, and add 10ml water to dissolve them. Heat it for 15 minutes and filter. Wash the residue with water and add washings to the filtrate.
Step 2- Acidification: Now acidify the filtrate with 8M nitric acid (HNO3) and boil gently to expel CO2(g) and allow it to cool.
Step 3- Neutralization: Add 2M ammonia solution to make it just alkaline, stir the solution while adding ammonia. Now boil gently to remove excess of ammonia. Allow it to cool.
This is called as neutralized soda extract which we will use for the analysis of anions. On boiling with sodium carbonate, metal cations form metal carbonates that can be removed as precipitates and anions remain in solution in the company of sodium ions.
Since there is no systematic scheme for the analysis of anions, you have to analyze each of them separately. In the given mixture first try to find out which group of anion is present then try specific tests to confirm it. Take a small amount of given mixture in a test tube and add 2ml dilute sulphuric acid and observe it, if there is no effervescence or bubbles then heat the solution and note the observation. Sign of any reaction with dilute sulphuric acid indicates the presence of dilute acid group anions. Preliminary observation can narrow down your search of anion, so observe very carefully.
Observation
Inference
Brisk effervescence and emission of colorless gas
Carbonate (CO3 2-) or Hydrogen carbonate (HCO3 -) may be present.
Colorless gas with rotten egg like smell
Sulphide (S2-) may be present.
Colorless gas with a smell of burning sulphur
Sulphite (SO32-) or Thiosulphate (S2O32-) may be present.
Colorless gas with vinegar like smell
Acetate (CH3COO-) may be present.
Colorless gas with odor of bitter almond
Cyanide (CN-) may be present.
Light brown gas
Nitrite (NO2-) may be present.
Greenish coloured gas with suffocating smell of chlorine
Hypochlorite (OCl-) may be present.
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