Inorganic salts are obtained with a base through either partial or complete neutralization of acid. The part that the acid contributes is known as an anion in the salt formation and the part that the base contributes is known as a cation. The preliminary examination results are important clues about the presence of some cations or anions. The systematic analysis of anions is an integral part of salt analysis (or the qualitative inorganic analysis).
To identify the anionic radicals that are present in an inorganic mixture of salts by performing different tests.
Qualitative analysis involves the identification and detection of acidic and basic radicals, which are present in inorganic salts. Inorganic salts are produced by the reaction of both acids and bases or the acidic oxides with either a base or basic oxides.
Some of the examples of the reaction of both acids and bases or the acidic oxides with a base or basic oxides are chemically represented below:
CO2 + 2NaOH → Na2CO3 + H2O
NaOH + HCl → NaCl + H2O
2NaOH + H2SO4 → Na2SO4 + 2H2O
KOH + HNO3 → KNO3 + H2O
Many organic compounds are the crystalline solids because they have the pre-defined geometrical shapes. In general, they contain the oppositely charged ions or particles, which are called radicals.
In the salt analysis, two fundamental principles are of great use of:
Common Ion Effect
Solubility products can be defined as a product of ion concentrations, which are elevated to a power equal to the occurrences count of ions in an equation by representing the electrolyte dissociation at a given specific temperature when the solution is saturated. Under all the conditions, the solubility product is not given as the ionic product, but only if the solution gets saturated.
The phenomenon which suppresses the degree of dissociation of any of the weak electrolytes by adding some amount of strong electrolyte which contains a common ion is known as the common ion effect. For example, by adding a strong electrolyte sodium acetate which contains a common acetate ion, ionization of weak electrolyte acetic acid can be suppressed.
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Confirmatory Tests for S2–, CO32-, SO32-, CH3COO– and NO2– anions:
When the salt is water-soluble, confirmatory anion testing can be carried out using the water extract and when the salt becomes water-insoluble, by using sodium carbonate extract. Confirmation of CO32– can be done either with the help of aqueous salt solution or with a solid salt as such, as the carbonate ions are composed in the extract of sodium carbonate. Water extraction is formed by dissolving salt in water.
Take 1 gram of salt in a porcelain dish or a boiling tube. Now, mix 3 g of solid sodium carbonate approximately with 15 mL of distilled water. And, remove the contents and cook for up to 10 minutes. Filter, cool, and collect the filtrate in the test tube and label it as a sodium carbonate extract.
The salt contains ________ (CO32‒, SO32‒, S2‒, NO2‒, SO42‒, Cl‒, NO3‒, I‒, Br‒, C2O42‒, PO43‒, CH3COO‒) anion.
Read the label carefully on a bottle before using chemicals or reagents. Never use reagent which is unlabeled.
In smelling vapours or chemicals, be careful. Always fan the vapours to your nose gently
Always use hand gloves and an apron as an eye protector in the chemical laboratory.
Unnecessarily, do not mix chemicals with reagents and do not taste the chemicals at all.
Never throw or add sodium metal into the dustbin or sink.
Always pour acid into water for dilution. Never add acid to the water.
Be careful when heating the test tube. When adding a reagent or heating, the test tube must never point to anyone.
Keep cleaning your working environment. Never ever throw in the sink any papers and also glass. Always use a dustbin for this purpose.
Always pour acid into water for dilution.
Be careful with the flammable substances, explosive compounds, electrical appliances, toxic gasses, glass products, hot substances, and flames.
Always wash hands after the laboratory work has been over.
Always use less quantity of reagents. The excessive use of reagents not only leads to chemicals being wasted, but they also cause environmental damage.
Q1. How to Test the Presence of Sulphide Ions?
Answer: H₂S rotten egg smell is observed when adding dilute sulphuric acid to salt. The confirmatory test is the Ag₂S black spot, which is observed when adding S₂-ion to the silver foil.
Q2. What is the Term Common Ion Effect?
Answer: The common ion effect defines the effect on balance that takes place when adding to the solution, a common ion, that is already present in the solution. In general, the common ion effect decreases the solubility of the solvent.
Q3. How to Test the Carbonate Ion’s Presence?
Answer: A dilute acid can be used to detect the carbonate ions, CO₃²⁻ bubbles release when the acid can be added to the test compound, generally diluted hydrochloric acid. And, the carbon dioxide causes bubbles using Limewater and that gas is carbon dioxide.
Q4. Why Does Iodine Result in a Blue Colour with a Starch Solution?
The iodine test helps to test the presence of starch. And starch becomes the intense “blue-black” colour because of the production of an intermolecular load-transfer complex by adding the aqueous solutions of triiodide anion.