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Salt analysis involves the identification of the anion and cation of an inorganic salt. It is also known as qualitative inorganic analysis or systematic qualitative analysis. The analysis of salt is done by conducting a series of tests and formulating observations to determine the absence or presence of specific cations and anions.
- Salt analysis is an important part of the CBSE Class 12 Chemistry Practical Examination.
- With the help of different experiments performed in a laboratory, inorganic salts are separated into different ions.
- After that, tests are performed to confirm whether certain ions are present or absent in the solution.
Download: Chemistry Practical Class 12 Salt Analysis Notes and Cheatsheet
What is Salt Analysis?
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Salt analysis, also known as qualitative inorganic analysis, is a process to identify the cations (positively charged ions) and anions (negatively charged ions) present in an unknown salt. In chemistry, it is performed through a series of steps that involves:
- Preliminary Tests: This is the first step in salt analysis through which the presence of a particular substance is detected. It involves multiple actions of chemicals on a substance.
- Group-Wise Analysis: Group-wise analysis is done after preliminary testing. Through this, physical properties like color and formation of precipitates can be detected.
- Confirmatory Tests: The substance found in the initial test is confirmed in this stage.
- Identification: The final identification of the salt is done by examining its physical properties and comparing them with other salts. After physical identification, the salt is named as per the rules (first – cation; second – anion).
It helps in ensuring the purity and composition of salts used in food, pharmaceuticals, and other industries. Studying the composition of salt in water or soil can reveal environmental pollution or contamination. Salt analysis is, therefore, a valuable tool providing important insights into the composition of compounds.
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Process of Salt Analysis
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The steps involved in the process of the salt analysis experiment are mentioned below-
- Step 1 – Take a reasonable amount of inorganic salt to identify the anions and cations.
- Step 2 – Conduct preliminary tests to find out which anion group is present inside the salt.
- Step 3 – After finding the group, perform the confirmatory test for the anion.
- Step 4 – The same process should be followed for finding the cations group-wise.
- Step 5 – After finding the cations group, perform the confirmatory test for the cation.
- Step 6 – After identifying both anions and cations, get the chemical formula of salt.
Important Points Related to Salt Analysis
Here are some important points related to salt analysis that are listed as:
- Anions and cations are classified as sharing the same group of reagents and that’s why they have similar preliminary tests.
- The chemical formula of salt is written by balancing the charges of cations and anions.
- If the salt contains the sulfate (SO42-) anion and the calcium (Ca2+) cation, the chemical formula for the salt will be CaSO4 (gypsum).
List of Cations for Salt Analysis
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Multiple ions that belong to the same group usually have the same preliminary tests but their confirmatory tests are different. The list of cations for salt analysis is mentioned below-
| Groups | Cations |
|---|---|
| Group 0 | NH4+ |
| Group 1 | Pb2+ |
| Group 2 | Cu2+ |
| Group 3 | Fe3+, Fe2+, Al3+ |
| Group 4 | Co2+, Mn2+, Ni2+, Zn2+ |
| Group 5 | Ba2+, Ca2+, Sr2+ |
| Group 6 | Mg2+ |
List of Common Anions (Acidic Radicals) for Salt Analysis
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The list of anions for salt analysis is mentioned below-
| Group | Anions |
|---|---|
| Group 1 | CO32-, NO2-, SO32-, S2- |
| Group 2 | Cl-, Br-, l-, CH3COO-, NO3-, C2O42- |
| Group 3 | PO43-, SO42- |
Preliminary Tests For Anions and their Groups
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The preliminary salt analysis test for anions involves the identification of the anion of the salt group. When a positive preliminary test is conducted for an anion, a confirmatory test is a must to confirm the presence of anion in the salt.
Preliminary Salt Analysis Test for Group 1 Anions
Experiment- Firstly, add a few drops of dilute H2SO4 (i.e., sulfuric acid) to a small quantity of salt in a clean and dried test tube. If this test doesn’t work or nothing happens then move on to the preliminary test for group 2 anions.
| Anion | Positive results |
|---|---|
| Carbonate (CO32-) | Colorless and odorless gas that turns limewater milky. |
| Sulfite (SO32-) | Colorless, pungent-smelling gas |
| Sulfide (S2-) | Colorless gas which smells like rotten eggs |
| Nitrite (NO2-) | Light brown gas having a pungent smell. |
Preliminary Salt Analysis Test for Group 2 Anions
Experiment- Take a small amount of salt in a test tube then add a few drops of concentrated H2SO4 (sulfuric acid) to it.
| Anion | Positive result |
|---|---|
| Chloride (Cl-) | White, pungent-smelling fumes intensify when a glass rod dipped in ammonium hydroxide is brought to the mouth of the test tube. |
| Bromide (Br-) | Reddish-brown fumes |
| Iodide (I-) | Violet fumes |
| Acetate (CH3COO-) | Pungent fumes that smell like vinegar |
| Nitrate (NO3-) | Brown fumes with a pungent smell |
| Oxalate (C2O4-) | The Bubbly effervescence of a combination of carbon dioxide and monoxide gas. |
Preliminary Salt Analysis Test for Group 3 Anions
The sulfate and phosphate ions of group 3 do not have any prominent preliminary test. If no positive test results are obtained for group 1 and 2 anions, you can directly carry out the confirmatory test for the phosphate and sulfate anions.
Confirmatory Tests For Anions
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Preparation of the water extract of salt can be done by dissolving a pinch of inorganic salt in some drops of water.
| Anion | Reagent | Observation |
|---|---|---|
| Carbonate (CO32-) | Magnesium Sulphate | A white precipitate |
| Sulphide (S2-) | i) Sodium nitroprusside, ii) aq lead acetate | (i) Solution turns purple/ violet, ii) A black precipitate |
| Nitrite (NO2–) | Boil water extract + dilute H2SO4. Add solid potassium iodide and starch solution. | A deep blue colored solution |
| Nitrate (NO3-) | Water extract + FeSO4+ Conc nitric acid (HNO3) | Brown ring at the junction of layers |
| Chloride (Cl-) | AgNO3 | White precipitate of AgCl, soluble in NH4OH |
| Bromide (Br-) | AgNO3 | Pale yellow precipitate of AgBr, partially soluble in NH4OH |
| Iodide (I-) | AgNO3 | Yellow precipitate of AgI, insoluble in NH4OH |
| Sulfate (SO42-) | Aq BaCl2 | White precipitate of BaSO4, insoluble in conc HCl |
| Sulfite (SO32-) | Aq. Barium Chloride | White precipitate that disappears on addition of dil HCl |
| Phosphate (PO43-) | Ammonium molybdate + Dil. HNO3 → boil | Yellow, crystalline precipitate of ammonium phosphomolybdate |
| Acetate (CH3COO-) | Conc H2SO4 + Ethanol | Fruity smell due to the formation of ester |
| Oxalate (C2O4–) | Acetic acid + calcium chloride and boil the solution. | A white precipitate that dissolves upon adding dilute HNO3 |
- Carbonate (CO32-)
- Confirmation Test – Mix Magnesium sulfate (MgSO4) with water extract of the salt.
- Observation – A white precipitate will be formed.
- Sulfite (SO32-)
- Confirmation Test – Combine aqueous barium chloride (BaCl2) into some water extract.
- Observation – A white precipitate will be formed that disappears after the addition of hydrochloric acid.
- Sulfide (S2-)
- Confirmation Test - There are two tests for the confirmation of the Sulfide –
- Combine sodium nitroprusside with water extract.
- Combine aqueous lead acetate with the water extract.
- Observation- There are two observations for the confirmatory test-
- The solution may turn purple or violet.
- The Black precipitate will be formed.
- Nitrite (NO2-)
- Confirmation Test - Boil diluted H2SO4 with water extract. Then add solid potassium iodide and starch solution to the boiled mixture.
- Observation- A deep blue color will be developed.
- Chloride (Cl-)
- Confirmation test- Dissolve silver nitrate in the water extract.
- Observation- White precipitate will be formed that can be dissolved in ammonium hydroxide (NH4OH)
- Bromide (Br-)
- Confirmation Test - Combine silver nitrate (AgNO3) in the water extract.
- Observation- A yellow precipitate will be formed that can be dissolved in ammonium hydroxide.
- Iodide (I-)
- Confirmation Test - Combine silver nitrate to the water extract.
- Observation- Yellow precipitate will be formed that cannot be dissolved in NH4OH
- Nitrate (NO3-)
- Confirmation Test - Dissolve iron (II) sulfate solution (FeSO4) into the water extract. Then add one drop of concentrated nitric acid (HNO3) in a test tube.
- Observation- A brown-colored ring is formed in the solution and also at a junction of acid.
- Acetate (CH3COO-)
- Confirmation Test - Combine some ethanol and concentrated H2SO4 into the salt.
- Observation- A fruity smell developed because of the formation of an ester.
- Oxalate (C2O4-)
- Confirmation Test - Dissolve acetic acid and calcium chloride into water extract and then boil the mixture.
- Observation- White precipitate will be formed that can be dissolved upon the addition of the dilute HNO3.4
- Sulphate (SO42-)
- Confirmation Test - Mix aqueous barium chloride to the water extract.
- Observation- White precipitate will be formed that cannot be dissolved in concentrated hydrochloric acid (HCI)
- Phosphate (PO43-)
- Confirmation Test Boil dilutes nitric acid (HNO3) and ammonium molybdate with water extract.
- Observation- Yellow, crystalline precipitate will be formed.
TipThe most common salt that contains the bromide ions is Ammonium bromide (NH4BR) which is in school laboratories. You can immediately try a confirmatory test for the ammonium cation (NH4+) if you are sure about the presence of bromide ions in the salt. |
Preliminary Tests for Cations and their Groups
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A Preliminary salt analysis test for cations is performed to check the different cations present in the inorganic salt. The process of these tests is similar to the test for anions. Some of the Cation groups like group 0 and group 6 do not have any preliminary test. So, the confirmatory tests for these cations can be directly conducted.
Note - One can prepare the original solution by mixing a small amount of inorganic salt with water and acid.
Preliminary Salt Analysis Test for Group 1 Cations
Experiment- Add some drops of dilute hydrochloric acid to the original solution.
| Cations | Positive results |
|---|---|
| Lead (Pb2+) | A White precipitate will be formed |
Preliminary Salt Analysis Test for Group 2 Cations
Experiment- Mix some drops of dilute HCI and hydrogen sulfate into the original solution.
| Cations | Positive results |
|---|---|
| Copper (Cu2+) | Formation of black precipitate |
Preliminary Salt Analysis Test for Group 3 Cations
Experiment- There are two experiments included in group 3 for cations as mentioned below-
- Ferrous salts (Fe2+) are green in color while ferric salt (Fe3+) is brown in color.
- For aluminium (Al3+ ion), when solid ammonium chloride (NH4Cl) and excess ammonium hydroxide are added to OS, a gelatinous white precipitate is obtained.
Preliminary Salt Analysis Test for Group 4 Cations
Experiment- Mix solid NH4CI with NH4OH to the original mixture and then pass H2S gas through it.
| Cations | Positive result |
|---|---|
| Cobalt (Co2+) and nickel (Ni2+) can conduct both confirmatory tests | A black precipitate will be formed. |
| Manganese (Mn2+) | Formation of a skin-colored precipitation |
| Zinc (Zn2+) | Formation of a greyish-white precipitate. |
Preliminary Salt Analysis Test for Group 5 Cations
Experiment- In the original solution, add ammonium carbonate ((NH4)2CO3), ammonium chloride (NH4CI), and ammonium hydroxide. If a white precipitate is obtained, then the cation might be of group 5 cation. To dissolve the white precipitate, add dilute acetic acid (CH3COOH).
| Cations | Positive results |
|---|---|
| Barium (Ba2+) | When K2CrO4 is added to the solution, a yellow precipitate is formed. |
| Strontium (Sr2+) | When aqueous (NH4)2SO4 is added to the solution, a white precipitate is formed. |
| Calcium (Ca2+) | When ammonium oxalate and NH4OH are added to the solution, a white precipitate is formed. |
Confirmatory Tests For Cations
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The tests performed to confirm the presence of certain cations are as follows –
| Cation Present | Test(s) for Confirmation | Observation |
|---|---|---|
| Ammonium (NH4+) | Add NaOH, then Nessler's reagent (K2HgI4) | Brown or yellow precipitate |
| Lead (Pb2+) | 1. Add KI 2. Add potassium chromate (K2CrO4) to the original solution | Yellow precipitate for both tests |
| Copper (Cu2+) | Add dil HCl & H2S (preliminary) to get black precipitate, then add excess ammonium hydroxide | Black precipitate, then blue-colored solution |
| Iron (Fe3+) | Heat concentrated HNO3 + OS, then add HCl & potassium ferrocyanide (K4[Fe(CN)6]) | Blue precipitate |
| Aluminum (Al3+) | Add NH4Cl & excess NH4OH, then dissolve the gelatinous white precipitate in HCl & add blue litmus & NH4OH dropwise | Gelatinous white precipitate, then a blue floating layer on the solution |
| Cobalt (Co2+) | Add NH4Cl, and excess NH4OH to OS. Pass through H2S gas. Dissolve the blue residue in water and add dil. CH3COOH and KNO2, then heat the mixture. | Yellow precipitate |
| Nickel (Ni2+) | Add NH4Cl and excess NH4OH to the original solution. Pass H2S gas. Dissolve the yellow residue formed in water to get a green-coloured solution. Add NaOH and bromine water to this mixture and boil it. | Black precipitate |
| Manganese (Mn2+) | Add dilute HCl & H2S to the skin-coloured precipitate, then boil with off H2S & add NaOH | Skin-colored precipitate, then white precipitate turning brown/black with bromine water |
| Zinc (Zn2+) | Add excess NaOH to greyish-white precipitate (preliminary) | White precipitate dissolved |
| Barium (Ba2+), Strontium (Sr2+), Calcium (Ca2+) | Flame test: Mix salt with a few drops of conc HCl (in the form of a paste). Skim off some of the paste with a glass rod and expose it to a Bunsen Burner’s flame. | Ba2+: Green-coloured flame |
| Magnesium (Mg2+) | Add NH4Cl, ammonium phosphate (NH4)3PO4, & excess NH4OH to original solution. | White precipitate |
Salt Analysis Chemistry Practical – Tips and Tricks
The salt analysis tricks and tips applied in chemistry are listed below in tabular form:
Cations –
| Cation | Tip | Benefit |
|---|---|---|
| Group 1 & 2 | Perform flame tests last, as residues from other tests can interfere. | Clear distinction of flame colours for identification. |
| Al3+ | Ensure excess NH4OH is added to dissolve the white precipitate and form the characteristic blue layer. | Accurate confirmation of Al3+ presence. |
| Cu2+ | Remember that a black precipitate in the preliminary test isn't unique to Cu2+. A confirmatory test with NH3 is crucial. | Proper identification and avoidance of false positives. |
| Fe3+ | Use concentrated HNO3 cautiously as it's a strong oxidizer. | Safe handling and accurate confirmation of Fe3+. |
Anions –
| Anion | Tip | Benefit |
|---|---|---|
| SO42- | Distinguish between a white precipitate of BaSO4 (SO42-) and BaCO3 (CO32-) by adding dilute HCl. BaSO4 remains insoluble. | Accurate differentiation of anions. |
| NO3- | Use a fume hood during the brown ring test as NO2 fumes can be released. | Safe handling and clear observation of the characteristic brown ring. |
| CO32- | Perform the test quickly after adding HCl, as excessive CO2 evolution can mask other test results. | Timely observation of effervescence for accurate identification. |
Things To Remember
- The salt analysis involves the identification of different anions and cations of inorganic salt.
- It is also known as qualitative analysis of inorganic salt or systematic qualitative analysis.
- When Magnesium sulfate (MgSO4) mixes with the water extract of the salt, it gives a white precipitate.
- When some drops of dilute HCl and hydrogen sulfate are poured into the original solution black precipitate is formed.
- When some drops of dilute hydrochloric acid are added to the original solution white precipitate is formed.
- The sulfate and phosphorus ions do not have any prominent preliminary test.
- Carbonate (CO32-) - Colorless and odourless gas that turns limewater milky.
- Sulfite (SO32-) - Colorless, pungent-smelling gas
- Sulfide (S2-) - Colorless gas which smells like rotten eggs
- Nitrite (NO2-) - Light brown gas having a pungent smell.
- Copper (CU2+) - Formation of black precipitate
- Zinc (Zn2+) - Formation of a greyish-white precipitate.
- Manganese (Mn2+) - Formation of a skin-coloured precipitation
- Acetate (CH3COO-) - Pungent fumes that smell like vinegar
- Nitrate (NO3-) - Brown fumes with a pungent smell
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Sample Questions
Ques: Which salts ionize when dissolved in water and why? (1 Mark)
Ans: The organic salts ionize when dissolved in water because water has a high dielectric constant and hence, the force of attraction holds ions in salt decrease.
Ques: Organic salts possess which type of bonding? (1 Mark)
Ans: The bond that exists in the organic salts is electrovalent.
Ques: What are the colours of nickel salts and manganese salt? (1 Mark)
Ans: The colour of the nickel salt is green or bluish salt and the colour of the manganese salt is Light pink or flesh colour.
Ques: What is meant by sublimation? (1 Mark)
Ans: When the solid directly turns into the gaseous form, the process is known as Sublimation. And on cooling the vapours directly from back to solid.
Ques: What is the need to perform the salt analysis? (2 Marks)
Ans: The main aim of performing salt analysis is to identify the basic and acidic radicals of the given inorganic salt. It gives a very clear idea about the present anions and cations.
Ques: Describe the basic principle of salt analysis. (2 Marks)
Ans: Fundamental principles that govern 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.
Ques: Describe the preliminary test for group 3 anion. (2 Marks)
Ans: There is no preliminary test for group 3 anion. These are the sulfate and phosphate ions groups. If no positive test results are obtained. A direct confirmatory test can be carried out.
Ques: How many electrons are involved in the following redox reaction?
Cr2O72- + Fe2+ + C2O42- → Cr3+ + Fe3+ + CO2 (unbalanced) (2 Marks)
Ans: Balanced Reaction:
Cr2O72- + 2Fe2+ + 2C2O42- → 2Cr3+ + 2Fe3+ + 4CO2
6 electrons are involved in this reaction.
Ques: What is the procedure for testing chloride? (3 Marks)
Ans: Take a few drops of concentrated sulfuric acid (H2SO4) in a test tube and then a very small amount of chloride salt to it. After this, a pungent-smelling gas is formed and is white. When a glass rod that is coated with ammonium hydroxide is brought close to the brim of the test tube, its intensity increases.
Ques: Why does Copper become green when exposed to moist air for a long period? (3 marks)
Ans: When exposed to air, Copper metal turns green in colour because of corrosion. The metal reacts with moisture and atmospheric gases to form a mixture of copper carbonate and copper hydroxide.
Ques: Explain the different stages of salt analysis. (3 marks)
Ans. The different stages of salt analysis are as follows –
- Preliminary Tests: Simple tests like solubility and physical appearance provide initial clues about the salt's properties.
- Group-Wise Analysis: Specific tests for major groups of cations and anions help narrow down the possibilities.
- Confirmatory Tests: Specific tests for individual ions confirm their presence and eliminate ambiguity.
- Identification: Combining all findings, the specific cations and anions are identified, revealing the salt's chemical formula.
Ques: List some common confirmatory tests for cations. (3 marks)
Ans. Examples include:
- Ammonium (NH4+): Nessler's reagent produces a yellow or brown precipitate.
- Lead (Pb2+): KI and K2CrO4 each form yellow precipitates.
- Copper (Cu2+): Excess NH3 turns a black precipitate blue.
- Iron (Fe3+): Concentrated HNO3 forms a brown precipitate, followed by blue with K4[Fe(CN)6] (potassium ferrocyanide).
Ques: What are some tips for accurate salt analysis? (1 mark)
Ans. Use a clean and organized workspace, prepare fresh solutions, use small drops of reagents, observe reactions, record observations systematically, and practice to hone your skills.
Ques: How can you differentiate between BaSO4 and BaCO3 precipitates? (1 mark)
Ans. Add dilute HCl. BaSO4 remains insoluble, while BaCO3 dissolves with CO2 gas evolution.
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