Salt Analysis

A Brief Introduction to Salt Analysis

The segregation of different anions and cations and identification of the same in inorganic salts is known as salt analysis. This process is known via different names like qualitative analysis of inorganic salts or systematic qualitative analysis. Inorganic salts are separated into different ions with the help of different sorts of experiments done under laboratory conditions and putting the compounds under different distinct tests which confirm whether certain ions are present or not in the solution. 

For both theory and practical examinations, class 12 chemistry practical salt analysis is a very important topic. If you were plagued until today with questions like ‘how to do salt analysis experiment class 12’, keep reading this article to get all your answers. 


A Walkthrough for Analysing Salts

  1. Procure a considerable amount of salt on which you want to conduct an experiment.

  2. Try to find out which anion group is present inside the salt. For most of this experiment, finding a wider group of ions is easier because, for groups, there is a common reagent against which a positive test result is obtained.

  3. Once you find the group, take each anion of that group and perform positivity tests. 

  4. Do the same group-wise experiment for cations, as you did for anions.

  5. Once you find the group, take each cation of that group and perform positivity tests.

  6. When both the cation and anion are obtained and identified, construct the chemical formula keeping in mind the valences of each ion. For example, if the cation found is Fe3+ and the anion found is Cl-, then the final inorganic salt result will be FeCl3

  7. It is not mandatory that anions have to be found first. The order of finding each ion can also be swapped. 


Sample Answer Format

Below we provide a table which will help you conduct and write any practical experiment related to salt analysis class 12 with ease. 

Aim: To separate and identify the cation and anion present in the given inorganic salt.

Apparatus Needed: To be done by students. 

Procedure:

1. Anion Group Test – Preliminary

2. Final Anion Test – Confirmatory

3. Cation Group Test – Preliminary

4. Final Cation Test – Confirmatory


Shortcuts to Identify Ions

There are thousands of cations and anions which are there in nature and being discovered regularly. That is the reason it is impossible for students to test for each and every one of them. Also, owing to academic reasons, there are a certain set of popular ions which are asked to be experimented upon. We provide here a small checklist and a table which will help you identify cations much more easily than your peers. 

  1. Make sure you correctly identify the colour of the cation. 

  2. Most cations secrete a certain colour when mixed with other compounds. If a cation is coloured, you can skip the steps in between and go directly for the confirmatory test. 


Colour of the Salt

Cation Present

Deep green or purple

Cr3+

Whitish pink

Mn2+

Deep red

Co2+ or HgI2

Green

Fe2+

Brown or yellow

Fe3+

Dark blue

Co2+

Green

Ni2+

Proper blue

Cu2+

Green or blue

Cu2+


  1. Do not be confused if the salt is colourless. There are more colourless salts present than coloured salts. For colourless salts, the most fruitful test is the flame test, which proves the presence of three different cations. The most effective way to perform the flame test is to hold a pinch of the given salt and pour a miniscule amount of concentrated acid (say, hydrochloric acid) on it and then put it on a burner.

  2. If even after this, there is no coloured cation seen to be present, move on to the preliminary test to identify the cation group, rather than single cations. 

  3. Remember that there are certain cations which do not react with certain anions. For example, Sr2+, Pb2+, Ca2+ and Ba2+ do not have any known inorganic salt with the sulphate ion (SO42-). Another such example is the phosphate ion (PO43-) which forms salts only with group 0, group 1 and group 2 ions.

  4. There are certain salts which are commonly asked in class 12 examinations. For example, NH4Br and CaCl2 are the two most popular salts which examiners ask students. Also, salts like calcium carbonate have a chalk-like appearance, which can be easily identified. Hence, even if it seems tough to identify salts, remembering these shortcuts can help save you a lot of time in the exam hall.


Pop Quiz 1

  1. Identify the anion in the given inorganic salt – MnO2

    1. Mn4+

    2. O2- (Answer)

    3. O-

    4. Mn+


A Guide to Common Cations to Help with Salt Analysis

Cations

Group

NH4+

Group 0

Pb2+

Group 1

Cu2+

Group 2

Fe3+, Fe2+, Al3+

Group 3

Co2+, Mn2+, Ni2+, Zn2+

Group 4

Ba2+, Ca2+, Sr2+

Group 5

Mg2+

Group 6


Keep in mind that multiple cations of the same group will have to undergo the same preliminary test, but undergo distinct confirmatory tests.


A Guide to Common Anions in Salt Analysis

Anions

Group

CO32-, NO2, SO32-, S2-

Group 1

Cl, Br, I, CH3COO, NO3, C2O42-

Group 2

PO43-, SO42-

Group 3


Preliminary Tests (Anions & Acid Radicals)

The salt analysis for anions involves carrying out preliminary tests and group-wise to find the salt’s anion. If the test yields positive results, a confirmatory test needs to be carried out in order to confirm if the anion is present or not in the salt.


Preliminary Tests (Group 1 Anions)

Procedure: Take a small amount of salt solution in a test tube and add some drops of sulphuric acid (H2SO4) to it. If you observe no change, then you can carry out preliminary tests for Group 2 anions.


Anions

Results

Carbonate (CO32-)

An odourless and colourless gas is released. It turns limewater milky.

Sulphite (SO32-)

Releases a pungent-smelling, colourless gas

Sulphide (S2-)

A colourless gas is released which smells of rotten eggs.

Nitrite (NO2)

A pungent-smelling gas is released, which is light brown in colour.


Preliminary Tests (Group 2 Anions)

Procedure: Take a few drops of concentrated sulfuric acid (H2SO4) in a test tube and add tiny amounts of salt to it. If you notice no change, then you can carry out preliminary tests for Group 3 anions.


Anions

Results

Chloride (Cl)

A pungent-smelling gas is released, that is white in colour. This further increases in intensity when a glass rod, coated with ammonium hydroxide is brought close to the brim of the test tube.

Bromide (Br)

Reddish-brown fumes are released.

Iodide (I)

Violet fumes are released.

Acetate (CH3COO)

Fumes, smelling like vinegar, are released.

Nitrate (NO3)

Pungent-smelling brown fumes are released.

Oxalate (C2O4)

A combination of carbon monoxide and carbon dioxide will be released in a bubbly effervescence.


Preliminary Tests (Group 3 Anions)

Significantly, Group 3 anions do not have any prominent preliminary test. These are the phosphate and sulphate ion groups, and if no positive test results are obtained, you must directly carry out the confirmatory tests for these.


Anions

Confirmatory Tests

Observation

Carbonate (CO32-)

Take the water extract of the salt and add magnesium sulphate (MgSO4) to it.

A white precipitate is formed.

Sulphite (SO32-)

Take the water extract and add aqueous barium chloride (BaCl2) to it.

A white precipitate is formed. This disappears when you add a small amount of dilute hydrochloric acid (HCl) to it.

Sulphide (S2-)

  1. Take the water extract and add sodium nitroprusside to it.

  2. Also, add a small amount of lead acetate(aq.) to this.

  1. A purple or violet solution is obtained.

  2. A black precipitate is formed.


Salt analysis is a very integral part of the CBSE chemistry syllabus for class 12. To learn more about the preliminary tests for cations, basic radicals and inorganic salts, check out our range of engaging study material and content available on the site. Download our Vedantu app and register yourself for our free live demo classes.

FAQ (Frequently Asked Questions)

1. Why do we Perform Salt Analysis?

Ans. The qualitative and quantitative analysis of salt often yields very vital information about it. The results of such tests may not be conclusive, but they still give us a very clear idea of the types of anions and cations that might be present in it.

2. What is the Basic Principle of Salt Analysis?

Ans. The fundamental principles governing salt analysis are ionic product and solubility product. For a precipitate to form in a reaction, the ionic product must always be greater than the solubility product.

3. What is the Procedure to Test for Chloride?

Ans. The procedure is taking a few drops of concentrated sulfuric acid (H2SO4) in a test tube and adding tiny amounts of chloride salt to it.

The results include a pungent-smelling gas which is released. This gas is white in colour. This further increases in intensity when a glass rod, coated with ammonium hydroxide is brought close to the brim of the test tube.

4. What is the Preliminary Test for Group 3 Anions?

Ans. Significantly, Group 3 anions do not have any prominent preliminary test. These are the phosphate and sulphate ion groups, and if no positive test results are obtained, you must directly carry out the confirmatory tests for these.