An Overview of Class 11 Chemistry Qualitative Analysis Experiment
Analytical chemistry deals or works with qualitative and quantitative analysis of substances. In inorganic qualitative analysis, the given compound is analysed or diagnosed for the radicals, i.e., cation (+ve) and the anion (-ve), that it contains. Physical procedures like nothing (taking) the colour, smell, or taste of the substance have a minimal scope because of the corrosive, poisonous nature of the chemical compounds. Therefore, what one has to resort (rectify) to is the chemical analysis of the substance that has to be carried out along with the physical examination of the compound under consideration. Examples are- Titration (volumetric analysis), Gravimetric analysis, Various wet chemistry tests, Combustion analysis, and Inert gas fusion.
Table of content
Aim
Physical Examination of the Salt
Dry Heating Test
Charcoal Cavity Test
Result
Aim
To deal with the concept of Qualitative analysis using the Qualitative analysis experiment.
Materials Required
Test Tubes
Test Tube Stands
Boiling Tube
Test Tube Holder
Measuring Cylinder
Delivery Tube
Filter Paper
Salts
Water
Blowpipe
Theory
1. Physical Examination of the Salt:
The examination of the unknown salt involves studying colour, smell and density. The test is not very reliable but is certainly helpful in identifying some coloured cations. Characteristic smell helps identify ions such as ammonium, acetate and sulphide.
Procedure
Observe the colour of the salt, which may provide useful information about the cations. The table below gives the characteristic colours of the salts of some cations.
Observations
2. Dry Heating Test
This test is performed by heating a small amount of salt in a dry test tube. Quite valuable information can be gathered by carefully performing and noting the observations. On heating, some salts undergo decomposition, thus evolving the gases or may undergo characteristic changes in the colour of the residue.
Procedure
Take about 0.1 g of the dry salt in a clean and dry test tube.
Heat the above test tube for about one minute and observe the colour of the residue when it is hot and when it becomes cold. Observing changes indicates the presence of cations, which may not be taken as conclusive evidence.
Observations
3. Charcoal Cavity Test
This test is based on the fact that metallic carbonates, when heated in a charcoal cavity decompose to give corresponding oxides. The oxides appear as coloured incrustation or residue in the cavity. In certain cases, the oxides formed partially undergo reduction to the metallic state producing metallic beads or scales.
Procedure
Make a small cavity in a charcoal block with the help of a charcoal borer. Do not apply pressure; otherwise, it will crack.
Fill the cavity with about 0.2 g of the salt and about 0.5 g of anhydrous sodium carbonate.
Moisten the salt in the cavity with one or two drops of water. Otherwise, the salt/mixture will blow away.
Use a blowpipe to heat the salt in a luminous (reducing) flame and observe the colour of the oxide/ metallic bead formed in the cavity when hot and cold. Obtain oxidising and reducing flame.
Always bore a fresh cavity for testing the new salt.
Observations
Result
The physical examination of the salt (their cations) can be found out with the study of their characteristic colours.
On heating, some salts undergo decomposition, thus evolving the gases or may undergo characteristic changes in the colour of residue.
The nature of oxides can also be found using the charcoal cavity test.
Precautions
If you have touched any salt, wash your hands at once. It may be corrosive to the skin.
Never taste any salt; it may be poisonous. Salts of arsenic and mercury are highly poisonous.
Use a perfectly dry test tube for performing the test. While drying a test tube, keep it in a slanting position with its mouth slightly downwards so that the drops of water which condense on the upper cooler parts do not fall back on the hot bottom, as this may break the tube.
For testing a gas, a filter paper strip dipped in the appropriate reagent is brought near the mouth of the test tube, or the reagent is taken in a gas detector, and the gas is passed through it.
Do not heat the tube strongly at one point, as it may break.
Lab Manual Questions
1. What is qualitative data analysis?
Ans. Qualitative data analysis involves organising, analysing, and interpreting qualitative data.
2. What is the significance of qualitative analysis in organic compounds?
Ans. Qualitative analysis of the organic compound helps determine the presence or absence of a particular compound. But it does not help in determining the presence of mass or concentration of the compound.
3. What is inorganic qualitative analysis?
Ans. Inorganic qualitative analysis is a method of analytical chemistry which seeks to find the elemental composition of inorganic compounds.
4. What is a qualitative analysis of carbohydrates?
Ans. The qualitative analysis of carbohydrates is used to characterise carbohydrates present in an unknown solution based on various chemical assays.
Viva Questions
1. What is qualitative analysis?
Ans. The type of analysis deals with the methods used to determine a compound's constituents.
2. Name any iron salt which is light green.
Ans. Ferrous sulphate.
3. What is the colour of nickel salts?
Ans. Bluish green or green.
4. What is a radical?
Ans. A radical may be defined as an atom or group of atoms that carries a charge and behaves as a single unit in chemical reactions.
5. What are acidic and basic radicals?
Ans. Radicals carrying a positive charge are called basic radicals, and those carrying a negative charge are called acidic radicals.
6. Why do inorganic salts ionise when dissolved in water?
Ans. Due to the high dielectric constant of water, the force of attraction holding the two ions in a salt decreases. Thus, the two ions separate. The ions are further stabilised by solvation.
7. What type of bond is present in an inorganic salt?
Ans. Electrovalent bond.
8. What is the colour of iron salts?
Ans. Ferrous salts are usually light green, while ferric salts are generally brown.
9. Give examples of some coloured basic radicals.
Ans. Cu2+,Fe2+, Fe3+, Cr3+, Ni2+, Co2+ and Mn2+.
Practical Questions
1. Identify the test which is not a part of the qualitative analysis.
Iodine test
Flame test
Litmus test
Kastle-Meyer test
Ans. The litmus test is not a part of qualitative analysis.
Which of the following is not a physical method?
Atomic emission spectroscopy
Inert gas fusion
Trace element analysis
none
Ans. Inert gas fusion is not a physical method.
Qualitative analysis is used for separating the specific constituents from a mixture.
True
False
Not known
None
Ans. False the given statement is not true.
Identify the one which does not come under the chemical methods of qualitative analysis?
Volumetric
Gravimetric
Titrimetric
Magnetic Susceptibility
Ans. Magnetic Susceptibility does not come under the chemical methods of qualitative analysis.
Covalent molecules can be identified using quantitative methods.
True
False
Can’t predicted
None
Ans. False covalent molecules can’t be identified using quantitative methods.
Identify the element that Lassaigne’s test cannot detect.
Sulfur
Fluorine
Nitrogen
Phosphorus
Ans. Lassaigne’s test cannot detect fluorine.
What is the colour of nickel salts?
White
Bluish green
Brown
Silver
Ans. Nickel salts are Bluish green in colour.
Which compound gets precipitated in the detection of carbon and hydrogen?
Calcium carbonate
Copper
Copper Sulphate
Carbon dioxide
Ans. Calcium carbonate gets precipitated in the detection of carbon and hydrogen.
What is the precipitate's colour obtained in the Sulphur test?
Blue
White
Green
Black
Ans. Black colour will be obtained.
Conclusion
From the above experiment, we can conclude that the physical examination of the salt (their cations) can be found by studying their characteristic colours. Also, on heating, some salts undergo decomposition, thus evolving the gases or may undergo characteristic changes in the colour of the residue. The nature of oxides can also be found using the charcoal cavity test.
FAQs on Class 11 Chemistry Qualitative Analysis Experiment
1. What are the most frequently asked topics in Qualitative Analysis for the Class 11 Chemistry exam?
For the Class 11 exams, the most important questions are typically based on the principles and reactions involved in specific tests. Key topics include:
- The reason for preparing a sodium fusion extract (Lassaigne's extract).
- The chemical tests for the detection of Nitrogen, Sulphur, and Halogens using this extract.
- The confirmatory test for Phosphorus in an organic compound.
- Reasoning-based questions on the specific reagents used or procedural steps followed in these tests.
2. How are marks typically distributed for questions on Qualitative Analysis in the CBSE 2025-26 paper pattern?
Questions on Qualitative Analysis are often integrated into the Organic Chemistry section. You can expect them to appear as short answer questions worth 2 or 3 marks. These questions usually require you to write the chemical equation for a test and state the observation (e.g., colour change or precipitate formation). Sometimes, a conceptual question from this topic might be included as part of a larger 5-mark question.
3. Why is Lassaigne's test considered so important for the qualitative analysis of organic compounds?
Lassaigne's test is fundamentally important because organic compounds have elements like nitrogen, sulphur, and halogens bonded covalently. These covalent bonds do not allow the elements to ionise in a solution, making them difficult to detect. The test uses molten sodium to fuse with the organic compound, converting these elements into water-soluble ionic salts (like NaCN, Na2S, and NaX). These ionic compounds can then be easily identified using simple chemical tests.
4. From an exam point of view, what's the main difference between important questions on qualitative and quantitative analysis?
The key difference is their objective. Important questions on qualitative analysis focus on 'what' elements are present. They test your knowledge of reaction principles, observations, and equations for identification. In contrast, questions on quantitative analysis focus on 'how much' of an element is present and test your ability to apply formulas and perform calculations, such as in the Carius or Duma's method.
5. What kind of Higher Order Thinking Skills (HOTS) questions can be asked from the tests for halogens?
A common HOTS question involves the procedure for testing halogens. For example, you might be asked: "Why is the sodium fusion extract first boiled with concentrated nitric acid before adding silver nitrate?" The answer is to decompose any sodium cyanide or sodium sulphide present, as they would otherwise interfere with the test by forming precipitates (AgCN and Ag2S) with silver nitrate, leading to a false positive result.
6. If a blood-red colour appears in a test, what does it signify, and what follow-up questions might be asked?
A blood-red colouration with ferric chloride indicates the presence of both Nitrogen and Sulphur in the organic compound. During sodium fusion, they combine to form sodium thiocyanate (NaSCN). An exam question might ask you to write the chemical equation for the formation of ferric thiocyanate [Fe(SCN)]2+, which is responsible for the colour. It's a classic signpost for a multi-element compound.
7. Are there any common mistakes students make in questions about the test for Nitrogen?
Yes, a frequent area for error is the reason for adding freshly prepared ferrous sulphate solution. A key part of the test for Nitrogen is the formation of sodium ferrocyanide. The purpose of adding ferrous sulphate is to react with the sodium cyanide to form this compound. Students often forget to mention that a small amount of ferric ions, needed for the final Prussian blue colour, is formed by the oxidation of some ferrous ions. Forgetting this detail can lead to losing marks.
