The CBSE Class 12th Chemistry Examination will be held on March 7, 2020. The students who are appearing for CBSE Class 12th Examination can go through the important questions mentioned in this article. The questions mentioned in this article are based on the previous year question papers, sample papers and NCERT textbook.
Key Points to be mentioned while writing the answers to the below mentioned important questions:
Question 1- Explain the cleaning action of soap. Why do soaps not work in hard water?
Answer: The Soap molecules form micelles around the oil droplets in such a way that hydrophobic part of stearate ions is in the oil droplet and hydrophilic part projects out of the grease droplet like the bristles. Since the polar groups can interact with water, the oil droplet surrounded by stearate ions is now pulled in water and removed from the dirty surface. Thus, soaps help in emulsification and washing away oils and fats. Soaps do not work in hard water because hard water contains calcium and magnesium ions. These ions form insoluble Ca and Mg salts. These salts act as scum. The insoluble scum sticks on the clothes, so the cleaning capacity of soap is reduced when Na or K soaps are dissolved in hard water.
Question 2- Define:
(i) Cationic detergents
(ii) Anionic detergents
(iii) Food preservatives
(vi) Broad-spectrum antibiotics
Answer: (i) Cationic detergents: They are quaternary ammonium salts of amines with acetates, chlorides or bromides as anions and the cationic part possess a long hydrocarbon chain and a positive charge on the nitrogen atom. Therefore they are called cationic detergents. Example: Cetyltrimethyl ammonium
(ii) Anionic detergents: The detergents in which large part of their molecules are anions and are used in cleansing action are called anionic detergents. These are obtained from long straight chain alcohols containing 12-18 carbon atoms by treatment with cone. H2S04 followed by neutralization with NaOH. Example: Sodium alkyl sulphates
(iii) Food preservatives: They are used to prevent the food from spoiling due to the microbial growth. Example: Table salt, vegetable oils, sodium benzoate etc.
(iv) Analgesics: Analgesics reduce or abolish pain without causing impairment of consciousness, mental confusion, incoordination or paralysis or some other disturbance of the nervous system.
They are of two types :
(a) Non-narcotic analgesics Example: Aspirin
(b) Narcotic analgesics Example: Morphine
(v) Antiseptics: These are chemical substances which prevent the growth of micro-organisms and may even kill them and safe to be applied on living tissues. Example: Furacin, soframycin etc.
(vi) Broad-spectrum antibiotics: Antibiotics which kill or inhibit a wide range of Gram¬(+ve) and Gram-(-ve) bacteria are called broad-spectrum antibiotics. Example: Chloro-amphical
Question 3- Differentiate between Antiseptics and Disinfectants
1. Antiseptics either kill or prevent the growth of microorganisms.
1. Disinfectants kill the microbes definitely.
2. Antiseptics do not cause harm to the living tissues.
2. Disinfectants are toxic to the living tissues and thus cause harm to the tissues of the skin etc.
Question 4-: (a) What are analgesic medicines? How are they classified and when are they commonly recommended for use?
(b) What are the main constituents of Dettol?
Answer: Drugs which reduce or abolish pain without causing reduction of consciousness, mental confusion, incoordination or paralysis or some other disorder of the nervous system are called analgesic medicines.
They are classified into:
(i) Non-narcotic (non-addictive) drugs. Example: Aspirin, Ibuprofen
(ii) Narcotic (addictive) drugs. Example: Morphine, Heroin.
They are recommended with proper prescription because they are habit forming drugs.
(b) Dettol is a mixture of chloroxylenol and α-terpineol in a suitable solvent.
Question 5- (a) Which one of the following is a food preservative?
Equanil, Morphine, Sodium benzoate
(b) Why is bithional added to soap?
(c) Which class of drugs is used in sleeping pills?
(d) What class of drug is Ranitidine?
(e) Why is the use of aspartame limited to cold foods and soft drinks?
(f) Name the sweetening agent used in the preparation of sweets for a diabetic patient.
Answer: (a) Sodium Benzoate: It is a food preservative.
(b) Bithional acts as a deodorant in soaps, hence it works as an antiseptic agent and reduces the odours produced by bacterial decomposition of organic matter on the skin.
(c) Tranquillizers like barbiturates are used in sleeping pills.
(d) Ranitidine is an Antacid.
(e) Aspartame is limited to cold foods and soft drinks as it decomposes at baking or cooking temperature.
(f) Saccharin is used for a diabetic patient for the preparation of sweets.
Question 6- What are biodegradable and non-biodegradable detergents? Give examples.
Answer: Detergents which have straight hydrocarbon chains are easily degraded or decomposed by a micro-organism, are known as biodegradable detergents. Example: Sodium lauryl sulphate whereas the detergents containing branched hydrocarbon chains and are not easily decomposed by the micro-organisms are known as non-biodegradable detergents. Example : Sodium 4 – (1, 3, 5, 7-tetramethyloctyl) benzene sulphonate.
These were some of the important questions from previous year question paper, sample papers and the NCERT textbooks. Students can also check other important articles from the links given below: