Chemistry: Solved Previous Year’s Question Paper for NCERT/CBSE Class 12th Chemistry Paper Code (HSEIIRKo14–1702—Y)
Long Answer Type Questions (Each carries 5 Marks)
Question: What is Osmotic pressure? Explain how the molecular mass of a non-volatile solute can be determined from it.
Answer: Osmotic pressure is the pressure that is generated by the movement of water molecules across a semi-permeable membrane. This pressure is created by osmosis, the movement of water molecules from a more dilute solution to a more concentrated solution to equalize the concentrations on either side of the membrane. Osmotic pressure is important in many biological processes and is used for a variety of applications in industry.
The molecular mass of a non-volatile solute can be determined from its chemical formula. The molecular mass is the sum of the atomic masses of all of the atoms in the molecule. For example, the molecular mass of sodium chloride (NaCl) can be determined by adding the atomic mass of sodium (22.99 g/mol) to the atomic mass of chlorine (35.45 g/mol), giving a total molecular mass of 58.44 g/mol.
Question: What are Primary and Secondary cells? Discuss one example in each case.
Answer: Primary cells are single-use, non-rechargeable cells that convert chemical energy into electrical energy and are then depleted. An example of a primary cell is a standard alkaline battery.
Secondary cells, also known as rechargeable batteries, are composed of electrochemical cells that can be charged and discharged multiple times. An example of a secondary cell is a lithium-ion battery, which is commonly used in mobile phones.
Question: What is the Electrode Potential and e.m.f. of a cell?
Answer: Electrode potential is the potential difference between a metal surface and its surrounding electrolyte solution. It is also known as electrode potential or redox potential. The electrode potential of a given electrode is determined by the relative proportions of oxidized and reduced species present in the solution.
Question: How is Nitric acid prepared by the Ostwards process? Give its reaction with Iron and Zinc.
Answer: Nitric acid is prepared by Ostwald’s process by the oxidation of ammonia gas with air in the presence of a platinum catalyst.
The reaction of nitric acid with iron is as follows:
Fe + 2HNO3 → Fe(NO3)2 + H2
The reaction of nitric acid with zinc is as follows:
Zn + 2HNO3 → Zn(NO3)2 + H2
Question: Give five Methods of preparation of Ketones.
Answer: 1. Grignard Reaction: This is a very important method for the preparation of ketones. In this reaction, an alkyl halide reacts with magnesium to form an alkyl magnesium halide (Grignard reagent). This Grignard reagent then reacts with a carbonyl compound like an aldehyde or a ketone to form the desired ketone.
2. Wolff-Kishner Reduction: This is a method used to reduce ketones to hydrocarbons. It involves the conversion of a carbonyl compound to an alkane using a base such as sodium hydroxide and a reducing agent like hydrazine.
3. Aldol Condensation: This is a reaction between two aldehydes or a mixture of an aldehyde and a ketone to form a β-hydroxy aldehyde or ketone. This reaction can be catalyzed using either an acid or a base.
4. Decarboxylation: This is a reaction in which a carboxylic acid is converted to an aldehyde or ketone. This can be achieved by heating the carboxylic acid in the presence of an alkali metal such as sodium or potassium.
5. Oxidation of Alcohols: This is a reaction in which alcohol is oxidized to a ketone using an oxidizing agent such as chromic acid or Dess-Martin Periodinane.
Short Answer Type Questions (Each carry 3 Marks)
Question: Explain Schotty’s defect.
Answer: Schotty defect occurs when there is an imbalance in the number of electrons present in different parts of a semiconductor material. The imbalance is caused by an interplay between the material’s electronic structure and the charge carriers present in the material. This imbalance leads to a buildup of positive charge in one region and a buildup of negative charge in another, creating a localized electric field. This electric field can cause an increased current flow between the regions, leading to a short circuit.
Question: Explain Coagulation.
Answer: Coagulation is the process of changing a liquid into a solid. It is a natural process that occurs when proteins in a liquid form a network, trapping other molecules and creating a gel-like structure. This process is used in a variety of industries, including food processing, water treatment, and medical treatments. In food processing, coagulation is used to make cheese, yoghurt, and other dairy products. In water treatment, coagulation is used to remove contaminants, such as dirt and metals, from water. In medical treatments, coagulation is used to stop bleeding, form scabs, and help heal wounds.
Question: Write the chemical properties of Phenol.
Answer: 1. Phenol is an acidic compound.
2. It is a highly polar compound with a high dielectric constant.
3. It is a strong oxidizing agent and readily reacts with reducing agents.
4. It is also a strong acid, and is capable of protonating other compounds.
5. It is highly reactive and forms esters, ethers, and other derivatives when reacted with other compounds.
6. It is soluble in water and many organic solvents.
7. Phenol has a high boiling point (181°C) and a low melting point (40°C).
8. It has a low flash point, making it a hazardous material to work with.
9. It has a high solubility in alcohols and other organic solvents.
10. Phenol is a strong acid and is corrosive to metal surfaces.
Question: Differentiate between RNA and DNA
Answer: RNA and DNA are both nucleic acids, but they have several differences.
1. DNA is a double-stranded, helical molecule found in the nucleus of cells, while RNA is a single-stranded molecule found in the cytoplasm.
2. DNA contains the bases adenine, guanine, cytosine, and thymine, while RNA contains the base uracil in addition to the other three.
3. DNA is more stable than RNA and is used to store genetic information, while RNA is used to encode and translate genetic information into proteins.
4. DNA is usually much longer than RNA, and RNA is usually more reactive than DNA.
Very Short Answer Type Questions (Each carry 2 Marks)
Question: Explain the Electrolytic method for refining copper.
Answer: Electrolytic refining is a process used to purify metals such as copper. It is a process that uses an electrolyte solution to extract impurities from the metal. The metal is placed in an anode and is then subjected to an electric current. This causes the metal to dissolve into positively charged ions. The positively charged ions are then attracted to the negative electrode, leaving the impurities behind. The positively charged ions are then deposited onto the negative electrode, forming pure copper. The impurities are then removed from the solution and the purified copper is collected.
Question: Give two substitution reactions of Alkyl halides.
Answer: 1) Nucleophilic Substitution: Alkyl halides can undergo nucleophilic substitution, where a nucleophile (such as a hydroxide or a cyanide ion) attacks the carbon of the alkyl halide, forming a new carbon-nucleophile bond, and breaking the carbon-halide bond.
2) Elimination Reactions: Alkyl halides can also undergo elimination reactions, where the halide is eliminated and a π bond is formed between the two carbon atoms of the alkyl halide. This reaction is typically done in the presence of a base, such as a hydroxide ion.
Question: Give two uses of Iodoform.
Answer: 1. Iodoform is used as an antiseptic to clean wounds and prevent infection.
2. Iodoform is also used as an insect repellent to keep away mosquitoes, fleas, and other pests.
Question: Give two uses of Bakelite.
Answer: 1. Bakelite was used to make a variety of products including radios, telephones, electrical insulators, and kitchenware.
2. Bakelite was also used to make jewellery, such as costume pieces and bangles.
Question: Why detergents are preferred over soaps?
Answer: Detergents are preferred over soaps because they are more effective in removing dirt, grease, and other stains. Detergents are also more effective at low temperatures, while soaps are less effective. Detergents are also less prone to forming scum on fabric or surfaces, and they often contain fewer harsh chemicals than soaps.
Objective Type Questions (Each carries 1 Marks)
(i) Tyndal effect is shown by ———– sols.
Answer: Colloidal particles
(ii) –COOH is the functional group of —————-
Answer: -Carboxylic acid
(iii) Sulphide ores are concentrated by the Gravity process (True/False)
(iv) Alcohols are soluble in water due to hydrogen bonding
(v) Phenols are acidic (True/False)
(vi) What is the functional group in Primary Amines.
Answer: The functional group in primary amines is an amine group, which is composed of a nitrogen atom bonded to two hydrogen atoms and one alkyl or aryl group.
(vii) What are Monosaccharides?
Answer: Monosaccharides are the simplest form of carbohydrates, made up of a single molecule of sugar. The most common monosaccharides are glucose, fructose and galactose. They are the building blocks for larger carbohydrates such as disaccharides and polysaccharides and play an important role in metabolism and energy production.
(viii) Polythene is a polymer of
(a) Vinyl chloride (B) Ethene (C) Ethyne (D) Chloroprene
Answer: B) Ethene
(ix) Penicilline is
(A) Antiseptic (B) Antipyretic (C) Antibiotic (D) Analgesic
Answer: C. Antibiotic