Chemistry: Solved Previous Year’s Question Paper for NCERT/CBSE Class12th Chemistry Paper Code (HSEIIRKO-13-Y)
Long Answer Type Questions (Each carries 5 Marks)
Question: How is KMno4 prepared from pyrolusite and gives its three oxidizing properties?
Answer: KMno4 is prepared by heating pyrolusite in the presence of air and then grinding the resulting product.
2MnO4−+5C2O42−+16H+→2Mn2++10CO2+8H2O.
The three oxidizing properties of KMno4 are
1. It readily reacts with combustible materials, releasing oxygen and creating heat.
2. It can oxidize other compounds, such as alcohols, to form aldehydes or acids.
3. It can reduce metals, such as iron, to form oxides or other compounds.
Question: Discuss the manufacture of NH3 by Habers Process
Answer: The Haber process is a chemical process used to produce ammonia (NH3) from nitrogen (N2) and hydrogen (H2).
The following reaction takes place in the reactor.
N2(g)+H2(g)⇌2NH3(g)
It was developed by the German chemist Fritz Haber in the early 20th century and is one of the most important industrial processes in the world today.
In the Haber process, nitrogen and hydrogen are combined at high temperatures (400-500°C) and pressures (100-200 atmospheres) in the presence of a catalyst (typically iron). The reaction produces ammonia, which is then recovered and used in a variety of applications. The main advantages of the Haber process are its efficiency, low cost, and ability to produce large quantities of ammonia. It is also relatively safe and environmentally friendly, as it does not produce significant amounts of harmful byproducts.
Question: Explain the Froth Floatation process.
Answer: Froth floatation is a process used for the separation of components of a mixture based on the difference in their ability to be wetted by a liquid. The process is commonly used to separate particles of valuable minerals from the rest of the ore. The process begins by crushing the ore into a fine powder and adding a mixture of water and a reagent, usually a surfactant, to the slurry. This mixture is then agitated, causing the valuable mineral particles to become attached to the bubbles, which rise to the surface. The froth is skimmed off and the remaining material, now known as tailings, is discarded. The separated valuable minerals are then further processed to produce a marketable commodity.
Question: Give a brief account of the following reactions
(i) Aldol condensation
(ii) Cannizzaro’s reaction
(iii) Hell Volhard Zelensky (HVZ) reaction.
Answer: (i) Aldol condensation: It is a reversible reaction between two aldehydes or ketones to form β-hydroxy aldehydes or β-hydroxy ketones. It can be catalyzed by base or acid.
(ii) Cannizzaro’s reaction: It is an oxidation-reduction reaction in which an aldehyde is oxidized to a carboxylic acid and the corresponding alcohol is reduced to an alkane. It is catalyzed by the base.
(iii) Hell Volhard Zelensky (HVZ) reaction: It is an organic reaction in which an aldehyde is converted to alcohol by reaction with an acid catalyst. It is an acid-catalyzed reaction and requires anhydrous conditions.
Question: Write the electronic configuration of Noble gases.
Answer: The electronic configuration for the noble gases is as follows: Helium: 1s2
Neon: 1s2 2s2 2p6 Argon: 1s2 2s2 2p6 3s2 3p6
Krypton: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6
Xenon: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6
Radon: 1s2 2s2 2p6 3s2 3p6 3d10 4s2 4p6 4d10 5s2 5p6 6s2 6p6
Question: State Faraday’s Ist law of Electrolysis.
Answer: Faraday’s First Law of Electrolysis states that “the mass of a substance produced during electrolysis is directly proportional to the quantity of electricity passed through the electrolyte.” This means that the amount of material released from an electrolyte is directly proportional to the amount of current that passes through it.
Short Answer Type Questions (Each carry 3 Marks)
Question: Name factors which affect the rate of reaction.
Answer: The factors that affect the rate of a reaction include:
1. The concentration of reactants: Increasing the concentration of reactants increases the rate of reaction.
2. Temperature: Increasing the temperature increases the rate of reaction.
3. Surface area: Increasing the surface area of a substance increases the rate of reaction.
4. Catalysts: Catalysts speed up the rate of reaction.
5. Pressure: Increasing the pressure increases the rate of reaction.
6. Light: In some cases, light can increase the rate of reaction.
Question: Differentiate between ore and mineral.
Answer: 1. Ore is a type of rock that contains minerals and metals that can be extracted from it.
2. Ore is a mineral or aggregate of minerals from which a valuable constituent, especially a metal, can be profitably mined or extracted.
3. Ore is formed when the minerals are concentrated in a particular area, which is then mined to extract the valuable metal or mineral.
1. Minerals are naturally occurring substances found in the Earth’s crust, composed of one or more elements.
2. Minerals, on the other hand, are inorganic substances that are naturally occurring, such as quartz, diamond, gold, and silver.
Question: Discuss the Carbylamine reaction
Answer: The Carbylamine reaction is a test for the presence of a primary amine. It involves the reaction of the amine with a mixture of chloroform, ethanol and concentrated hydrochloric acid. This reaction produces an isocyanide, which can be detected by its characteristic odour.
The reaction is as follows:
Primary amine + Chloroform + Ethanol + HCl → Isocyanide + HCl
The isocyanide produced in this reaction has a strong, pungent odour, and is used as a diagnostic test for the presence of primary amines. The reaction is also used to determine the identity of the primary amine since different primary amines produce different products under the same reaction conditions.
Question: Why do transition elements form coloured compounds
Answer: Transition elements form coloured compounds because they possess partially filled d-orbitals. These orbitals are split when they interact with ligands, resulting in a change in energy levels between orbitals. This energy difference causes the absorption of visible light, leading to the formation of coloured compounds.
Very Short Answer Type Questions (Each carry 2 Marks)
Question: Define unit cell.
Answer: A unit cell is a repeating unit of a crystal lattice that is used to describe the overall structure of the crystalline material. It is the smallest repeating unit of a crystal lattice and is composed of a set of atoms or molecules arranged in three dimensions.
Question: Give the sources of Vitamins A, C and E.
Answer: Vitamin A: Milk, cheese, eggs, butter, carrots, sweet potatoes, kale, spinach, apricots, and peaches.
Vitamin C: Oranges, lemons, limes, grapefruit, kiwi, strawberries, bell peppers, broccoli, and tomatoes.
Vitamin E: Nuts, seeds, spinach, olive oil, avocados, and fortified foods, such as breakfast cereals.
Question: Define Linkage Isomerism. Give one example.
Answer: Linkage isomerism is a type of isomerism in which compounds have the same molecular formula but different connectivity of atoms due to the difference in the way the atoms are linked together. An example of linkage isomerism is cis-1,2-dichloroethene and trans-1,2-dichloroethene.
Question: How racemic mixture is formed?
Answer: A racemic mixture is formed when an equal amount of two enantiomers, or mirror image molecules, are mixed. Enantiomers are molecules that have the same chemical composition but differ in the arrangement of their atoms, making them non-superimposable mirror images of each other. Racemic mixtures are commonly used in the pharmaceutical industry, as they can be used to create medications that are equally effective regardless of the isomer present.
Question: What are Antifertility Drugs?
Answer: Antifertility drugs are medications that are used to temporarily prevent pregnancy or reduce fertility. They can either inhibit or reduce the production of hormones that are necessary for pregnancy to occur, or interfere with the ability of sperm to fertilize an egg.
Common types of antifertility drugs include birth control pills, hormonal injections, intrauterine devices, and barrier methods such as condoms and diaphragms.
Objective Type Questions (Each carries 1 Marks)
(i) Total Number of atoms per unit cell in fcc is ——–
Answer: 4
(ii) Two types of Geometric Isomerism in Co—ordination compounds are cis and ———— isomers
Answer: trans
(iii) DDT is not an insecticide (True/False)
Answer: False
(iv) The formula of chloroform is CHCL3 (True/False)
Answer: True
(v) The precipitation of the dispersed phase of colloidal sol is called as
Answer: coagulation.
(vi) The chemical which relieves the body from pain is called as
Answer: Acetaminophen.
(vii) Write the structure of Butanone
Answer: Butanone is an organic compound containing the formula CH3C(O)CH2CH3, also known as methyl ethyl ketone (Methyl ethyl ketone).
(viii) Write the structure of Glucose
Answer: The chemical formula of Glucose is C6H12O6.
