Chemistry: Solved Previous Year’s Question Paper for NCERT/CBSE  Class 12th Chemistry Paper Code (HSEIIRKo14–1702—Y)

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: Define Elevation in boiling point. Derive its relation with the Molecular Mass of Non-volatile solute.

Answer: Elevation in boiling point is the increase in the temperature at which a liquid boils as atmospheric pressure is decreased. This is a result of the decrease in pressure reducing the amount of energy required for a liquid to change from a liquid to a vapour.

The elevation in the boiling point is given by the expression 

The molality is given by the expression m=M2​⋅W1​W2​​……(2)

Substitute equation (2) with equation (1)


Hence, the expression for the molar mass of the solute is


Question: Write five methods of preparation of Aldehydes.

1. Oxidation of primary alcohols: Primary alcohols can be oxidized using reagents such as chromic acid, potassium permanganate, or pyridinium chlorochromate (PCC) to form aldehydes.

2. Reduction of carboxylic acids: Carboxylic acids can be reduced using reagents such as lithium aluminum hydride (LiAlH4) or sodium borohydride (NaBH4) to form aldehydes.

3. Oxidation of styrenes: Styrenes can be oxidized using reagents such as chromium trioxide (CrO3), pyridinium chlorochromate (PCC), or dimethyldioxirane (DMDO) to form aldehydes.

 4. Ozonolysis of alkenes: Alkenes can be ozonolyzed using ozone to form aldehydes.

5. Hydrolysis of nitriles: Nitriles can be hydrolyzed using acid or base to form aldehydes.

Question: Give the chemical properties of Carboxylic acids.

Answer: 1. Carboxylic acids are organic compounds that contain a carboxyl group (-COOH).

2. They are generally weak acids, and are soluble in water due to the presence of the hydroxyl group.

3. Carboxylic acids tend to react with bases to form salts and can form esters with alcohols.

4. They can also react with other carboxylic acids to form carboxylic acid derivatives, such as amides and anhydrides.

5. Carboxylic acids can also undergo a variety of other reactions, including oxidation, reduction, aldol condensation, and decarboxylation.

Short Answer Type Questions (Each carry 3 Marks)

Question: Explain the magnetic properties of solids.

Answer: Magnetic properties of solids refer to the response of a material to a magnetic field.

1. Solids can be divided into two categories: ferromagnetic and non-ferromagnetic.

2. Ferromagnetic materials are those that are strongly affected by an external magnetic field and can become permanently magnetized. Examples of ferromagnetic materials include iron, nickel, and cobalt.

 3. Non-ferromagnetic materials, on the other hand, are not strongly affected by external magnetic fields and do not become magnetized. Examples of non-ferromagnetic materials include most metals, ceramics, and plastics.

Question: Differentiate between the order of Reaction and the Molecularity of reaction.

Answer: Order of Reaction: The order of a chemical reaction is the power to which a reactant is raised in the rate equation of a reaction. It is determined experimentally by carrying out a rate experiment.

 The molecularity of Reaction: The molecularity of a reaction is the number of molecules taking part in the overall reaction. It is determined by counting the number of molecules (reactants and products) involved in the reaction.

Question: Explain Brownian motion.

Answer: Brownian motion is the random movement of particles suspended in a liquid or gas due to the bombardment of surrounding particles. It is named after the Scottish botanist Robert Brown, who first observed it in 1827.

Brownian motion is a physical phenomenon that is visible under a microscope and is a direct result of the molecular motion of the surrounding medium. The motion is random, meaning that the particles move in a seemingly random pattern that cannot be predicted. It has been used as evidence for the existence of atoms and molecules, which were not yet accepted at the time of its discovery.

Question: Give three oxidizing properties of Ozone.

Answer: 1. Ozone acts as an oxidizing agent to break down organic substances such as oils and fats.

2. Ozone can oxidize inorganic substances such as metals and certain gases.

3. Ozone can act as a catalyst for a variety of chemical reactions.

Question: Write the importance of co-ordination compounds.

Answer: 1. Coordination compounds are important in the fields of chemistry and biochemistry because they allow for the study of chemical processes at a molecular level.

2. Coordination compounds are used to study the behaviour of metals, the formation of chemical bonds, and the coordination of electron-rich centres.

3. Coordination compounds are also important in the synthesis of pharmaceuticals and the development of catalysts for industrial processes.

4. Coordination compounds are used in the study of the structure and properties of materials, as well as in the development of new materials and technologies.

Question: Explain the classification of Alcohols.

Answer: Alcohols are classified by the number of carbon atoms in the molecule.

Primary (1°) alcohols have a single carbon atom with a hydroxyl group attached, secondary (2°) alcohols have two carbon atoms with a hydroxyl group attached, and tertiary (3°) alcohols have three carbon atoms with a hydroxyl group attached.

Primary alcohols can be further classified into primary, secondary, and tertiary alcohols. Primary alcohols contain a single hydroxyl group attached to a single carbon atom,

Secondary alcohols contain two hydroxyl groups attached to a single carbon atom.

Tertiary alcohols contain three hydroxyl groups attached to a single carbon atom.

Question: Explain Lanthanide contraction

Answer: Lanthanide contraction is a phenomenon that describes the decrease in atomic radii of the lanthanide elements as one moves down the lanthanide series of the periodic table. This decrease is due to the lanthanide elements having an increasing number of f-electrons, which causes increased shielding of the valence electrons, resulting in the electrons being held more tightly by the atom’s nucleus.

Question: Give three sources of vitamins A and D.

Answer: 1. Vitamin A: Carrots, sweet potatoes, kale, spinach, pumpkin, squash, cantaloupe, apricots, eggs, fortified dairy products.

2. Vitamin D: Salmon, tuna, mackerel, sardines, beef liver, egg yolks, fortified dairy products, fortified cereal, fortified orange juice.

3. Cod liver oil, fortified margarine, and some types of mushrooms.

Very Short Answer Type Questions (Each carry 2 Marks)

Question: Calculate half-life periods for ist order reaction

Answer: The half-life period for a first-order reaction can be calculated using the following equation:

t1/2 = 0.693 / k

where k is the rate constant for the reaction.

Question: Define ore and give two ores of Iron

Answer: Ore is a naturally occurring solid material from which a metal or valuable mineral can be extracted profitably.

Two ores of iron are hematite (Fe2O3) and magnetite (Fe3O4).

Question: Give two uses of DDT.

Answer: 1. DDT is a chemical used in pest control and agricultural insect control.

2. It has been used to control mosquitos that carry malaria, and to protect crops from damage by pests.

Question: Give two substitution reactions of Alkyl halides.

Answer: 1. SN1 (nucleophilic substitution, first order) reaction: Alkyl halide + Nu- → Alkyl product + Halide ion

2. SN2 (nucleophilic substitution, second order) reaction: Alkyl halide + Nu- → Alkyl product + Halide ion

Question: How Polythene is prepared

Answer: Polythene is prepared through a process called polymerization. This process involves the combination of two or more monomers (small molecules) to create a larger molecule. The monomers used to create polythene are typically ethylene, which is derived from natural gas or petroleum and can be combined through a variety of different methods. The result is a plastic that is lightweight, yet strong and durable.

Question: What are Antibiotics and give two examples.

Answer: Antibiotics are a type of medication used to treat bacterial infections. They are made from natural substances produced by certain types of bacteria and fungi. Examples of antibiotics include penicillin and amoxicillin.

Objective Type Questions (Each carries 1 Marks)

(i) There are ————- types of voids

Answer: Five

(ii) Copper pyrite is an ore of copper (True/False)

Answer: True

(iii) Isopropyl Alcohol is a primary alcohol (True/False)

Answer: True

(iv) What is the functional group in Aldehydes

Answer: The functional group in aldehydes is a carbonyl group (C=O).

(v) Define Diazotisation

Answer: Diazotization is a chemical reaction in which a compound is treated with a diazonium salt to form a diazonium compound. This reaction is used to convert primary amines into diazonium salts, which can then be used in a variety of reactions such as the Sandmeyer reaction and the reaction of diazonium salts with aromatic compounds to form azo compounds.

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