Chemistry: Solved Previous Year’s Question Paper for NCERT/CBSE Class 12th Chemistry Paper Code (HSEIIRKON17 15319—A)
Long Answer Type Questions (Each carries 5 Marks)
Question: What are galvanic cells? Describe the construction of the Daniell cell and the reactions involved. How is it represented?
Answer: Galvanic cells, also known as voltaic cells, are electrochemical cells that convert chemical energy into electrical energy. They consist of two half-cells, each with an electrode and an electrolyte. The electron flow between the two half-cells creates a potential difference that can be used to do work.
A Daniell cell is a type of galvanic cell. It consists of two half-cells, one with a copper electrode and a copper sulfate solution as the electrolyte, and the other with a zinc electrode and a zinc sulfate solution as the electrolyte. The two half-cells are connected by a salt bridge, which allows ions to move freely between the two solutions.
The reactions that occur in a Daniell cell are redox reactions, in which electrons are transferred from one species to another. In the copper half-cell, copper ions gain electrons, resulting in the formation of copper metal at the copper electrode. In the zinc half-cell, zinc ions lose electrons, resulting in the formation of zinc ions at the zinc electrode.
The Daniell cell is represented by the chemical equation:
Cu (s) + Zn2+ (aq) → Cu2+ (aq) + Zn (s)
This equation shows that electrons are transferred from zinc ions to copper ions, resulting in the formation of copper metal and zinc ions.
Question: State Kohlraush’s law for the electric conductance of an electrolyte at infinite dilution. Give examples
Answer: Kohlraush’s law states that the electric conductance of an electrolyte at infinite dilution is proportional to the square root of its molar concentration. Mathematically, it can be expressed as G = k√C, where G is the electric conductance, k is a constant, and C is the molar concentration of the electrolyte.
Examples of electrolytes that obey Kohlraush’s law at infinite dilution include sodium chloride, potassium chloride, calcium chloride, ammonium chloride, and magnesium chloride.
Question: How is ammonia manufactured industrially? Draw a flow chart for the manufacture of ammonia. Give any two uses of ammonia.
Answer: Industrial manufacture of ammonia is done by the Haber-Bosch process. The process involves the reaction of nitrogen and hydrogen gas at high temperatures and pressure in the presence of a catalyst.
A flow chart of the process is given below:
1: Nitrogen and Hydrogen gases are taken from the atmosphere.
2: The gases are compressed and cooled to form a liquid state.
3: The liquid is fed into a reaction chamber along with a catalyst.
4: The reaction chamber is heated to a high temperature and pressure.
5: The reaction takes place, forming ammonia.
6: The ammonia is collected and purified.
Uses of Ammonia:
1. Ammonia is used as a fertilizer in agriculture.
2. Ammonia is also used in the production of nitric acid, which is used in the manufacture of explosives.
Question: What is Lanthanide Contraction? What is its cause and what are its consequences?
Answer: Lanthanide contraction is the decrease in the atomic radius of the elements that occur when going from the lanthanide series to the actinide series.
It is caused by the increase in nuclear charge experienced by elements in the lanthanide series due to the presence of more filled inner f-shells. This increase in nuclear charge causes a decrease in the atomic radius of the lanthanide elements.
The consequence of lanthanide contraction is an increase in the ionic radii of the lanthanide elements, making them more suitable for use in ionic bonding. Additionally, lanthanide contraction decreases the ionization energies of the elements, making them easier to oxidize and reduce.
Question: What are carboxylic acids? Describe briefly the general methods of preparation of carboxylic acids.
Answer: Carboxylic acids are organic acids that contain a carboxyl group (-COOH) attached to an alkyl or aryl group. They are generally weak acids, but stronger than alcohols.
The general methods of preparation of carboxylic acids include:
1. Oxidation of primary alcohols: Primary alcohols can be oxidized to carboxylic acids using strong oxidizing agents such as potassium dichromate (K2Cr2O7) in acetic acid.
2. Hydrolysis of nitriles: Nitriles can be hydrolyzed to carboxylic acids using acid catalysts.
3. Oxidation of aldehydes: Aldehydes can be oxidized to carboxylic acids using strong oxidizing agents such as potassium permanganate (KMnO4).
4. Oxidation of alkylbenzenes: Alkylbenzenes can be oxidized to carboxylic acids using strong oxidizing agents such as chromic acid (H2CrO4).
5. Oxidation of carboxylic acid esters: Carboxylic acid esters can be oxidized to carboxylic acids using strong oxidizing agents such as potassium permanganate (KMnO4).
Short Answer Type Questions (Each carry 3 Marks)
Question: Give characteristics of physical adsorption and chemisorptions.
Answer: Physical Adsorption:
1. Occurs on the surface of solids or liquids
2. Occurs when weak van der Waals forces are present
3. Is reversible and can be easily broken
4. Occurs at low temperatures
5. Is a weak form of adsorption
1. Occurs on the surface of solids or liquids
2. Occurs when strong covalent or ionic bonds are present
3. Is irreversible and does not break easily
4. Occurs at high temperatures
5. Is a strong form of adsorption
Question: What are Phenols? How do they differ structurally from aromatic alcohols?
Answer: Phenols are a class of organic compounds that contain a hydroxyl functional group (-OH) connected directly to an aromatic hydrocarbon group.
Question: What are Interhalogens? How are they formed?
Answer: Interhalogens are compounds that contain two different halogen atoms. They are formed when different halogens react with each other; for example, chlorine and fluorine can react to form chlorine fluoride (ClF).
Question: Distinguish between ideal and non-ideal solutions.
Answer: An ideal solution is a solution that is composed of two or more substances, where all of the substances are completely dissolved and form a homogeneous mixture.
A non-ideal solution is composed of two or more substances, but the components do not mix completely, and the solution is not homogeneous.
Question: Give three physical and chemical properties of haloalkanes.
Answer: Physical properties:
1. Halogenated compounds have a low boiling point, due to the presence of weak intermolecular forces.
2. Halogenated compounds have a high melting point, due to the stronger intermolecular forces.
3. Halogenated compounds are generally nonpolar, due to the presence of electronegative halogen atoms.
1. Halogenated compounds are generally more reactive than non-halogenated compounds due to their partial negative charge.
2. Halogenated compounds can undergo substitution and elimination reactions due to the presence of halogen atoms.
3. Halogenated compounds can undergo oxidation reactions due to the presence of halogen atoms.
Question: What are carbohydrates? How are they classified?
Answer: Carbohydrates are a type of macronutrient found in a variety of foods.
They are classified as simple or complex, depending on their chemical structure.
Simple carbohydrates include monosaccharides and disaccharides, which are made up of a single sugar molecule or two sugar molecules, respectively.
Complex carbohydrates include polysaccharides such as starches and dietary fibres, which are made up of multiple sugar molecules.
Question: Give at least three points of difference between molecularity and order of reactions.
Answer: 1. Molecularity of a reaction refers to the number of molecules involved in a single step in a reaction, while an order of a reaction refers to the degree of the rate equation that corresponds to the concentration of a reactant.
2. Molecularity is always a whole number while the order of a reaction may be a fraction or a whole number.
3. The molecularity of a reaction is independent of the concentrations of the reactants, while the order of a reaction is dependent on the concentrations of the reactants.
Very Short Answer Type Questions (Each carry 2 Marks)
Question: What is the actual reducing agent of haematite in the blast furnace?
Answer: The actual reducing agent of haematite in the blast furnace is carbon monoxide (CO).
Question: What do you mean by saying that the molality of a solution is 0.1? Give an example.
Answer: A solution with a molality of 0.1 means that there are 0.1 moles of solute per kilogram of solvent. For example, 0.1 moles of salt dissolved in 1 kilogram of water would have a molality of 0.1.
Question: How are Carbylamines formed?
Answer: Carbylamines are formed by a nucleophilic substitution reaction between an alkyl halide and a primary amine.
Question: Name a broad-spectrum antibiotic and state two diseases for which it is prescribed.
Answer: A broad-spectrum antibiotic is effective against a wide variety of bacteria. One example is ciprofloxacin. It is prescribed for treating bacterial infections such as urinary tract infections, sinusitis, and bronchitis, as well as skin and soft tissue infections.
Question: What is an ambident group? Give two examples.
Answer: An ambident group is a type of atom or molecule that can act as either an acid or a base. Examples include the nitrogen atom in ammonia (NH3) and the carbonate ion (CO32-).
Question: Write the information asked for the Polymer:
(a) Bakelite: Materials used for its preparation.
(b)Synthetic rubber: Monomer unit.
Answer: (a) Materials used for the preparation of Bakelite include phenol, formaldehyde, and other chemicals.
(b) Monomer unit for Synthetic rubber is isoprene.
Objective Type Questions (Each carries 1 Marks)
(i) What is the coordination number of Cs+ and Cl- ions in the CsCl structure?
Answer: The coordination number of Cs+ and Cl- ions in the CsCl structure is 8.
(ii) What is annealing?
Answer: Annealing is a heat treatment process used to alter the physical and sometimes chemical properties of a material.
(iii) The well-known refrigerant Freon has the formula————
(iv) What type of aldehydes and Ketones undergo adol condensation?
Answer: Aldehydes and ketones with an alpha-hydrogen atom that can be abstracted will undergo Adol condensation. Examples include benzaldehyde, acetophenone, and acetone.
(v) Nylon is a Vinyl polymer. (true/false)
(vi) Phenols form coloured complier with ferric chloride (true/false)
(vii) Porphyrin ligand in haemoglobin is —————– dentate
Answer: Haemoglobin contains four porphyrin ligands that are bound to four iron atoms. These porphyrin ligands are called protoporphyrin IX and are dentate, meaning they bind to the iron atoms via nitrogen-containing side chains.
(viii) Amino acids are building blocks of
(a)Carbohydrates (b) Vitamins (c) Fats (d) Proteins
Answer: d) Proteins
(ix) Action of a Catalyst depends
(a)Mass (b) Solubility (c) Particle size (d) None of the above
Answer: D) None of the above
(x) Which is used as a preservative to protect processed food?
(a)Sodium sulphate (b) Saccharin (c) BHT (d) Sodium metabisulphite
Answer: C) BHT