Chemistry: Solved Previous Year’s Question Paper for NCERT/CBSE Class 12th Chemistry Paper Code (XIIRKN16–11020—X)
Long Answer Type Questions (Each carries 5 Marks)
Question: Explain the following terms
(a) Molarity (b) Molality (c) Mole-fraction (d) Normality (e) PPM.
Answer: (a) Molarity: Molarity is a unit of concentration that is defined as the number of moles of a solute in one litre of a solution.
(b) Molality: Molality is a unit of concentration that is defined as the number of moles of a solute per kilogram of solvent.
(c) Mole-fraction: Mole-fraction is a unit of concentration that is defined as the ratio of the number of moles of a solute to the total number of moles of all substances present in a solution.
(d) Normality: Normality is a unit of concentration that is defined as the number of equivalents of a solute per litre of a solution. Equivalents refer to the number of moles of a solute multiplied by the number of charges it carries.
(e) PPM: Parts per million (PPM) is a unit of concentration that is defined as the number of parts of a solute per million parts of the solution.
Question: Explain the construction and working of a Galvanic cell.
Answer: A galvanic cell, also known as a voltaic cell, is an electrochemical cell that converts chemical energy into electrical energy. It consists of two different metals connected by a salt bridge or a porous barrier that allows ions to flow between the two metals. When the two metals are connected, a chemical reaction occurs which produces electrons. These electrons flow through the external circuit and generate electricity. The two metals used in a galvanic cell are the anode and the cathode. The anode is the electrode where oxidation occurs and the cathode is the electrode where reduction occurs. The oxidation-reduction reactions at the electrodes are driven by the difference in the standard electrode potential of the two metals. The salt bridge is used to maintain electrical neutrality between the anode and the cathode. It also allows ions to flow between the two electrodes, completing the circuit and making it possible for electricity to be generated.
Question: Why oxygen shows the anomalous behaviour
Answer: Oxygen is anomalous because it has six valence electrons, but it tends to form molecules with only two covalent bonds instead of the expected four. This is due to the stability of its electron configuration; by forming two covalent bonds, it can achieve an octet of electrons in its valence shell, and thus is more stable than if it formed four bonds.
Question: How will you convert ethanol into
(i) Ethyl alcohol (ii) Cyanohydrin (iii) Ethanal oxime (iv) Ethane
Answer: (i) Ethyl alcohol: Ethanol can be converted into ethyl alcohol by dehydration, where water is removed from the ethanol molecule using an acid catalyst, such as sulfuric acid.
(ii) Cyanohydrin: Ethanol can be converted into cyanohydrin by reacting it with hydrogen cyanide in the presence of a base catalyst, such as sodium hydroxide.
(iii) Ethanal oxime: Ethanol can be converted into ethanal oxime by reacting it with hydroxylamine in the presence of a base catalyst, such as potassium hydroxide.
(iv) Ethane: Ethanol can be converted into ethane by reacting it with hydrogen in the presence of a catalyst, such as nickel.
(v) Z-Hydroxybutanal: Ethanol can be converted into Z-Hydroxybutanal by reacting it with hydrogen bromide in the presence of a base catalyst, such as sodium hydroxide.
Short Answer Type Questions (Each carry 3 Marks)
Question: Explain the Frankel defect in crystals
Answer: The Frankel defect is a type of point defect in crystals, which occurs when an atom of a different species from the rest of the lattice replaces a lattice atom. This defect is named after the American physicist, David Frankel, who proposed the idea in 1940. This defect can be either a vacancy or an interstitial, depending on whether the foreign atom is missing a lattice position or occupying an interstitial site. This defect can alter the electrical, thermal, and magnetic properties of the crystal, as well as its optical and electrical conductivity.
Question: What are the factors on which the rate of reaction depends
Answer: The rate of reaction depends on several factors, including the concentration of reactants, temperature, catalysts, surface area, and pressure. The presence of a catalyst can increase the reaction rate, while a decrease in temperature can slow the reaction rate.
Question: What are the diseases caused due to deficiency of vitamins A, D and C?
Answer: Vitamin A Deficiency: Night blindness, dry eyes, and xerophthalmia (inflammation of the cornea and conjunctiva).
Vitamin D Deficiency: Rickets, osteomalacia, and osteoporosis.
Vitamin C Deficiency: Scurvy, impaired wound healing, and increased risk of infection.
Question: What is meant by unidentate and bidentate ligands? Give examples
Answer: Unidentate ligands are ligands that have one atom bound to a central metal atom. Examples of unidentate ligands include chloride (Cl-), bromide (Br-), and iodide (I-).
Bidentate ligands are ligands that have two atoms bound to a central metal atom. Examples of bidentate ligands include ethylenediamine (en) and diethylenetriamine (dien).
Question: Draw the structure of three Oxo-acids of Phosphorous.
Question: What is the Esterification reaction?
Answer: Esterification is a chemical reaction in which an organic acid and an alcohol react to form an ester. This reaction requires a catalyst, usually an acid or a base, and is often reversible. Esters are important components of many products, including fragrances, flavourings, and lubricants.
Very Short Answer Type Questions (Each carry 2 Marks)
Question: Define half-life periods
Answer: Half-life is the time it takes for half of an element’s atoms to decay. It is a measure of the radioactivity or decay rate of a substance and is an important concept in chemistry, physics, and biology. Half-life is used to describe the decay of both unstable isotopes, as well as radioactive elements.
Question: Define calcination and roasting
Answer: Calcination is a process in which a material is heated to a high temperature, typically below its melting point, without contact with air.
Roasting is a form of heat treatment that involves heating a material in the presence of air or other gases at temperatures below the melting point of the material.
Question: Why do d-block elements form coloured ions?
Answer: D-block elements form coloured ions due to their ability to absorb visible light. This occurs when electrons in the atoms of the element move from a lower energy level to a higher energy level. This movement absorbs the energy of the visible light, causing the element to appear coloured.
Question: Give an example for primary, secondary and tertiary amines
Answer: Primary amine: Methanamine (CH3NH2)
Secondary amine: Dimethylamine (CH3-NH-CH3)
Tertiary amine: Trimethylamine (N(CH3)3)
Question: Why are artificial sweetening agents needed? Give two examples
Answer: Artificial sweetening agents are needed because they provide a sweet taste to food and beverages without the added calories or health risks associated with consuming large amounts of sugar. Examples include aspartame and sucralose.
Question: What is natural rubber?
Answer: Natural rubber is a kind of rubber that is produced from the sap of rubber trees. It is a milky white liquid that is processed to create a variety of rubber products. Natural rubber is used in a variety of applications including tires, rubber bands, hoses, seals, and more.
Objective Type Questions (Each carries 1 Marks)
(i) No. of atoms per unit cell for a cubic unit cell is————–
Answer: 8 atoms
(ii) The phenomenon of osmosis was reported by—————-
Answer: Thomas Mullner
(iii) Sulphide ores are concentrated by gravity by process (True/False)
(iv) Give the reaction of Aniline with conc. H2SO4
Answer: C6H5NH2 + H2SO4 → C6H5NH3+ + HSO4-
(v) Give the reaction of acetone with NH2OH
Answer: Acetone + NH2OH → Imine + H2O
(vi) The human body does not produce
(a) Enzymes (b) DNA (c) Vitamins (d) Hormones
Answer: c) Vitamins
(vii) Ethyl amine reacts with the chloride to give
(a)Ethyl chloride (b) Ethyl nitrite (c) Ethyl alcohol (d) Nitro-ethane
Answer: a) Ethyl chloride
(viii) Penicillin is
(a) Hormone (b) Antiseptic (c) Antibiotic (d) Lipid
Answer: c) Antibiotic
(ix) PVC is a polymer of
(a) Ethene (b) Isoprene (c) Vinyl chloride (d) Neoprene
Answer: (c) Vinyl chloride