Chemistry: Solved Previous Year’s Question Paper for NCERT/CBSE Class 12th Chemistry Paper Code (HSEIIRKO-13)
Long Answer Type Questions (Each carries 5 Marks)
Question: Describe the electronic theory of rusting of iron.
Answer: The electronic theory of rusting of iron states that rusting is an electrochemical reaction in which the metal atoms in iron react with oxygen from the air to form an oxide layer on the metal’s surface. This layer is known as rust and is composed of iron oxides. The electrons from the iron atoms are then transferred to the oxygen atoms, forming an electrical current. This current then causes the oxidation of the iron atoms, resulting in the formation of rust. Rusting is a slow process and can be prevented by coating the metal in a protective layer.
Question: Write Elrctronic configuration of the elements of group—17. Why fluorine shows anomalous behavior.
Answer: The electronic configuration of the elements of group 17 are as follows:
Fluorine (F): 1s2 2s2 2p5
Chlorine (Cl): 1s2 2s2 2p6 3s2 3p5
Bromine (Br): 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p5
Iodine (I): 1s2 2s2 2p6 3s2 3p6 4s2 3d10 4p6 5s2 4d10 5p5
Fluorine shows anomalous behavior because it has more than one oxidation state. This is unusual because elements in the same group on the periodic table usually have the same oxidation state. Fluorine can have a range of oxidation states from -1 to +7, which is much more varied than other elements in its group. This is due to fluorine’s small size and high electronegativity which allow it to form strong bonds with other atoms.
Question: Give preparation, properties and uses of
(i) Phosphorous trichloride
(ii) Phosphorous Pentachloride
Answer: (i) Preparation: Phosphorous trichloride (PCl3) can be prepared by the direct combination of white phosphorus and chlorine gas, in the presence of a catalyst such as copper chloride.
Properties: 1. Phosphorous trichloride is a colorless, fuming, corrosive liquid with a characteristic pungent odor.
2. It is slightly soluble in water and miscible with most organic solvents.
3. It is a non-flammable compound, but it is highly reactive and toxic.
Uses: 1. It is widely used in the chemical industry as a reagent and catalyst in the manufacture of organic and inorganic compounds.
2. It is also used in the production of phosphoric acid, phosphates, pharmaceuticals, and dyes.
(ii) Preparation: Phosphorous pentachloride (PCl5) can be prepared by treating white phosphorus with chlorine gas at high temperatures.
Properties: 1.Phosphorous pentachloride is a colorless, fuming liquid with a pungent odor.
2. It is soluble in water, but it is highly corrosive and toxic.
3. It is a non-flammable compound, but it is highly reactive.
Uses: 1. It is widely used as a reagent and catalyst in the production of organic and inorganic compounds.
2. It is also used in the production of phosphoric acid, phosphates, pharmaceuticals, and dyes.
Short Answer Type Questions (Each carry 3 Marks)
Question: Describe Electrophoresis
Answer: Electrophoresis is a laboratory technique used to separate macromolecules, such as DNA, RNA, and proteins, based on size and charge. It involves the application of an electric field to a mixture of molecules suspended in a gel-like matrix. The molecules are forced to move through the gel in response to the electric field, and their movement is determined by their size and charge.
Question: What are Ionisation Isomers? Explain with suitable Examples
Answer: Ionisation Isomers are forms of chemical compounds that possess the same molecular formula but differ in their ionic charge. This may be due to the rearrangement of electrons within the molecule. An example of this is the two isomers of carbon dioxide, CO2 and CO3-2. The former has a neutral molecular charge, while the latter has a negative charge due to the unbonded pair of electrons on the carbon atom.
Question: How primary, Secondary and Tertiary Alcohols can be obtained from Grignard reagent?
Answer: Primary alcohols can be obtained by adding an aldehyde or ketone to a Grignard reagent.
Secondary alcohols can be obtained by adding an ester to a Grignard reagent.
Tertiary alcohols can be obtained by adding an acid chloride to a Grignard reagent.
Question: What are Proteins? How are they classified on the basis of Molecular Structure?
Answer: Proteins are complex, macro-molecules composed of one or more long chains of amino acids. They are essential for the functioning of all living organisms, and are found in all food sources.
Proteins can be classified on the basis of molecular structure into four categories: fibrous proteins, globular proteins, membrane proteins, and disordered proteins.
Fibrous proteins are elongated and structurally rigid, providing structural support to cells, while globular proteins are more spherical in shape and often involved in enzymatic activities.
Membrane proteins are located in the cellular membranes and are involved in the transport of molecules into and out of the cell. Finally, disordered proteins lack a regular 3-dimensional structure and are often involved in the regulation of various metabolic processes.
Very Short Answer Type Questions (Each carry 2 Marks)
Question: Define Calcination? Give an Example?
Answer: Calcination is the process of heating a solid substance to a high temperature to drive off its volatile components or to achieve a desired chemical or physical change. An example of calcination is the process of roasting gypsum to produce plaster of Paris.
Question: Oxygen is a Gas, While Sulphur is a solid. Explain
Answer: Oxygen and sulphur have different physical states because of their different molecular structures and interactions. Oxygen is a gas at room temperature because its individual molecules are not strongly attracted to one another and can move freely, forming a gas. Sulphur, on the other hand, has a more complex molecular structure and its molecules are strongly attracted to each other, so they form a solid at room temperature.
Question: Why do transition elements exhibit variable oxidation states
Answer: Transition elements exhibit variable oxidation states because they have partially filled d-orbitals in their outer electron shell. These partially filled d-orbitals are capable of accepting or losing electrons to form different oxidation states, allowing transition elements to have different oxidation states.
Question: What are Amines. How are they classified.
Answer: Amines are organic compounds that contain at least one nitrogen atom in their molecular structure.
They are classified according to the number of nitrogen atoms they contain, as primary (1 nitrogen), secondary (2 nitrogen), and tertiary (3 nitrogen) amines. Additionally, amines can be classified as aliphatic or aromatic, depending on the type of chemical bonds the nitrogen atoms form.
Question: What are Polymers? How are they Classified on the basis of their source or origin?
Answer: Polymers are macromolecules composed of repeating structural units that are connected by covalent bonds.
They are classified on the basis of their source or origin into two main categories: natural polymers and synthetic polymers.
Natural polymers are polymers that are found in nature and include proteins, cellulose, and polysaccharides.
Synthetic polymers are polymers that are made in the laboratory, such as polystyrene, polyethylene, and nylon.
Question: What is depression in Freezing Point?
Answer: Depression in freezing point is a decrease in the freezing point of a solvent caused by the addition of a solute.
Objective Type Questions (Each carries 1 Marks)
(i) Define Piezoelectricity
Answer: Piezoelectricity is the electric charge that accumulates in certain solid materials (notably crystals, certain ceramics, and biological matter such as bone, DNA and various proteins) in response to applied mechanical stress. The word piezoelectricity means electricity resulting from pressure. It is derived from the Greek piezo or piezein, which means to squeeze or press, and electric or electron, which stands for electricity.
(ii) Order of a reaction increases with rise in temperature (True/False)
Answer: True
(iii) The C—X bond in haloarenes is more polar than C—X bond in haloalkanes (True/False)
Answer: True
(iv) Phenols react with Sodium liberating ———— gas
Answer: Hydrogen
(v) Aldehydes are more easily oxidized than Ketones (True/False)
Answer: True
(vi) Which base is found only in the nucleotides of RNA
Answer: Uracil (U)
(vii) Natural rubber is a polymer of
Answer: isoprene molecules.
(viii) Give the name of one broad spectrum antibiotic
Answer: Ciprofloxacin