Kerala Plus Two Chemistry Question Paper March 2021 with Answers

Reviewing Kerala Syllabus Plus Two Chemistry Previous Year Question Papers and Answers Pdf March 2021 helps in understanding answer patterns.

Kerala Plus Two Chemistry Previous Year Question Paper March 2021

Time: 2 Hours
Total Scores: 60

Answer the following questions from 1 to 40 upto a maximum score of 60.
Answer questions from 1 to 11. Each carries 2 scores. (11 × 2 = 22)

Question 1.
(i) Which of the following is an anisotropic solid? (1)
(A) NaCl
(B) Glass
(C) Rubber
(D) Plastic
(ii) Glass is called pseudo solid. Give reason. (1)
Answer:
(i) NaCl
(ii) Because it is a supercooled liquid.

Question 2.
An element has a cubic close-packed structure.
(i) What is the coordination number of each atom? (1)
(ii) Give the total number of voids in N mol of it. (1)
Answer:
(i) Total no. of surrounding atoms = coordination number in ccp = 12
(ii) 3N voids or 3 × 6.022 × 10²³

Question 3.
A mixture of two liquids A and B form an ideal solution. Draw the vapour pressure composition curve for this solution. (2)
Answer:

Question 4.
(i) The electrolyte used in Leas-storage battery ______________ (1)
(ii) Give one example of a primary cell. (1)
Answer:
(i) H₂SO₄ (38%)
(ii) Drycell, Mercury cell

Question 5.
What is a zero-order reaction? Give the unit of rate constant for zero order reaction. (2)
Answer:
If the sum of powers of concentration terms in the rate equation is zero it is called zero order reaction.
Unit of K for zero order reaction is ie., mol L^-1 s^-1.

Question 6.
Classify the following as homogeneous and heterogeneous catalysis.

Answer:
(A) In homogenous catalysis reactants and catalysts are in the same phase.

(B) In heterogenous catalysis reactants and catalysts are in different phases.

Question 7.
(i) Which of the following ore can be concentrated by the froth floatation method? (1)
(A) Bauxite
(B) Siderite
(C) Cuprite
(D) Zinc blende
(ii) Zinc and Mercury are low-boiling liquids. Name the technique used to refine these metals. (1)
Answer:
(i) D. Zinc blend
(ii) Distillation

Question 8.
(i) Name the important Oxo acid of Nitrogen. (1)
(ii) Name the method used for the manufacture of this acid. (1)
Answer:
(i) Nitric Acid (HNO₃)
(ii) Ostwald’s Process

Question 9.
Give a reason for the following:
(i) PCl₃ fumes in moist air. (1)
(ii) PCl₅ is highly reactive. (1)
Answer:
(i) PCl₃ reacts with moisture to give HCl. Which is fuming nature.
PCl₃ + 3H₂O → H₃PO₃ + HCl
(ii) Due to the presence of two axial Cl atoms in trigonal bipyramidal structure. Axial bonds are longer than equatorial bonds.

Question 10.
(i) Write the IUPAC name of K₂[Zn(OH)₄] (1)
(ii) Metal present in chlorophyll is _____________ (1)
Answer:
(i) Potassium tetra hydroxo zincate (II) or Potassium tetra hydroxido zincate (II).
(ii) Mg (Magnesium)

Question 11.
Identify the main product in the following reactions:

Answer:

Questions from 12-29 carry 3 scores each. (18 × 3 = 54)

Question 12.
Define unit cell. Calculate the number of particles per unit cell in the Body-centered cube and Face-centered cube. (3)
Answer:
Unit cell: Smallest repeating unit of a crystal.
B.C.C
No. of particles at the corner = 8
Corner particles contribute \(\frac{1}{8}\)
i.e. \(\frac{1}{8}\) × 8 = 1
In addition to this one particle is present in the centre without sharing. So total particles present is \(\frac{1}{8}\) × 8 + 1 = 2

F.C.C
Corner particles contribute \(\frac{1}{8}\)
∴ No. of particles due to corner atoms \(\frac{1}{8}\) × 8 = 1
Face centred particles contribute \(\frac{1}{2}\)
No. of particles due to face centred particles 6 × \(\frac{1}{2}\) = 3
Total no. of particles = 1 + 3 = 4

Question 13.
(i) What type of magnetic substances are used to make permanent magnets? (1)
(ii) Draw the schematic alignment of magnetic moments in ferromagnetic and ferrimagnetic substances. (2)
Answer:
(i) Ferromagnetic substances
(ii) Ferromagnetic – ↑ ↑ ↑ ↑
Magnetic moments are in the same direction.
Ferrimagnetic – ↑↓ ↑↓ ↑↑
Magnetic moments are unequal and in opposite directions.

Question 14.
State Henry’s Law. Give two applications of it. (3)
Answer:
The amount of gas dissolved in a liquid is directly proportional to the pressure applied p = k_H.x
p – pressure, k_H – Henry’s constant, x – mole fraction.
Applications:
(i) Soda water.preparation or soft drinks.
(ii) Bends in Scuba divers

Question 15.
(i) Daniel’s cell is represented as
\(\mathrm{Zn}(\mathrm{~s}) / \mathrm{Zn}_{(\mathrm{aq})}^{2+} \| \mathrm{Cu}_{(\mathrm{aq})}^{2+} \mid \mathrm{Cu}(\mathrm{~s})\)
Write the Nernst equation for Daniel’s cell. (1)
(ii) The conductivity of 0.2 M solution of KCl at 298 K is 0.0248 Scm^-1. Calculate its molar conductivity. (2)
Answer:

= 124 S cm² mol^-1

Question 16.
Variations of molar conductivity (λ_m) versus concentration (√c) for strong and weak electrolytes are given below:

(i) Identify I and II as strong and weak electrolytes. (1)
(ii) What does \(\lambda_{\mathrm{m}}^0\) indicate? (1)
(iii) Suggest a method to determine \(\lambda_{\mathrm{m}}^0\) for the electrolyte II. (1)
Answer:
(i) I for strong electrolytes
II for weak electrolyte
(ii) Molar conductivity at infinite dilution – \(\lambda_{\mathrm{m}}^0\)
(iii) Kohlrausch’s law

Question 17.
(i) The vapour pressure of pure liquids A and B is 400 mm and 600 mm of Hg respectively, calculate the vapour pressure of the solution in which the mole fraction of B is 0.4. (2)
(ii) Which of the following is true for an ideal solution? (1)
(A) ΔH_mix > 0
(B) ΔH_mix = 0
(C) ΔV_mix > 0
(D) ΔH_mix < 0
Answer:

Question 18.
The integrated rate equation for a first-order reaction is
K = \(\frac{2.303}{t} \log \frac{[R]_0}{[R]}\)
(i) What is half life period? (1)
(ii) Derive an expression for the half-life period of a first-order reaction. (2)
Answer:
(i) Period required for a radioactive substance to become exactly half of its initial concentration.

Question 19.
(i) Write any two characteristics of Chemisorption. (2)
(ii) Why are finely powdered substances more effective adsorbents than their crystalline form? (1)
Answer:
(i) Irreversible, specific
(ii) Surface area increases more adsorption occurs.

Question 20.
Differentiate between the following:
(i) Calcination and Roasting
(ii) Pig iron and Wrought iron
(iii) Mineral and Ore
Answer:
(i) Calcination: Heating in the limited supply of air.
Roasting: Heating in the presence of plenty of air.
(ii) Wrought iron: The purest form of iron.
Pig iron: Impure iron obtained from the blast furnace.
(iii) Ore: A mineral from which metals can be extracted profitably.
Minerals: Form of metals present in the earth’s crust.

Question 21.
Potassium dichromate is a very useful oxidizing agent.
(i) Name the ore of Potassium dichromate. (1)
(ii) Explain the preparation of Potassium dichromate from Sodium chromate. (2)
Answer:
(i) Chromite Ore/FeCr2O4

1. Iron chromate is treated with Na₂CO₃ in the presence of air to give Sod. chromate.
2. Sod. chromate is acidified with dil. HCl to give sod. dichromate.
3. Sod. dichromate is treated with KCl to get potassium dichromate.

Question 22.
(i) Account for the following:
A. Zr and Hf have identical radii. (1)
B. Transition metals are very good catalysts. (1)
(ii) Calculate the spin-only magnetic moment of \(M_{(a q)}^{2+}\) iron (Z = 27). (1)
Answer:
(i) A. Due to lanthanide contraction.
B. Ability to show variable oxidation state.

Question 23.
Explain the following reactions:
(i) Rienrier-Tieman reaction.
(ii) Williamson’s synthesis.
Answer:
Reimer-Tiemann Reaction:

Williamson’s Synthesis
Alkyl halide + Sod. alkoxide → ether R-X + R’ONa → R – OR’

Question 24.
(i) How are the following conversions carried out?
A. Propene to propane-2-ol.
B. Ethanal to Ethanol. (2)
(ii) Name the enzyme which converts glucose to ethanol. (1)
Answer:
(i) A. Propene to propan-2-ol.

B. Ethanal to Ethanol

(ii) Zymase

Question 25.
(i) The test to distinguish Propanal and Propanone is (1)
(A) Tollens’ test
(B) Lucas test
(C) Hinsbergtest
(D) Bromine-Water test
(ii) Which is more reactive towards nucleophilic addition, CH₃CHO or C₆H₅-CHO? Give reason. (2)
Answer:
(i) (A) Tollens’ test
(ii) CH₃CHO
C₆H₅CHO is less reactive due to the presence of phenyl group.

Question 26.
Identify the products and name the reactions.

Answer:
(i) Cannizzaro reaction.

(ii) Aldol condensation

Question 27.
(i) Classify the following into monosaccharides and disaccharides. (1)
Ribose, Fructose, Maltose, Sucrose.
(ii) How is starch different from glycogen? (1)
(iii) Name the two hormones which work together to regulate glucose levels in the body. (1)
Answer:
(i) Monosaccharides: Ribose, fructose
Disaccharides: Maltose, Sucrose
(ii) Starch storage of carbohydrate plants.
Glycogen – Animal starch. Carbohydrates are stored in animals.
(iii) Insulin and glucagon

Question 28.
Write the monomeric units and one uses each of the following polymers:
(i) PVC
(ii) Teflon
(iii) Nylon-6,6
Answer:
(i) PVC – Vinyl chloride, for making pipes
(ii) Teflon – Tetra fluoro ethene for making nonstick utensils
(iii) Nylon 6,6 – Adipic acid + hexamethylene diammine for making net.

Question 29.
(i) Explain the role of the following as food additives: (1)
(A) BHT
(B) Saccharin
(ii) A low level of noradrenaline is the cause of depression. What type of drugs are needed to cure this problem? Give one example. (2)
Answer:
(i) A. BHT (Butylated hydroxytoluene) – It is used as an antioxidant in food.
B. Saccharin – It is used as an artificial sweetener in food.
(ii) Tranquilizer

Questions from 30-40 carry 4 scores each. (11 × 4 = 44)

Question 30.
(i) Explain the following terms: (3)
A. Schottky defect
B. Frenkel defect
C. F-centre
(ii) Which of the following shows both Schottky and Frenkel defects? (1)
(A) KCl
(B) AgCl
(C) AgBr
(D) NaBr
Answer:
(i) A. Schottky defect: Equal no. of cations and anions are missed from the lattice and density decreases.
B. Frenkel defect: Cations are missed from the lattice and are seen in the interstitial site. No change in densities.
C. f-centres: Electron-trapped anion vacancies are known as F-centres.
(ii) AgBr

Question 31.
(i) What are colligative properties? (2)
(ii) 400 cm3 of an aqueous solution of a protein contains 1.26 g of the protein. The osmotic pressure of such solution at 300 K is found to be 2.57 × 10^-4 atm. Calculate the molar mass of the protein. (R = 0.0821 L atm K^-1 mol^-1) (2)
Answer:
(i) Colligative properties are the properties that depend only on the number of solute particles and not on their nature.
(ii) Molar mass (M₂) = \(\frac{w_2 R T}{\pi V}\)
Here w₂ = 1.26 g, V = 400 cm³ = 0.4 L, T = 300 K, π = 2.57 × 10^-4 atm and R = 0.0821 L atm K^-1 mol^-1
So, M₂ = \(\frac{1.26 \times 0.0821 \times 300}{2.57 \times 10^{-4} \times 0.4}\) = 301885

Question 32.
(i) Explain the construction and working of the H₂-O₂ fuel cell. (3)
(ii) Write two methods to prevent corrosion of metals. (1)
Answer:
(i) Two graphite (electrodes) are placed in conc.NaOH solution (electrolyte). The electrodes are connected to the battery. H₂ gas is passed through the anode and O₂ gas is bubbled through the cathode.
Reactions at anode 2H₂ + 4OH^– → 4H₂O + e^–
and at Cathode O₂ + 2H₂O + 4e^– → 4OH^–
The overall reaction is 2H₂ (g) + O₂ (g) → 2H₂O (l)
(ii) The methods to prevent corrosion of metals are:

• By giving a non-metallic coating on the metal surface with paint, varnish, etc.
• By coating the metal surface with electro-positive metals like zinc, magnesium, etc.
• By coating it with an anti-rust solution. (any two)

Question 33.
(i) Write the Arrhenius equation. (1)
(ii) The rate of a reaction doubles when the temperature is increased from 298 K to 308 K. Calculate the activation energy. (2)
(iii) Give two differences between order and molecularity. (1)
Answer:
(i) The Arrhenius equation is k = \(\mathrm{A} \cdot \mathrm{e}^{-E a / R T}\)
(ii) We know that, \(\log \frac{k_2}{k_1}=\frac{E a}{2.303 R} \frac{\left[T_2-T_1\right]}{T_1 \cdot T_2}\)
Here T₁ = 298 K, T₂ = 308 K, and R = 8.314 J K^-1 mol^-1
Suppose k₁ = x, then k₂ = 2x
Then \(\frac{\log 2 x}{x}=\frac{E a}{2.303 \times 8.314} \frac{[308-298]}{298 \times 308}\)
E_a = \(\frac{0.3010 \times 2.303 \times 8.314 \times 298 \times 308}{10}\) = 52897.78 J mol^-1.
(iii)

Order	Molecularity
The sum of powers to which the concentration terms are raised in the rate-low expression.	Total number of molecules taking part in the reaction.
It can be zero or fractional.	It cannot be zero or fractional.

Question 34.
(i) What are (yophilic and lyophobic sols? Give one example for each type.
(ii) Explain the different types of emulsions. (2)
Answer:
(i) In lyophilic sols, the force of attraction between the dispersed phase and the dispersion medium is strong.
Eg. Starch solution, gum, gelatin, starch, rubber, etc. in the suitable dispersion medium.
But in lyophobic sols, the force of attraction between the dispersed phase and the dispersion medium is weak. eg. Arsenic sulfide (As₂S₃) sol, Sulpher soi, and metal sols like gold sol, silver sol, etc.
(ii) Emulsions are of two types: Oil in water (O/W) type and Water in oil (W/O) type
In oil in water type emulsion, oil is dispersed. phase and water is the dispersion medium, eg. milk
Inthe water in a type emulsion, water is the dispersed phase and oil is the dispersion medium, eg. butter and cream.

Question 35.
(i) Explain the steps involved in the leaching of Bauxite ore. (3)
(ii) What is the role of cryolite in the extraction of Aluminium? (1)
Answer:
(i) Bauxite ore is powdered and treated with NaOH to get sodium Aluminate. To this CO₂ is added and hydrated Al₂O₃ is precipitated it is filtered and dried.

(ii) Cryolite is added to lower the melting point of alumina and to increase the conductivity.

Question 36.
(i) Give the preparation and structure of XeF₂. (2)
(ii) Which of the following does not exist: (1)
(A) XeOF₄
(B) XeF₄
(C) XeO₄
(D) NeF₂
(iii) Why ICl is more reactive than I₂? (1)
Answer:
(i) Excess amount of Xe reacts with F₂ at about 673 K and 1 bar pressure to produce XeF₂.
Or, The equation:

The structure is linear as follows:

(ii) (D) NeF₂
(iii) The I-Cl bond is weaker than the I-I bond

Question 37.
(i) List the various structural isomerisms possible for coordination compounds. (2)
(ii) [Fe(H₂O)₆]³⁺ is strongly paramagnetic whereas [Fe(CN)₆]^3-, is weakly paramagnetic. Explain. (2)
Answer:
(i) The different types of structural isomerism shown by co-ordination compounds are:
1. Ionisation isomerism
2. Linkage isomerism
3. Solvate or hydrate isomerism
4. Co-ordination isomerism
(ii) This is because [Fe(H₂O)₆]³⁺ is an outer orbital complex while [Fe(CN)₆]^3- is an inner orbital complex/H₂O is a weak field ligand and hence electron pairing does not occur while CN^– is a strong field ligand and hence electron pairing occurs due to greater number of unpaired electrons in [Fe(H₂O)₆]³⁺ than that in [Fe(CN)₆]^3-.

Question 38.
(i) Give two differences between S_N1 and S_N2 reactions. (1)
(ii) Arrange 1-chloropropane, 2-chloropropane, and 1-chlorobutane in the increasing order of their boiling points. (1)
(iii) Give one use of chloroform. (1)
Answer:
(i)

SN1	SN2
1. Takes place in two steps.	1. Takes place in one step.
2. Through carbocation formation.	2. Through intermediate.
3. Retention occurs.	3. Inversion occurs.

(ii) 2-chloropropane < 1-chloropropane < 1-chloro-butane
(iii) Chloroform is used as a solvent for the production of freon refrigerant, as an anesthetic.

Question 39.
(i) How will you prepare Benzaldehyde from the following: (3)
A. Toluence
B. Benzene
C. Benzoyl Chloride
(ii) Identify the product obtained when Acetic acid is heated with P₂O₅. (1)
Answer:
(i) Etards reaction

Gatterman-Koch reaction

Rosenmund’s reaction

Question 40.
(i) Which of the following amines cannot be prepared by Gabriel Phthalimide synthesis? (1)

(ii) Explain the method to distinguish primary, secondary, and tertiary amines. Also, write the chemical equations involved. (3)
Answer:

(ii) Hinsberg’s test
Benzenesulphonyl chloride – Hinsberg reagent
1° amine + C₆H₅SO₂Cl → A precipitate soluble in alkali
2° amine + C₆H₅SO₂Cl → A precipitate insoluble in alkali
3° amine + C₆H₅SO₂Cl → No reaction