Kerala Plus Two Chemistry Question Paper March 2020 with Answers

Reviewing Kerala Syllabus Plus Two Chemistry Previous Year Question Papers and Answers Pdf March 2020 helps in understanding answer patterns.

Kerala Plus Two Chemistry Previous Year Question Paper March 2020

Time: 2 Hours
Total Scores: 60

Answer any 7 questions from 1-9. Each carries 1 score. (7 × 1 = 7)

Question 1.
Which of the following lattices has the highest packing efficiency (assuming that atoms are touching each other)?
(a) Simple cubic
(b) Body centred cubic
(c) Face centred cubic
Answer:
(c) Face centered cubic

Question 2.
The limiting molar conductivity of weak electrolytes can be calculated by using the law
(a) Faraday’s law
(b) Kohlrausch law
(c) Henry’s law
(d) Raoult’s law
Answer:
(b) Kohlrausch law

Question 3.
The Bredig’s arc method is used to prepare which of the following solutions?
(a) Silver sol
(b) Gelatine sol
(c) CdS sol
(d) As₂S₃ sol
Answer:
(a) Silver sol

Question 4.
The product obtained by the reaction of calcium phosphide with water is
(a) Phosphoric acid
(b) Phosphine
(c) Phosphorous acid
(d) Phosphorus trichloride
Answer:
(b) Phosphipe

Question 5.
Among the following, which is more acidic?
(a) HCOOH
(b) CH₃CH₂COOH
(c) CH₃COOH
(d) CH₃CH₂CH₂COOH
Answer:
(a) HCOOH

Question 6.
In the presence of light, chloroform is slowly oxidised by air to an extremely poisonous gas called ___________
Answer:
Phosgene

Question 7.
Benzene diazonium chloride when treated with Cu₂Cl₂ and HCl, the product formed is chlorobenzene. This reaction is known as ___________
Answer:
Sand Meyer’s reaction

Question 8.
The monomer unit of natural rubber is ___________
Answer:
Isoprene or 2-methyl 1,3 butadiene

Question 9.
Name a substance which can be used as an antiseptic and disinfectant at different concentrations.
Answer:
Phenol, Chlorine or Sulfur dioxide

Answer any 10 questions from 10-22. Each carries 2 scores. (10 × 2 = 20)

Question 10.
Classify each of the following as being either a p-type or n-type semiconductor: (2 × 1 = 2)
(a) Ge doped with B
(b) Si doped with As
Answer:
(a) P type semiconductor
(b) N-type semiconductor

Question 11.
Schottky and Frenkel defects are two types of stoichiometric point defects shown by ionic solids. Give two points of difference between Schottky defect and Frenkel defect.
Answer:

Schottky Defect	Frenkel Defect
1. Due to the lack of an equal number of cations & anions from the lattice.	1. Due to the missing cation from the lattice, it is seen in the interstitial space.
2. Density decreases.	2. No change in density.

Question 12.
Complete the table by giving the value of Van’t Hoff factor ‘i’ for complete dissociation of solute. (4 × ½ = 2)

Salt	Vant Holf factor ‘i’ for complete dissociation of solute
NaCl	__________________
Al(NO3)3	__________________
K2SO4	__________________
Al2(SO4)3	__________________

Answer:
(a) NaCl (i = 2)
(b) Al(NO₃)₃ (i = 4)
(c) K₂SO₄ (i = 3)
(d) Al₂(SO₄)₃ (i = 5)

Question 13.
For a reaction A + B → C + D, the rate equation is, Rate = K [A]^3/2 [B]^1/2. Give the overall order and molecularity of reaction.
Answer:
(a) Order = 2 (\(\frac{3}{2}\) + \(\frac{1}{2}\) = \(\frac{4}{2}\) = 2)
Molecularity = 2 (one molecule A + one molecule B)

Question 14.
Give the general method used for the concentration of the following ores: (2 × 1 = 2)
(a) Bauxite ore
(b) Zinc sulphide ore
Answer:
(a) Bauxite – Leaching
(b) Zine Sulphide – Froth Floatation

Question 15.
Semiconductors of very high purity can be obtained by zone refining. Explain the principle behind zone refining. (2)
Answer:
The impurities are more soluble in the melt rather than the solid state of a metal.

Question 16.
The composition of bleaching powder is Ca(OCl)₂.CaCl₂.Ca(OH)₂.2H₂O. Give one method for the preparation of bleaching powder. (2)
Answer:
Bleaching powder is prepared by passing dry chlorine through slaked lime.
2Ca(OH)₂ + 2Cl₂ → [Ca(OCl)₂] + CaCl₂ + 2H₂O

Question 17.
(a) In d-block elements the radii of elements of third transition series are similar to those of the elements of second transition series. Give reason.
(b) Outer electronic configuration of Cu²⁺ ion is 3d⁹. Calculate its spin only magnetic moment. (2 × 1 = 2)
Answer:
(a) Lanthanoid contraction.
The overall decrease in atomic and ionic radii from lanthanum to lutetium is known as lanthanoid contraction.
(b) µ = \(\sqrt{n(n+2)}\)
n = number of unpaired electrons
= \(\sqrt{1(3)}\)
= \(\sqrt{3}\)
= 1.73 BM

Question 18.
Assign the primary valence and secondary valence of the central metal in [Ni(CO)₄].
Answer:
Primary valency = 0
Secondary valency = 4

Question 19.
Aryl halides are less reactive towards nucleophilic substitution reactions. Write any two reasons for the less reactivity of aryl halides.
Answer:
Resonance effect
Delocalisation of π electron in the benzene ring.

Question 20.
Ethanol and methoxymethane are functional isomers. But ethanol has a higher boiling point than methoxy-methane. Give reason.
Answer:
Due to the presence of hydrogen bonds.

Question 21.
Give a chemical test to distinguish between propanal and propanone.
Answer:
Propanal – Aldehyde
It gives a silver mirror with Tollens reagent.
or
With Fehling’s solution, it gives a red ppt.
or
With Schiffs reagent it gives a purple colour.
Propanone – Ketone does not give any of the above test.

Question 22.
Analgesics and antibiotics are drugs having different therapeutic actions. Define each class of drugs.
Answer:
Analgesics: Pain Killer
eg. Aspirin, Heroine, Paracetamol, Ibuprofen
Antibiotics: Drugs which kill or inhibit the growth of bacteria
eg. Penicillin, Amoxycillin, Azithromycin

Answer any 7 questions from 23-31. Each carries 3 scores. (7 × 3 = 21)

Question 23.
For ethanol-acetone mixture solute-solvent interaction is weaker than solute-solute and solvent-solvent interaction.
(a) Does this solution obey Raoult’s law?
(b) Give the vapour pressure-mole fraction graph for this solution.
Answer:
(a) No
(b) Positive deviation

Question 24.
The temperature dependence of the rate of a chemical reaction can be explained by the Arrhenius equation.
(a) Give Arrhenius equation.
(b) The rate of a chemical reaction doubles for an increase of 10 K in absolute temperature from 300 K. Calculate the activation energy (Ea)? [R: 8.314 J K^-1 mol^-1, log 2 = 0.3010]
Answer:
(a) Arrhenius equation is k = \(A \cdot e^{-E a / R T}\)

Question 25.
The existence of charge on colloidal particles is confirmed by the electrophoresis experiment.
(a) What is meant by electrophoresis?
(b) In the coagulation of a negative sol, the coagulating power is in the order Al³⁺ > Ba²⁺ > Na⁺. Name and state the rule behind this.
Answer:
(a) Electrophoresis: Movement of colloidal particles under an applied electric field is called electrophoresis.
(b) Hardy: Schulze rule
The greater the valency of the flocculating ion added, the greater is its power to cause precipitation.

Question 26.
Give the steps involved in the preparation of potassium dichromate (K₂Cr₂O₇) from chromite ore.
Answer:
1. Chromite ore is fused with sodium carbonate in free access of air to form sodium chromate.
4FeCr₂O₄ + 8Na₂CO₃ + 7O₂ → 8Na₂CrO₄ + 2Fe₂O₃ + 8CO₂
2. Sodium chromate is acidified with sulpuric acid to give sodium dichromate.
2Na₂CrO₄ + 2H⁺ → Na₂Cr₂O₇ + 2Na⁺ + H₂O
3. Sodium dichromate is treated with KCl to give potassium dichromate.
Na₂Cr₂O₇ + 2KCl → K₂Cr₂O₇ + 2NaCl

Question 27.
C is an isomer of [Pt(NH₃)₂Cl₂] is used to inhibit the growth of tumours.
(a) Give the IUPAC name of [Pt(NH₃)₂Cl₂].
(b) Give the structure of cis and trans isomers of [Pt(NH)₃Cl₂].
Answer:
(a) [Pt(NH₃)₂Cl₂] diammine dichlorido Plainum (II)
(b)

Question 28.
(a) Which is the major product obtained when 2-bromopentane is heated with alcoholic solution of potassium hydroxide?
(b) Name and state the rule that governs the formation of major product.
Answer:
(a) But-2-ene
(b) Saytzeff Rule: More symmetrical products are favoured.

Question 29.
Complete the following table: (3 × 1 = 3)

Answer:
1. CH₃CH₂NC or Ethyl Isocyanide
2. Hoffman Bromamide Reaction
3. C₆H₅NH₂/Aniline

Question 30.
(a) Vulcanisation is carried out to improve the physical properties of rubber. Explain the process of vulcanisation of rubber.
(b) Classify the following into addition and condensation polymers: (4 × ½ = 2)
PVC, nylon 66, teflon, terylene
Answer:
(a) Heating natural rubber in the presence of sulphur is known as vulcanisation.
(b) Addition polymers: PVC, Teflon
Condensation polymers: Nylon 66, Terylene

Question 31.
(a) Differentiate between globular and fibrous proteins. (2)
(b) The deficiency of which vitamin causes night blindness. (1)
Answer:
(a)

Globular Proteins	Fibrous Protein
1. Spherical.	1. Thread like shape.
2. Water soluble eg. Haemoglobin, Albumin	2. Insoluble in water eg. Keratin, Myosin

(b) Vitamin A

Answer any 3 questions from 32-35. Each carries 4 scores. (3 × 4 = 12)

Question 32.
Daniell cell converts the chemical energy liberated during the redox reaction to electrical energy.
\(\mathrm{Zn}_{(\mathrm{s})}+\mathrm{Cu}^{2+}{ }_{(\mathrm{aq})} \rightarrow \mathrm{Zn}^{2+}{ }_{(\mathrm{aq})}+\mathrm{Cu}_{(\mathrm{s})} ; \mathrm{E}_{\text {cell }}^0=1.1 \mathrm{~V}\)
(a) Identify the anode and cathode in Daniell cell. (1)
(b) Calculate the standard Gibbs energy (∆_rG°) for the reaction. (2)
(c) Give the Nernst equation of the above cell reaction. (1)
Answer:
(a) Anode: Zinc or Zn
Cathode: Cu or Copper
(b) ∆_rG° = -nFE°cell
= -2 × 96500 × 1.1
= -212300 J
(c) \(E_{\text {cell }}=E^{\circ} \text { cell }-\frac{0.0591}{2} \log \left[\frac{\mathrm{Zn}^{2+}}{\mathrm{Cu}^{2+}}\right]\)

Question 33.
Account for the following:
(a) N₂ is less reactive at room temperature. (1)
(b) PCl₃ fumes in moisture. (1)
(c) Cl₂, is a powerful bleaching agent. (1)
(d) H₃PO₃ is dibasic
Answer:
(a) In N₂ molecule one N atom is triply bonded to another N (N ≡ N). To break this bond, a high bond dissociation energy is needed. So N₂ is less reactive at room temp.
(b) PCl₃ + 3H₂O → H₃PO₃ + 3HCl ↑
It is due to the presence of HCl formed.
(c) Cl₂ + H₂O → HClO
HClO → HCl + [O]
The nascent oxygen causes bleaching action.
(d)

(H₃PO₃) – Presence of two OH groups indicates two replaceable H⁺. So its basicity is two.

Question 34.
(a) A mixture of anhydrous ZnCl₂ and conc. HCl is an important reagent used to distinguish primary, secondary, and tertiary alcohols. How the above reagent is used to distinguish the three types of alcohols? (3)
(b) Predict the product formed in the reaction:

Answer:

Question 35.
Explain the following reactions:
(a) Rosenmund reduction (2)
(b) Cannizzaro reaction (2)
Answer:
(a) Acid chloride reacts with H₂ in the presence of Pd/BaSO₄ to give aldehyde, which is known as Rosenmund Reduction.

(b) Cannizaro Reaction
Aldehydes with no hydrogen atom undergo oxidation and reduction in the presence of strong alkali to produce a primary alcohol and a salt of carboxylic acid.