CBSE Sample Papers for Class 12 Chemistry Paper 8

CBSE Sample Papers for Class 12 Chemistry Paper 8 are part of CBSE Sample Papers for Class 12 Chemistry. Here we have given CBSE Sample Papers for Class 12 Chemistry Paper 8.

CBSE Sample Papers for Class 12 Chemistry Paper 8

Board	CBSE
Class	XII
Subject	Chemistry
Sample Paper Set	Paper 8
Category	CBSE Sample Papers

Students who are going to appear for CBSE Class 12 Examinations are advised to practice the CBSE sample papers given here which is designed as per the latest Syllabus and marking scheme as prescribed by the CBSE is given here. Paper 8 of Solved CBSE Sample Paper for Class 12 Chemistry is given below with free PDF download solutions.

Time Allowed : 3 Hours
Max. Marks: 70

General Instructions

• All questions are compulsory.
• Question number 1 to 5 are very short answer questions and carry 1 mark each.
• Question number 6 to 10 are short answer questions and carry 2 marks each.
• Question number 11 to 22 are also short answer questions and carry 3 marks each.
• Question number 23 is a value based question and carry 4 marks.
• Question number 24 to 26 are long answer questions and carry 5 marks each.
• Use log table, if necessary. Use of calculators is not allowed.

Questions

Question 1.
Write the formula of an oxo-anion of Manganese (Mn) in which it shows the oxidation state equal to its group number.

Question 2.
Write IUPAC name of the following compound:
(CH₃CH₂)₂ NCH₃

Question 3.
For a reaction R → P, half-life (t_1/2) is observed to be independent of the initial concentration of reactants. What is the order of reaction?

Question 4.
Write the structure of 1-Bromo-4-chlorobut-2-ene.

Question 5.
Write one similarity between physisorption and chemisorption.

Question 6.
Complete the following reactions:

1. NH₃ + 3Cl₂ (excess) →
2. XeF₆ + 2H₂O →

OR
What happens when

1. (NH₄)₂Cr₂O₇ is heated?
2. H₃PO₃ is heated?

Write the equations.

Question 7.
Define the following terms:

1. Colligative properties
2. Molality (m)

Question 8.
Draw the structures of the following:
(i) H₂S₂O₇
(ii) XeF₆

Question 9.
Calculate the degree of dissociation (α) of acetic acid if its molar conductitiy (Δ_m ) is
39.05 S cm² mol^-1.
Given λ°(H⁺) = 349.6 S cm² mol^-1 and λ°(CH₃COO^–) = 40.9 S cm² mol^-1

Question 10.
Write the equations involved in the following reactions:
(i) Wolff-Kishner reduction
(ii) Etard reaction

Question 11.
A 10% solution (by mass) of sucrose in water has freezing point of 269.15 K. Calculate the freezing point of 10% glucose in water, if freezing point of pure water is 273.15 K.
Given : (Molar mass of sucrose = 342 g mol^-1)
(Molar mass of glucose = 180 g mol^-1)

Question 12.

1. Calculate the mass of Ag deposited at cathode when a current of 2 amperes was passed through a solution of AgNO₃ for 15 minutes.
   (Given : Molar mass of Ag = 108 g mol^-1 IF = 96500 C mol^-1)
2. Define fuel cell.

Question 13.

1. What type of isomerism is shown by the complex [Co(NH₃)₆] [Cr(CN)₆]?
2. Why a solution of [Ni(H₂O)₆]²⁺ is green while a solution of [Ni(CN)₄]^2- is colourless? (At.no. of Ni = 28)
3. Write the IUPAC name of the following complex : [CO(NH₃)₅(CO)₃]Cl.

Question 14.
Write one difference in each of the following:

1. Lyophobic sol and Lyophilic sol
2. Solution and Colloid
3. Homogeneous catalysis and Hetrogeneous catalysis

Question 15.
Following data are obtained for the reaction:
N₂O₅ → 2NO₂ + \(\frac { 1 }{ 2 }\)O₂

t/s	0	300	600
[N2O5]/mol L-1	1.6 x 10-2	0.8 x 10-2	0.4 x 10-2

(a) Show that it follows first order reaction.
(b) Calculate the half-life. 3
(Given log 2 = 0.3010, log 4 = 0.6021)

Question 16.
Following compounds are given to you:
2-Bromopentane, 2-Bromo-2-methylbutane, 1-Bromopentane

1. Write the compound which is most reactive towards S_N2 reaction.
2. Write the compound which is optically active.
3. Write the compound which is most reactive towards β-elimination reaction.

Question 17.

1. Write the principle of method used for the refining of germanium?
2. Out of PbS and PbCO₃ (ores of lead), which one is concentrated by froth floatation process preferably?
3. What is the significance of leaching in the extraction of aluminium?

Question 18.
Write structures of compounds A, B and C in each of the following reactions:

OR
Do the following conversions in not more than two steps:
(i) Benzoic acid to benzaldehyde
(ii) Ethyl benzene to Benzoic acid
(iii) Propanone to Propene

Question 19.
Write the structures of the monomers used for getting the following polymers:
(a) Dacron
(b) Melamine – formaldehyde polymer
(c) Buna-N

Question 20.
Define the following:

1. Anionic detergents
2. Broad spectrum antibiotics
3. Antiseptics

Question 21.
Give reasons:

1. Thermal stability decreases from H₂O to H₂Te
2. Fluoride ion has higher hydration enthalpy than chloride ion.
3. Nitrogen does not form pentahalide.

Question 22.
Give reasons:

1. Acetylation of aniline reduces its activation effect.
2. CH₃NH₂ is more basic than C₆H₅NH₂.
3. Although -NH₂ is o/p directing group, yet aniline on nitration gives a significant amount of m-nitroaniline.

Question 23.
After watching a programme on TV about the presence of carcinogens (cancer causing agents) Potassium bromate and Potassium iodate in bread and other bakery products, Ritu a class XII student decided to aware others about the adverse effects of these carcinogens in foods. She consulted the school principal and requested him to instruct the canteen contractor to stop selling sandwiches, pizzas, burgers and other bakery products to the students. Principal took an immediate action and instructed the canteen contractor to replace the bakery products with some proteins and vitamins rich food like fruits, salads, sprouts etc. The decision was welcomed by the parents and students.
After reading the above passage, answer the following questions:

1. What are the values (at least two) displayed by Ritu?
2. Which polysaccharide component of carbohydrates is commonly present in bread?
3. Write the two types of secondary structure of proteins.
4. Give two examples of water soluble vitamins.

Question 24.
(a) Account for the following:

1. Transition metals form large number of complex compounds.
2. The lowest oxide of transition metal is basic whereas the highest oxide is amphoteric or acidic.
3. E° value for the Mn³⁺/Mn²⁺ couple is highly positive (+1.57 V) as compared to Cr³⁺/ Cr²⁺ couple.

(b) Write one similarity and one difference between the chemistry of lanthanoid and actinoid elements.
OR
(a)

1. How is the variability in oxidation states of transition metals different from that of the p-block elements?
2. Out of Cu+ and Cu²⁺, which ion is unstable in aqueous solution and why?
3. Orange colour of Cr₂O^2-₇ ion changes to yellow when treated with an alkali. Why?

(b) Chemistry of actinoids is complicated as compared to lanthanoids. Give two reasons.

Question 25.
(a) An element has atomic mass 93 g mol^-1 and density 11.5 g cm^-3. If the edge length of its unit cell is 300 pm, identify the type of unit cell.
(b) Write any two differences between amorphous solids and crystalline solids.

OR
(a) Calculate the number of unit cells in 8.1 g of aluminium if it crystallises in a fee structure. (Atomic mass of Al = 27 g mol^-1)
(b) Give reasons:

1. In stoichiometric defects, NaCl exhibits Schottky defect and not Frenkel defect.
2. Silicon on doping with phosphorus forms n-type semiconductor.
3. Ferrimagnetic substances show better magnetism than antiferromagnetic substances.

Question 26.
(a) Write the product(s) in the following reactions:

(b) Give simple chemical tests to distinguish between the following pairs of compounds:

1. Ethanol and Phenol
2. Propanol and 2-methylpropan-2-ol

OR
(a) Write the formula of reagents used in the following reactions:

1. Bromination of phenol to 2,4,6-tribromophenol
2. Hydroboration of propene and then oxidation to propanol.

(b) Arrange the following compound groups in the increasing order of their property indicated:

1. p-nitrophenol, ethanol, phenol (acidic character)
2. Propanol, Propane, Propanal (boiling point)

(c) Write the mechanism (using curved arrow notation) of the following reaction:

Answers

Answer 1.
1. MnO^–₄/KMnO₄

Answer 2.
N-Ethyl-N-methylethanamine

Answer 3.
First order

Answer 4.
Br – CH₂ – CH – CH – CH₂ – Cl

Answer 5.
Both are surface phenomenon/both increases with increase in surface area (or any other correct similarity)

Answer 6.

1. NH₃ + 3 Cl₂ (excess) → NCl₃ + 3HCl
2. XeF₆ + 2H₂O → XeO₂F₂ + 4HF

OR

1. (NH₄)₂Cr₂O₇ \(\underrightarrow { heat } \) N₂ + 4H₂O + Cr₂O₃
2. 4H₃PO₃ \(\underrightarrow { heat } \) 3H₃PO₄ + PH₃

Answer 7.

1. Properties that are independent of nature of solute and depends only on the number of moles of solute are called colligative properties.
2. Number of moles of solute dissolved per kg of the solvent.

Answer 8.

Answer 9.

Answer 10.

Answer 11.

Answer 12.

1. m = ZIt
   = \(\frac { 108\times 2\times 15\times 60 }{ 1\times 96500 } \) = 2.01 g (or any other correct method)
2. Cells that converts the energy of combustion of fuels directly into electrical energy.

Answer 13.

1. Coordination isomerism
2. Unpaired electrons in [Ni(H₂O)₆]²⁺/d-d transition; No impaired electrons in [Ni(CN)₄]^2-
3. Pentaamminecarbonatocobalt (III) chloride.

Answer 14.

1. Lyophobic sols are liquid(dispersion medium)-hating and lyophillic sols are liquid(dispersion medium)-loving colloids.
2. Solution is a .homogenous mixture while colloids are heterogenous mixture. Solutions does not show Tyndall effect, while colloids show Tyndall effect. (Any one)
3. Homogenous catalysis: reactants and catalyst are in same phase.
   Heterogeneous catalysis: reactants and catalyst are not in same phase. (or any other correct difference)

Answer 15.

k is constant when using first order equation therefore it follows first order kinetics or we can say that, in equal time interval, half of the reactant gets converted into product and the rate of reaction is independent of the concentration of reactants, so it is a first order reaction.

(b) t_1/2 = 0.693/k
= 0.693/2.31 × 10^-3 = 300 s
(If student writes directly that half life is 300 s, award full marks)

Answer 16.

1. 1-Bromopentane
2. 2-Bromopentane
3. 2-Bromo-2-methylbutane

Answer 17.

1.  The impurities are more soluble in the melt than in the solid state of the metal.
2. PbS
3. Impurities like SiO₂ etc are removed by using NaOH solution and pure alumina is obtained.

Answer 18.

Answer 19.

Answer 20.

1. Anionic detergents are sodium salts of sulphonate long chain alcohols or hydrocarbons. In other words, alkylbenzene sulphonates or detergents whose anionic part is involved in cleansing action.
2. Antibiotics which kills or inhibits a wide range of gram-positive and gram-negative bacteria.
3. Antiseptics are the chemicals which either kill or prevent the growth of microbes on living tissues.

Answer 21.

1. Due to the decrease in bond dissociation enthalpy/due to increase in atomic size from O to Te.
2. Due to small size of fluoride ion it has high charge density.
3. Absence of d-orbitals

Answer 22.

1. Due to the resonance, the electron pair on nitrogen atom gets delocalised towards the carbonyl group.
2. Because of +I effect in methylamine electron density at nitrogen atom increases whereas in aniline resonance takes place and electron density on nitrogen atom decreases.
3. Due to protonation of aniline/formation of anilinium ion.

Answer 23.

1. Concerned, caring, socially alert, leadership (or any other 2 values)
2. Starch
3. a-Helix and p-pleated sheets
4. Vitamin B/B₁/B₂/B₆/C (any two)

Answer 24.
(a)

1. Due to small size and high ionic charge and availability of empty d-orbitals.
2. Higher the oxidation state, higher is the acidic character. As the oxidation state of metal increases, ionic character decreases.
3. Because Mn²⁺ has a stable d⁵ configuration, whereas Cr³⁺ is more stable due to stable t³_2g configuration.

(b) Similarity – Both are stable in +3 oxidation state/both show contraction/irregular electronic configuration (or any other suitable similarity).
Difference: Actinoids are radioactive and lanthanoids are not/actinoids show wide range of oxidation states but lanthanoids does not (or any other correct difference)

OR
(a)

1. In p block elements the difference in oxidation state is 2 and in transition metals the difference is 1.
2. Cu⁺, as it undergoes disproportionation reaction due to low hydration enthalpy.
3. Due to formation of chromate ion/CrO^2-₄ ion, which is yellow in colour.

(b) Actinoids are radioactive, actinoids show wide range of oxidation states.

Answer 25.
(a) p = (Z × M)/a³ × Na
11.5 = Z × 93/[(300 × 10^-10)³ × 6.02 × 10²³]         Z = 2.0
Body centered cubic(bcc)
(b)

Amorphous solids	Crystalline solids
Short range order	Long range order
Isotropic	Anisotropic

OR
(a) n = given mass/molar mass
= (8.1/27) mol
Number of atoms \(\frac { 8.1 }{ 27 }\) × 6.022 × 10²³
Number of atoms in one unit cell = 4 (fee)
Number of unit cells [ \(\frac { 8.1 }{ 27 }\) × 6.022 × 10²³]/4
= 4.5 × 10²²

OR
27 g of Al contains = 6.022 × 10²³ atoms
8.1 g of Al contains = (6.022 × 10²³/27) × 8.1
No. of unit cells = Total no. of atoms/4
= [\(\frac { 8.1 }{ 27 }\) × 6.022 × 10²³]/4
= 4.5 × 10²²
(b)

1. Due to comparable size of cation and anion or large size of sodium ion does not allow it to take interstitial position.
2. Si has 4 valence electrons and P has 5 valence electrons thus, an extra electron results in the formation of n-type semiconductor.
3. In ferrimagnetic substances, domains/magnetic moments are aligned in opposite direction in unequal numbers, while in antiferromagnetic substances the domains align in opposite direction in equal numbers, so they cancel their magnetic moments completely, i.e. net magnetism is zero.

Answer 26.

(ii) (CH₃)₂CHOH and CH₃CH₂I
(iii) CH₃CH=CHCHO
(b)

1. Add neutral FeCl₃ to both the compounds, phenol gives violet complex.
2. Add anhydrous ZnCl₂ and conc. HCl to both the compounds.
   2-methylpropan-2-ol gives turbidity immediately. (or any other correct test)

OR
(a)

1. Aqueous Br₂
2. B₂H₆, H₂O₂ and OH^–

(b)

1. ethanol < phenol < p-nitrophenol
2. Propane < propanal < propanol

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