CBSE Sample Paper for Class 11 Chemistry

Annual Examination (2020-21)

General Instructions

This question paper comprises four Sections – A, B,C and D. There are 37 questions in the question paper. All questions are compulsory.
Section A – Questions no. 1 to 20 are very short answer type questions carrying 1 mark each. Answer these questions in one word or one sentence.
Section B – Questions no. 21 to 27 are short answer type questions, carrying 2 marks each.
Section C –Questions no. 28 to 34 are long answer type-I questions, carrying 3 marks each.
Section D –Questions no. 35 to 37 are long answer type-II questions, carrying 5 marks each.
There is no overall choice in the question paper.

Q. Read the passage given below and answer questions 1 to 5 that follows-

Buffer solutions plat an important role in a number of biological as well as industrial process. We can prepare buffer solutions of different pH values by selecting suitable concentrations of a weak acid and its salt with a strong base or a weak base and its salt with a strong acid. There are also many single salts whose solutions act as buffers. The ph of acidic buffers can be calculated using Henderson equation. Likewise a similar equation is used for the calculation of pH of basic buffers.

1- What is a buffer?

2- Give one example of a single salt whose solutions acts as a buffer.How does it acts as a buffer?

3- Which buffer is present in our blood? What is the pH value of this buffer?

4- By how much value will the pH of the acidic buffer of CH3COOH+CH3COONa change if concentration of salt is doubled?

5- What do you understand By ‘Buffer capacity” or “Buffer index”?

6- Write the IUPAC name of the element with Z=120(not yet discovered).

7- Find out oxidation no of oxygen in K₂O₂ and KO₂.

8- Name the alkali metal which emits longest wavelength of light in flame test.

9- Name the element of group 13 which shows maximum inert pair effect.

10- Write the product of reduction OF 2-butyne with Na in liquid NH3.

11- Given the IUPAC name of the compound

i) 1,1,3-Trimethylcyclohex-2ene

ii) 1,3,3-Trimethylcyclohex-1-ene

iii) 1,1,5-Trimethylcyclohex-5-ene

iv) 2,6,6-Trimethylcyclohex-1-ene

12- What is the maximum no of electrons which can be accommodated in an atom in which the highest principal quantam no is 4 ?

i) 10

ii)18

iii)36

iv)54

13- 5mole of gas A and x mole of gas B exert a pressure of 200 Pa in a container of volume 10 m³ at 1000k. Given R is the gas constant in JK^-1mol^-1, x is-

i) 2R/4+R

ii)2R/4-R

iii)4-R/2R

iv)4+R/2R

14- Based on first law of thermodynamics, which one of the following is correct ?

i) For an isochoric process, ∆U=-q

ii) For an adiabatic process,∆U=-w

iii) For an isothermal process,q=+w

iv) For a cyclic process,q=-w

15- Which of the following combination will produce H2 gas-

i) Cu metal and conc.HNO₃

ii) Zn metal with NaOH(aq)

iii) Au metal and NaCN(aq) in present of ore

iv) Fe metal and conc.HNO₃

For questions number 16 to 20, two statements are given – one labelled Assertion (A) and the other labelled Reason (R). Select the correct answer to these questions from the codes (i), (ii), (iii) and (iv) as given below:

(i) Both Assertion (A) and Reason (R) are correct,statements, and Reason (R) is the correct explanation of the Assertion (A).

(ii) Both Assertion (A) and Reason (R) are correct statements, but Reason (R) is not the correct explanation of the Assertion (A).

(iii) Assertion (A) is correct, but Reason (R) is incorrect statement.

(iv) Assertion (A) is incorrect, but Reason (R) is correct statement.

16- Assertion:Of all the halogen,Fluorine is the most electronegative element. Reason:Fluorine has most negative electron gain enthalpy.

17- Assertion:The water gas shift reactiob can be used to increase the amount of H₂ in the syngas mixture.

Reason:In the reaction,CO reduces steam to H₂

18- Assertion : First ionisation enthalpy of Galium is higher than aluminium.

Reason : Weak sheliding effect of 3d subshell is Galium.

19- Assertion (A): SF₆ molecule is unstable.

Reason (R): A stable molecule must have 8 electrons around the central atom. i.e. octet rule should be satisfied.

20- Assertion (A): Pi bond is never formed alone. It is formed along with a sigma bond.

Reason (R): Pi bond is formed by sideway overlap of p- orbitals only

21- Arrange the following ions in order of increasing ionic radii:Li⁺,Mg⁺²,K⁺,Al⁺³.

22- Which out of NH₃ and NF₃ has highest dipole moment and why ?

23- carbon monoxide gas is more dangerous than carbon dioxide gas.Why ?

24- Nitric acid avts only as an oxidizing agent while nitrous acid acts both as an oxidising as well as reducing agent. Explain why ?

25- Density of a gas is found to be 5.46g/dm³ at 27⁰C and 2 bar pressure . What will be its density at STP ?

26- Explain following:

i) Of all alkali metals lithium chloride has the lowest melting point.

ii) Lithium has the highest ionization energy among alkali metals .yet it is the strongest reducing agent.

27- Balance the following redox reactions by ion electron method.

P₄(s) +OH^–(aq) ——————PH₃(g)+H₂PO₂^–

28- (a)At 450K.Kp=2.0*10¹⁰bar for the following reaction at equilibrium:

2SO₂(g) + O₂(g)———–2SO₃(g)

What is Kc at this temperature ?

(b) The ionic product of water at 310K is 2.7*10^-14. What is the pH of neutral water at this temperature?

29- (a)What will be the mass of one C12 atom in g ?

(b)Determine the molecular formula of an oxide of iron in which the mass percent of iron and oxygen are 69.9 and 30.1 respectively.Given that the molar mass of the oxide is 159.8 gmol^-1(Atomic mass:fe=55.85, O=16.000amu)

30- Calculate the enthalpy change for the process

CCl₄(g) —————C(g) +4Cl(g) and calculate bond enthalpy of C-Cl in CCl₄ (g)

Given: ∆_vap H⁰(CCl4)=30.5KJmol^-1, ∆_fH⁰ (CCl4)=-135.5KJmol^-1∆aH⁰(C)=715.0KJmol-1, ∆aH⁰ (Cl2)=242KJmol-^-1.

31- (i) Write chemical reaction to justify that hydrogen peroxide can function as an oxidisingas well as reducing agent.

(ii) calculate the strength of 10 Volume hydrogen peroxide solution.

32- (a)What is the difference between molality and molarity ?

(b)Dinitrogen and dihydrogen react with each other to produce ammonia according to the chemical equation:

N₂(g) + 3H₂ (g) ———–2NH₃(g)

i) Calculate the mass of ammonia produced if 2.00*10³g dinitrogen reacts with 1.00*10³g dihydrogen.

ii) Will any of the two reactants remain unreacted?

iii) If yes,Which one and what would be its mass?

33- Give reasons for the following:

i) (SiH₃)₃N is a weaker base than N(CH₃)₃.

ii) SnCl₂is a reducing agemt while PbO₂ is an oxidising agent.

iii) CO₂ is a gas but SiO₂ is a solid.

34- (i) Write down the products of ozonolysis of 1,2-dimethylbenzene.How does the result support kekule structure of benzene?

ii) Out of Cyclopentadienyly cation and cyclopentadienyl anion which one is aromatic ? comment.

35- Write the molecular orbital configuration of the species:

N₂ N₂⁺` N₂^– N₂^2-

i) Calculate their bond orders.

ii) Predict their paramagnetic behavior.

iii) Which of these shows highest paramagnetism?

36- Give reason for the following;

i) H₂O has higher boiling point than HF.

ii) Ice floats on the surface of water.

iii) Ethyl alcohol has higher boiling point (351K) than ethylamine(290K)

iv) KHF₂ exists but KHCl₂ does not.

v) Boiling point of HCl is less than HF as well as HBr.

37- (i) Write the state of Hybridization of all the carbon atom in CH₂=C=CH₂.

ii) Write the structures and IUPAC names of the functional isomers having the molecular formula C₂H₅O₂

iii) Out of HO- and HS- which one is a better nucleophile and which one is a better base ?

iv) The mass of an electron is 9.1*10^-31 If its K.E. is 3.0*10^-25J. Calculate its wave length.

v) Dehydration of alcohols is always carried out with conc.H2SO4 and not with HCl. Explain.