EDIFY SCHOOL

Midterm Exam Oct 2024

Class Xl - CHEMISTRY (043)

Max. Marks: 70 Time: 3hrs 15 mins

Date: 19/10/2024

GENERAL INSTRUCTIONS:
Read the following instructions carefully.
(a) There are 33 questions in this question paper with internal choice.
(b) SECTION A consists of 16 multiple-choice questions carrying 1 mark each.
(c) SECTION B consists of 5 short answer questions carrying 2 marks each.
(d) SECTION C consists of 7 short answer questions carrying 3 marks each.
(e) SECTION D consists of 2 case-based questions carrying 4 marks each.
(f) SECTION E consists of 3 long answer questions carrying 5 marks each.
(g) All questions are compulsory.
(h) Use of log tables and calculators is not allowed.
SECTION A
The following questions are multiple-choice questions with one correct answer. Each
question carries 1 mark. There is no internal choice in this section.

1) What is the mass percent of carbon in carbon dioxide?

a) 0.034% b) 3.4%
c) 27.27% d) 0.455%

2) The empirical formula and molecular mass of a compound are CH2O and 180g respectively.
What will be the molecular formula of the compound?
a) C2H4O2 b) C6H10O6
c) C6H6O6 d) C6H12O6

3) The significant figures in 2.0034 is

a) 3 b) 5
c) 6 d) 4

4) The pair of ions having same electronic configuration is

a) Fe3+ , Mn2+ b) Cr3+ , Fe3+
3+ 3+
c) Fe , Co d) Cr3+ , Sc3+

5) Which of the following statements about the electron is incorrect?

a) The mass of electron is equal to the mass of neutron.
b) The magnitude of the charge on an electron and proton is same.
c) It is a basic constituent of all atoms.
d) It is a negatively charged particle.

6) The elements with atomic numbers 35, 53 and 85 are all

a) Noble gases b) Halogens
c) Transition metals d) Alkali metals

7) Which of the following is not an actinoid?

a) Curium (Z = 96)
b) Californium (Z = 98)
c) Uranium (Z = 92)
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 d) Terbium (Z = 65)

8) Which among the following has trigonal bipyramidal shape?

a) IF7 b) XeF4
c) AsF5 d) SF6

9) According to VSEPR theory, pair of electrons ___________ each other.

a) stay as they are b) get positively charged
c) attract d) repel

10) The number of σ and π bonds in the following structure respectively is

a) 4 and 21 b) 20 and 5
c) 21 and 4 d) 4 and 22

11) The formula of Iron(III) sulphate is

a) Fe3(SO4) b) Fe2(SO4)3
c) Fe(SO4)3 d) Fe(SO4)

12) In the reaction, when H2 combines with O2 to form water, there is an electron transfer from
a) H to O b) O to H
c) O to O d) No electron transfer

13) Assertion (A): All isotopes of a given element show the same type of chemical behaviour.
Reason (R): The chemical properties of an atom are controlled by the number of electrons in the
atom.
Select the most appropriate answer from the options given below:
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A.
c) A is true but R is false.
d) A is false but R is true.

14) Assertion (A): Sodium chloride formed by the action of chlorine gas on sodium metal is a
stable compound.
Reason (R): This is because sodium and chloride ions acquire octet in sodium chloride
formation.
Select the most appropriate answer from the options given below:
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A.
c) A is true but R is false.
d) A is false but R is true.

15) Assertion (A): Electron gain enthalpy becomes less negative as we go down a group.
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 Reason (R): Size of the atom increases on going down the group and the added electron
would be farther from the nucleus.
Select the most appropriate answer from the options given below:
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A.
c) A is true but R is false.
d) A is false but R is true.

16) Assertion (A): Among halogens fluorine is the best oxidant.

Reason (R): Fluorine is the most electronegative atom.
Select the most appropriate answer from the options given below:
a) Both A and R are true and R is the correct explanation of A
b) Both A and R are true but R is not the correct explanation of A.
c) A is true but R is false.
d) A is false but R is true.

SECTION B
This section contains 5 questions with internal choice in one question. The following
questions are very short answer type and carry 2 marks each.

17) Thermal decomposition of KClO3 gives KCl and O2. Calculate the volume of oxygen gas liberated
at STP by heating 12.25g of solid KClO3.

18) Calculate the wavelength and wave number of a light wave whose frequency is 2.0 x 10-10 s-1.

19) How does atomic radius vary in a period and in group? How do you explain the variation?
OR
Name a species that will be isoelectronic with each of the following atoms or ions:
a) Ar
b) Mg2+

20) Write any two differences between hydrogen bond and covalent bond.

21) The compound AgF2 is unstable compound. However if formed the compound acts as a very
strong oxidising agent. Why?

SECTION C
This section contains 7 questions with internal choice in one question. The following
questions are short answer type and carry 3 marks each.

22) An organic compound on analysis gave the data: C = 57.82%, H = 3.6% and rest oxygen.
Calculate its empirical formula.
OR
a) Define empirical formula.
b) Empirical formula of a compound is BNH2. What is its molecular formula if molar mass of the
compound is 80.50 g mol-1?

23) a) List the quantum numbers (l and ml ) for electrons of 3d orbital.

b) Which of the following orbitals are possible? : 2d, 1s, 2p and 3f
24) In astronomical observations, signals observed from the distant starts are generally weak. If the
photon detector receives a total of 3.15 x 10-18 J from the radiations of 600 nm, calculate the number
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 of photons received by the detector.

25) The amount of energy released when one million atoms of iodine in vapour state are converted to
–
I ions is 4.9 x 10-13 J according to the reaction,
–
I(g) + e- I (g)
Express the electron gain enthalpy of one mole iodine in terms of kJ mol-1 and eV per atom.

26) Draw the Lewis dot structure of CCl4, H2O2 and NCl3.

27) Write any three postulates of VSEPR theory.

28) a) Define disproportionation reaction. Give an example.

b) Calculate the oxidation number of S in KAl(SO4)2 .12H2O

SECTION D
The following questions are case-based questions. Each question has an internal choice and
carries 4 (2+1+1) marks each. Read the passage carefully and answer the questions that
follow.

29) The distribution of electrons in different orbitals is known as electronic configuration of the atom.
The number of valence electrons in an atom determines how readily an atom will react other
atoms. If it has 7 or 1 valence electron, then it only needs to gain /loose 1 electron which is
relatively easier than gaining/loosing 3 or 4 electrons. The completely filled and half filled
subshells are stable due to the following reasons: (1) Symmetrical distribution of electrons (2)
Exchange energy: Higher maximum energy leads to higher stability. The electronic configuration
of the ions may be written almost similar to those of the atoms. In case of negatively charged ions,
the extra electrons equal to the charge are added to the appropriate orbitals and in case of
positively charged ions, the electrons are removed equal to the charge.

a) State Aufbau principle and Pauli Exclusion Principle.

b) Write the tripositive ion represented by the electronic configuration: 1s2, 2s2 2p6
c) Which has more energy: 5f or 6p ?
OR
Write the electronic configuration of Chromium (24)

30) The energy needed to remove the neutral atom’s loosely bonded electron is known as the first
ionization enthalpy (IE1). The second ionization enthalpy (IE2) is the energy needed to remove
the second electron from the resultant cation and so on. The energy needed to remove an s-
electron from the same shell would require more ionization enthalpy than it would to remove a p-
electron, which in turn would take more energy than it would to remove a d-electron and so on.
Due to a rise in the number of inner electrons that balance off the increase in nuclear charge, there
is an increase in the shielding effect on the outermost electron, and the removal of the outermost
electron takes less energy down a group.

a) Explain any two factors affecting ionization enthalpy.

c) The ionization enthalpy of nitrogen is higher than that of oxygen. Why?

OR
Among Mn2+ and Fe2+, which has higher third ionization enthalpy?

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 SECTION E
The following questions are long answer types and carry 5 marks each. All questions
have an internal choice.

31) a) What is the difference between molarity and molality?

b) The molarity of a solution of sulphuric acid is 1.35M. Calculate its molality.

(Given: Density of acid solution = 1.02 g cm-3 )
(2+3)
OR
20g of CaCO3 and 20g of H2SO4 react to give CaSO4 along with water and CO2.
i) Define limiting reagent.
ii) Determine the limiting reagent for the above reaction.
iii) How much CaSO4 will be formed?
iv) If one mole of gas occupies 22.4 L at STP then calculate the volume of evolved in the
above reaction.

–
32) Draw the molecular orbital energy level diagram for O2 and write its electronic configuration
and calculate its bond order. (2½ + 1+ 1½)
OR
Explain the formation of SF6 using valence bond theory and write its hybridization and
geometry. (5)

33) Potassium dichromate (K2Cr2O7) reacts with sodium sulphite (Na2SO3) in an acid solution to
give chromium (III) ion and sulphate ion. Write the balanced ionic equation for the reaction by
half reaction method. (5)
OR

a) Identify the oxidising and reducing agents in each case.

i. 3 HCl + HNO3 Cl2 + NOCl + 2 H2O
ii. Fe2O3 + 3 CO 2 Fe + 3 CO2
iii. 4 NH3 + 3 O2 2 N2 + 6H2O

b) Calculate the oxidation number of chromium in Cr2O7 2- and draw its structure.
(3+2)

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