Chemistry · Sample Paper 2

General instructions

Section A · Objective

1. Question 11 mark

   The number of molecules in 9 g of water is

   1. A.$6.022\times 10^{23}$
   2. B.$3.011\times 10^{23}$
   3. C.$1.5\times 10^{23}$
   4. D.$9\times 10^{23}$
2. Question 21 mark

   The volume occupied by 2 g of $H_2$ at STP (taking molar volume 22.4 L) is

   1. A.11.2 L
   2. B.22.4 L
   3. C.44.8 L
   4. D.2.24 L
3. Question 31 mark

   The electronic configuration of chromium (Z = 24) is

   1. A.$[Ar]3d^{4}4s^2$
   2. B.$[Ar]3d^{5}4s^1$
   3. C.$[Ar]3d^6$
   4. D.$[Ar]3d^{3}4s^{2}4p^1$
4. Question 41 mark

   The number of radial nodes in a 3s orbital is

   1. A.0
   2. B.1
   3. C.2
   4. D.3
5. Question 51 mark

   Which of these has the largest atomic radius?

   1. A.Na
   2. B.Mg
   3. C.K
   4. D.Ca
6. Question 61 mark

   Which element has the most negative electron gain enthalpy?

   1. A.F
   2. B.Cl
   3. C.O
   4. D.S
7. Question 71 mark

   The hybridisation of carbon in ethyne ($C_2{H}_2$) is

   1. A.sp³
   2. B.sp²
   3. C.sp
   4. D.dsp²
8. Question 81 mark

   Which of these molecules has a zero dipole moment?

   1. A.NH₃
   2. B.H₂O
   3. C.CO₂
   4. D.HCl
9. Question 91 mark

   For a spontaneous process at constant temperature and pressure,

   1. A.ΔG > 0
   2. B.ΔG < 0
   3. C.ΔG = 0
   4. D.ΔS < 0 always
10. Question 101 mark

    For $N_2+3H_2\rightleftharpoons 2N{H}_3$, the relation between $K_p$ and $K_c$ is

    1. A.$K_p=K_c$
    2. B.$K_p=K_c(RT{)}^{-2}$
    3. C.$K_p=K_c(RT{)}^2$
    4. D.$K_p=K_c(RT{)}^{-1}$
11. Question 111 mark

    In the reaction $Zn+C{u}^{2+}\to Z{n}^{2+}+Cu$, the reducing agent is

    1. A.Zn
    2. B.Cu²⁺
    3. C.Zn²⁺
    4. D.Cu
12. Question 121 mark

    The IUPAC name of $C{H}_{3}C{H}_{2}CHO$ is

    1. A.propanal
    2. B.propanone
    3. C.propanol
    4. D.ethanal
13. Question 131 mark

    Assertion (A): The 4s orbital is filled before the 3d orbital.

    Reason (R): The (n + l) value of 4s is lower than that of 3d.

    1. A.Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
    2. B.Both Assertion (A) and Reason (R) are true, but R is not the correct explanation of A.
    3. C.Assertion (A) is true, but Reason (R) is false.
    4. D.Assertion (A) is false, but Reason (R) is true.
14. Question 141 mark

    Assertion (A): The pH of pure water decreases when it is heated.

    Reason (R): Pure water becomes acidic on heating.

    1. A.Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
    2. B.Both Assertion (A) and Reason (R) are true, but R is not the correct explanation of A.
    3. C.Assertion (A) is true, but Reason (R) is false.
    4. D.Assertion (A) is false, but Reason (R) is true.
15. Question 151 mark

    Assertion (A): Alkynes are acidic in nature.

    Reason (R): The sp-hybridised carbon in terminal alkynes has 50% s-character and holds the bonding electrons tightly.

    1. A.Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
    2. B.Both Assertion (A) and Reason (R) are true, but R is not the correct explanation of A.
    3. C.Assertion (A) is true, but Reason (R) is false.
    4. D.Assertion (A) is false, but Reason (R) is true.
16. Question 161 mark

    Assertion (A): The +R (resonance) effect of –OH group increases electron density on the benzene ring.

    Reason (R): –OH is an electron-withdrawing group by the inductive effect.

    1. A.Both Assertion (A) and Reason (R) are true, and R is the correct explanation of A.
    2. B.Both Assertion (A) and Reason (R) are true, but R is not the correct explanation of A.
    3. C.Assertion (A) is true, but Reason (R) is false.
    4. D.Assertion (A) is false, but Reason (R) is true.

Section B · Very short answer

1. Question 172 marks

   Calculate the mass percent of each element in $H_{2}S{O}_4$. (H = 1, S = 32, O = 16)

2. Question 182 marks

   Calculate the frequency and energy of a photon of wavelength 600 nm. ($h=6.6\times 10^{-34}$ J s, $c=3\times 10^8{\text{m s}}^{-1}$)

3. Question 192 marks

   What is a hydrogen bond? Why does water have a higher boiling point than $H_{2}S$?

4. OR

   Question 192 marks

   Draw the Lewis dot structures of (i) $C{O}_3^{2-}$ (ii) $HN{O}_3$ (description acceptable).

5. Question 202 marks

   Find the oxidation number of (i) S in $S_2{O}_3^{2-}$ (average) (ii) Mn in $Mn{O}_4^{-}$.

6. Question 212 marks

   What is Markovnikov's rule? Give the product of HBr addition to propene (without peroxide).

Section C · Short answer

1. Question 223 marks

   What mass of $C{O}_2$ is produced when 12 g of carbon burns in 16 g of oxygen? Which is the limiting reagent?

2. Question 233 marks

   State Heisenberg's uncertainty principle. Why is it not significant for macroscopic objects?

3. Question 243 marks

   What is ionisation enthalpy? Explain why (i) it decreases down a group (ii) the second ionisation enthalpy is higher than the first.

4. Question 253 marks

   Calculate the standard enthalpy of formation of $C{H}_4$, given: ${\Delta }_{c}H(C{H}_4)=-890$ kJ/mol, ${\Delta }_{f}H(C{O}_2)=-393.5$ kJ/mol, ${\Delta }_{f}H(H_{2}O,l)=-285.8$ kJ/mol.

5. Question 263 marks

   State Le Chatelier's principle. Predict the effect of (i) increasing pressure (ii) adding heat on the equilibrium 2SO₂(g) + O₂(g) ⇌ 2SO₃(g), ΔH < 0.

6. OR

   Question 263 marks

   Calculate the pH of 0.01 M acetic acid solution. ($K_a=1.8\times 10^{-5}$)

7. Question 273 marks

   Explain the principle and one use each of (i) distillation (ii) crystallisation (iii) sublimation.

8. Question 283 marks

   What is aromaticity? State Hückel's rule and apply it to benzene.

Section D · Case-based

1. Question 294 marks

   Case study — A Daniell cell. In a Daniell cell, a zinc rod dips in zinc sulphate solution and a copper rod dips in copper sulphate solution; the two are connected by a salt bridge. The overall reaction is $Zn(s)+C{u}^{2+}(aq)\to Z{n}^{2+}(aq)+Cu(s)$.

   (i) Write the oxidation half-reaction. (1 mark)

   (ii) Which electrode is the anode? (1 mark)

   (iii) What is the role of the salt bridge? Give two points. (2 marks)

   OR

   (iii) Why does the blue colour of copper sulphate fade but the colour of zinc sulphate solution does not change in such reactions? (2 marks)

2. Question 304 marks

   Case study — Fuel from crude oil. Petrol is a mixture of hydrocarbons, mainly alkanes with 5 to 10 carbon atoms. Straight-chain alkanes knock badly in engines, while branched alkanes burn more smoothly. Isooctane (2,2,4-trimethylpentane) is given an octane number of 100. Petrol is also blended with ethanol to reduce pollution.

   (i) Write the general formula of alkanes. (1 mark)

   (ii) Write the balanced equation for complete combustion of octane. (1 mark)

   (iii) Draw (describe) the structure of isooctane and explain why branched alkanes have lower boiling points than straight-chain isomers. (2 marks)

   OR

   (iii) What is meant by octane number, and why is a higher octane number preferred? (2 marks)

Section E · Long answer

1. Question 315 marks

   State the main postulates of VSEPR theory. Predict the shapes of (i) $S{F}_4$ (ii) $Cl{F}_3$ (iii) $Xe{F}_4$ with reasons.

2. OR

   Question 315 marks

   Explain hybridisation. Describe the hybridisation and shape of (i) $B{F}_3$ (ii) $C{H}_4$ (iii) $PC{l}_5$.

3. Question 325 marks

   (a) State the first law of thermodynamics and write its mathematical form. (b) Define entropy. (c) For a reaction, $\Delta H=30$ kJ/mol and $\Delta S=105{\text{J K}}^{-1}{\text{mol}}^{-1}$. At what temperature will the reaction become spontaneous?

4. Question 335 marks

   Explain with examples: (a) homolytic and heterolytic cleavage (b) electrophiles and nucleophiles (c) the Lassaigne test for nitrogen.