Chemistry · Sample Paper 1

General instructions

Section A · Objective

1. Question 11 mark

   The number of moles in 22 g of $CO_2$ is

   1. A.0.25
   2. B.0.5
   3. C.1
   4. D.2
2. Question 21 mark

   Which concentration term does not change with temperature?

   1. A.molarity
   2. B.normality
   3. C.molality
   4. D.formality
3. Question 31 mark

   The maximum number of electrons in a subshell with $l = 2$ is

   1. A.2
   2. B.6
   3. C.10
   4. D.14
4. Question 41 mark

   Which set of quantum numbers is not possible?

   1. A.$n = 2, l = 1, m_l = 0$
   2. B.$n = 3, l = 2, m_l = -2$
   3. C.$n = 2, l = 2, m_l = 1$
   4. D.$n = 4, l = 0, m_l = 0$
5. Question 51 mark

   Which element has the highest electronegativity?

   1. A.O
   2. B.F
   3. C.Cl
   4. D.N
6. Question 61 mark

   The first ionisation enthalpy is higher for nitrogen than oxygen because

   1. A.N is smaller
   2. B.N has a half-filled 2p subshell
   3. C.O is more electronegative
   4. D.N has more protons
7. Question 71 mark

   The shape of $NH_3$ according to VSEPR theory is

   1. A.trigonal planar
   2. B.tetrahedral
   3. C.trigonal pyramidal
   4. D.T-shaped
8. Question 81 mark

   The bond order of $O_2$ is

   1. A.1
   2. B.1.5
   3. C.2
   4. D.2.5
9. Question 91 mark

   Which of these is a state function?

   1. A.heat
   2. B.work
   3. C.enthalpy
   4. D.path length
10. Question 101 mark

    The pH of a $10^{-3}$ M HCl solution is

    1. A.1
    2. B.3
    3. C.11
    4. D.7
11. Question 111 mark

    The oxidation number of Cr in $K_2Cr_2O_7$ is

    1. A.+3
    2. B.+6
    3. C.+7
    4. D.+12
12. Question 121 mark

    Addition of HBr to propene in the presence of peroxide gives

    1. A.2-bromopropane
    2. B.1-bromopropane
    3. C.1,2-dibromopropane
    4. D.propane
13. Question 131 mark

    Assertion (A): Tertiary carbocations are more stable than primary carbocations.

    Reason (R): Alkyl groups release electrons through the +I effect and hyperconjugation.

    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): Adding a catalyst changes the equilibrium constant of a reaction.

    Reason (R): A catalyst lowers the activation energy of both forward and backward reactions.

    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): The enthalpy of formation of an element in its standard state is zero.

    Reason (R): Elements in their standard states are taken as the reference.

    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): Benzene undergoes substitution more readily than addition.

    Reason (R): Substitution keeps the stable aromatic π-electron system intact.

    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 molarity of a solution made by dissolving 4 g of NaOH in enough water to make 250 mL of solution.

2. Question 182 marks

   Calculate the wavelength of an electron moving at $1.0\times10^6\ \text{m s}^{-1}$. ($m = 9.1\times10^{-31}$ kg, $h = 6.6\times10^{-34}$ J s)

3. Question 192 marks

   Why is $BeCl_2$ linear while $H_2O$ is bent, though both have three atoms?

4. Question 202 marks

   Balance by the ion-electron method in acidic medium: $MnO_4^- + Fe^{2+} \to Mn^{2+} + Fe^{3+}$

5. OR

   Question 202 marks

   What is a disproportionation reaction? Give one example.

6. Question 212 marks

   Write the IUPAC names of (i) CH₃CH(CH₃)CH₂OH and (ii) CH₃COCH₂CH₃.

Section C · Short answer

1. Question 223 marks

   A compound has 40% C, 6.67% H and 53.33% O by mass. Its molar mass is 60 g/mol. Find its empirical and molecular formulae.

2. Question 233 marks

   Calculate the energy and wavelength of the radiation emitted when the electron of a hydrogen atom falls from $n = 3$ to $n = 2$. ($E_n = -\dfrac{2.18\times10^{-18}}{n^2}$ J)

3. Question 243 marks

   Explain the trend of atomic radius (i) across a period and (ii) down a group. Why is a cation smaller than its parent atom?

4. Question 253 marks

   For $N_2(g) + 3H_2(g) \to 2NH_3(g)$, $\Delta H = -92.4$ kJ at 298 K. Calculate $\Delta U$.

5. Question 263 marks

   Calculate the pH of a buffer containing 0.1 M acetic acid and 0.1 M sodium acetate. What happens to the pH when the concentration of salt is made 1.0 M? ($pK_a = 4.76$)

6. Question 273 marks

   Explain with equations: (i) Wurtz reaction (ii) ozonolysis of propene (iii) Friedel–Crafts alkylation of benzene.

7. OR

   Question 273 marks

   What is the inductive effect? Arrange the following in order of increasing acidity and justify: CH₃COOH, ClCH₂COOH, Cl₂CHCOOH.

8. Question 283 marks

   Draw the molecular orbital energy diagram of N₂ (labels are enough). Find its bond order and magnetic nature.

Section D · Case-based

1. Question 294 marks

   Case study — Haber process. Ammonia is made by $N_2(g) + 3H_2(g) \rightleftharpoons 2NH_3(g)$, $\Delta H = -92$ kJ. Industry uses about 200 atm, 700 K and an iron catalyst.

   (i) Write the expression for $K_p$. (1 mark)

   (ii) How does increasing pressure affect the yield of ammonia? (1 mark)

   (iii) A lower temperature gives more ammonia, yet 700 K is used. Explain. (2 marks)

   OR

   (iii) What is the role of the iron catalyst? Does it change the value of K? (2 marks)

2. Question 304 marks

   Case study — Purifying a plant extract. A student extracts coloured pigments from spinach leaves and separates them by paper chromatography. A spot moves 3.0 cm while the solvent front moves 6.0 cm. Later she tests the extract for nitrogen using Lassaigne's test.

   (i) Calculate the $R_f$ value of the spot. (1 mark)

   (ii) What does a higher $R_f$ value tell you about a component? (1 mark)

   (iii) Describe how Lassaigne's test shows the presence of nitrogen. (2 marks)

   OR

   (iii) Why is steam distillation used for aniline–water mixtures? (2 marks)

Section E · Long answer

1. Question 315 marks

   State the postulates of Bohr's model of the hydrogen atom. Give two of its limitations. What is the de Broglie relation?

2. Question 325 marks

   Define Gibbs energy. Write the relation between $\Delta G$, $\Delta H$ and $\Delta S$ and use it to predict spontaneity in four cases. For a reaction, $\Delta H = 30$ kJ mol⁻¹ and $\Delta S = 100$ J K⁻¹ mol⁻¹. Above what temperature is it spontaneous?

3. OR

   Question 325 marks

   Define solubility product. The solubility of $AgCl$ in water at 298 K is $1.0\times10^{-5}$ mol/L. Calculate $K_{sp}$. What happens to its solubility in 0.1 M NaCl? Calculate it.

4. Question 335 marks

   Write the structures of all isomers of pentane ($C_5H_{12}$) with IUPAC names. Which has the highest boiling point and why? Draw the Newman projections of the staggered and eclipsed forms of ethane.