Chemistry - B.Tech 2nd Semester Exam., 2022

2022•Semester 3•Civil-CA•End Semester
Bihar Engineering University, Patna
B.Tech 2nd Semester Exam., 2022

Chemistry

Time: 3 hoursCode: 100203Full Marks: 70

Instructions:

  1. The marks are indicated in the right-hand margin.
  2. There are NINE questions in this paper.
  3. Attempt FIVE questions in all.
  4. Question No. I is compulsory.
Q.1 Answer in brief any seven of the following:[2x7=14]

  1. State de Broglie's principle.

  2. What is an orbital?

  3. Arrange the covalent bonds C—F, C—Br, C—Cl and C—I in increasing order of strength.

  4. Which of \( \text{NH}_3 \), \( \text{PH}_3 \), \( \text{AsH}_3 \) and \( \text{SbH}_3 \) possesses largest bond angle? Give reason.

  5. Out of \( \text{Cr}^{2+} \) and \( \text{Cr}^{3+} \), which one is stable in aqueous solution?

  6. \( \text{Cu}^+ \) is colourless, but \( \text{Cu}^{2+} \) is coloured. Why?

  7. What is selection rule?

  8. A gas expands against vacuum. What is the work done on it?

  9. What is the condition for a reaction to be in equilibrium?

  10. The presence of \( \text{CO}_2 \) in boiler feed water should be avoided. Why?

Q.2 Solve both questions :[5+5+4=14]

  1. Write short notes on the following:

    1. Wave-particle duality
    2. Heisenberg's uncertainty principle

  2. Discuss photoelectric effect (with mathematical equations) for explaining the particle nature of light.

  3. How many photons of light having a wavelength of 4000 Å are necessary to provide 1 J of energy? \( (h = 6.626 \times 10^{-34} \, \text{J s}) \)

Q.3 Solve this question :[6+8=14]

  1. Which of the following two molecules has a higher bond length? (i) \( \text{O}_2 \) (ii) \( \text{O}_2^+ \) (iii) \( \text{O}_2^- \) Explain using molecular orbital theory.

  2. Draw the MO energy level diagram for NO molecule. Using this diagram, calculate and explain bond order and magnetic behaviour of (i) NO, (ii) \( \text{NO}^+ \) and (iii) \( \text{NO}^- \).

Q.4 Solve all parts :[5+5+4=14]

  1. The internuclear distance of NaCl is \( 2.36 \times 10^{-10} \text{ m} \). Calculate the reduced mass and moment of inertia of NaCl. (Atomic mass of Cl = \( 35 \times 10^{-3} \text{ kg mol}^{-1} \) and Na = \( 23 \times 10^{-3} \text{ kg mol}^{-1} \)).

  2. Calculate the force constant for CO, if it absorbs at \( 2.143 \times 10^{5} \, \text{m}^{-1} \). (Atomic mass of C = \( 12 \times 10^{-3} \, \text{kg mol}^{-1} \) and O = \( 16 \times 10^{-3} \, \text{kg mol}^{-1} \))

  3. Which type of electronic transition(s) is/are observed in UV-visible spectrum of phenol in the range 200 nm to 900 nm? Justify your answer.

Q.5 Solve all parts :[5+4+5=14]

  1. How many types of \( ^{1}\text{H} \) NMR signals are expected for (i) \( \text{CH}_2\text{BrCH}_2\text{Cl} \) and (ii) \( \text{CH}_3\text{OCH}_3 \)? Mention relative intensity ratio for the signal(s) observed for (i) and (ii).

  2. At what frequency shift from TMS, would a group of nuclei with δ = 1:5 resonate in NMR spectrometers operating at 60 MHz and 400 MHz?

  3. 2 mol of \( \text{NH}_3 \) at 300 K occupy a volume of \( 5 \times 10^{-3} \, \text{m}^3 \). Calculate the pressure using van der Waals equation \( (a = 0.417 \, \text{Nm}^4 \, \text{mol}^{-2} \) and \( b = 0.037 \times 10^{-3} \, \text{m}^3 \, \text{mol}^{-1}) \). Compare the above result with the pressure calculated using ideal gas equation.

Q.6 Solve both questions :[7+7=14]

  1. 7 mol of a monatomic ideal gas are compressed reversibly and adiabatically. The initial volume is 16 dm³ and the final volume is 7 dm³. The initial temperature is 27 °C.

    1. What would be the final temperature in this process?
    2. Calculate \( w \), \( q \) and \( \Delta U \) for the process.

    Given, \( C_v = 20 \cdot 91 \, \text{JK}^{-1} \, \text{mol}^{-1} \), \( \gamma = 1 \cdot 4 \).

  2. Write a cell (in proper cell representation) whose cell reaction is \( \text{AgCl} \rightarrow \text{Ag}^+ + \text{Cl}^- \), using the following standard electrode potentials at 298 K:

    \( E°_{\text{AgCl}/\text{AgCl}^-} = 0 \cdot 22 \, \text{V} \), \( E°_{\text{Ag}^+/\text{Ag}} = 0 \cdot 80 \, \text{V} \)

    Calculate \( E° \) of the cell. Calculate solubility product (or solubility constant) of AgCl and its solubility at 298 K.

Q.7 Solve both questions :[10+4=14]

  1. A water sample had the following constituents per litre:

    \( \text{CaCO}_3 = 65 \, \text{mg} \), \( \text{MgHCO}_3 = 80 \, \text{mg} \)

    \( \text{CaSO}_4 = 155 \, \text{mg} \), \( \text{MgSO}_4 = 135 \, \text{mg} \)

    \( \text{NaCl} = 8 \, \text{mg} \)

    Calculate the quantity of temporary and permanent hardness in the water sample. Calculate the quantity of lime (80% purity) and soda (90% purity) required for softening of 1 million litre of above water sample.

  2. In an experiment to determine the hardness of a sample of water, 25 ml of N/50 \( \text{Na}_2\text{CO}_3 \) solution was added to 100 ml of water sample. After complete precipitation of insoluble carbonate, the unreacted \( \text{Na}_2\text{CO}_3 \) was titrated against N/50 \( \text{H}_2\text{SO}_4 \) solution, when 10 ml of acid was required. Calculate the hardness and comment on the nature of hardness so determined.

Q.8 Solve both questions :[8+6=14]

  1. Write notes on the following:

    • Optical isomerism of lactic acid
    • Optical isomerism of tartaric acid

  2. Differentiate between the following:

    • Enantiomers and diastereomers
    • Racemic mixture and meso-compounds
Q.9 Solve both questions :[8+6=14]

  1. Explain the following:

    1. Acetic acid is stronger acid than phenol.
    2. The amino group in aniline is o- and p-directing but amide group is meta-directing.

  2. Arrange the following carbocations in order of increasing stability with suitable reasons:

    \( \text{C}_6\text{H}_5\text{CH}_2^+ \)
    \( (\text{CH}_3)_3\text{C}^+ \)
    \( (\text{C}_6\text{H}_5)_2\text{CH}^+ \)
    \( \text{CH}_3\text{CH}_2^+ \)