Chemistry - B.Tech 2nd Semester Exam., 2021

2021•Semester 3•Civil-CA•End Semester
Bihar Engineering University, Patna
B.Tech 2nd Semester Exam., 2021

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. 1 is compulsory.
Q.1 Answer any seven questions in brief:[2x7=14]

  1. State de Broglie's principle.

  2. What is an orbital?

  3. What are the shapes of \( \text{BF}_3 \) and \( \text{ClF}_3 \) molecules?

  4. Out of \( \text{NH}_3 \), \( \text{PH}_3 \), \( \text{AsH}_2 \) and \( \text{SbH}_2 \), which 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 :[9+5=14]

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

    \( \text{CaCO}_3 = 160 \, \text{mg} \)

    \( \text{MgHCO}_3 = 150 \, \text{mg} \)

    \( \text{CaSO}_4 = 136 \, \text{mg} \)

    \( \text{MgSO}_4 = 120 \, \text{mg} \)

    \( \text{NaCl} = 10 \, \text{mg} \)

    Calculate the quantity of temporary and permanent hardness in the water sample. Calculate the quantity of lime (78% purity) and soda (92% purity) required for softening of 25 million litre of above water sample.

  2. In an experiment to determine the hardness of a sample of water, 50 mL of \( N/50 \, \text{Na}_2\text{CO}_3 \) solution was added to 200 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 20 mL of acid was required. Calculate the hardness and comment on the nature of hardness so determined.

Q.3 Solve both questions :[10+4=14]

  1. Write short notes on the following:

    1. Photoelectric effect
    2. Heisenberg's uncertainty principle

  2. How many photons of light having a wavelength of 3000 Å are necessary to provide 1 J of energy? \( (h = 6 \cdot 626 \times 10^{-34} \, \text{J-s}) \)

Q.4 Solve both questions :[6+8=14]

  1. Explain the behaviour of CO as ligand with different metal ions 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.5 Solve all parts :[6+4+4=14]

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

  2. The internuclear distance of NaCl is \( 2 \cdot 36 \times 10^{-10} \, \text{m} \). Calculate the reduced mass and moment of inertia of NaCl. (Atomic mass of Cl = \( 35 \times 10^{-3} \, \text{kg mol}^{-1} \) and Na = \( 23 \times 10^{-3} \, \text{kg mol}^{-1} \))

  3. Calculate the force constant for CO, if it absorbs at \( 2 \cdot 143 \times 10^{5} \, \text{m}^{-1} \). (Atomic mass of C = \( 12 \times 10^{-3} \, \text{kg mol}^{-1} \) and O = \( 16 \times 10^{-3} \, \text{kg mol}^{-1} \))

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

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

  2. 0-6 mol of \( \text{NH}_3 \) at 25°C occupies a volume of 3 dm³. Calculate the pressure using van der Waals equation \( (a = 0.417 \, \text{N m}^4 \, \text{mol}^{-2} \) 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.7 Solve both questions :[7+7=14]

  1. 7 mol of a monatomic ideal gas are compressed reversibly and adiabatically. The initial volume is 15 dm³ and the final volume is 9 dm³. The initial temperature is 27 °C. (i) What would be the final temperature in this process? (ii) Calculate w, q and ΔU for the process. Given, \( C_v = 20 \cdot 91 \, \text{J K}^{-1} \, \text{mol}^{-1} \) and \( \gamma = 1 \cdot 4 \).

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

    \( E_{\text{AgCl}/\text{Ag, Cl}}^o = 0 \cdot 22 \, \text{V} \)

    \( E_{\text{Ag}^+/\text{Ag}}^o = 0 \cdot 80 \, \text{V} \)

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

Q.8 Solve both questions :[7+7=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 :[6+4+4=14]

  1. Explain the following:

    1. Trichloroacetic acid is stronger acid than acetic acid.
    2. The amino group in aniline is o- and p-directing but nitro group is m-directing.

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

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

  3. Write short notes on the following:

    1. Markownikoff's rule
    2. Kharasch's rule