RGU Question Paper Chemistry Semester II 2020: Inorganic, Organic and Physical Chemistry

 

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B.Sc. (II Semester) Examination

CHEMISTRY

Paper : CHEM (T)–121 (New Course)

( Inorganic, Organic and Physical Chemistry—II )

Full Marks : 60

Pass Marks : 35%

Time : Two and Half Hours

Note : 1. Answer all questions.

2. The figures in the margin indicate full marks for the questions.

1. Answer any five of the following questions : 2×5=10
(a) Define bond length. Arrange the following molecules in the increasing order of bond length : 1+1=2
$C_2{H}_2, C_2{H}_4, C_2{H}_6, C_6{H}_6$

(b) Why aryl halide do not undergo nucleophilic substitution unlike alkyl halide? 2

(c) Explain why phenol is acidic. 2

(d) Discuss the effect of temperature on the viscosity of a liquid. 2

(e) Calculate the pH of 0·01 M $H_{2}S{O}_4$. 2

(f) What are the factors which affect the degree of ionization of electrolytes? 2

(g) State Markovnikov’s rule with one example. 2

2. Answer any five of the following questions : 4×5=20
(a) Draw and discuss the shape of $S{F}_6$ by VSEPR theory. 4

(b) What are nucleophilic substitution reactions? Give the differences between $S{N}_1$ and $S{N}_2$ reactions. 1+3=4

(c) Discuss the effect of electron withdrawing and electron-donating substituents on the acidity of phenol. 4

(d) Define root-mean-square and average velocity. Calculate the temperature at which average velocity of $O_2$ equals to that of $H_2$ at 20 K. 1+1+2=4

(e) Derive the relationship between $K_{\mathrm{p}}$ and $K_{\mathrm{c}}$. 4

(f) (i) Give one method each for the preparation of alkyl halide and aryl halide. 2
(ii) Explain why epoxides are much more reactive than ether. 2

(g) Calculate the pH of a buffer mixture of 0·20 M acetic acid and 0·30 M
sodium acetate. Given $p{K}_a$ of acetic acid is 4·76.

3. Answer any five of the following questions : 6×5=30

(a) What is surface tension of a liquid? What is its SI unit? Give an experimental method for the determination of surface tension of a liquid. 1+1+4=6

(b) (i) Starting from benzene diazonium salts, prepare the following compounds : 1+1+1=3

Chlorobenzene, Phenol, Fluorobenzene

(ii) Discuss stereochemical aspects of $S{N}_1$ and $S{N}_2$ reactions. 3

(c) What happens when (write chemical reactions also)—
(i) 1°, 2° and 3° alcohols are oxidized with $N{a}_{2}C{r}_2{O}_7$ and $H_{2}S{O}_4$; 2
(ii) phenol is treated with chloroform in aq. NaOH followed by acid hydrolysis; 2
(iii) ethylene oxide is treated with $C_2{H}_{5}OH/H^{+}$ ; 1
(iv) diethyl ether is treated with HI? 1

(d) Discuss the defects in solids. 6

(e) Define solubility product. Establish the relation between solubility and solubility product. At 298 K, the solubility of AgCl is 0·0015 g $L^{-1}$. Calculate its solubility product at the same temperature. 1+3+2=6

(f) (i) What is common-ion effect? Explain with an example. 2
(ii) Discuss Le Chatelier’s principle with a suitable example. 4

(g) (i) Calculate the percentage ionic character of HCl molecule. Given that bond length of HCl is 1·27Å. Experimental dipole moment is $0.343\times {10}^{-29}$ cm. 4

(ii) What is Grignard reagent? What happens when $C{H}_{3}MgB\mathrm{r }$is treated with $C{H}_{3}COC{H}_{\mathrm{3 }}$followed by hydrolysis?