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

 

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B.Sc. (II Semester) Examination

CHEMISTRY

Paper : CHEM–121 (Old Course)

( Physical, Inorganic and Organic Chemistry )

Full Marks : 50

Pass Marks : 35%

Time : Two 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) What do you mean by parachor? Derive its mathematical expression.

(b) Consider the dissociation of calcium carbonate :
$CaC{O}_3 \left(s\right)\leftrightharpoons CaO \left(s\right)+C{O}_2 \left(g\right)$
What is the expression for the equilibrium constant?

(c) Define bond length and bond order.

(d) Mention the condition that must be satisfied by a molecule to be aromatic.

(e) Explain why aryl halides are less reactive towards nucleophilic substitution reaction.

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

(g) What are the drawbacks of Wurtz reaction?

2. Answer any five of the following questions : 3×5=15

(a) Define unit cell. Calculate the number of atoms present in b.c.c. unit cell. 1+2=3

(b) Define homogeneous equilibrium. Find the equilibrium constant of a homogeneous reaction of $\Delta n=0$. 1+2=3

(c) Draw and explain the shape of $S{F}_6$ by VSEPR theory. 3

(d) What is Friedel-Crafts alkylation reaction? Give the mechanism of Friedel-Crafts alkylation of benzene. 3

(e) Give one method each for the preparation of ethyl chloride, propyl bromide and ethyl iodide from the corresponding alcohols. 3

(f) Explain why : 1×3=3
(i) p-bond is weaker than s-bond
(ii) Viscosity of glycerol is higher than that of ethanol
(iii) Pyridine is aromatic

(g) How would you prepare the following? 3
(i) 1-bromopropane from propene
(ii) Aniline from benzene

3. Answer any five of the following questions : 5×5=25

(a) Write the SI unit of surface tension. Describe the drop weight method for the determination of surface tension of a liquid. 1+4=5

(b) What are the thermodynamic criteria for a chemical reaction in equilibrium? Derive the expression $\Delta G=-RT ln K$. 1+4=5

(c) What is hybridization? Explain the shape of ethene molecule on the basis of hybridization. Define bond angle. 1+3+1=5

(d) How will you convert the following (any two)? 2½×2=5
(i) Ethyl chloride to butane
(ii) Bromobenzene to ethylbenzene
(iii) Methylbromide to ethanoic acid

(e) What happens when (write chemical reactions)— 1×5=5
(i) benzene is treated with acetyl chloride in presence of $AlC{l}_3$;
(ii) chlorobenzene is nitrated by a mixture of conc. $HN{O}_3$ and conc. $H_{2}S{O}_4$;
(iii) benzene is treated with $B{r}_2$ in presence of $FeB{r}_3$;
(iv) toluene is treated with $C{H}_{3}C\mathrm{l }$in presence of $AlC{l}_3$;
(v) benzene is treated with fuming $H_{2}S{O}_4$?
(f) What are imperfections in solids? What are the different types of imperfection observed in ionic solids? Define them with examples. 5
(g) Explain why —OH group is orthopara-directing and $-N{O}_2$ is metadirecting group by drawing necessary diagram. 5