Chemistry NEB 2082 question paper

Group B

Short answer questions(8 × 5 = 40)

1. 12.

   Define instantaneous rate of reaction. Write down the rate expressions of the following reaction. $2\mathrm{N}{}_2\mathrm{O}{}_5(\mathrm{g})\to 4\mathrm{NO}{}_2(\mathrm{g})+\mathrm{O}{}_2(\mathrm{g})$ If 2.24 litres of $\mathrm{O}{}_2$ at NTP is produced in 30 minutes, what is the rate of disappearance of $\mathrm{N}{}_2\mathrm{O}{}_5(\mathrm{g})$ ? [5]

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2. 13.

   Define standard heat of formation. Calculate the heat of formation of acetic acid from the following data : [5] $\mathrm{C}(\mathrm{s})+\mathrm{O}{}_2(\mathrm{g})\to \mathrm{CO}{}_2(\mathrm{g})$ ; $\Delta H=-99\text{ kcal/mol}$ $\mathrm{H}{}_2(\mathrm{g})+\frac{1}{2}\mathrm{O}{}_2(\mathrm{g})\to \mathrm{H}{}_2\mathrm{O}(\mathrm{l})$ ; $\Delta H=-68\text{ kcal/mol}$ $\mathrm{CH}{}_3\mathrm{COOH}+2\mathrm{O}{}_2(\mathrm{g})\to 2\mathrm{CO}{}_2(\mathrm{g})+2\mathrm{H}{}_2\mathrm{O}(\mathrm{l})$ ; $\Delta H=-208\text{ kcal/mol}$

   OR

   You are given the standard reduction potentials, $E^0\mathrm{Zn}{}^{2+}/\mathrm{Zn}=-0.76\text{ V}$, $E^0\mathrm{Mg}{}^{2+}/\mathrm{Mg}=-2.38\text{ V}$ Answer the following questions :

   • a) What is standard electrode potential ? [1]
   • b) Construct the galvanic cell notation for the given electrodes indicating anode and cathode. [2]
   • c) Write the complete cell reaction for the given cell. [1]
   • d) Calculate the cell potential for the given cell at $25^{\circ }\text{C}$. [1]

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3. 14.

   A chemical reaction occurs as follows : $\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2\mathrm{Br}+\mathrm{aq}\cdot \mathrm{KOH}\to \mathrm{B}+\mathrm{KBr}$ (A)

   • a) Identify the compound 'B' in the above reaction. [1]
   • b) Which substitution reaction mechanism occurs in the above reaction and why ? [2]
   • c) What is the product formed when alc. KOH solution is used instead of aq. KOH in the above reaction ? [1]
   • d) How can you obtain nitropropane from compound 'A' ? [1]

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4. 15.

   A list of compounds is given as follows :

   P-aminoazobenze, Benzenediazonium chloride, Aniline, Nitrobenzene, Phenol and Benzene

   From the above list of compounds, prepare a sequence of reaction chain with suitable conditions and reagents. [5]

   OR

   An aliphatic compound (A) reacts with $\mathrm{SOCl}{}_2$ to give (B). The compound (B) is heated with ammonia to produce (C). The compound (C) is further heated with $\mathrm{Br}{}_2/\mathrm{KOH}$ to yield (D). The compound (D) gives (E) when treated with $\mathrm{NaNO}{}_2/\mathrm{HCl}$ at low temperature. The compound (E) is a primary alcohol which gives positive iodoform test. Identify compound (A) to (E) with the reactions involved. [5]

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5. 16.

   Write the chemical equations to illustrate the following reactions : [5×1=5]

   • a) 2,4-DNP test
   • b) Reimer-Tiemann reaction
   • c) Williamson's reaction
   • d) Perkin's condensation reaction
   • e) Wurtz-Fittig's reaction

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6. 17.

   You are given the mixture of two compounds A and B. $A=\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{CH}{}_2-\mathrm{NH}{}_2$ and $B=\mathrm{CH}{}_3\mathrm{CH}{}_2\mathrm{NHCH}{}_3$ How would you separate their mixture by applying Hoffmann's method ? Give the nitrous acid test to distinguish between compounds A and B. [3+2]

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7. 18.

   The metal 'M' with electronic configuration $[\mathrm{Ar}]3d^{10}4s^2$ belongs to group IIB in the periodic table and is commonly called 'Jasta'.

   • a) Identify metal 'M' and write its main ore. [1]
   • b) Why is metal 'M' not considered as transition element ? [1]
   • c) Draw the vertical retort. Write its reduction reaction. [2]
   • d) What happens when metal 'M' is exposed to air for a long time ? [1]

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8. 19.

   What is rusting ? Describe the electrochemical theory of rusting of iron. List any two methods for the prevention of rusting. [5]

   GROUP: C | Long answer questions | 3 × 8 = 24

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