Class 12 Chemistry NEB Past Questions

1. Why do these compounds give positive iodoform test?

2. How would you convert compound (Y) into pseudonitrol?

3. A sequence of reactions is represented as: Benzene $\xrightarrow{CH_3Cl/Anhy. AlCl_3} (A) \xrightarrow{CeO_2/H^+, [O]} (B) \xrightarrow{alc. KCN, Reflux} (C)$ Predict the name of reaction that converts (B) to (C).

1. A. Benzoin condensation
2. B. Perkin's condensation
3. C. Aldol condensation
4. D. Claisen condensation

4. Write the chemical equations to illustrate the following reaction: 2, 4-DNP test

5. Write any two methods for the preparation of compound (Z).

6. Write any two methods for the preparation of compound (Z).

7. An organic compound (X) reacts with Grignard's reagent to give (Y), which on oxidation gives (Z). All of the compounds (X), (Y) and (Z) give positive iodoform test. a. Identify the compounds (X), (Y) and (Z) with reactions and conditions involved. b. Why do these compounds give positive iodoform test? c. How would you convert compound (Y) into pseudonitrol? d. Write any two methods for the preparation of compound (Z).

8. An organic compound (X) reacts with Grignard's reagent to give (Y), which on oxidation gives (Z). All of the compounds (X), (Y) and (Z) give positive iodoform test. a. Identify the compounds (X), (Y) and (Z) with reactions and conditions involved. b. Why do these compounds give positive iodoform test? c. How would you convert compound (Y) into pseudonitrol? d. Write any two methods for the preparation of compound (Z).

9. How would you convert compound (Y) into pseudonitrol?

10. Why do these compounds give positive iodoform test?

11. Write the chemical equations to illustrate the following reaction: 2, 4-DNP test

12. Identify the compounds (X), (Y) and (Z) with reactions and conditions involved.

13. Identify the compounds (X), (Y) and (Z) with reactions and conditions involved.

14. Which of the following compounds gives positive carbylamine reaction?

1. A. (CH3)2NH
2. B. (CH3)3N
3. C. (CH3)4N+
4. D. CH3NH2

15. You are given the mixture of two compounds A and B. $A=CH_{3}CH_{2}CH_{2}-NH_{2}$ and $B=CH_{3}CH_{2}NHCH_{3}$. How would you separate their mixture by applying Hoffmann's method? Give the nitrous acid test to distinguish between compounds A and B.

16. How will you carry out the following conversions? Aniline into chlorobenzene

17. A list of compounds is given as follows: p-aminoazobenzene, Benzenediazonium chloride, Aniline, Nitrobenzene, Phenol and Benzene. From the above list of compounds, prepare a sequence of reaction chain with suitable conditions and reagents.

18. Give the nitrous acid test to distinguish between compounds A and B.

19. An aliphatic compound (A) reacts with SOCl2 to give (B). The compound (B) is heated with ammonia to produce (C). The compound (C) is further heated with Br2/KOH to yield (D). The compound (D) gives (E) when treated with NaNO2/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.

20. A compound 'Z' with molecular formula $C_3H_4O_4$ is heated to produce compound 'Y' and $CO_2$ gas. Heating of compound 'Y' with $P_2O_5$ forms compound 'X' and water molecule. Identify the compound 'X'.

1. A. Ethanoic acid
2. B. Ethanoic anhydirde
3. C. Methanoic anhydride
4. D. Ethanal

21. Answer the following questions: Draw the flowsheet diagram for the manufacture of Portland cement.

22. Define instantaneous rate of reaction. Write down the rate expressions of the following reaction. $2N_2O_5(g) \rightarrow 4NO_2(g) + O_2(g)$ If 2.24 litres of $O_2$ at NTP is produced in 30 minutes, what is the rate of disappearance of $N_2O_5(g)$?

23. The half-life of a certain reaction is 50 seconds and it remains constant even if the initial concentration of the reactant is doubled. What is the order of the reaction?

1. A. Zero order reaction
2. B. First order reaction
3. C. Second order reaction
4. D. Pseudo-first order reaction

24. How are addition and condensation polymers formed? Write an example of each.

25. Construct the galvanic cell notation for the given electrodes indicating anode and cathode.

26. Calculate the cell potential for the given cell at 25°C.

27. You are given the standard reduction potentials, $E^{\circ}_{Zn^{2+}/Zn} = -0.76 V$, $E^{\circ}_{Mg^{2+}/Mg} = -2.38 V$. Answer the following questions: a. What is standard electrode potential? b. Construct the galvanic cell notation for the given electrodes indicating anode and cathode. c. Write the complete cell reaction for the given cell. d. Calculate the cell potential for the given cell at 25°C.

28. Write the complete cell reaction for the given cell.

29. Standard reduction potential values for P, Q, R and S are +0.34V, -0.76V, +0.0V and -3.05V, respectively. What is the correct order of their reducing power?

1. A. P > R > Q > S
2. B. S > R > Q > P
3. C. Q > P > S > R
4. D. S > Q > R > P

30. What is standard electrode potential?

31. Write the chemical equations to illustrate the following reaction: Williamson's reaction

32. How will you carry out the following conversions? c. Ethoxyethane into methoxymethane

33. How will you carry out the following conversions? a. Ethanol into chloroform

34. A chemical reaction occurs as follows: CH₃CH₂CH₂Br + aq. KOH → B + KBr (A). a. Identify the compound 'B' in the above reaction. b. Which substitution reaction mechanism occurs in the above reaction and why? c. What is the product formed when alc. KOH solution is used instead of aq. KOH in the above reaction? d. How can you obtain nitropropane from compound 'A'?

35. Which substitution reaction mechanism occurs in the above reaction and why?

36. Which substitution reaction mechanism occurs in the reaction of 1-bromopropane with aqueous KOH and why?

37. Write the chemical equations to illustrate the following reaction: Reimer-Tiemann reaction

38. What is the product formed when alc. KOH solution is used instead of aq. KOH in the above reaction?

39. How can you obtain nitropropane from compound 'A'?

40. Identify the compound 'B' in the above reaction.