Tag: organic chemistry : some basic principles and techniques

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Questions Related to organic chemistry : some basic principles and techniques

Multiple choice chemistry organic chemistry : some basic principles and techniques methods of purification of organic compounds methods of purification - organic compounds biochemical techniques

Styrene can be purified by:

  1. Simple distillation

  2. Fractional distillation

  3. Vacuum distillation

  4. Steam distillation
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Styrene is heat-sensitive and tends to polymerize at its normal boiling point. Therefore, it must be purified by vacuum distillation to lower its boiling point.

Multiple choice chemistry organic chemistry : some basic principles and techniques methods of purification of organic compounds methods of purification - organic compounds biochemical techniques

The standard reduction potentials of $Pt|Cr {2}O _{7}^{2-}, Cr^{+3}; Pt|MnO _{4}^{-}, Mn^{+2}; Pt|Ce^{+4}, Ce^{+3}$ in the presence of acid are 1.33 V, 1.51 V and 1.61 V, respectively, at $25^{\circ}C$. The decreasing order of oxidizing power is _________________.

  1. $Cr _{2}O _{7}^{2-} > MnO _{4}^{-} > Ce^{+4}$
  2. $MnO _{4}^{-}> Cr _{2}O _{7}^{2-} > Ce^{+4}$
  3. $Ce^{+4} > MnO _{4}^{-}> Cr _{2}O _{7}^{2-}$
  4. $MnO _{4}^{-} > Ce^{+4} > Cr _{2}O _{7}^{2-}$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Oxidizing power is directly proportional to the standard reduction potential. The values are Ce4+ (1.61 V) > MnO4- (1.51 V) > Cr2O7 2- (1.33 V).

Multiple choice chemistry organic chemistry : some basic principles and techniques methods of purification of organic compounds methods of purification - organic compounds biochemical techniques

Which of the following compounds can be purified by vacuum distillaiton?

  1. Glycerine

  2. Glycerol
  3. Propane-$1, 2, 3$-triol

  4. Ethanol
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

Vacuum distillation is used when the boiling point of the compound or the solvent is too high in order to distill the compound or the solvent off without significant decomposition. It is based on the fact that under vacuum the boiling point of the materials is lower than at normal atmospheric pressure. Glycerine, glycerol and propone 1,2,3-triol are the three names of the same compound. It has a boiling point of 290$^oC$ while ethanol has BP 79$^oC$ .

Option A, B and C are correct.

Multiple choice chemistry organic chemistry : some basic principles and techniques methods of purification of organic compounds methods of purification - organic compounds biochemical techniques

p-nitrophenol and o-nitrophenol are separated by?

  1. Crystallisation

  2. Fractional distillation

  3. Distillation

  4. Steam distillation
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

o-Nitrophenol exhibits intramolecular hydrogen bonding, making it more volatile than p-nitrophenol, which exhibits intermolecular hydrogen bonding. Steam distillation exploits this difference in volatility.

Multiple choice chemistry organic chemistry : some basic principles and techniques methods of purification of organic compounds methods of purification - organic compounds biochemical techniques

$ H _{2}O _{2}$ can be prepared by successive reactions:
$ 2NH _{4}HSO _{4}\rightarrow H _{2}+(NH _{4})^{2}S _{2}O _{8}$
$ (NH _{4}) _{2}S _{2}O _{8}+2H _{2}O \rightarrow  2NH _{4}HSO _{4}+ H _{2}O _{2}$
The first reaction is an electrolytic reaction and second is steam distillation. What amount of current would have to be used in first reaction to produce enough intermediate to yield 102 g pure $ H _{2}O _{2}$ per hour. Assume current efficiency 50 %.

  1. 643.33 A

  2. 321.67 A

  3. 160.83 A

  4. 1286.67 a
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

102 g H2O2 is 3 moles. The reaction produces 1 mole H2O2 per mole of (NH4)2S2O8. Electrolysis requires 2 moles of electrons per mole of persulfate. Total electrons = 6 moles. Faraday = 96500 C. Q = 6 * 96500 = 579,000 C. Current = Q/t = 579,000 / 3600 = 160.83 A. With 50% efficiency, I = 160.83 / 0.5 = 321.67 A.

Multiple choice chemistry organic chemistry : some basic principles and techniques methods of purification of organic compounds methods of purification - organic compounds biochemical techniques

Turpentine oil can be purified by:

  1. steam distillation

  2. vaccum distillation

  3. fractional distillation

  4. sublimation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

Steam distillation of a liquid in a current of steam used especially to purify liquids that are not very volatile and are immiscible with water. The boiling point of turpentine oil is between 90 and 115 °C or 195 and 240 °F and is immiscible with water. Thus, it is purified by steam distillation.

Multiple choice chemistry organic chemistry : some basic principles and techniques methods of purification of organic compounds methods of purification - organic compounds biochemical techniques

Which of the following is not an exact differential?

  1. $dq$
  2. $dG$
  3. $d(\bar { V } )$
  4. $dS$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
Exact differential are those function if 
$\cfrac { \delta  }{ \delta T } (\cfrac { \delta f }{ \delta P } )=\cfrac { \delta  }{ \delta P } (\cfrac { \delta f }{ \delta T } )$ where f is the function of P and T. increase of q, it will not be equal , so it will be not exact function.
Multiple choice chemistry organic chemistry : some basic principles and techniques methods of purification of organic compounds methods of purification - organic compounds biochemical techniques

A substance which decomposes at or below its boiling point cannot be purified by?

  1. Steam distillation

  2. Simple distillation

  3. Fractional distillation

  4. Distillation under reduced pressure
Reveal answer Fill a bubble to check yourself
A,B,C Correct answer
Explanation

Steam distillation is used for natural aromatic compounds which are immiscible in water.
Simple and fractional distillation uses the property of difference in the boiling point. These techniques can not be used for the substance which decomposes at or below its boiling point.
Distillation under reduced pressure is basically Vaccum distillation. This method is used to boil such substances without their decomposition

Option A, B and C are the answer.