Tag: chemistry

Quizzes (490) Questions (9892)

Questions Related to chemistry

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

An organic liquid vaporizes at a temperature _________ its boiling point in steam distillation.

  1. above

  2. below

  3. equal to

  4. none of the above
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

In steam distillation, the mixture boils when the sum of vapour pressures of water and the organic liquid becomes equal to the atmospheric pressure. Since the vapour pressure of water is appreciably higher than that of the organic liquid, it vaporizes at a temperature much lower than its normal boiling point. 

In this way, many organic compounds insoluble in water can be purified at a temperature well below the point at which decomposition occurs. 

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

In the destructive distillation of coal, at 443-503 K temperature, a middle oil or carbolic oil fraction is obtained. This fraction contains :

  1. Phenol

  2. Xylenes

  3. Naphthalene

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

 (3) Distillation of coal tar : Arenes are isolated by fractional distillation of coal tar,

Table : 

Name of the fraction

Temperature range (K)

Main constituents

Light oil (or crude oil) fraction
Middle oil fraction (Carbolic oil)
Heavy oil fraction (Creosote oil)
Green oil (Anthracene oil)
Pitch (left as residue)

 So at 443-503 K temperature phenol and naphthalene is formed

Hence options A & 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

Which of the following procedures will give you water free from all impurities?

  1. Adding chlorine tablets

  2. Distillation

  3. Boiling

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

Distillation procedures will give us water free from all impurities. The distillation process removes almost all impurities from water. Distillers are commonly used for removing nitrate, bacteria, sodium, hardness (dissolved solids), most organic compounds, heavy metals and radionuclides from water. Distillers remove about 99.5% of the impurities from the original water.

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

The fragrance of the flower is due to the presence of some steam volatile organic compounds called essential oils. These are generally insoluble in water at room temperature but are miscible with water vapour in the vapour phase. A suitable method for the extraction of these oil from the flower is:

  1. distillation

  2. crystallisation

  3. distillation with reduced pressure

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

As the component is miscible with water vapour in vapour phase so steam distillation will be most suitable method for extraction.

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

Glycerin can be purified by:

  1. vacuum distillation

  2. simple distillation

  3. steam distillation

  4. fractional distillation
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation
The liquids which decompose at its boiling point can be purified by vacuum distillation. Glycerol decomposes at its boiling point (563K). It can be distilled by vacuum distillation without decomposition at 453K and under 12mm Hg pressure.
Multiple choice chemistry organic chemistry : some basic principles and techniques methods of purification of organic compounds methods of purification - organic compounds biochemical techniques

Distillation under reduced pressure is generally used to purify those liquid which:

  1. have very low boiling points

  2. are volatile

  3. have high boiling points and which decompose below their boiling points

  4. have a large difference in their boiling points.
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Distillation under reduced pressure lowers the boiling point of a liquid, which prevents the thermal decomposition of substances that are heat-sensitive. This technique is essential for liquids with high boiling points that would otherwise break down before reaching their boiling point at atmospheric pressure.

Multiple choice chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

Statement I: An exothermic reaction has a positive $\Delta H$.
Statement II: Heat must be added to the system for the reaction to occur.

  1. Statement 1 and Statement 2 are correct and Statement 2 is the correct explanation of Statement 1

  2. Both the Statement 1 and Statement 2 are correct and Statement 2 is NOT the correct explanation of Statement 1

  3. Statement 1 is correct but Statement 2 is not correct

  4. Statement 1 is not correct but Statement 2 is correct.

  5. Both the Statement 1 and Statement 2 are not correct.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

Option $E$ is the correct answer. Both the statements are incorrect.

In an exothermic reaction, heat is produced or given out when the reaction occurs.
And exothermic reaction has a negative delta $H$ value.

Multiple choice chemistry endothermic and exothermic reactions endothermic reactions what are enthalpy changes energy change in chemical reactions

Which of the following is the most exothermic reaction?

  1. $\displaystyle { Ag }^{ + }\left( aq \right) +{ Cl }^{ - }\rightarrow AgCl(aq) $
  2. $\displaystyle { C } _{ 5 }{ H } _{ 12 }\left( s \right) +8{ O } _{ 2 }\left( g \right) \rightarrow 5{ CO } _{ 2 }\left( g \right) +6{ H } _{ 2 }O\left( l \right) $
  3. $\displaystyle { NH } _{ 3 }\left( s \right) +{ H } _{ 2 }O\left( s \right) \leftrightharpoons { NH } _{ 4 }^{ + }\left( s \right) +{ OH }^{ - }\left( s \right) $
  4. $\displaystyle H{ C } _{ 2 }{ H } _{ 3 }{ O } _{ 2 }\left( l \right) +{ OH }^{ - }\left( aq \right) \rightarrow { H } _{ 2 }O\left( O \right) +{ C } _{ 2 }{ H } _{ 3 }{ O } _{ 2 }^{ - }\left( aq \right) $
  5. $\displaystyle Ca{ CO } _{ 3 }\left( s \right) \rightarrow CaO\left( s \right) +C{ O } _{ 2 }\left( g \right) $
Reveal answer Fill a bubble to check yourself
B Correct answer
Explanation

Option B is the correct answer.

The reaction written in option B is a combustion reaction. It is combustion of Propane. Combustion reactions are exothermic in nature.
Thus, combustion of propane is an exothermic reaction and a lot of heat is generated, which causes more propane to combine with Oxygen.