Tag: chemistry

Questions Related to chemistry

Component of urine can be separated by________.

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

  1. distillation

  2. filtration

  3. sedimentation

  4. decantation

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Correct Option: A
Explanation:

Due to the difference between the boiling point of components, distillation can be used for separation.

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

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

  1. above

  2. below

  3. equal to

  4. none of the above

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Correct Option: B
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. 

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

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

  1. Phenol

  2. Xylenes

  3. Naphthalene

  4. Benzene

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Correct Option: A,C
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.

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

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

  1. Adding chlorine tablets

  2. Distillation

  3. Boiling

  4. Filtration

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Correct Option: B
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.

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:

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

  1. distillation

  2. crystallisation

  3. distillation with reduced pressure

  4. steam distillation

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Correct Option: D
Explanation:

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

Glycerin can be purified by:

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

  1. vacuum distillation

  2. simple distillation

  3. steam distillation

  4. fractional distillation

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Correct Option: A
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.

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

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

  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.

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Correct Option: C

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

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

  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.

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Correct Option: E
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.

Which of the following is the most exothermic reaction?

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

  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) $

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Correct Option: B
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.

Reactions, involving liberation of heat, are called ___________ .

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

  1. decomposition

  2. endothermic

  3. exothermic

  4. combination

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Correct Option: C
Explanation:

In exothermic reactions heat is liberated.