Tag: chemistry

Questions Related to chemistry

A mixture of oxygen and ethyne is burnt for welding. Why a mixture of ethyne and air is not used?

chemistry hydrocarbons introduction to alkenes - ethyne acetylene alkynes

  1. ethene can not burn in air

  2. incomplete combustion takes place

  3. ethene burn in air with explosion 

  4. none of these

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Correct Option: B
Explanation:

When ethyne is burnt in air incomplete burning takes place and produce sooty flame due to limited supply oxygen present in the air.


 However, if ethyne is burnt in oxygen, it gives a clean flame with high temperature (3000°C ) due to complete combustion of ethyne.

 Hence, This oxy-acetylene flame is used for welding and it is not possible to attain such a high temperature with air. Due this reason a mixture of ethyne and air is not used for welding.

Acetylene may be prepared using Kolbes electrolytic method employing:

chemistry hydrocarbons introduction to alkenes - ethyne acetylene alkynes

  1. Pot. acetate

  2. Pot. succinate

  3. Pot. fumarate

  4. None of these

Show answer
Correct Option: C
Explanation:

Acetylene may be prepared using Kolbes electrolytic method employing potassium fumerate. Acetylene is obtained at anode. The solution is basic due to formation of KOH at cathode.
$\displaystyle  (CHCOONa) _2 \xrightarrow {Electrolysis} C _2H _2+2CO _2+2KOH + H _2$

$C _{2}H _{2}$ on reaction with Na followed by reaction with $C _{2}H _{5}I$ gives 'X'. The molecular formula of 'X' is:

chemistry hydrocarbons introduction to alkenes - ethyne acetylene alkynes

  1. $C _{2}H _{6}$

  2. $C _{4}H _{8}$

  3. $C _{4}H _{6}$

  4. $C _{3}H _{6}$

Show answer
Correct Option: C
Explanation:

Reaction: $CH \equiv CH \xrightarrow{Na} Na - C \equiv  CH \xrightarrow{C _2H _5I} C _2H _5 - C \equiv  CH + NaI$


Hence, the correct option is $C$

1, 1, 2, 2-Tetra bromoethane $\xrightarrow {Zn}A$ $\xrightarrow{red hot \ tube}B$,


 Then B is:

chemistry hydrocarbons introduction to alkenes - ethyne acetylene alkynes

  1. Acetylene

  2. Ethylene

  3. Ethane

  4. Benzene

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Correct Option: D
Explanation:

$H-\overset{Br}{\overset{|}{\underset{Br}{\underset{|}{C}}}}-\overset{Br}{\overset{|}{\underset{Br}{\underset{|}{C}}}}-H\xrightarrow[\triangle]{2n}H-C\underset{(A)}{\equiv} C-H\xrightarrow{ red hot \ tube} C _6H _6$


Option D is correct.

$H-C\equiv C-H+NaNH _{2}\longrightarrow A\overset{2 \ mole \ CH _3I}{\longrightarrow}B$


Then B is :

chemistry hydrocarbons introduction to alkenes - ethyne acetylene alkynes

  1. 1-Butyne

  2. 2-Butyne

  3. 2-Pentyne

  4. Propyne

Show answer
Correct Option: B
Explanation:

Reaction of process:
$CH\equiv CH+2NaNH _2\rightarrow NaC\equiv CNa\xrightarrow {2 mole CH _3I} CH _3CH\equiv CHCH _3$


Option B is correct.

$X+2Zn\overset{Alcohol}{\rightarrow}H-C\equiv C-H$ 


Here X is :

chemistry hydrocarbons introduction to alkenes - ethyne acetylene alkynes

  1. 1, 1-Dibromoethane

  2. 1, 2-Dibromoethane

  3. Dibromo ethane

  4. 1, 1, 2, 2-Tetrachloroethane

Show answer
Correct Option: D
Explanation:

This is dehalogenation process:


$CHCl _2-CHCl _2+2Zn\overset{Alcohol}{\longrightarrow}H-C\equiv C-H$

Option D is correct.

Kolbes electrolytic method can be applied on?

chemistry hydrocarbons introduction to alkenes - ethyne acetylene alkynes

  1. $CH _{3}-CH _{3}-COOK$

  2. $CH _2-COOK$

     $|$
    $CH _2-COOK$

  3. $CH _2-CH _3$

     $|$
    $CH _2-COOK$

  4. $CH _2-COONa$

     $|$
    $CH _2-COONa$

Show answer
Correct Option: A,B,D

What is the by-product formed when calcium carbide reacts with cold water?   

chemistry hydrocarbons introduction to alkenes - ethyne acetylene alkynes

  1. Calcium hydroxide

  2. Calcium oxide

  3. Carbon dioxide

  4. Calcium hydride

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Correct Option: A
Explanation:

When carbide reacts with cold water, the by-product formed is calcium hydroxide.

Calcium carbide reacts with water to produce :

chemistry hydrocarbons introduction to alkenes - ethyne acetylene alkynes

  1. ethane

  2. ether

  3. acetylene

  4. alcohol

Show answer
Correct Option: C
Explanation:

The chemical reaction can be shows as follows which indicates the formation of acetylene
$CaC _2(s) + 2H _2O(l) \rightarrow C _2 H _2(g) + Ca(OH) _2 (g)$

Which of the following is used for the production of oxy-acetylene flame for welding and cutting metals?

chemistry hydrocarbons introduction to alkenes - ethyne acetylene alkynes

  1. Ethane

  2. Ethene

  3. Ethyne

  4. None of the above

Show answer
Correct Option: C
Explanation:

Ethyne is used for the production of oxy-acetylene flame for welding and cutting metals.