Hydrocarbons Test

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Hydrocarbons Test - 69

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Weekly Quiz Competition

Question 1
1 / -0

Alkenes readily undergo

A
substitution reactions

B
addition reactions

C
elemination reactions

D
rearrangement reactions

Solution

Alkenes readily undergo addition reactions.
Hence, Option "B" is the correct answer.
Question 2
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Neopentyl bromide, undergoes dehydrohalogenaton to give alkenes even though it has no hydrogen. This is due to:

A
$$E_2$$ mechanism

B
$$E_1$$ mechanism

C
Rearrangement of carbocations by $$E_1$$ mechanism

D
$$E_1cB$$ mechanism

E
$$E_1$$ mechanism

Solution

Neopentyl bromide gives a carbocation as an intermediate which undergoes for rearrangement and shows a $$E_1$$ mechanism (even has no $$\beta$$-H atom).

Thus rearrangement of carbocations by $$E_1$$ mechanism is the correct option.
Question 3
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Which of the following compounds will give the maximum yield of alkane on hydrogenation?

A
$$ H_{2}C=CH_{2}$$

B
$$CH_{3}-CH=CH_{2}$$

C

D

Solution

Maximum yield of alkane on hydrogenation will be in the compound with the least steric hinderance.
Of all the given options, least steric hinderance is in case of $$\mathrm{CH_2=CH_2}$$.

Hence, Option "A" is the correct answer.
Question 4
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Which of the following statements are correct?

A
HCl shows peroxide effect.

B
HBr shows peroxide effect.

C
Fluorine has the highest electron gain enthalpy.

D
Chlorine has the highest electronegativity.

Solution

Of all the hydrogen halides, only HBr shows the peroxide effect.
Fluorine has the highest electronegativity.
Chlorine has the highest electron gain enthalpy.

Hence, Option "B" is the correct answer.
Question 5
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Which among the following carbides on hydrolysis give alkane?

A
$$Al_{4}C_{3}$$

B
$$CaC_{2}$$

C
$$Be_{2}C$$

D
$$SiC$$

Solution

$$Al_4C_3+12H_2O\rightarrow 4Al(OH)_3+3CH_4$$

Hydrolysis is a reaction that takes place between a substance and water, as a result of which the substance and water break down and new compounds form.

Aluminium carbide on hydrolysis produces methane, and aluminium hydroxide.

Hence the correct answer is option A.
Question 6
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Which compound in each of the following pairs will add HCl readily?

A
$$ H_2C = CH_2 $$ or $$ CH_3 - CH= CH-CH_3 $$

B
$$ CH_3 - CH = CH - CH_3 or H_2C = CH-CH= CH_2 $$

C
$$ or \ CH_3 - CH = CH = CH_2 $$

D
$$ CH_3 - CH= CH- CH_3 $$ or

Solution

Addition of HCl will be done according to saytzeff's rule.

Saytzeff rule states that more substituted the alkene is more stable in nature.

In option A, first compound $$CH_2= CH_2$$ is non-substituted and second compound $$CH_3-CH= CH-CH_3$$ is disubstituted. So, second compound will undergoe reaction with HCl readily.

In option B, First compound $$CH_3-CH= CH-CH_3$$ is disubstituted alkene and second compound $$CH_{2}=CH-CH=CH_{2}$$ is a conjugated alkene. So, second compound undergoes reaction with $$HCl$$ readily.

In option C, first compound is a disubstituted alkene which shows conjugation and second compound $$CH_3-CH= CH-CH_3$$ is disubstituted alkene. So, first compound undergoes reaction with $$HCl$$ readily.

In option D, first compound is tetrasubstituted and second compound $$CH_3-CH= CH-CH_3$$ is disubstituted. So first compound undergoes reaction with $$HCl$$ readily.

So, A-(II), B-(II), C-(I) and D-(I)
Question 7
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Following are the isomers of molecular formula for $$C_{5}H_{12}$$ :
Decreasing order of their boiling points is:

A
$$I < II < III$$

B
$$I>II>III$$

C
$$II>I>III$$

D
$$III>I>II$$

Solution

The given structures are isomers of $$C_5H_{12}$$, which means all the compounds have the same number of carbon atoms. So, the boiling point of the compounds cannot be compared considering the number of carbon atoms of the compound.

Now we have to observe the branching of the compounds. More branching in a compound, less its boiling point. In structure I, no branching present. In structure II, one branching present and in structure III, two branching present. So, structure I has the highest boiling point, then structure II and then structure III.

So, decreasing order of boiling point is,

$$I>II>III$$
Question 8
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The highest boiling point is expected for

A
iso-octane

B
n-octane

C
n-butane

D
neo-heptane

Solution

Boiling point $$\propto$$ Molecular weight
Boiling point $$\propto$$ Branching.

Of all options, iso-octane has the highest branching and molecular weight.
So, it has the highest boiling point of all the given options.

Hence, Options "A" is the correct answer.
Question 9
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The process by which vegetable ghee is manufactured is known is:-

A
Saponification

B
hydrogenation

C
esterification

D
hydrolysis

Solution

Hydrogenation is the process of converting vegetable oil to vegetable ghee. During hydrogenation, vegetable oils are reacted with hydrogen gas at about $$60^oC$$. A nickel catalyst is used to speed up the reaction.
Hence option (B) is correct.
Question 10
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Product formed in the below reaction is
$$\mathrm{CH_3I +Na \xrightarrow{Dry \ Ether}}$$

A
$$ CH_{4} $$

B
$$ CH_{3}CH_{3} $$

C
$$ CH_{3}-CH_2-CH_2-CH_3 $$

D
$$ CH_{2}C_2H_{5}CH_3 $$

Solution

The given reaction is wurtz reaction and the complete reaction is:
$$\mathrm{CH_3I +Na \xrightarrow{Dry \ Ether}CH_3-CH_3}$$

So, the product formed is $$\mathrm{CH_3-CH_3}$$
Hence, Option "B" is the correct answer.