Chemistry Test 224

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Chemistry Test 224

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Weekly Quiz Competition

Question 1
4 / -1

The following reaction takes place in the presence of

A
NaOH/Pd

B
H₂/Pd

C
HCl/Pd

D
None of these

Solution

−NO₂ group is reduced to –NH₂ using H₂/Pd.
Question 2
4 / -1

Ethers are :

A
Basic

B
Amphoteric substances

C
Acidic

D
Neutral

Solution

Ethers are compounds which are basic in nature. There is no acidic H in the compound while it has a donor O atom.
Question 3
4 / -1

Acetylenic hydrogens are acidic because

A
Sigma electron density of C – H bond in acetylene is nearer to carbon, which has 50% s-character

B
Acetylene has only open hydrogen in each carbon

C
A c etylen e co n ta in s le ast nu mb e r o f hydrogens among the possible hydrocarbons having two carbons

D
Acetylene belongs to the class of alkynes with molecular formula, C_nH_{2n – 2}

Solution

The acidity of acetylene or 1--alkynes can be explained on the basis of molecular orbital concept according to which formation of C — H bond in acetylene involves sphybridised carbon atom. Now since s electrons are closer to the nucleus than p electrons, the electrons present in a bond having more s character will be correspondingly more closer to the nucleus.

Thus owing to high s character of the C — H bond in alkynes (s = 50%), the electrons constituting this bond are more strongly held by the carbon nucleus (i.e., the acetylenic carbon atom or the sp orbital acts as more electronegative species than the sp² and sp³ with the result the hydrogen present on such a carbon atom (≡C — H) can be esily removed as a proton.
Question 4
4 / -1

Ethanol is converted into ethoxyethane,

A
by heating excess of ethanol with conc. H₂SO₄ at 413 K or 140ºC

B
by heating Ethanol with excess of conc. H₂SO₄ at 443 K

C
by treating with conc. H₂SO₄ at room temperature

D
by treating with conc. H₂SO₄ at 273 K

Solution

In order to obtain ethoxy ethane from ethanol, the ethanol must be subjected to the effect of concentrated sulphuric acid at 413 Kelvin or 140°C as shown below:
Question 5
4 / -1

The molecular formula C₅H₁₂ contains how many isomeric alkanes?

A
1

B
2

C
3

D
4

Solution

The three isomeric alkanes of C₅H₁₂ are n-pentane, 2-methylbutane (isopentane), and 2,2-dimethylpropane (neopentane).
Question 6
4 / -1

In dehydrohalogenation reactions the preferred product is that alkene which has the greatest number of alkyl groups attached to the doubly bonded carbon atoms. This rule is known as:

A
Saytzeff’s rule

B
Markoniknov’s rule

C
Anti markoniknov’s rule

D
None of these

Solution

In dehydrohalogenation reactions the preferred product is that alkene which has the greatest number of alkyl groups attached to the doubly bonded carbon atoms. This rule is also known as Saytzeff’s rule.
Question 7
4 / -1

The observed order of the stability of the cabocation is:

A
(CH₃)₂CH⁺ < (CH₃)₃C⁺ 3⁺ < CH₃CH₂⁺

B
CH₃⁺ < CH₃CH₂⁺ <(CH₃)₂CH⁺ < (CH3)₃C⁺

C
CH₃CH₂⁺ <(CH₃)₂CH⁺ < (CH₃)₃C⁺ < CH₃⁺

D
CH₃⁺ < CH₃CH₂⁺ < (CH₃)₃C⁺ <(CH₃)₂CH⁺
Solution
The observed order of the stability of the carbocation is:

To solve this, recall the general order of carbocation stability:

Tertiary (3°) > Secondary (2°) > Primary (1°) > Methyl

This is due to:
- Hyperconjugation
- +I (inductive) effect of alkyl groups
- Resonance (not involved here directly)
Analyzing the given carbocations:
- CH₃⁺ → methyl carbocation (least stable)
- CH₃CH₂⁺ → primary (1°) carbocation
- (CH₃)₂CH⁺ → secondary (2°) carbocation
- (CH₃)₃C⁺ → tertiary (3°) carbocation (most stable)
Correct stability order:

CH₃⁺ < CH₃CH₂⁺ < (CH₃)₂CH⁺ < (CH₃)₃C⁺
Question 8
4 / -1

Phosgene is a common name for

A
phosphoryl chloride

B
Thionyl chloride

C
Carbon dioxide and phosphine

D
Carbonyl chloride.

Solution

Carbonyl chloride (COCl₂).
Question 9
4 / -1

Which one of the following compounds has the most acidic nature?

A

B

C

D

Solution

The presence of electron withdrawing substituent increases the acidity while electron releasing substituent, when present, decrease the acidity.

Phenyl is an electron withdrawing substituent while -CH₃ is an electron releasing substituent, Moreover, phenoxide ion is more resonance stabilised as compared to benzoyl oxide ion, thus, release proton more easily. That's why is a strong acid among the given.
Question 10
4 / -1

Chlorobenzene is prepared commercially by

A
Raschig process

B
Deacon process

C
Etard’s process

D
Dow’s process

Solution