Question

How many statements are incorrect? (a) Boiling point of alcohol and phenol increases with increase in number of carbon chain due to increase in van der Waal forces (b) Solubility of alcohol decreases with increase in size of alkyl group (c) Boiling point order: Butan-1-ol > Butan-2-ol \(>\) Propan-1-ol (d) Dehydration of primary, secondary, tertiary alcohol required \(443 \mathrm{~K}, 440 \mathrm{~K}, 358 \mathrm{~K}\) respectively (e) Solubility of ether and alcohol is nearly same because of ether can also form H-bonding with water

Short answer

There are 3 incorrect statements in the given exercise: (c), (d), and (e).

Step-by-step solution

Statement (a) Analysis

The statement mentions that the boiling point of alcohol and phenol increases with an increase in the number of carbon chains due to an increase in van der Waals forces. This statement is correct because as the size of carbon chains increases, the strength of van der Waals forces also increases, leading to a higher boiling point of the compounds.

Statement (b) Analysis

The statement says that the solubility of alcohol decreases with an increase in the size of the alkyl group. This statement is correct because as the alkyl group gets larger, the hydrophobic interactions between the compounds increase, resulting in lower solubility in polar solvents like water.

Statement (c) Analysis

The statement provides the boiling point order for three different alcohols: Butan-1-ol > Butan-2-ol > Propan-1-ol. This statement is incorrect because the correct boiling point order should be Butan-1-ol > Propan-1-ol > Butan-2-ol. This is due to hydrogen bonding in primary alcohols being stronger than secondary alcohols.

Statement (d) Analysis

The statement in part (d) says that the dehydration heat of primary, secondary, and tertiary alcohols is 443 K, 440 K, and 358 K, respectively. This statement is incorrect because the required heat for dehydration should actually decrease as the alcohol's carbon structure gets more branched. The correct order should be primary > secondary > tertiary alcohols, with heat requirements of 443 K, 423 K, and 413 K, respectively.

Statement (e) Analysis

This statement suggests that the solubility of ether and alcohol is nearly the same because ether can also form hydrogen bonding with water. This statement is incorrect because ethers have weaker hydrogen bonding abilities than alcohols due to the presence of only one oxygen atom with a lone pair of electrons. As a result, the solubility of ethers is less than alcohols in water.

Counting Incorrect Statements

We found three incorrect statements: (c), (d), and (e). So the answer is that there are 3 incorrect statements in the given exercise.

Key concepts

Boiling Point

Boiling points are the temperatures at which substances change from a liquid phase to a gas phase. In alcohols, the boiling point increases as the number of carbon atoms in the chain increases. This is because larger molecules have stronger van der Waals forces, which are attractive forces between molecules that increase with more atoms.
The strength of these forces requires more energy to break, resulting in a higher boiling point.
Additionally, the structure of the alcohol affects its boiling point. Primary alcohols usually have higher boiling points than secondary and tertiary alcohols due to their ability to form stronger hydrogen bonds. This is why isomers like *Butan-1-ol* have a higher boiling point than *Butan-2-ol*.

• Higher carbon count = stronger van der Waals forces
• Primary alcohols form stronger hydrogen bonds

Solubility

Solubility is the ability of a substance to dissolve in a solvent. For alcohols, solubility in water decreases as the size of the alkyl group increases. This is due to the increasing hydrophobic nature of larger alkyl groups, which resist mixing with water.
In simpler terms, the nonpolar carbon chains do not easily mix with the polar water molecules.
When the alkyl chain is long, it outweighs the hydroxyl group's ability to solubilize the molecule.

• Solubility decreases with larger alkyl groups
• Larger alcohols are more hydrophobic
• Hydroxyl group tries to attract water, but large chains counteract this

Hydrogen Bonding

Hydrogen bonding is a special type of attraction between molecules, particularly impacting the properties of alcohols. Alcohols have a hydroxyl group (-OH) which is highly polar, allowing them to form hydrogen bonds with water and other alcohol molecules.
These bonds are stronger than van der Waals forces, impacting crucial properties like boiling point and solubility.
While both alcohols and ethers can engage in hydrogen bonding, alcohols do so more effectively because the hydrogen in the -OH group is more directly involved in bonding, unlike ethers which lack this direct hydrogen linkage.

• Hydrogen bonds impact boiling point and solubility
• -OH group in alcohols is key for hydrogen bonding
• Hydrogen bonding is stronger in alcohols compared to ethers

Dehydration Reactions

Dehydration reactions involve the removal of a water molecule from an alcohol, a common transformation in organic chemistry. The ease of this reaction depends on the structure of the alcohol, with tertiary alcohols typically dehydrating at lower temperatures than secondary or primary ones.
This order (tertiary < secondary < primary) is due to the stability of the carbocation intermediate formed during the reaction.
Understanding this temperature variance is essential, especially in laboratory settings. Often catalyzed by acidic conditions, dehydration can lead to the formation of alkenes.

• Tertiary alcohols dehydrate more easily
• Lower temperature is needed for tertiary alcohol dehydration
• Stability of carbocation affects the reaction rate and conditions