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Practice each question, then open the answer or worked solution.
Why is the C—O—H bond angle in alcohols slightly less than the tetrahedral angle, whereas the C—O—C bond angle in ether is slightly greater?
The C—O—H bond angle in alcohols is slightly less than the tetrahedral angle due to the repulsion between the unshared pair of electrons or the lone pair of electrons on the oxygen atom.
Explain why low molecular mass alcohols are soluble in water.
This is due to the presence of intermolecular hydrogen bonding due to the presence of OH group between alcohol molecules. With an increase in the alkyl group of alcohol or case of high molecular mass alcohols, it suppresses the effect of polar nature of –OH group of alcohol. Thus, the solubility of alcohol decreases with increases in molecular size.
Explain why p-nitrophenol is more acidic than phenol.
Para-nitrophenol is more acidic than phenol due to the presence of an electron-withdrawing group, -NO2 group, which enhances the acidic strength of the compound by stabilizing the phenoxide ion.
Explain why alcohols and ethers of comparable molecular mass have different boiling points?
Alcohols and ethers of comparable molecular mass have different boiling points because of the presence of intermolecular hydrogen bonding in alcohols.
The carbon-oxygen bond in phenol is slightly stronger than that in methanol. Why?
Reason:
i) Due to the resonance, it develops a partial double bond character in the carbon-oxygen bond. Thus, the decrease in the size of the carbon-oxygen bond in phenol.
ii) In phenol, Oxygen is directly attached to a sp2hybridized carbon atom, whereas in methanol, Oxygen is directly attached to an sp3 hybridized carbon atom. Thus, the bond formed between oxygen and the sp2 hybridized carbon atom is slightly stronger than that in methanol.
Arrange water, ethanol and phenol in increasing order of acidity and give a reason for your answer.
The increasing order of acidity is: Ethanol < water < phenol
Phenol is more acidic because it forms a phenoxide ion after deprotonation and gets stabilized by resonance. Ethanol is less acidic because the ethoxide ion is stabilized by the positive inductive effect. The electron-releasing group in ethanol increases the density of oxygen, and deprotonation gets difficult to occur. Water is a good proton donor than ethanol.
NCERT Exemplar Solutions for Class 12 Chemistry Chapter 11 Alcohols, Phenols and EthersIn this chapter, students will learn the classification of alcohols, phenols, and ethers. The structure of the functional group is one of the most important parts of this chapter. Every year in the board exam, one question related to the functional group is always asked.
To master the concepts covered in this chapter, students are advised to solve the NCERT Exemplar Solutions for Class 12 Chemistry Chapter 11 Alcohols, Phenols, and Ethers.
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