Which is most acidic?
Correct answer: A. H2O
- A. H2O
- B. C2H5OH
- C. C4H9OH
- D. CH3-CH2-CH2OH
Explanation
Water is more acidic than ethanol because the oxygen atom in water has two lone pairs of electrons, which can be donated to a proton. Ethanol only has one lone pair of electrons on the oxygen atom, so it is less acidic. Isopropyl alcohol and n-propyl alcohol are both primary alcohols, and they have the same acidity. The acidity of an alcohol is determined by the strength of the O-H bond. The stronger the O-H bond, the less acidic the alcohol. The O-H bond in water is the strongest of the four alcohols, so water is the most acidic. The acidity of an alcohol can also be affected by the electronegativity of the alkyl group attached to the oxygen atom. The more electronegative the alkyl group, the weaker the O-H bond and the more acidic the alcohol. In the four alcohols given, the alkyl groups are all methyl groups, so they have the same electronegativity.
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About Alcohols and Phenols
Alcohols are classified as primary, secondary or tertiary and studied through their hydrogen bonding, acidity, oxidation and reactions with active metals, acids and halogenating agents. Phenols require separate treatment because the hydroxyl group is attached to an aromatic ring, making their acidity and electrophilic substitution different from ordinary alcohols.
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535 free Alcohols and Phenols MCQs from Chemistry, each with the correct answer and an explanation. Unlimited attempts, no account needed.
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