This set of Chemistry Multiple Choice Questions & Answers (MCQs) focuses on “Alcohols and Phenols – 2”.
1. Phenol can be obtained by ________ of sodium phenoxide.
Explanation: When halobenzene is fused with NaOH at 623K and 320atm with a copper salt as catalyst, sodium phenoxide is produced which on treatment with dilute HCl yields phenol. This is also known as Dow’s process.
2. Cumene hydroperoxide on hydrolysis with dilute H2SO4 gives _________
a) alcohol and phenol
b) only phenol
c) phenol and acetone
d) alcohol and acetone
Explanation: When cumene hydroperoxide is hydrolysed with a solution of dilute acid, it results in the formation of phenol and acetone, of which the latter is obtained in large quantities.
3. How is carbolic acid prepared from benzene diazonium chloride?
a) Treating it with nitrous acid at 275K
b) Preparing an aqueous solution and warming it
c) Treating it with sodium hydroxide
d) Freezing it
Explanation: Carbolic acid is another name for phenol. Simply warming an aqueous solution of benzene diazonium chloride salt or treating it with a dilute acid, will result in the formation of phenol.
Explanation: Oleum is a mixture of H2SO4 and SO3 that is added to benzene to form benzene sulphonic acid, which on subsequent treatment as shown, gives phenol.
5. Which of the following isomeric alcohols is the most soluble in water?
a) n-Butyl alcohol
b) Isobutyl alcohol
c) sec-Butyl alcohol
d) tert-Butyl alcohol
Explanation: tert-Butyl alcohol is the most heavily branched isomer and is tightly packed compared to the others. This decreases the effective surface area of the alkyl part which is hydrophobic in nature.
6. Which of the following is the least soluble in water?
a) n-Butyl alcohol
b) n-Pentyl alcohol
c) n-Hexyl alcohol
d) n-Heptyl alcohol
Explanation: As the size of the alkyl group becomes larger, it prevents the formation of hydrogen bonds with water molecules and hence the solubility goes on decreasing with the increase in the size or mass of the compound.
7. Which of the following is necessary for the bromination of phenol?
Explanation: FeBr3, AlCl3 and BF3 are Lewis acids, that are required for the substitution in benzene. Phenol has an OH group that activates the aromatic ring and requires the presence of only slightly or non-polar solvents for its halogenation.
8. Phenol is approximately how much times acidic than ethanol?
Explanation: Phenol is more acidic than alcohols because of their better stability and resonant structures. The pKa values of phenol and ethanol are 10 and 15.9 respectively, which when converted to Ka values gives a ratio of about a million.
9. Phenols are not soluble in which of the following?
d) Sodium hydroxide
Explanation: Phenols are almost insoluble in water because of the presence of a very large non-polar aryl group which overcomes the polar character of the OH group.
10. What is the correct order of boiling points of alcohols having the same number of carbon atoms?
Explanation: As the branching in the structure increases, the surface area decreases and hence, the van der Waal forces decrease. This results in the reduction of boiling points of isomeric alcohols from primary to tertiary structures.
11. Four compounds A, B, C and D having similar molecular masses were tested for their boiling points. It was found that compound C has the highest boiling point of all four. What is the compound C most likely to be?
Explanation: Of compounds having similar molecular masses, alcohols will certainly have the highest boiling point due to the presence of intermolecular hydrogen bonding which is lacking in hydrocarbons, haloalkanes and ethers.
12. If the boiling point of methoxymethane is 248K, predict the boiling point of ethanol.
Explanation: Methoxymethane and ethanol are of comparable masses and it can be easily pointed out that ethanol will have a higher boiling point than it because of the presence of intermolecular hydrogen bonding. 455K is very high and is actually the boiling point of phenol.
13. Which of the following has the highest boiling point?
Explanation: As the size the molecule increases, the number of carbon atoms increases and the van der Waal forces increase, resulting in an increase in boiling points.
14. Propan-1-ol boils at a higher temperature than propan-2-ol.
Explanation: Propan-2-ol is a secondary alcohol and has some degree of branching compared to propan-1-ol. This results in the decreases in surface area and van der Waals forces and hence reduction in boiling point.
15. Toluene and phenol have similar boiling points.
Explanation: Phenols have much higher boiling points than aromatic compounds of similar molecular mass. This is because they exist as associated molecules due to intermolecular hydrogen bonding.
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