Question

Which of the following has the highest boiling point ?
A. ${C_2}{H_5}OH$
B. $C{H_3}COOH$
C. $C{H_3}COC{H_3}$
D. ${C_2}{H_6}$

Answer 1

Boiling point of a compound depends on the intermolecular forces between molecules of that compound, if intermolecular attraction between molecules is greater than boiling point of compound will be higher and if intermolecular attraction force between molecules is weaker than boiling point of compound will be lower, intermolecular attraction force is the resultant force of many attractive forces and repulsive forces.

Complete step-by-step answer: The temperature at which a liquid substance boils and turns to vapour is known as boiling point.
At boiling point pressure exerted by the atmosphere is equaled by the pressure exerted by vapour of liquid.
Factors affecting the boiling point :
Strength of bonds : Bonds are formed between the molecules of the compound. If the bond is stronger boiling point will be higher and if the bond is weaker, the boiling point will be lower.
Bond between the molecules is an attractive force.
There are many types of bonds in nature
1. Ionic bonds
2. Covalent bond
3. Hydrogen bonds
Molecular weight of compound : we know that if the molecular weight of the compound is increased then boiling point will increase and the molecular weight of a compound is decreased then boiling point will decrease
Branching in chain : if we increase the branching in the carbon chain then surface area of compound decreases, so boiling point of compound also decreases and decreasing in branching of chain increases boiling point of compound.
Let's take a look at the options given in the question
${C_2}{H_5}OH$ : Ethanol molecular weight is $46\dfrac{{gram}}{{mol}}$ and it has a straight chain of carbon atoms but due to presence of OH group it can form hydrogen bonds between molecules of it.
$C{H_3}COOH$ : Molecular weight of Acetic acid is 60 gram and it has a straight chain of carbon atoms but due to presence of COOH group it can form hydrogen bonds between the molecules of it.
Due to presence of an extra oxygen atom it can form more hydrogen bonds than ethanol and its molecular weight is higher than that of ethanol
$C{H_3}COC{H_3}$ : Molecular weight of acetone is 58 gram and it also has a straight chain of carbon atoms but due to absence of hydrogen atoms linked with an electronegative atom it cannot form hydrogen bonds.
${C_2}{H_6}$ : Molecular weight of ethane is 30 gram and it has a straight chain of carbon atoms but due to absence of electronegative atoms linked with hydrogen atoms it cannot form hydrogen bonds.
Among given options, we can say ethanol and acetic acid has higher boiling point but due to more hydrogen bonding between the molecules of Acetic Acid and higher molecular weight of Acetic Acid the boiling point of Acetic acid is higher than that of ethanol.
Hence, we can say Acetic Acid has the highest boiling point in given options.

Hence, option (B) is correct.

Note: At boiling point heat supplied to substance doesn't raise the temperature but is used to convert liquid into vapour, boiling point depends on the pressure of the surrounding. Acetic acid boiling point is $118^\circ C$ at normal pressure, ethanol boiling point is $78^\circ C$ at normal pressure. Ethanol is used as a non-polar solvent ethanol is an important component of many alcoholic beverages such as beer and wine.