The substances below have molar masses that are the same within $\pm 2 g / mol$ . Which substance has the lowest boiling point?

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${CH}_{3} {CH}_{2} {CH}_{3}$

${CH}_{3} {OCH}_{3}$

${CH}_{3} {CH}_{2} OH$

${CH}_{3} CHO$

answer is A.

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Detailed Solution

The boiling point rises due to hydrogen bonding because more energy is needed for the separation process. Since the OH group comes last in ethanol, one hydrogen immediately bonds to an extremely electronegative atom (oxygen). Thus, hydrogen and oxygen both become polar. Therefore, hydrogen bonding is feasible in this situation, raising the boiling point of ethanol. Dimethyl ether has a lower boiling point than ethanol because hydrogen bonding cannot occur since oxygen is not directly connected to hydrogen.

Hence, option A is correct.

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