Question

Suppose the two unknowns were determined to be methanol and ethanol. How can you determine which unknown corresponds to which alcohol? Explain your answer taking into account various intermolecular forces in these two liquids and how those forces affect the vapor pressure.

Answer 1

If we talk about methanol and ethanol, we can distinguish them by reaction of methanol and ethanol by iodoform.

As we know, ethanol is only alcohol which gives iodoform reaction whereas methanol does not give iodoform reaction.

This reaction mechanism as follows;-

If we talk about their characteristics, Both methanol (CH3OH) and ethanol (CH3CH2OH) have the capacity to form hydrogen bonds because of the -OH group and the difference comes when the weaker London dispersion forces come into play. Ethanol has a molecular weight of 46 amu, while methanol has a molecular weight of 32 amu.

Due to the difference in molecular weight means stronger London dispersion forces in the heavier molecule - ethanol - which leads to a lower vapour pressure.

Due to which ethanol has low vapour pressure than methanol.

Hope, you got what you want.