posted by Natash .
Rank the following compounds in order of decreasing boiling point:
KCI CO2 CH2O
KCl is an ionic compound. Ionic compounds generally have the highest boiling points.
CO2 you know is a gas and CH2O is formaldehyde(we learned it as
"sea water") which is a liquid.
As Dr Bob says the compound with the highest boiling point will be the ionic solid, KCl.
The other two componds are both covalently bonded so we would expect the one with the highest molecular mass (CO2) to have the higher boiling point. As in all these type of questions the thing to also consider is the possibility of dipoles. Here the dipole in the carbonyl group of formaldehyde (methanal), CH2O means that it will have a higher boiling point than CO2.
Both methanal (formaldehyde) and CO2 are gases at room temperature.
Dr Bob might be thinking of formaldehyde solution in water, which is a common reagent and is a liquid.