Rank the following compounds in order of decreasing boiling point:

KCI CO2 CH2O

To rank the compounds in order of decreasing boiling point, we need to consider factors such as molecular weight, polarity, and intermolecular forces. Generally, heavier molecules with stronger intermolecular forces tend to have higher boiling points.

1. CH2O (Formaldehyde):
Formaldehyde is a small molecule with a molecular weight of 30 g/mol. It is polar due to the presence of a carbonyl group. It can form hydrogen bonds, which are relatively strong intermolecular forces compared to other compounds on the list. Therefore, it would have the highest boiling point.

2. CO2 (Carbon Dioxide):
Carbon dioxide is a linear molecule with a molecular weight of 44 g/mol. It is nonpolar because of its symmetrical arrangement, and it cannot form hydrogen bonds. The intermolecular forces in carbon dioxide are London dispersion forces, which are weaker than hydrogen bonds. Hence, it would have a lower boiling point than formaldehyde.

3. KCI (Potassium Chloride):
Potassium chloride is an ionic compound composed of potassium cations (K+) and chloride anions (Cl-). It has a high molecular weight and strong ionic bonds, which require a significant amount of energy to break. As a result, it would have the highest boiling point among the given compounds.

Therefore, the ranking from highest to lowest boiling point would be: CH2O > KCI > CO2.

To rank the compounds in order of decreasing boiling point, we need to consider the intermolecular forces present in each compound. Different intermolecular forces determine the boiling points of substances. The stronger the intermolecular forces, the higher the boiling point.

Let's analyze each compound:

1. KCI (potassium chloride): KCI is an ionic compound with a metal and non-metal. Ionic compounds, like KCI, have strong electrostatic attractions between positive and negative ions. These bonds are called ionic bonds. Due to the strong forces holding the ions together, they have high boiling points.

2. CO2 (carbon dioxide): CO2 is a linear molecule with a carbon atom in the center and oxygen atoms on either side. Carbon dioxide is a non-polar molecule, which means it does not have a permanent dipole moment. It only experiences weak intermolecular forces called London dispersion forces. These forces are relatively weaker compared to ionic bonds.

3. CH2O (formaldehyde): CH2O is a polar molecule with a central carbon atom and hydrogen and oxygen atoms bonded to it. It has a bent molecular shape, which results in a net dipole moment. As a result, formaldehyde can experience dipole-dipole interactions between its molecules. These forces are stronger than London dispersion forces but weaker than ionic bonds.

Based on the analysis of intermolecular forces, we can rank the compounds in order of decreasing boiling point:

1. KCI (ionic compound)
2. CH2O (polar compound with dipole-dipole interactions)
3. CO2 (non-polar compound with London dispersion forces)

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.