Physical properties of pure substances

Question 1

Are the boiling and melting point of substances physical or chemical properties?

Answer 1

Physical

Boiling point and melting point are considered physical properties because they describe changes in the state of matter (solid, liquid, gas) without altering the substance’s chemical composition.

Question 2

Does water or carbon dioxide have higher boiling point?

Answer 2

Water

Water has stronger intermolecular forces, including dipole-dipole interactions and hydrogen bonding, compared to carbon dioxide, which only experiences London dispersion forces. As a result, more energy is needed to overcome the attractions between water molecules for it to transition into the gas state..

Question 3

Which property of a molecule is key to determine its solubility in a given solvent?

Answer 3

Mainly the polarity

Polar molecules interact more effectively with polar solvents, whereas nonpolar substances are more compatible with nonpolar solvents.

Question 4

Is the relationship between the strength of interparticle interactions and the temperature at which a substance changes state direct or indirect?

Answer 4

Direct

This means that stronger interparticle interactions give rise to higher melting and boiling points of a substance.

Question 5

Arrange the following substances in rising order of their vapor pressure at a given temperature: hexane, ethanol and dimethyl ether.

Answer 5

ethanol < dimethyl ether < hexane

This is related to the interparticle interactions present in each substance. Generally, stronger interactions result in lower vapor pressure. Ethanol exhibits hydrogen bonding, dimethyl ether has dipole-dipole interactions, while hexane relies solely on London dispersion forces.