orgo 1.3
Which of the following is most soluble in benzene (C6H6)? CH3CH2CH2OH CH3CH2OH HOCH2CH2OH CH3CH2CH2CH2OH
CH3CH2CH2CH2OH The governing principle in solubility is like dissolves like. Benzene is non-polar and therefore whichever of the choices is least polar will be most soluble in benzene. In this case all of the choices are capable of hydrogen bonding making them at least somewhat polar. The key then is the compound with the largest non-polar region (in this case the longest carbon chain). The hydrocarbon portion of each molecule is non-polar and is largest in choice D. Therefore, choice D is the least polar and most soluble in benzene.
Which of the following will have the lowest vapor pressure? CH4 CH3CH3 CH3CH2CH3 CH3CH2CH2CH3
CH3CH2CH2CH3 The compound with the greatest overall intermolecular forces will have the lowest vapor pressure. All four answer choices are nonpolar and therefore only exhibit London Dispersion Forces. CH3CH2CH2CH3 has the greatest weight and surface area and therefore has the greatest intermolecular forces and the lowest vapor pressure.
Which of the following has the highest boiling point? CH3CH2CH2OH CH3CH2CH2CH3 CH3CH2CH2F CH3CH2CH3
CH3CH2CH2OH The compound with the highest intermolecular forces will have the highest boiling point. Only choice C is capable of hydrogen bonding (having an O-H bond) and has the highest overall intermolecular forces and therefore the highest boiling pt. Choice A is polar and therefore has dipole-dipole forces but isnt capable of hydrogen bonding. And choices B and D are non-polar and therefore only have the relatively weak London dispersion forces.
Which of the following has the lowest boiling point? CH3CH2CH2F CH3CH2CH3 CH3CH2CH2OH CH3CH2CH2CH3
CH3CH2CH3 The lowest boiling point will be for the compound with the lowest intermolecular forces. Choice C is capable of hydrogen bonding and choice A has dipole-dipole forces whereas choices B and D are non-polar and only have the relatively weak London dispersion forces. But choice B has a smaller surface area than choice D and therefore lower londong dispersion forces. It therefore has the lowest overall intermolecular forces of the choices listed and the lowest boiling point.
Which of the following has the highest vapor pressure? CH4 CH3CH2CH3 CH3CH3 CH3CH2CH2F
CH4 The compound with the weakest intermolecular forces will have the highest vapor pressure. CH3CH2CH2F is the largest and only polar compound and therefore has the greatest intermolecular forces (both dipole-dipole and the greatest London Dispersion forces) and is eliminated. The remaining three choices are all nonpolar and have only London Dispersion forces but CH4 has the weakest as it is the smallest of the remaining answer choices and therefore has the highest vapor pressure.
Which of the following has the highest boiling point? CH3CH2CH2CH2CH2OH CH3CH2CH2CH2CH2CH2OH HOCH2CH2CH2CH2CH2OH CH3CH2CH2CH2OH
HOCH2CH2CH2CH2CH2OH The compound with the greatest intermolecular forces will have the highest boiling point. All of the answer choices have a hydroxyl group and are therefore capable of hydrogen bonding but only HOCH2CH2CH2CH2CH2OH has two hydroxyl groups and is therefore capable of a greater degree of hydrogen bonding and therefore has the greatest intermolecular forces and the highest boiling point.
Which of the following has the highest boiling point? CH3CH2OH CH3OH NaOCH3 CH3CH2Cl
NaOCH3 All of the answer choices listed are molecular compounds except for NaOCH3 which is ionic. To boil molecular compounds the intermolecular forces of the molecules in the liquid phase have to be overcome, but to boil an ionic compound ionic bonds have to be broken. Ionic bonds are typically much stronger than the intermolecular forces of molecular compounds and therefore ionic compounds tend to have much higher boiling points. This is the case here as NaOCH3 has the highest boiling point.