Chapter 42 Flashcards
Are alkane molecules denser than water and why?
Alkane molecules pack less efficiently than water molecules. Thus, all liquid alkanes are less dense than water.
Describe the solubility of alkanes.
Soluble in non-polar organic solvents such as benzene and tetrachloromethane.
What does the solubility of a molecule depend on?
Attraction between solute-solute particles and solute-solvent particles, and attraction between solute and solvent particles.
Explain why butane does not dissolve in water.
For butane to dissolve in water, the Van der Waals’ forces between butane molecules and hydrogen bonds between water molecules have to be overcome. This process is endothermic.
However, the energy released from the formation of Van der Waals’ forces between water and butane molecules is not enough to compensate for the energy needed to break the attractive forces between butane molecules and between water molecules. Thus, butane does not dissolve in water.
Describe the density of alcohols compared to water.
Most alcohols are less dense than water, but alcohols with more than one hydroxyl group are denser than water.
Explain why ethanol is soluble in water while pentanol is not.
For alcohols with less than four carbon atoms, the amount of energy released from the formation of new hydrogen bonds is more than that required to break the original hydrogen bonds. Thus, ethanol is miscible with water in all proportions.
However, for alcohol with four or more carbon atoms, the hydroxyl group can form hydrogen bonds with water molecules while the bulky hydrocarbon chain cannot. Thus, less hydrogen bonds form between water molecules and alcohol molecules.
The energy released from the formation of new hydrogen bonds is not enough to compensate for the energy required to break the original hydrogen bonds. Thus, they are less soluble in water.
Describe the two parts of butanol in terms of how it interacts with water.
The hydrocarbon chain is hydrophobic, while the hydroxyl group is hydrophilic.
What is the smell and taste of carboxylic acids?
Pungent smell, sour taste
In the (?) state, carboxylic acid molecules exist as dimers.
Gaseous
Butanoic acid is miscible with water in all proportions while butanol is not. Explain.
The carboxyl group can form more hydrogen bonds with water molecules.
Explain whether Iodomethane or Fluoromethane has a higher boiling point.
Iodomethane has a higher boiling point than fluoromethane. This is because CH3I has a much larger molecular size. Although CH3Cl is more polar than CH3I, the difference in polarity has a much smaller effect on the strength of Van der Waals’ forces than that of molecular size.
Explain why the density of haloalkanes decreases with increasing molecular mass.
Less packing efficiency
Describe the solubility of haloalkanes.
Only lower members of the series are soluble in water, as the energy released from the Van der Waals forces formed between haloalkane molecules are usually not enough to compensate for the energy required to break the Van der Waals forces between haloalkane molecules and hydrogen bonding between water molecules.
Haloalkanes are soluble in most organic solvents, such as CCl4 and CHCl3.
State the smell of aldehydes.
Unpleasant and pungent.
State the smell of ketones.
Pleasant and sweet. (NOT FRUITY)
