Unit 4 - Properties of Organic Compounds

Question 1

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Intermolecular Forces

Answer 1

Symmetrical molecular shapes make the structure non -polar (CO2, H2CO)
Asymmetrical molecular shapes makes the structure polar (H20)

Question 2

Boiling Points

Answer 2

Molecules with stronger bond forces generally take longer to break down so have higher boiling points

Question 3

Boiling Points of Hydrocarbons

Answer 3

Molecules of hydrocarbons are non-polar (symmetrical), which means the only intermolecular force is weak dispersion forces
Hydrocarbons generally have a lower boiling points than organic compoounds of similar molecular mass that contain polar functional groups.

Question 4

Boiling Points of Aldehydes, Ketones and Ester

Answer 4

These are a asymmetrical, polar, trigonal planar structure which are held together by dipole-dipole and dispersonion forces .
Polar carbon - oxygen double bond (oxygen is more electronegative).
Strength of these dipole - dipole forces gives these components a higher boiling points.

Question 5

Boiling points of alcohols, carboxylic acids, amines and amides

Answer 5

These molecules have hydrogen bonds which are the strongest of the intermolecular forces
Molecules can form hydrogen bonds with neighbouring molecules when they contain an electronegative oxygen, nitrogen, or flourine atom attached to a hydrogen atom

Question 6

Effect of brancing on boiling points

Answer 6

Branching involves hydrocarbon chains resulting in the molecules not fitting close together, weaker dispersion forces
Boiling point decreases as brancing increases, primary has highest boiling point and tertiary has lowest.
Not to be confused with number of carbon chains, which as chains increase, boiling point also increases

Question 7

Volatility

Answer 7

The volatility of an organic compond depends on upon the strength of its intermolecular force in its liquid state.
A volatile organic compound contains weak intermolecular forces of attaractiion which are easily overcome so the liquid readily evaporates

Question 8

Volatlity of hydrocarbons

Answer 8

They are volatile as they have weak disperson forces from a non-polar bond
As the number of carbon chains increase, the dispersion force gain strength and hence become less volatile

Question 9

Volatility of haloalkanes, aldehydes and ketones

Answer 9

All polar compounds and more stronger than hydrocarbons, hence less volatile

Question 10

Volatility of alcohols and carboxylic acids

Answer 10

Much less voltaile because of their hydrogen bonds

Question 11

Solubility in hydrocarbons in organic solvents

Answer 11

Hydrocarbons readily dissolve in non-polar solvents such as other hydrocarbons or symmetrical haloalkanes

Question 12

Solubility of haloalkanes

Answer 12

Slightly more soluble in water than hudrocarbons because of the polar halogen-carbon bond.
However solubility is still very low because the overall influence of the dipole-dipole interactions is small

Question 13

Solubility of aldehydes and ketones

Answer 13

Hydrogen bonds can from between a lone pair of electrons on the oxygen atom of the carbonyl group ad the partialy positive hydrogen atoms in water molecules
Causes these to be quite soluble in water

Question 14

Solubility in the homologous series

Answer 14

Although aldehydes and ketons are soluble, the hydrocarbon tail is not so much
Increasing length = decreasing solubilty
Dispersion forces connecting with non-polar part of the hydrocarbon chains are strong enough to break the hydrogen bonds between the water molecules

Question 15

Solubility in organic solvents

Answer 15

Aldehydes and ketones become more soluble in organic solvents as they get larger
Since organic solvents are generally non-polar, which causes the hydrocarbon chains being able to form stronger dispersion forces with the non-polar solvents

Question 16

Solubility of alcohols and carboxylic acids

Answer 16

Are very soluble because the water can form strong hydrogen bonds with the polar functional group of their molecules such as the OH in the alcohol
Alcohols become less soluble as the hyrdrocarbon chain increases as the amount of hydrogen bonding is reduced