Organic Chemistry: Alkanes, Alkenes, Alcohols and Haloalkanes

Question 1

What are alkanes?

Answer 1

A saturated hydrocarbon where each carbon is surrounded by four pairs of electrons.

Question 2

What is the general formula of alkanes?

Answer 2

CₙH₂ₙ₊₂

Question 3

How and why does boiling point vary as the chain length of alkanes increase?

Answer 3

The boiling point increases with chain length because a longer chain length means that there’s more points of contact for London Forces. Consequently, less energy is required to break the London Forces.

Question 4

How does branches in Alkanes affect boiling point?

Answer 4

Branched isomers have lower boiling points because the branches result in fewer points of contact resulting in less London Forces. Consequently, less energy is required to break the London Forces.

Question 5

How do you obtain specific chemicals from crude oil?

Answer 5

Distillation.

Question 6

Why are Alkanes not very reactive?

Answer 6

Because σ bonds are quite strong. C-C bonds are non-polar and C-H bonds are so similar in electronegativity that they might as well be non-polar.

Question 7

What makes Alkanes good combustors?

Answer 7

They are easy to obtain, Easy to transport, do not release toxins when combusted and burn in plentiful oxygen supply.

Question 8

What are Alkenes?

Answer 8

Unsaturated hydrocarbons with at least one carbon-carbon in the structure.

Question 9

What is the general formula of alkenes?

Answer 9

CₙH₂ₙ

Question 10

What two bonds make up a carbon-carbon double bond.

Answer 10

π bond and σ bond

Question 11

What do π bonds do to the structure of alkenes?

Answer 11

The π bond locks the rotation of the molecule at the double bond.

Question 12

How are π bonds formed?

Answer 12

π bonds are the sideways overlap of p-orbitals and are located above and below the σ bond. One electron is taken from each carbon to make the bond.

Question 13

What is the shape and bond angle of atoms around the double bond?

Answer 13

The angle is 120° and the shape is trigonal planar.

Question 14

What is a σ bond?

Answer 14

The overlap and sharing of two electrons. (Basically a covalent bond)

Question 15

In alkanes, what is the shape and bond angle of a carbon atom surrounded by 4 other atoms.

Answer 15

The angle is 109.5° and the shape is a tetrahedral one.

Question 16

Why does stereo isomerism only occur in Alkenes?

Answer 16

Because the rigid double bond locks the rotation of the alkene.

Question 17

When does stereo isomerism occur?

Answer 17

When there’s a double bond and two different groups on both sides of the double bond.

Question 18

Why are alkenes more reactive than alkanes?

Answer 18

Because the π bonds electrons are on the outside of the double bond and are therefore easier to pull away making them not as strong as the σ bond.

Question 19

What are polymers?

Answer 19

Extremely large molecules made up of small monomers which are in repeating units.

Question 20

What are downsides with man-made polymers?

Answer 20

Most polymers don’t biodegrade meaning they don’t break down naturally.
Large dumping of polymers can endanger wildlife and marine life.
Some polymers like PVC can release toxins (e.g. hydrogen chloride) into the air when burnt

Question 21

What is an alcohol?

Answer 21

A molecule with the -OH functional group.

Question 22

Why are alcohols less volatile and have higher melting points when compared to alkanes?

Answer 22

Because in alcohols, the intermolecular forces holding the molecules together are actually hydrogen bonds. Hydrogen bonds are a lot stronger and require more energy to break compared to London forces which are weaker. Therefore, alcohols need more energy to change state and have a higher boiling point.

Question 23

How does the differences between alcohols and alkanes change with chain length?

Answer 23

The difference between alkanes and alkenes gets smaller as chain length increases.

Question 24

Why do alcohols have higher water solubility than alkanes?

Answer 24

Alcohols have hydrogen bonds allowing them to form bonds with water. Alkanes have no hydrogen bonds so they can’t form bonds with water.

Question 25

How does increasing chain length in alcohols affect the water solubility?

Answer 25

As chain length increases, alcohols become less soluble as the -OH functional group has less influence.

Question 26

What is a haloalkane?

Answer 26

A compound containing the elements carbon and hydrogen with at least one halogen.

Question 27

Out of these bonds which is the strongest and which is the weakest? C-F C-Cl C-Br C-I

Answer 27

C-F Is the strongest

C-I is the weakest

Question 28

What is the Ozone layer?

Answer 28

A layer in our atmosphere that absorbs dangerous UV radiation from the sun.

Question 29

What is Ozone?

Answer 29

O₃

Question 30

What are CFC’s?

Answer 30

Chlorofluorocarbons.

Question 31

What are the problem with CFC’s?

Answer 31

CFC’s break down when exposed to UV light producing chlorine radicals. These chlorine radicals speed up the depletion of the Ozone layer.

Question 32

How do we test the reactivity of haloalkanes?

Answer 32

Place the chloroalkane, bromoalkane and iodoalkane into three separate tubes and add silver nitrate with ethanol to each tube. Then time how long it takes for the precipitate to form in each one.

Question 33

How do CFC’s speed up the depletion of the Ozone layer?

Answer 33

1) UV light breaks down C-Cl bond into 2 Cl•
2) Cl• + O₃ —> ClO• + O₂
3) ClO• + O₃ —> 2O₂ + Cl•
4) Overall Equation: 2O₃ —> 3O₂

Question 34

Apart from Chlorine radicals, what other radicals can destroy Ozone?

Answer 34

Nitrogen Oxides from vehicle emissions and thunderstorms can destroy Ozone

Question 35

Why did we use CFC’s in the first place?

Answer 35

They were stable, unreactive and non-toxic meaning they were ideal for refrigerators and propellants.