Unit 3: Section 2 - Alkanes and Halogenoalkanes

Question 1

What are alkanes?

Answer 1

1. Have the general formula CnH2n+2
2. Only contain carbon and hydrogen atoms, so they’re hydrocarbons
3. Every carbon atom has 4 single bonds with other atoms, so they’re saturated (only contain single bonds)

Question 2

What are cycloalkanes?

Answer 2

1. Ring of carbon atoms with 2 hydrigens attached to each carbon
2. General formula - CnH2n
3. Still saturated

Question 3

What is crude oil?

Answer 3

Petroleum - mixture of hydrocarbons - isn’t very useful but can be separated into useful fractions

Question 4

How does fractional distillation work?

Answer 4

1. The crude oil is vaporised at about 350°
2. The vaporised crude oil goes into a fractionating column and rises up through the trays
3. The largest hydrocarbons don’t vaporise at all because their boiling points are too high - run to the bottom and form a residue
4. As the crude oil vapour goes up the fractionating column, it gets cooler - as the alkane molecules have different chain lengths, they have different boiling points, so each fraction condenses at a different temperature - fractions are drawn off at different levels
5. The hydrocarbons with the lowest boiling points don’t condense - they’re drawn off as gases at the top of the column

Question 5

What is thermal cracking?

Answer 5

1. Takes place at high temperatures (up to 1000°C) and high pressure (up to 70atm)
2. Produces alot of alkenes - used to make heaps of valuable products, like polymers

Question 6

What