Topic 7

Question 1

What is the general formula for alkanes

Answer 1

CnH2n+2

Question 2

Explain how fractional distillation works.

Answer 2

• the bottom of the fractionating column is hottest
• the top of the fractionating column is coolest
• the crude oil enters the bottom of the fractionating column
• the hydrocarbons condense when they reach their condensing point and are collected in separate containers

Question 3

How does the length of a carbon chain affect its boiling point

Answer 3

The longer the carbon chain the higher the compounds boiling point

Question 4

How does the length of the carbon chain affect the viscocity of a compound

Answer 4

The longer the carbon chain the more viscous it is

Question 5

How does the length of the carbon chain affect flammability

Answer 5

The shorter the carbon chain the less flammable it is

Question 6

What is meant by complete combustion

Answer 6

When a compound burns completely in oxygen

Question 7

What is cracking?

Answer 7

Breaking down longer hydrocarbons into shorter, more useful hydrocarbons

Question 8

What are the two types of cracking?

Answer 8

Catalytic cracking and steam cracking

Question 9

What conditions are required for steam cracking?

Answer 9

• temp over 800 degrees

Question 10

What conditions are required for catalytic cracking?

Answer 10

• a catalyst
• temps over 500

Question 11

What is the key difference between an alkene and an alkane

Answer 11

An alkene contains a c=c (a carbon carbon double bond)
Alkanes do not

Question 12

What effect does the double bond have on alkenes?

Answer 12

Makes it very reactive

Question 13

What is the test for alkenes?

Answer 13

• add bromine water
• if alkenes are present the solution will turn from brown to colorless

Question 14

Why do we use cracking to produce shorter hydrocarbons?

Answer 14

• there is a higher demand for shorter hydrocarbons
• they can be used as fuels