P2-Topic 7- Organic chemistry

Question 1

What is crude oil?2

Answer 1

a finite resource found in rocks

remains of an ancient biomass consisting mainly of plankton that was buried
in mud

Question 2

What is a hydrocarbon?

Answer 2

A compound made up exclusively of hydrogen and carbon atoms

Question 3

What are alkanes?

Answer 3

Saturated hydrocarbons of a general formula Cn

H2n+2

Question 4

What is a homologous series??

Answer 4

Series of compounds with same general formula, same functional groups and similar chemical properties

Question 5

Describe the combustion of hydrocarbons 3

Answer 5

• Exothermic reaction= hydrocarbons+ oxygen.
• Complete combustion =carbon dioxide+water (carbon and hydrogen atoms are completely oxidised).
• Incomplete combustion produces carbon or carbon monoxide and water.

Question 6

Describe the physical

properties of alkanes 4

Answer 6

• First few in series are gases, then change to liquids, then to solids.
• In general, boiling points and viscosity increase as molecules get bigger.
• Volatility and flammability decrease as molecules get bigger.
• Poor reactivity.

Question 7

Explain how fractional
distillation of crude oil takes
place 6

Answer 7

• Crude oil is heated and vaporised.
• Vapor rises up the fractionating column (tower)
  .
• The column is hotter at the bottom and cooler at the top.
• Hydrocarbons cool as they go up the column and condense at different heights, as they have different boiling points.
• Large molecules, high boiling points - collected at the bottom.
• Small molecules, low boiling points - collected at the top.
• This gives fractions, which can be used in various ways

Question 8

What is cracking?

Answer 8

When large hydrocarbons are thermally broken down into smaller and useful
molecules

Question 9

define viscosity, flammability, volatility

Answer 9

flam-how easily it can ignite

viscosity- less viscous= more runny

volatility-to vaporise

Question 10

properties of hydrocarbons4

Answer 10

● Shorter the molecules, the less viscous it is. (more runny)

● The longer the molecules, the more viscous it is.

● The shorter the molecules, the lower the temperature at which that
fraction is vaporised or condensed – and the lower its boiling point.

● The shorter the molecules, the more flammable it is.

Question 11

What type of reaction is cracking?

Answer 11

Thermal decomposition

Question 12

What are the conditions for cracking? 3

Answer 12

Reactant heated to vapor,
passed over a hot catalyst (catalytic cracking)

or heated to vapor,

mixed with steam and heated to high temperatures (steam cracking)

Question 13

How are the products of cracking used?

Answer 13

The products are alkanes and alkenes – used as polymers and starting materials for synthesis

Question 14

What is an alkene? 2

Answer 14

Unsaturated hydrocarbon. Contains a C=C bond.
double carbon bond.

General formula for alkenes is: CnH2n.

Question 15

What is the test for alkenes?

Answer 15

Add bromine water. Colour change occurs from orange to colourless.

Question 16

Describe the combustion of alkenes

Answer 16

They burn with smoky flames due to incomplete combustion