Paper 2 mark scheme

What conditions are needed for cracking?

High temperatures and either steam or a catalyst

Why are larger hydrocarbon molecules cracked to produce smaller hydrocarbon molecules?

Higher demand for small molecules as they are more useful

Does stainless steel rust?

No because it is resistant to corrosion

Why do aluminium window frames not corrode after they are made?

They have a coating of aluminium oxide which protects the metal/prevents water, air, oxygen reaching the metal

Why is wood more sustainable than natural gas as a fuel for central heating boilers?

Wood is renewable

Wood produces the same amount of carbon dioxide as the trees absorb so carbon neutral

Why does polyester melt when it is heated?

Polyester is thermosoftening so has no cross links/intermolecular forces are weak

Why is an outer skin added to a polystyrene core?

To make it harder/stronger/waterproof/more rigid/tougher

Investigation find the total mass of dissolved solids in a 100 cm3 sample of the drinking water.

• weigh (evaporating) basin / dish

• add measured volume of water • weigh (evaporating) basin / dish and water

• heat to evaporate water

• reweigh

• repeat heating until constant mass obtained

• subtract mass of (evaporating) basin / dish from mass

• repeat and calculate a mean, discarding anomalous results

• calculate the mass in 100 cm3 water if necessary