Jacob S5 Chem 20251217 - cracking

What chemical class does petroleum mainly consist of?

Hydrocarbon.

Which petroleum fraction has greater demand than supply?

Petrol.

Why is petrol demand greater than supply globally?

There are too many vehicles around the world.

Name one petroleum fraction that is in excess supply.

Fuel oil.

Name another petroleum fraction that is in excess supply.

Lubricating oil.

How do fuel oil molecules compare to petrol molecules regarding molecular mass?

Fuel oil has greater relative molecular masses.

How does the carbon chain of fuel oil compare to petrol?

Longer carbon chain.

What is the method used to break larger hydrocarbon molecules into smaller ones?

Cracking.

What is one main industrial purpose of cracking?

To convert heavy oil to petrol.

Cracking produces smaller molecules to meet what requirement?

Industrial demand.

The catalyst is used to crack larger hydrocarbon molecules into smaller ones to produce what valuable industrial material?

Compounds such as plastics.

What must be absent when heating large hydrocarbon molecules for cracking?

Air.

What two products are formed if cracking occurs in the presence of air?

CO2 and H2O.

What substance is needed along with heating to crack large hydrocarbon molecules?

A catalyst.

What valuable product of cracking is used to make compounds such as plastics?

Alkene.

Cracking always produces a mixture of alkene and what other chemical class?

Alkane.

What is the overall conclusion about the result of cracking on molecular size?

Cracking can break larger hydrocarbon molecules into smaller hydrocarbon molecules.

What is the overall conclusion about the nature of the product mixture?

The product of cracking is a mixture of smaller alkane and alkene.

What is the chemical process shown by the equation C8H18 → C3H8 + C5H10?

Cracking.

What term is used to describe the type of paraffin used in the experiment?

Medicinal paraffin.

Name one specific catalyst used in the lab cracking reaction.

Unglazed porcelain.

Name the other specific catalyst used in the lab cracking reaction.

Aluminium oxide.

What is the state of the product collected from lab cracking?

A colour gas.

What specific component in the setup is heated strongly?

Unglazed porcelain.

What is soaked in the mineral wool in the lab cracking setup?

Medicinal paraffin.

What must be done only occasionally to the mineral wool?

Heat.

What consequence occurs if mineral wool is heated directly?

Paraffin may just vaporise and escape before cracking.

What specific chemical process is happening to the paraffin when it is heated with the catalyst?

Cracking.

The gaseous product is collected through the displacement of what liquid?

Water.

Why is the gas collected using the displacement of water?

The gas is insoluble in water.

How is the test tube positioned over water to collect the gas?

Invert the tube over water.

How do we know the gaseous product successfully fills up the test tube?

Water level will drop.

If collecting several tubes, which tube is not used for testing?

The first tube.

Why is the first tube of product not used for testing?

It is mainly air.

What part of the apparatus secures the test tube in Figure 1c?

Clamp.

What material makes up the catalyst pieces shown in Figure 1b?

Unglazed porcelain pieces.

How does the gaseous product reach the collecting test tube?

Via the delivery tube.

The absence of air prevents the hydrocarbon from performing what action?

Burn.

What type of test tube contains the mineral wool and catalyst during the reaction?

Hot test tube.

What type of energy is applied to the unglazed porcelain pieces?

Heat.

What specific safety action must be performed immediately after stopping heating?

Remove the delivery tube from water.

Why must the delivery tube be removed from water before cooling?

To prevent sucking back of water.

What is the risk to the apparatus if water is sucked back into the hot test tube?

Crack the test tube.

Why must the unglazed porcelain be heated strongly?

To ensure effective cracking (implied opposite of "may just vaporise and escape").

What conclusion is drawn about the relative reactivity of alkene and alkane?

Alkene is more reactive than alkane.

What purple solution is used to test for the presence of alkene?

Acidified potassium permanganate.

What visible colour change occurs when alkene is added to purple acidified potassium permanganate?

Decolourise.

How quickly does alkene react with purple acidified potassium permanganate?

Immediately.

What visible colour is the standard bromine solution used for testing?

Brown.

What happens to the brown bromine solution when alkene is added?

Decolorise brown bromine solution.

How quickly does alkene react with brown bromine solution?

Immediately.

What class of product shows immediate decolourisation of testing solutions?

Alkene.

The immediate decolourisation of purple acidified potassium permanganate demonstrates what property?

Alkene is more reactive than alkane.

If the gas product is collected over water, what chemical property must it have?

Insoluble in water.

What must be heated strongly according to the precautions?

The unglazed porcelain.

What is the main reason why the hydrocarbon will burn if air is present?

To give CO2 and H2O.

What does the cracking of larger hydrocarbon molecules produce a mixture of?

Smaller alkane and alkene.

What is the general name for the substances like C10H22 that undergo cracking?

Larger hydrocarbon molecule.

How are the catalyst pieces (unglazed porcelain) usually used in the tube?

Heated strongly.