Cracking and Alkenes – Virtual Lab, Equations and Addition Reactions
ChemistryOrganic ChemistryAges 16–17
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Sign in to playA virtual lab for cracking liquid paraffin: heat the porous pot or aluminium oxide catalyst, flick the flame to vaporise the paraffin, collect the gas over water, avoid suck-back and test each tube with bromine water. Then balance cracking equations such as C₁₀H₂₂ → C₈H₁₈ + C₂H₄, compare catalytic, steam and thermal cracking, see how cracking matches the supply of crude oil fractions to demand, and watch alkenes add bromine, hydrogen, steam and hydrogen bromide.
Lesson: Cracking of alkanes; alkenes and their addition reactions
What it shows
Large alkane molecules from crude oil are cracked into smaller, more useful ones. Cracking needs a high temperature and either a catalyst or steam; the products are a shorter alkane and one or more alkenes. Alkenes have a C=C double bond, so they are unsaturated: they decolourise orange bromine water, while alkanes do not. Cracking matches the supply of crude oil fractions to the demand for petrol and gives alkenes for making polymers. In addition reactions, atoms add across the double bond to give a single product.
How to use
In the Virtual lab, press Light the burner, wait until the catalyst is hot, then use Flick flame to paraffin. Use Next tube when a tube is full, and Lift delivery tube out before turning the burner off. Choose a tube and press Add bromine water and shake. In Equations, set the Alkane cracked and add alkenes with the + buttons. Use the Heavy fraction cracked slider, then choose an Alkene and what to Add.
Parameters you can change
- Starting screen Virtual lab: cracking liquid paraffin, Balancing cracking equations, Supply and demand of fractions, Addition reactions of alkenes
- Catalyst (virtual lab) Porous pot pieces, Aluminium oxide, No catalyst
- Carbon atoms in the alkane cracked (Equations) 6–20
- Cracking method (Equations) Catalytic cracking, Steam cracking, Thermal cracking (high pressure)
- Heavy fraction cracked (Supply and demand) 0–60 %
- Alkene (Addition reactions) Ethene, Propene, But-1-ene, But-2-ene
- Reagent added (Addition reactions) Bromine, Hydrogen, Steam, Hydrogen bromide
Questions to explore
- Why should the first tube of gas collected be discarded or tested separately?
- Why must the delivery tube be lifted out of the water before heating stops?
- Why does bromine water stay orange with liquid paraffin but turn colourless with the gas?
