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Across 5. forces within a molecule 7. an element that is a metal of low density and has an atomic number of 13 9. propane or butane or a mixture of both propane and butane 11. a compound of iron and oxygen. It occurs naturally as haematite 12. the force with which positive and negative ions attract each other or that molecules attract each other 13. a viscous dark liquid drilled out of the ground or from under the sea. It is a mixture of hydrocarbons which are separated by fractional distillation to produce useful fuels and other products 15. taking from, obtaining from (usually using another chemical or electrolysis) 17. are carried out to assess the environmental impact of products in each of several stages 18. common name for sodium hexafluoroaluminate which is the substance used to lower the temperature of the melted electrolyte used to obtain aluminium by electrolysis 19. the resistance of liquid to flow 21. the positive electrode in a electrolysis that is inert 22. to catch fire 23. an easily evaporated liquid 25. the amount of a substance that is available and the amount of the substance required, used in context of cracking hydrocarbons 26. poisonous metals such as lead 27. a resource that was made millions of years ago and cannot be made again and will eventually run out, for example crude oil

Down 1. removes oxygen from an oxide to formed the element 2. a family of hydrocarbons with with at least one double C=C bond 3. crude oil is separated into fraction using this process of distillation where fraction of different boiling points distil off at different times 4. an ore of aluminium consisting of aluminium oxide 6. process that uses bacteria to leach metals 8. the recovery and processing of materials after they have been used in order to reuse them 10. the process of breaking down larger hydrocarbons into more useful molecules 14. plants that absorbs heavy metals 16. compounds containing only hydrogen and carbon 20. process that uses plants to extract metals 24. a family of hydrocarbons found in crude oil with single covalent bonds, e.g. methane