C15 Flashcards
What are the conditions for rust ?
oxygen and water
What is a barrier method ?
- prevents rust by covering the iron
- can use paint, oil/grease or even plastic
- stops water/air from touching the iron and causing it to rust
What is a sacrificial method ?
- prevents rust by covering iron with more reactive metal (like zinc)
- called galvanised
- if coating is scratched, the air + water will react w/the more reactive metal, not the iron
Why is the Haber process needed ?
To make ammonia which has nitrates
- nitrogen in the air is insoluble in water so plants cannot use it as a mineral
- they can only take in nitrogen from the soil
- have to get it through fertilisers
What are the raw materials for the Haber process ?
- nitrogen from the air
- hydrogen from natural gas (methane)
What are the conditions for the Haber process ?
- iron catalyst
- 200 atm
- 450 degrees celsius
Describe the Haber process.
- nitrogen and hydrogen gas heated + compressed
- passed through reaction vessel with iron catalyst
- gas passed to a cooling chamber - ammonia has higher mp than nitrogen or hydrogen so liquefies whilst any unreacted gases are cycled back through to the compressor
Why is 200 atm specifically used in the Haber process (in reference to the economics of the process) ?
- high pressure shifts position of equilibrium to the right, so higher yield of ammonia
- can’t have pressure too high though, as plants working at high pressures are expensive to build + run
- 200 atm is a good compromise
Why is 450’C specifically used in the Haber process (in reference to the economics of the process) ?
- Haber process is exothermic forwards
- need cool temperatures to shift position of equilibrium right to get high yield of ammonia (because according to Le Chatelier’s principle, reaction will heat itself up again to balance out)
- can’t have too low temp otherwise reaction too slow
- 450’C good compromise
What is the effect of the iron catalyst on the Haber process ?
- speeds up rate of reaction
- doesn’t affect yield
- important in industry as means ammonia can be produced more quickly to market
How is the ammonia from the Haber process used ?
- ammonia turned into nitric acid
- ammonia reacted w/nitric acid (ammonium nitrate)
- ammonia reacted with sulfuric acid (ammonium sulfate)
- ammonia reacted with phosphoric acid (ammonium phosphate)
These are neutralisation reactions (apart from ammonium nitrate) and can be done using titrations.
Where do the nitrogen, phosphorus and potassium in NPK fertilisers come from ?
nitrogen - the Haber process used to make ammonium nitrate and ammonium sulfate
phosphorus - phosphate rock treated w/acids to make ammonium phosphate and calcium phosphate
potassium - salts like potassium chloride and potassium sulfate which are mined
Describe how ammonium sulfate is made in industry.
- sulfuric acid sprayed onto anhydrous ammonia gas at 60’C in reacting towers at high conc.
- reaction is explosive and dangerous
- pipes + reaction vessels must be made of strong stainless steel (withstand high temp + corrosion)
- heat energy released during the reaction is used to heat neighbouring towers where ammonium sulfate slurry is heated and aerated to form equal sized fertiliser pellets for market
Why are alloys harder than pure metals ?
Layers of metal atoms distorted by differently sized metal atoms, making layers harder to slide.
What can bronze (copper + tin) be used for and why ?
- propellers of ships
- statues
- decorative items
Bronze is corrosion resistant and tough
