Heres some more model answers:
Making a halogenoalkane from an alcohol
- Shake methylpropan-2-ol with conc. HCl (keep releasing the pressure)
- Allow the mixture to settle and run off the lower aqueous layer, leaving the impure halogenoalkane
- Neutralise the excess acid by adding sodium hydrogen carbonate solution and run the lower layer off
- Add distilled water and run off the lower layer (this gets rid of any remaining inorganic impurities)
- Remove any remaining water by adding anhydrous sodium sulfate (a drying agent)
- Remove remaining organic impurities by distilling the mixture
The greenhouse effect
- The sun emits energy, in the form of UV light, onto the Earth
- The Earth absorbs this energy and re-emits IR
- CO2, in the troposphere, absorbs some IR in the 'IR window'
- making the bonds vibrate more
- this turns into kinetic energy, raising the temp.
- some O2 molecules radiate IR which warms the Earth
- more CO2 means more radiation and hence a warmer Earth
What happens to the temperature in the atmosphere as you move away from the Earths surface to the top of the stratosphere?
- the temperature decreases in the troposphere and you move away from the Earth
- because hot gases near the Earths surface rise and cool
- within the stratosphere
- the temperature of the atmosphere rises as you move away from the Earth
- due to exothermic reactions
How do we know that halogenoalkanes deplete ozone?
- They break down in the presence of UV light to form radicals
- the radicals catalyse the breakdown
- low concentrations of ozone were found above the antarctic
Why do reactions between atoms occur more quickly at the top of the troposphere?
- conc of gases is higher at the top of the troposphere
- so more collisions occur between the molecules per second