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Similar to june 2018 higher chemistry with solutions and explanations
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june 2018 higher chemistry with solutions and explanations
- 19. When the Earth’s atmosphere first formed, it consisted of approximately 95% carbon dioxide, 3% nitrogen and 0.05% oxygen. Now, it is approximately 78% nitrogen, 20% oxygen and only 0.05% carbon dioxide,
- 20. carbon dioxide decreased • because algae and plants used carbon dioxide • by photosynthesis • Oceans - carbon dioxide is highly soluble, so as the oceans formed it dissolved, removing it from the atmosphere • because carbon dioxide formed carbonates, which precipitate as sediments or formed sedimentary limestone rocks • because algae / plants and animals
- 21. The level of oxygen increased from 0.05% of the atmosphere to its current levels of around 20%. The main reason for this is photosynthesis; as plants began to grow, they converted carbon dioxide into oxygen via photosynthesis
- 23. nitrogen increased • because volcanoes produced nitrogen • because (denitrifying) bacteria produced nitrogen • because ammonia was converted to nitrogen
- 28. Potable water contains dissolved substances. Potable water is not ‘pure’ water, because it contains dissolved substances
- 31. Filtration is the first step in the process. This is done by passing fresh water through filter beds to remove any large particles like stones, or small particles like sand. •Sterilising agents are then used. After the filtration process, sterilising agents are then used to treat the rainwater. These sterilising agents include chlorine gas, ozone and ultraviolet light. These kill microbes to reduce levels so they are sufficiently low.
- 32. Using Seawater •Surface water and groundwater may not be available. In some extremely hot countries, there may not be any surface water or groundwater available to make potable water. extremely salty •Reverse osmosis can remove the salt. we can remove the salt from sea water. A membrane is used to do this. High pressure is applied to the sea water, to push water molecules through the membrane; the salt is left behind. expensive
- 33. •Desalination can be produced by distillation of sea water. In distillation, sea water is heated to over 100°C. The water vapour produced does not contain salt. It is cool and condenses to make pure water through desalination. This is an expensive process, as lots of energy is needed to boil large volumes of water.