IGCSE Coordinated Science: Air and Water Air and Water Describe a chemical test for water Here are a few ways in which you can use to test for the presence of water: ❖ Test the liquids boiling point. Water boils at precisely 100 degrees andfreezes at exactly 0 degrees. ❖ If you add water to Anhydrous Copper Sulphate Powder, it forms a blue solution and may give out heat. ❖ Add Anhydrous Cobalt Chloride which is blue in color. If water is present, should change to color pink. Describe and explain, in outline, the purification of the water supply byfiltration and chlorination. Water extracted from the earth is always infested with impurities. This watermight be contaminated with disease and bacteria. That is why it is crucial to“purify” the water before it is drank. This is done by two processes, Filtration and Chlorination. Here is how it works: ❖ Water is extracted from reservoirs and sent to be “treated” ❖ The water is first passed through a filter to filter out large objects such asrocks or mud. ❖ Smaller particles in the water is removed by adding Aluminium Sulfate which causes the smaller particles to stick together in large pieces andsettle down the filter. ❖ Water is now passed through sand and gravel filters which continue tofilter off the smaller particles and kills bacteria. ❖ Now its time for chlorination ❖ Chlorine gas is first bubbled through the water to kill the bacteria thatexists in the water.
❖ Sodium Hydroxide may be added in the water to prevent the water from being acidic from the chlorine. ❖ Water is delivered to the people that need them. State some of the uses of water in industry and in the home ❖ Irrigation ❖ Cooling ❖ Recreation ❖ Agricultural ❖ Industrial use ❖ Shower Describe the separation of oxygen and nitrogen from liquid air byfractional distillation. ❖ Clean air is cooled to around -80 degrees, Carbon Dioxide sublimes into asolid, water vapour condenses then freezes into ice to be collected. ❖ Cold Air is put into a compressor which increases the pressure to around100 atm. This causes the air to warm up. ❖ The re-cooled, compressed is now allowed to expand and lose itspressure, which allows it to cool further. ❖ The air is again compressed and then expanded to continue to be cooled.This continues until all liquids liquefy.
❖ The cold air is brought into a fractionating column (as seen above) andslowly left to warm. ❖ Gases separate according to their boiling points. The gas with the lowestboiling points evaporate first. ❖ Gases such as Nitrogen and oxygen can now be collected. Describe the composition of clean air as being a mixture of 78% nitrogen,21% oxygen and small quantities of noble gases, water vapour and carbondioxide.
● In GCSE, we don’t have to be so specific so we usually just round theresults to one decimal place. Hence, nitrogen will compose of 78% of allgases in the air, Oxygen 21%, and so on. State the common air pollutants as carbon monoxide, sulfur dioxide andoxides of nitrogen, and describe their sources. Carbon Monoxide ❖ Poisonous pollutant of air ❖ Main source is factories that burning Carbon-containing fossil fuels ascarbon is one of the products of incomplete combustion of fossil fuels. Sulphur Dioxide ❖ Contributes to acidic rain ❖ Main Source comes from two products: 1. Combustion of sulphur2. Extraction of metals from their sulfide ores ❖ Mixes with water vapour of cloud and air. ❖ This forms Sulphuric Acid (H2SO4) ❖ When it rains, the rain water becomes acidic . ❖ Acidic water is dangerous because it causes the death of sea creatures,acidifies soil which can cause death to plants and cause deforestation. ❖ May also cause lung cancer Oxides of Nitrogen ➢ Formed in high temperatures when nitrogen and oxygen react. ➢ In Cars, the engine operates at a high temperature, giving the nitrogen andthe oxygen in the air and engine a chance to react, hence forming nitrogen monoxide. Nitrogen monoxide further reacts with the oxygen in the air to form Nitrogen Oxide. ➢ Nitrogen oxide is dangerous in that it also rises in the air and mixes withrain water to form nitric acid. This can also cause acid rain ➢ Additionally, Nitrogen oxygen can cause certain respiratory problems. Explain the presence of oxides of nitrogen in car exhausts and theircatalytic removal.
As we mentioned earlier, oxides of nitrogen are present in car exhausts, andthese can cause problems both to the environment and us humans. Therefore,scientists need to find a way to remove the “oxides of nitrogen” in cars. This is done through a catalytic converter ● The catalytic converter is fitted at the end of the car exhaust. ● The purpose of the catalytic converter which catalyzes the reactionbetween the Nitrogen Oxide and Carbon Monoxide, which in turnproduces two harmless separate gases, nitrogen and carbon dioxide. The carbon dioxide comes from the fact that carbon is already present in thecars engine. Equation of the Reactions 2NO + 2CO → 2CO2 + N2Nitrogen Oxide + Carbon Monoxide → CarbonDioxide + Nitrogen 2NO2 + 4CO → 4CO2 + N2 Nitrogen Dioxide + Carbon Monoxide → CarbonDioxide + Nitrogen Explain why the proportion of carbon dioxide in the atmosphere isincreasing, and why this is important. ❖ The Sun sends energy to the earth in two discrete forms, heat and light. ❖ Some of the heat is reflected back to the sun/space, but some is trapped inthe earth. ❖ This is caused by the existence of some gases and we call this the Greenhouse effect. ❖ The primary Greenhouse gases are Carbon Dioxide and Methane. The greenhouse effect is a serious threat to our world. The reason for this can bedescribed by the proliferation of greenhouse gases which causes the greenhouseeffect. Increased combustion of carbon in industries which mass produce
Carbon Dioxide as a side product and the cutting down of trees which releaseCO2 via respiration are two major reasons why the greenhouse effect isbecoming more serious.The increase of heat trapped in the earth causes an average rise in sea level andglobal average temperatures, and we call this effect Global warming Describe the formation of carbon dioxide: ❖ Formed in power stations by the complete combustion of Carboncontaining fuels. ❖ Formed as a product as respiration. ❖ When an acid reacts with a carbonate, Carbon Dioxide is usually formed. Describe the essential conditions for the manufacture of ammonia by theHaber process including the sources of the hydrogen and nitrogen, i.e.hydrocarbons or steam and air. ● The Haber Process manufactures Ammonia from Hydrogen and Nitrogen ) The reaction is as follows:N 2 + 3 H 2 ⇌ 2 NH 3 Conditions required to manufacture this: ● High temperature (400-450°C ) ● Iron catalyst ● High pressure Sources: ● Hydrogen – from natural gases ● Nitrogen – from the air Describe the rusting of iron in terms of a reaction involving air and water,and simple methods of rust prevention, including paint and other coatingsto exclude oxygen. Rusting is the reaction of iron with oxygen, which causes the iron to corrode. Inorder for iron to react with oxygen, water and air must be present. If allowed to
react, iron will form hydrate iron oxide with hydrogen. A lot of steel is made outof iron, so steel can definitely rust as well. The formula of rust is Fe2O3. xH2O Rust Prevention Painting ● Iron or steel object is painted ● The paint creates a barrier which prevents the air or water from coming incontact with the iron/steel object. This is commonly done in car bodiesand bridges. Electroplating ● Electroplated with another metal that doesn’t corrode. ● Metals commonly used are chromium and tin since they are very unreactive. ● Used in food cans. Galvanization ● Covering the whole object by a layer of zinc ● Done either dipping the object into some molten zinc or by electroplatingthe object with zinc. ● The zinc provides a barrier to prevent the air and water from coming incontact with the iron/steel, as the zinc is corroded instead of the iron Sacrificial Protection ● This method revolves on the idea that metals higher up in the reactivityseries will react in preference, so a metal in the higher in the reactivityseries (e.g. zinc and magnesium) is used as a “protection”, and iscorroded instead of the iron ● Must be replaced from time to time as when the metal finishes corroding,the iron/steel starts to rust again. ● Used often in ships, or bridge columns Describe the need for nitrogen-, phosphorus- and potassium-containingfertilisers.
Nitrogen ● Makes plant greener ● Helps plants grow faster Phosphorus ● Good for root growth ● Disease resistance ● Seed and Fruit Growth ● Blooming ● Flowering Potassium ● Increasing root growth ● Drought resistance Describe the displacement of ammonia from its salts by warming with analkali. ● When an ammonium salt is heated with an alkali react with an alkali,ammonia gas is displaced from the ammonium salt Alkali + Ammonium → Ammonia + Water + Metal Salt