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Chemistry Section D : A Closer Look at Organic Materials Part 2: Information A. Reactions of organic materials with water, acids and alkalis Most organic materials particularly plastics are unreactive to this substances, hence plastic containers are often used to store these materials. Glass is also used to store these chemicals as it is also generally unreactive, but plastics are more commonly used as have better physical properties, they are less dense and tougher. B. Reactions of organic materials with oxygen (Combustion) All organic materials contain at least carbon and hydrogen, others also contain oxygen, nitrogen and chlorine. The products of combustion depend on the organic material. All will produce carbon dioxide and water vapour due to the presence of carbon and hydrogen. Other products are produced depending on the organic material.
The production of carbon dioxide and water vapour during combustion is used as evidence for an organic material. We can test chemically for these substances: Carbon dioxide: When bubbled through lime water turns it 'milky' Water vapour: When added to white anhydrous copper sulphate turns it to blue hydrated copper sulphate. In the reactions heat is also produced. Reactions that produce heat are known as EXOTHERMIC reactions. This is put to use, for example in burning substances as fuels to warm our homes e.g. Wood, oil and gas.Examples of combustion of organic materials.
The production of carbon is evident from the black sooty flame. Too much soot can block chimneys if too much paper is burnt in a fire.
Your teacher will demonstrate this reaction to you to show the large amounts of carbon (soot) that are produced, in a fire this is very dangerous as it causes people to choke and also makes it very difficult to see.
Hydrogen chloride is a dangerous acid gas that can be tested using damp blue litmus paper, it will go red in the presence of an acid.
This is perhaps one of the most dangerous combustion reactions as apart from the normal combustion products it also produces a deadly gas called hydrogen cyanide (HCN) .Polyurethanes are plastics that are often used in mattresses, but we have strict safety laws to show that the plastic is often protected to stop as much as possible combustion, it is made inflammable. You will see on most household furniture safety labels. Try and find a label and read what it says. C. Complete + Incomplete combustion Apart from the dangers seen above of the combustion of certain plastics, dangers can also occur depending on if the combustion is complete or incomplete. In complete combustion it means there is adequate oxygen to produce the gas carbon dioxide, however if there is not adequate oxygen, for example burning fuels where there is not enough ventilation, then instead of getting carbon dioxide we get carbon monoxide (CO), which is potentially a deadly gas, If inhaled it prevents the oxygen going around our body, so we become starved of oxygen and can die. It is often known as the silent killer as it can not be smelt seen or easily identified. There are again strict safety laws to prevent as much as possible the production of this gas. For example gas fires and boilers should be checked regularly by a qualified person. Cars are checked for exhaust emissions. Summary: Complete combustion gives water vapour + carbon dioxide + other products + heatIncomplete combustion gives water vapour + carbon monoxide + heat + other products. |
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