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docbexindchem updated Mar 10th 2008 |
1. Limestone - a very useful material
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Other thermal decompositions (not
needed by some syllabus's)
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| 2.
Enzymes and Biotechnology
(see
also rates
notes at end of 2.) Aspects of the vitamin, food and drugs GCSE chemistry are on the "Extra Organic Chemistry" page. Living cells use chemical reactions to produce new materials. Living things produce catalysts called enzymes which allow chemical reactions to occur quite quickly at ordinary temperatures and pressures. Enzymes are powerful 'biochemical catalysts' and are widely used in the food industry and are being used more and more to manufacture many other chemicals. These biological catalysts promote most of the reactions in living tissue. The names of enzymes end in ...ase e.g. amylase, protease, invertase, isomerase etc.
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Rates of Reaction - kinetics of Enzymes
(full
rates of reaction notes)
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Concentration: If either the substrate reactant e.g. sugar, or the yeast cell (enzyme) concentration is increased, the rate of reaction increases in a simple proportional way. However, if the concentration of enzyme is low but the substrate concentration is very high, the rate of reaction rises to a maximum and then stays constant. This is because the maximum number of catalyst sites for the 'key and lock' mechanism are in use and the rate of reaction depends on the rate of diffusion of substrate in and product out. |
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pH effect: The structure of the protein enzyme
can depends on how acid or alkaline the reaction medium is, that is, it is
pH dependent. If it is too acid or too alkaline, the structure of the protein
is changed and it is 'denatured'. If the enzyme does not have the correct 'lock' structure, it
cannot function efficiently by accepting the 'key' substrate molecule. Most enzymes have an optimum pH of between 4
and 9, and quite frequently near the neutral point of 7. However, the
enzyme pepsin has a peak at pH2 and can operate in the very acid
(hydrochloric) conditions of the stomach to help breakdown proteins for
digestion in the small intestine. |
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Temperature: The structure of the protein enzyme can depend the temperature. If the enzyme does not have the correct 'lock' structure, it cannot function efficiently. The shape of the graph is due to two factors. (1) The initial rise in rate of reaction is what you normally expect for any chemical reaction. The increase in temperature increases the average kinetic energy (KE) of the molecules to increase the chance of the product forming from the higher KE 'fruitful collisions. (2) However as the temperature rises further, the increasing thermal vibration of the enzyme molecule causes its structure to break down (denature) and so the 'lock' is damaged so the enzyme is less efficient (see key-lock below). This may be due to the failure of weak intermolecular forces or actual ionic/covalent bonds, but the 3D molecular structure of the enzyme is changed so that the substrate molecule cannot 'dock in' to be changed into products. The optimum temperature for the fastest rate of reaction is often around 30-40oC (note our body temperature is about 37oC, no coincidence!). Eventually at high temperatures the enzyme ceases to function. |
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Explaining
enzyme biochemical catalysis
Extra
Advanced chemistry notes on Enzyme structure on the stereochemistry
page
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| 3.
Why is sulphuric acid a useful material? How is it made?
Contact Process
Because sulfuric acid has so many uses the industrial development of a country is sometimes measured by the amount of sulphuric acid that is used each year. Sulphuric acid is made starting from the element sulphur which is found in the Earth's crust.
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| 4.
How can metals be made more useful?
Extraction details page: Aluminium can be made more resistant to corrosion by a process called anodising. Iron can be made more useful by mixing it with other substances to make various types of steel. Many metals can be given a coating of a different metal to protect them or to improve their appearance.
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5. What is titanium and how is it produced ? Titanium is a very important metal for various specialised uses. It is more difficult to extract from its ore than other, more common metals.
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6. Why are instrumental methods of detection so useful? Typical chemical tests for GCSE and A level chemistry are on a separate web page Instead of testing for chemicals using standard laboratory equipment such as test tubes etc. Special instruments have been developed to carry out such testing. These are quick, accurate and can be used on very small samples.
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7. Chemical Economics - A variety of costs involved! Sociological, environmental issues etc.
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