Aspirin Coursework Example | Topics and Well Written Essays - 3500 words

Aspirin - Coursework Example ration, a standard titration and a colourimetry experiment will be undertaken to determine the amount of acetylsalicylic acid in each of three commercially available aspirin brands (as well as acetylsalicylic acid created in the laboratory – see below). Back titration involves using phenolphthalein as an indicator, as well as the principles of the pH scale to determine how much of the acid is present by using known quantities of a basic solution (in this case NaOH). Colorimetry involves the use of iron (III) chloride, a strongly coloured compound, to determine how much of the acetylsalicylic acid is available by using a previously calibrated scale of light reflection and colour density. 2) (AS) Which purification method is the most appropriate and accurate? To answer this aim, we need to compare the three methods outlined above, colourimetry, standard titration and back titration. We can do this by seeing which produces the most consistent results by adding the results to a ch art and measuring the standard deviation of the results given. 3) (AS) Which type of titration (back or forward) is the most appropriate in this situation? There are two types of titration that can be used in this experiment. Back titration relies on the use of an excess of alkali and reacting this excess with acid to determine the concentration. Forward titration relies on the acid + base = salt + water principle. We can see which one works faster and gives standardised results. 4) (AS) Which type of acid (monoprotic or diprotic or triprotic) is the most effective in the purification process? A monoprotic acid is one that can donate one proton per molecule during the dissociation process; a diprotic can donate two and a triprotic can donate three. Hydrogen chloride (HCl) is an example of a... There are certain chemically proven ways to show the purity of aspirin, or the % yield of salicylic acid in these tablets. The first aim here suggests that it is important to test the effectiveness of several different methods, and this means completing at least two different types of test on the commercially available aspirin. One of the most widely used ways of testing the purity of aspirin is known as back titration. This involves destroying the aspirin using a known concentration of an alkali. This leaves a certain quantity of the alkali remaining, and back titration then involves using a known quantity and concentration of an acid to help determine the amount of alkali remaining. Colorimetry is a widely used way of testing chemicals based on the principal of light reflection. In this case, the equipment is available in the laboratory. We need to use more than one different method to answer aim two. Chemically, it is always important to do a number of tests. In this case, part of the method suggests that each type of aspirin be tested three times; this will help give us a mean that is a more accurate result than the use of simply one test which could be false. Another important thing in chemistry is comparison, and this is why the methods here suggest using at least three different brands of commercially available aspirin to show how much salicylic acid is found in these tablets. Repeating the experiment will also give a more accurate rate of reaction, which will help to answer some of the aims above.