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A Colorimetric Determination of Manganese In Steel

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A Colorimetric Determination of Manganese In Steel Advanced Higher Chemistry Unit 1 PPA 2 Eilidh L Hawkins Candidate Number 972840254 The aim of this investigation is to determine the percentage Manganese in steel through colorimetric determination. Colorimetry is used to determine the concentrations of coloured substances in solution. It works on the basis that a coloured substance absorbs light of a colour complementary to its own and also that the amount of light absorbed (absorbance) is proportional to the substance's concentration. This technique is especially suited to determining the percentage manganese in steel because manganese can be converted into permanganate ions. Permanganate ions are coloured. There are two stages in the conversion: the first uses nitric acid to oxidise manganese to manganese (II) ions. Mn(s) Mn2+(aq) + 2e The manganese (II) ions are then oxidised to permanganate ions by potassium periodate. Mn2+(aq) + 4H2O MnO4-(aq) + 8H+ + 5e To find the filter which gives maximum absorbance. ...read more.


Once the reaction occurred the beaker was continuously heated gently to maintain the reaction. After the solution had cooled 5cm3 of 85% phosphoric acid, 0.2g of potassium persulphate and two anti-bumping crystals were added to the it. The solution was then boiled for 5 minutes. To this solution was then added 15cm3 of acidified potassium periodate solution plus a couple of fresh anti-bumping granules and it was gently boiled. The solution started to turn pink. The solution was boiled until the intensity of the pink colour remained constant. The solution was allowed to cool to room temperature and then transferred to a 100cm3 standard flask leaving the anti-bumping granules in the beaker. The beaker was then rinsed with deionised water and the rinsings were added to the flask. This procedure was repeated until the flask was full to the graduation mark. The flask was stoppered and inverted. Using the colorimeter, fitted with the filter that gave maximum absorbance, the absorbance of the solution was measured and recorded. ...read more.


The percentage manganese in steel paper clip = mass of manganese/mass of total paper clip x 100 = 0.0068625/2x100 = 0.34125% It can be concluded from these results that the percentage mass of manganese present in the steel paper clip was 0.34125%. Discussion. During the experiment variables were controlled by using the same filter for all the different concentrations, this means the results can be compared. IT is important to use an optically matched filter (520nm) as this allows for the maximum absorbance, meaning the results are clear and more reliable. It is necessary to prepare a calibration graph to enable the concentrations of acidified potassium permanganate of the unknown solutions, which in turn enables the percentage manganese in eh steel paper clip to be determined. I t is necessary to wait until the pink colour in the solution remains a constant colour before measuring absorbance as this ensures results obtained are reliable. This however is a source of error as the solution is observed until the pink colour is constant and observation allows for human error. ?? ?? ?? ?? Eilidh L Hawkins A Colorimetric Determination of Manganese in Steel. SCN. 972840254 ...read more.

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