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The principles of colorimetry - testing the composition of a paperclip

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Introduction

Principles of colorimetry Colorimetry is used to measure the intensity of absorption of coloured compounds over a narrow range of frequencies. It is a useful way of determining the concentration of a chemical in a coloured solution. Beers law states that the amount of light absorbed by a solution is directly proportional to path length and concentration. A = abc This graph shows the relationship between absorbance and concentration that they are proportional to each other. In a colorimeter a narrow beam of light passed through a filter towards a tube containing the coloured solution. Any light that passes through the solution is detected by a photocell and a reading of absorbance is displayed on the meter. Before you start to measure the absorbance of any sample you firstly have to calibrate or reference the colorimeter with distilled water so that the baseline will be placed at 0.00Abs or 100% T. Also appropriate wavelengths have to be selected before starting to measure the absorbance of your sample. How much manganese is there in a paperclip? Method 1. Cut up a paper clip in to small pieces and place in a weighing boat to weigh accurately about 0.2g using a weighing balance. 2. Measure approximately 70cm3 nitric acid using a measuring cylinder and pour it into a beaker. Then add the small pieces of paperclip to it. ...read more.

Middle

Therefore this graph agrees with Beers law which states hat the amount of light absorbed by a solution is directly proportional to path length and concentration. This can be written as A C; A is the amount of light absorbed and C is the concentration of the Mn solution. You can work out the concentration of the Manganese by using the line of best fit from the concentration against the absorbance knowing that the absorbance of the Manganese sample is 0.08. Therefore the concentration is 0.22%. We know that the 2% Manganese contained 0.2g of paperclip. From this we can work out how much 2% of 0.2g of steel will be. 0.2/ 100 = 0.002 0.002 x 2 = 0.004g Mn � Mn�+ �MnO4� After this we can then work out the % of Mn in KMnO4-. % Mn in KMnO4 = RFM Mn RFM of KMnO4 X 100 RFM of KMnO4 RFM of Mn K 39.1 Mn 54.9 = 54.9 Mn 54.9 158 4O 64 158.0 Mass KMnO4 from 0.004g Mn = 100 34.7 X 0.004 = 0.0115g If Mn is 2% of paperclip, we could end up with 0.0115g in 100cm3. However this standard solution is too hard to make up because the amount is too small to weigh. Therefore we can do 1.15g instead in 1 dm3 and then dilute it. This will be equivalent to a solution from a paperclip with 20% of Mn. ...read more.

Conclusion

If spilt on skin or clothes flood the effected area with large quantities of water and remove contaminated clothing. Finally, if spilt in laboratory wash the area of the spill thoroughly. Phosphoric acid Corrosive Eye protection and lab coat must be worn at all times. If splashed in the eye flood the eye with gently running tap water for 10 minutes. If spilt on skin or clothing remove contaminated clothing and quickly wipe as much liquid as possible off the skin with a dry cloth before flooding the area with a large excess of water. If spilt in laboratory rinse the area of spill. Potassium Iodate (2.0 mol dm-3) Harmful Oxidising Eye protection and lab coat must be worn at all times. If solution gets into the eye flood the eye with gently running tap water. If spilt on skin or clothing remove contaminated clothing and soak well with water and wash off the skin with gently running tap water. If spilt in laboratory rinse the area of spill. Potassium Manganate Harmful Danger to the environment Oxidising Eye protection, lab coat and gloves must be worn at all times as it stains the hands. If solution gets into the eye flood the eye with gently running tap water. If spilt on skin or clothing remove contaminated clothing and soak well with water and wash off the skin with gently running tap water. If spilt in laboratory rinse the area of spill. ?? ?? ?? ?? Shaima khelfa ...read more.

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