A practical resources to measure the concentration of nitrates in water using UV-VIS spectroscopy.
UV-Vis is introduced along with details about the Beer-Lambert Law. The first part of the practical involves the students preparing standards and then measuring the absorbances using a spectrometer(1). The students then plot absorbance against concentration and determine the molar absorptivity. The second part involves the students preparing solutions of water samples and using the absorbance values and the Beer-Lambert law to determine the concentration of nitrates in the samples. As a discussion the students are asked to compare their values to the UK accepted safe levels and also consider sources of nitrates in water.
The first part of the practical can be done in 1 h 30 mins (although students will need to be organised) and the second part in an hour.
The following materials will be needed for each group:
• 250 cm3 Erlenmeyer flask (x8)
• Polystyrene cuvettes (1 cm x 1 cm) (x8)
• 100 cm3 Measuring cylinder (x2)
• 10 cm3 Measuring Cylinder
• 1 cm3 Pipette (x4)
• 10 cm3 Graduated pipette
• Pipette fillers
• Access to UV/VIS spectrophotometer (1)
• Stop Watch
• 50 mg/dm3 Potassium nitrate solution (40 cm3)
• Zinc powder in sodium chloride solid 1:200 w/w (10 cm3)
• Conc. hydrochloric acid in water 1:4 v/v (10 cm3)
• 6g/dm3 Sulfanilic acid solution (10 cm3)
• 2 mol/dm3 Sodium acetate solution (10 cm3)
• 6g/dm3 Acidified N-1-naphylenediamine dihydrochloride solution (10 cm3)
• Vacuum filtration kit
• Marker pens
If you do not have access to a spectrometer the RSC have published a wonderful resource in how to build a simple one using cheap materials (~£10). The simple photometer will be perfectly adequate for this practical.
www.rsc.org/images/EiC-05_2007-spectrophotometer_tcm18-214788.pdf
UV-Vis is introduced along with details about the Beer-Lambert Law. The first part of the practical involves the students preparing standards and then measuring the absorbances using a spectrometer(1). The students then plot absorbance against concentration and determine the molar absorptivity. The second part involves the students preparing solutions of water samples and using the absorbance values and the Beer-Lambert law to determine the concentration of nitrates in the samples. As a discussion the students are asked to compare their values to the UK accepted safe levels and also consider sources of nitrates in water.
The first part of the practical can be done in 1 h 30 mins (although students will need to be organised) and the second part in an hour.
The following materials will be needed for each group:
• 250 cm3 Erlenmeyer flask (x8)
• Polystyrene cuvettes (1 cm x 1 cm) (x8)
• 100 cm3 Measuring cylinder (x2)
• 10 cm3 Measuring Cylinder
• 1 cm3 Pipette (x4)
• 10 cm3 Graduated pipette
• Pipette fillers
• Access to UV/VIS spectrophotometer (1)
• Stop Watch
• 50 mg/dm3 Potassium nitrate solution (40 cm3)
• Zinc powder in sodium chloride solid 1:200 w/w (10 cm3)
• Conc. hydrochloric acid in water 1:4 v/v (10 cm3)
• 6g/dm3 Sulfanilic acid solution (10 cm3)
• 2 mol/dm3 Sodium acetate solution (10 cm3)
• 6g/dm3 Acidified N-1-naphylenediamine dihydrochloride solution (10 cm3)
• Vacuum filtration kit
• Marker pens
If you do not have access to a spectrometer the RSC have published a wonderful resource in how to build a simple one using cheap materials (~£10). The simple photometer will be perfectly adequate for this practical.
www.rsc.org/images/EiC-05_2007-spectrophotometer_tcm18-214788.pdf
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