Group 1 Laboratory work

Laboratory work.

Our last task, after field work activities was to measure all of the parameters, that are responsible for water quality. Our group was divided and with another students, we created new teams to work in laboratory. For this reason, everyone could make different measurements and then we could combine all of them and make one big summary.

1      Color

Determining color is the easiest task in laboratory. We used method 8025, so Platinum- Cobalt Standard Method with the wavelength of 455nm. We needed only square sample cells and spectrophotometer. We were putting 10ml of each sample to the cuvette and then using spectrophotometer we were determining value of color. First we were measuring blank sample to zeroed the machine and then rest of them. Always the cell had to be wiped and dry and with the fill line facing right. Results were in mg/L PtCo. Completely pure water is colorless, but water from our samples was more or less brown.

2       Nitrate

To make a Nitrate measurement, we used prepared samples from Color measurement and method powder pillows. First we were zeroing spectrophotometer with the sample and then we were adding powder solution, mixing carefully and waiting 5 minutes to settle. Then sample was ready to measure. We were expecting results below 5mg/l, cause usually the concentration of nitrate in Finland has this value.

3       Ammonium

Ammonium was more difficult and we had to focus more, because to each sample we had to add 3 different reagents, then mix and wait. After this long preparation, our sample was ready to measure in a spectrophotometer. Results were in mg/l.

This day, very important was team work to avoid mistakes. Each of us could learn how to proper use pipettes, how to act in laboratory, use all of the equipment and finally learn how to determine all of the parameters, that are important in Water Quality Management.

           COD

We quantified the chemical oxygen demand of water. We did the same determination for all water samples of all groups. Chemical oxygen demand quantified by permanganate oxidation.

At first, water samples were diluted with ionized water. We shaked sample bottle and moved 10,0 ml of sample water and its dilution to erlenmeyer flask. Then we added there 0,50 ml of sulphuric acid and 2,0 ml of potassium permanganate solution. When all 13 water samples (including zero samples) were mixed with above-mentioned solutions, we set nice little foils to the top of erlenmeyer flasks and put those bottles in the kettle where they boiled 20 minutes. After getting those bottles out of boiling water, we chilled them in the cold water. Then we added 1,0 ml of potassium iodide solution and 0,25 ml of starch solution to the all samples. We stirred samples with magnetic stick and at the same tame titrated samples with sodium subsulphite solution until the blue color of samples vanished. With volume of sodium subsulphite went to titrating, we were able to calculate the COD of sample with following mathematical formula:

COD_Mn= (V₂-V₁) * c₁ * 800 * f

COD_Mn  Chemical oxygen demand of sample, mg/l
V₁            volume of sodium subsulphite went to titrating, ml
V₂                  volume of sodium subsulphite went to titrating the zero sample, ml
c₁             consentration of sodium subsulphite solution, mol/l
800         half of oxygens molar mass (mg)  divided with sample volume
f               dilution factor

Results:

nollat = average of zero samples

5       

      
     Total phosphorus

Measurements were done by following the instruction made according to the standard D8001.

We made measurements two times in two weeks. Reason for that was that the measuring device that we used was not functioning properly on first time as we got only negative results. On the second week we got better results. The device was working properly this time and the tasks involved to measurements were familiar to us. Measurements required us to follow the step closely as there were many different steps, such as adding few reagents to the samples mixing and heating.