Week 2: Prelab Organizational Questions 5. 6. How can you determine the best wav
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Week 2: Prelab Organizational Questions 5. 6. How can you determine the best wavelength to analyze the phosphate ion content of solutions? What is the source of phosphate provided in the lab? Show calculations for determining the concentration of the phosphate solutions you will make. Write a procedure for preparing a calibration curve for phosphate in solution. Write a procedure for determining the phosphate content in colas. Include sample preparation as well as what should be used as a blank solution for the spectrophotometer. How can you use a calibration curve to determine the phosphate concentration of a sample of cola? 7. 8. 9.Explanation / Answer
Colorimetric analysis of phosphate ion in colas
5. The best wavelength for the estimation of phosphate ion in a solution can be determined by maki g a solution of phaosphate of known concentration and then taking absorption meaurement of this solution at various wavelengths. The wavelength at which it shows maximum absorbance is choosen as the best wavelength.
6. Source of phosphate ion in lab is cola drink.
The concentration of phosphate is determined by using Beer's law,
concentration = absorbance/molar absorptivity x path length
with,
absorbance an experimentally determined term and path length a constant.
molar absorptivity is a constant determined by slope of the calibration curve.
7. For calibration curve, a stock solution of phosphate with known concentration of phosphate ion in it is taken and it is diluted to make solutions of various concentrations. The absobance of each solution is recorded. A plot of absorbance vs concentration is made. The slope of calibration curve gives us the molar absorptivity value for phosphate ion.
8. The sample of cola is diluted in the same fashion as the stock solution and its absorption measurement is taken. A blank solution with only the solvent water and no cola is also made and absorption value is extimated. The final absorption due to cola sample = absorption due to sample - absorption of blank
The concentration of phosphate is then determined by the equation shown in 6. above.
9. The concentration corresponding to the absorption value of the sample in the calibration curve is the actual concentration of phosphate in cola sample.
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