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Phosphate Analysis
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You will measure spectroscopically the concentrations of phosphate in:
  • STANDARDS (computer assigned)
  • TAP WATER (from home or lab)
  • UNKNOWN (from the stockroom)
  • COLA or TEA (computer assigned)
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The STANDARDS are made from a stock solution prepared by you from the Primary standard, NaH2PO4.
To maintain 3-4 sig fig accuracy in making these solutions, you will weigh out 500-575 mg of the pure dry NaH2PO4 using an Analytical Balance (0.0001 g). This will be dissolved and diluted to 100 mL to make an approximately 40-50 mM phosphate solution.  A10 mL portion of this will then be diluted to 100 mL to make the 4-5 mM solution which you then dilute and react to make your STANDARDS.
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You will make yellow Phosphomolybdate solutions of known concentration which will be analyzed for transmission of blue, 380 nm, light.

The the higher the concentration of phosphate, the more intense the yellow color, the more blue light will be absorbed.

Which of these solutions was made from the higher phosphate concentration?

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The STANDARD PLOT
A good standard Plot is linear and goes through (0.00,0.00).

The plotted STANDARD data, Absorbance vs Concentration, will allow you to determine, graphically, the Phosphate concentration in:

  • tapwater (from home or school)
  • an UNKNOWN
  • a canned drink (cola or tea)

There is a TUTORIAL on PHOSPHATE ANALYSIS
To return to the SYLLABUS
ONE WEEK LATER

RWK 3/2/98