User:Asya L. Tucker/Notebook/Asya 571/2015/09/16

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Objective

  1. Prep 1 mL fiber samples for analysis
  2. Make 500 mL of 10 mM Tris buffer, pH 9
  3. Make 500 mL of 10 mM phosphate buffer, pH 7

Procedure

To Prep 1 mL fiber samples

  1. We centrifuge our samples and removed the supernatant
  2. We left the tubes open so that rest of the water can evaporate

To prepare a 500 mL of 10 mM Tris buffer at pH 9

  1. Make a 500mL solution of 10mM Tris Buffer, pH 9
  2. Weigh 0.06057g of Tris powder. Actual amount weighed: 0.0629g
  3. In a 500mL volumetric flask, add approximately 300mL of water, and a stirring pill
  4. Add the weighed powder
  5. Fill up to the 500mL mark using a pipette
  6. Place on stirring plate, and let it stir for a few minutes
  7. Measure conductivity and pH
  8. If first pH reading is not 9, add HCl until wanted pH is measured

To prepare a 500 mL of 10 mM phosphate buffer at pH 7

  1. sodium phosphate monobasic, MM = 137.99 g/mol
  2. potassium phosphate dibasic: 174.18 g/mol
  3. Need 0.0005mol of each to make the solution.
  4. Weigh 0.398g of sodium phosphate monobasic. Actual amount weighed: 0.40053g
  5. Weigh 0.368g of potassium phosphate dibasic. Actual amount weighed: 0.36682g
  6. In a 500mL volumetric flask, add approximately 300mL of water, and a stirring pill.
  7. Add both the sodium phosphate monobasic, and the potassium phosphate dibasic.
  8. Fill up to the 500mL mark using a pipette.
  9. Place on stirring plate, and let it stir for a few minutes.
  10. Measure conductivity and pH.
  11. If first pH reading is not very close to 7, or 7, add either potassium phosphate dibasic or sodium phosphate monobasic to reach the desired pH.

Calculations:

  Wanted concentration: 10mM = (10-3)M = 10(-3) mol/L 
  Wanted volume: 500mL = 0.5L
  Number of moles: (10-3  mol/L)/2 = (5-4) mol 
  Amount of solute needed: MM of solute·(5*10-4) mol = amount that should be weighed

Results

The final pH and conductivity reading for the tris buffer was 9.01 and 293 μS/cm. The final pH and conductivity reading for the phosphate buffer was 6.89 and 14.63 μS/cm.