Objective
Make our own phosphate buffer and tris buffer solutions at their specific pHs.
Procedure
Following the basic guidelines stated in Dr. Hartings' lab notebook
- Make a 500mL solution of 10mM Phosphate buffer, pH 7.
- Use:
- sodium phosphate monobasic, MM = 137.99 g/mol
- potassium phosphate dibasic: 174.18 g/mol
- Need 0.0005mol of each to make the solution.
- Weigh 0.398g of sodium phosphate monobasic. Actual amount weighed: 0.40053g
- Weigh 0.368g of potassium phosphate dibasic. Actual amount weighed: 0.36682g
- In a 500mL volumetric flask, add approximately 300mL of water, and a stirring pill.
- Add both the sodium phosphate monobasic, and the potassium phosphate dibasic.
- Fill up to the 500mL mark using a pipette.
- Place on stirring plate, and let it stir for a few minutes.
- Measure conductivity and pH.
- 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.
- Make a 500mL solution of 10mM Tris Buffer, pH 9
- Weigh 0.06057g of Tris powder. Actual amount weighed: 0.0629g.
- In a 500mL volumetric flask, add approximately 300mL of water, and a stirring pill.
- Add the weighed powder.
- Fill up to the 500mL mark using a pipette.
- Place on stirring plate, and let it stir for a few minutes.
- Measure conductivity and pH.
- If first pH reading is not 9, add HCl until wanted pH is measured.
Calculations:
Wanted concentration: 10mM = 10^-3M = 10^-3mol/L
Wanted volume: 500mL = 0.5L
Number of moles: (10^-3mol/L)/2 = 5*10^-4 mol
Amount of solute needed: MM of solute·(5*10^-4 mol)=amount that must be weighed
Description
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Data
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Notes
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