Project Objectives
Standardization of NaOH (titrant) & HCl stock solutions
Preparation of 2.7 mM chlorauric acid solution
Preparation of buffer solutions
Today's Tasks
Preparation of 50 mM Tris (8.2 pH) buffer
- Placed 1.211 g Tris base (121.14 g/mol) in 200 mL volumetric flask
- Rinsed weighing dish & transfered solution to flask
- Added 4.430 mL 0.948 M HCl using automatic micropipet (100 - 1000 μL)
- Filled with deionized water & inverted 10 times
- pH = 8.39 as measured by VWR SympHony meter
Analysis
pH discrepency
- inaccurate calibration (unlikely; new standards used & readings were stable)
- [HCl] of stock actually lower than 0.948 M? (unlikely; potentiometrically determined)
- Base impurities in glassware? (unlikely; clean & dry glassware with no visible residue)
- Too much Tris added? (unlikely; precision balance used & mass was stable)
- Not enough HCl added (probable)
- micropipet used was not previously calibrated (instrument error)
- technique may have been poor, including incomplete time to draw up solution (human error)
Other buffers needed
- 7 - 7.5 pH dihydrogen phosphate - hydrogen phosphate (50 - 100 mM)
- 8.2 pH Tris - TrisH+ (50 - 100 mM) in saline (0.9% NaCl)
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Project 3: Solution Preparations
