Uncertainty in pH MEASUREMENT

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Uncertaintyin pH MEASUREMENT
2
SIM pH measurement
Celda de vidrio tipo Harned
9 cells HCl 0,01 m T, P, mV
1
m 0.005
2
P(aH,?Cl)-log(mH, ?H, ?Cl)
mCl
--- --- ---
0,005 0,010 0,015
3
....
m 0.010
4, 5, 6
....
m 0.015
7, 8, 9
3
SIM pH measurement

• GOAL To measure the pH of an unknown sample
• Step 1. Measure E for Ag/AgCl electrode in the
  harned cell using HCl. The value of the HCl
  concentration was determined by
  gravimetric-potenciometric titration using
  Tris(hydroxymethyl)aminomethane.
• Step 2. Measure Ecell for the harner cell for the
  buffer solution with unknown pH, using 0,005,
  0,010 y 0,015 m added NaCl.
• Step 3. Extrapolation of the acidity function to
  mNaCl0 to obtain p(aH?Cl)

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SIM pH measurement

• Step 4. Use of the Bates-Guggenheim convention
• Step 5. Obtain paH from the steps 3 and 4

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Uncertainty contribution in pH
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Uncertainty evaluation in p(aH?Cl)
Repeateb
Repeateb
Traceab
Traceab
Resol
Resol
Resol
mass Na Cl
mass solution
Traceab
mCl
7
Uncertainty contribution in p(aH?Cl)
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Uncertainty evaluation in EAg/AgCl
Resol
Correction, pH2
Resol
Traceab
Traceab
Repeateb
Repeateb
9
Uncertainty contribution inEAg/AgCl
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Uncertainty evaluation in mHCl
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Uncertainty contribution in mHCl