1. Alejandro Pérez Castorena1 Uncertainty in pH MEASUREMENT

2. Alejandro Pérez Castorena2 Celda de vidrio tipo Harned 1 3 2 7, 8, 9.... 4, 5, 6 9 cells HCl 0,01 m T, P, mV m 0.005 m 0.010 m 0.015 P(a H,  Cl )=-log(m H,  H,  Cl ) mClmCl --- 0,005 0,010 0,015 SIM pH measurement

3. Alejandro Pérez Castorena3 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 E cell 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 m NaCl =0 to obtain p(a H  Cl )°

4. Alejandro Pérez Castorena4 SIM pH measurement Step 4. Use of the Bates-Guggenheim convention: Step 5. Obtain pa H from the steps 3 and 4:

5. Alejandro Pérez Castorena5 Uncertainty contribution in pH

6. Alejandro Pérez Castorena6 Uncertainty evaluation in p(a H  Cl ) m Cl Resol Traceab Repeateb Resol Traceab mass Na Cl mass solution Resol Traceab Repeateb

7. Alejandro Pérez Castorena7 Uncertainty contribution in p(a H  Cl )

8. Alejandro Pérez Castorena8 Uncertainty evaluation in E° Ag/AgCl Resol Traceab Repeateb Resol Traceab Repeateb Correction, p H2

9. Alejandro Pérez Castorena9 Uncertainty contribution inE° Ag/AgCl

10. Alejandro Pérez Castorena10 Uncertainty evaluation in m HCl

11. Alejandro Pérez Castorena11 Uncertainty contribution in m HCl