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22 Cards in this Set
- Front
- Back
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ERRORS IN pH MEASUREMENT:
Standard Error |
a pH measurement cannot be more accurate than our standards +- .01pH
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a pH measurement cannot be more accurate than our standards +- .01pH
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Standard Error
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junction potential
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if the ionic composition of the analyte solution is different from tat of the standard buffer, the junction potential will change even if the pH of the two solutions is the same. +- .01
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if the ionic composition of the analyte solution is different from tat of the standard buffer, the junction potential will change even if the pH of the two solutions is the same. +- .01
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junction potential
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junction potential drift
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most combination electrodes ha a Ag/AgCl reference electrode containing saturated KCl solution More that 350 mg Ag per liter dissolve in the KCl. In the porous plug, KCl is diluted and AgCl can precipitate. if analyte solution contains a reducing agent, Ag(s) can precipitatein the plug. Causin a slow drift of the pH reading. Fix by recalibrating.
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most combination electrodes ha a Ag/AgCl reference electrode containing saturated KCl solution More that 350 mg Ag per liter dissolve in the KCl. In the porous plug, KCl is diluted and AgCl can precipitate. if analyte solution contains a reducing agent, Ag(s) can precipitatein the plug. Causin a slow drift of the pH reading. Fix by recalibrating.
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junction potential drift
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Sodium error
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When H+ is very low and Na+ is high, the electrode responds to Na+ and the apparent pH is lower than the true pH.
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When H+ is very low and Na+ is high, the electrode responds to Na+ and the apparent pH is lower than the true pH.
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Sodium error
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Acid error
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In strong acid, the measured pH is higher than the actual pH. perhaps because the glass is saturated with H+ and cannot be further protonated.
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In strong acid, the measured pH is higher than the actual pH. perhaps because the glass is saturated with H+ and cannot be further protonated.
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Acid error
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Hydration of Glass
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A dry electrode requires several hours of soaking before it responds to H+ correctly
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A dry electrode requires several hours of soaking before it responds to H+ correctly
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Hydration of Glass
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Equilibration time
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It takes time for an electrode to equilibrate with a solution. a well buffered solution requires approx 30s with adequate stirring. A poorly buffered solution needs any minutes.
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It takes time for an electrode to equilibrate with a solution. a well buffered solution requires approx 30s with adequate stirring. A poorly buffered solution needs any minutes.
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Equilibration time
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Temperature
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a pH meter should be calibrated at the same temperature at which the measurement will be made
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a pH meter should be calibrated at the same temperature at which the measurement will be made
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Temperature
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Cleaning
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if an electrode has been exposed to a hydrophobic liquid it should be cleaned with a solvent and then conditioned well in aqueous solution. Will cause drift.
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if an electrode has been exposed to a hydrophobic liquid it should be cleaned with a solvent and then conditioned well in aqueous solution. Will cause drift.
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Cleaning
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Beer's "Law" conditions:
1. ????? 2. valid for monochromatic radiation 3. valid for homogeneous solutions 4. must know all absorbing species in equilibrium |
Beer's "Law" conditions:
1. valid for dilute solution (<.01M) 2. valid for monochromatic radiation 3. valid for homogeneous solutions 4. must know all absorbing species in equilibrium |
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Beer's "Law" conditions:
1. valid for dilute solution (<.01M) 2. ????? 3. valid for homogeneous solutions 4. must know all absorbing species in equilibrium |
Beer's "Law" conditions:
1. valid for dilute solution (<.01M) 2. valid for monochromatic radiation 3. valid for homogeneous solutions 4. must know all absorbing species in equilibrium |
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Beer's "Law" conditions:
1. valid for dilute solution (<.01M) 2. valid for monochromatic radiation 3. ??????? 4. must know all absorbing species in equilibrium |
Beer's "Law" conditions:
1. valid for dilute solution (<.01M) 2. valid for monochromatic radiation 3. valid for homogeneous solutions 4. must know all absorbing species in equilibrium |
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Beer's "Law" conditions:
1. valid for dilute solution (<.01M) 2. valid for monochromatic radiation 3. valid for homogeneous solutions 4. ??????? |
Beer's "Law" conditions:
1. valid for dilute solution (<.01M) 2. valid for monochromatic radiation 3. valid for homogeneous solutions 4. must know all absorbing species in equilibrium |
