Potentiometric Titration of Iron with Mohr's Salt
Potentiometric Titrations
Accuracy
The accuracy of a potentiometric analysis is limited by the measurement error for the cell's potential. Several factors contribute to this measurement error, including the contribution to the potential from interfering ions, the finite current drawn through the cell while measuring the potential, differences in the analyte's activity coefficient in the sample and standard solutions, and liquid junction potentials. Errors in accuracy due to interfering ions often can be eliminated by including a separation step before the potentiometric analysis.
Precision
The precision of a potentiometric measurement is limited by variations in temperature and the sensitivity of the potentiometer.
Time, cost & equipment
In comparison with competing methods, potentiometry provides a rapid, relatively low-cost means for analyzing samples. Commercial instruments for measuring pH or potential are available in a variety of price ranges and include portable models for use in the field.
Classical Titrations
Accuracy
An important limitation when using a visual indicator is the need to observe the change in color signaling the end point. This may be difficult when the solution is already colored. When working with macromajor and macrominor samples, acidbase titrations can be accomplished with relative errors of 0.10.2%. The principal limitation to accuracy is the difference between the end point and the equivalence point.
Precision
The relative precision depends primarily on the precision with which the end point volume can be measured and the precision of the end point signal. The relative precision can be improved by using the largest volume buret that is feasible and ensuring that most of its capacity is used to reach the end point. The precision of the end point signal depends on the method used to locate the end point. With a visual indicator, the precision of the end point signal is usually between ±0.03 mL and
Accuracy
The accuracy of a potentiometric analysis is limited by the measurement error for the cell's potential. Several factors contribute to this measurement error, including the contribution to the potential from interfering ions, the finite current drawn through the cell while measuring the potential, differences in the analyte's activity coefficient in the sample and standard solutions, and liquid junction potentials. Errors in accuracy due to interfering ions often can be eliminated by including a separation step before the potentiometric analysis.
Precision
The precision of a potentiometric measurement is limited by variations in temperature and the sensitivity of the potentiometer.
Time, cost & equipment
In comparison with competing methods, potentiometry provides a rapid, relatively low-cost means for analyzing samples. Commercial instruments for measuring pH or potential are available in a variety of price ranges and include portable models for use in the field.
Classical Titrations
Accuracy
An important limitation when using a visual indicator is the need to observe the change in color signaling the end point. This may be difficult when the solution is already colored. When working with macromajor and macrominor samples, acidbase titrations can be accomplished with relative errors of 0.10.2%. The principal limitation to accuracy is the difference between the end point and the equivalence point.
Precision
The relative precision depends primarily on the precision with which the end point volume can be measured and the precision of the end point signal. The relative precision can be improved by using the largest volume buret that is feasible and ensuring that most of its capacity is used to reach the end point. The precision of the end point signal depends on the method used to locate the end point. With a visual indicator, the precision of the end point signal is usually between ±0.03 mL and