Map sapling learning Which of the following are errors that can occur when measu
ID: 947493 • Letter: M
Question
Map sapling learning Which of the following are errors that can occur when measuring the pH with a glass combination electrode? the variable potential of the internal AglAgCl reference electrode sodium error at high pH junction potential drift small selectivity for H over other ions uncertainty in the pH of the standard buffer solutions Previous Check Answer Next I Exit Hint When determining what errors can occur when measuring the pH, think about how the H concentration of the solution is measured by the glass membrane and the general steps taken when measuring the ph of a solution. Consider how error might be introduced during these processes.Explanation / Answer
2) sodium error at high pH.
sodium ion error occurs at high pH, where hydrogen ion concentration is very low in comparison to sodium ion concentration. The sodium ion concentration can be so high relative to hydrogen ion contration that the electrode begins to respond to the sodium ion. This results in a reading that is lower than the actual pH. Depending on the pH glass formulation, this can occur as low as 10 pH. Where accurate high pH readings are required, the upper pH limit of the pH electrode should be checked and a specially formulated, high pH electrode used if necessary. Compared to sodium, lithium ions will produce a larger error, while the effect of potassium ions is negligible.
The junction potential is the source of the most hidden error in pH measurements. It develops in the reference junction separating the internal filling solution of the reference electrode from the buffer or sample solutions. The cause of the development is the different diffusion rate of cations and anions on both sides of the reference junction.
It is difficult to detect, difficult to measure, depends on the kind of reference electrode used, the type of junction employed and the composition and concentration of the buffer or sample solutions.
Repeated use of the buffer will exhaust buffer capacity and cause an error in calibration.
Dilution of the buffer with deionized of distilled water will also change the pH value of the solution. The lesser the change by the addition of the same amount of water represents a higher resistance to dilution.
The addition of solid salt will result in a so-called salt effect shifting the equilibrium of the components and changing the pH value of the buffer solution.