A glass electrode and its reference are calibrated with two buffers…
Contributed by StemPy LabTry it on paper first. A hint, the key idea and the worked solution are here when you need them.
A glass electrode and its reference are calibrated with two buffers. In the pH buffer the meter reads , and in the pH buffer it reads . A solution of unknown pH reads . The ideal slope at is per pH unit. Find (a) the slope of this electrode, (b) its efficiency, and (c) the pH of the unknown solution.
Need a reminder? The key ideaShow
The hydrogen electrode at has , so with a reference electrode of potential the cell emf is . A glass electrode is calibrated with two buffers: the slope is the change in reading divided by the change in pH. For a silver halide, , and the same form holds for another metal with .
The worked solution
Have you tried it?
Work it out on paper first. It is fine to get stuck or make a mistake: that is how we learn. When you are ready, go through the solution one step at a time, and check each step against your own.
Plan. Fix the line with the two buffers, then read the unknown from it.
Step 1. The slope. for each pH unit.
Step 2. The efficiency. per cent.
Step 3. The unknown. .
Answer: per pH unit, per cent, and pH .
What if? With the ideal slope through the pH point the answer would be . The two answers differ in the second decimal place, which is why a real meter is calibrated.
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