One more point, the pH pen do not measure [H+] directly. I probably measure conductivity or something like that... ie related some electrical property to pH.
Whether it is a straight line or not... i do not know.
BC
Jinxed fishy photographer
[Specialist]
No. No one is worked up. It depends on how you want to interpret the message. IMO, it is still a very very civil discussion and has not erupt into a flamewar yet.
Gary, I understand your point of view that a one-line answer doesn't help much, but my point is that a one-line question doesn't warrant much to discuss either. This is along the same line as the "why my tank have algae" type of question.
maybe I should start putting smilies everywhere in my reply.
ck[] [
Jinxed fishy photographer
[Specialist]
You didn't get mine either. It really depends on the meter how many calibration points the machine has. More points more accurate, expensive.[----------------
On 3/7/2003 11:44:09 AM
U didn't get wat I meant. u said e pH pen has 3 calibration pts : 4,7 n 10. But u only calibrate it using pH 7.0 fluid. So wats the purpose of the pH 4 n 10 calibration pts if u dun calibrate it at these 2 pts using pH 4 n 10 fluid ? BTW pH = -log [H+], its not a straight line.
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The ones that we have in labs are usually either 2 points or 3 points, i.e. you can use 2 or 3 calibration solution. For two points, it is either 4 and 7, or 7 and 10, depending on which range you are looking for.
Try using a log scale for the graph.
ck [
What you said has some logic but unfortunately you have to understand the principles of how a pH meter works.----------------
On 3/7/2003 9:45:21 AM
The main purpose of using calibration fluid is becos the pH of tat fluid is already known so tat u can adjust the pen's reading to this value. I dun see any reason y mineral water or distilled water can't be used for calibration purpose if e pH of these liquid is also known beforehand.
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pH7 and pH7 solutions are actually KCL solution mixed to a certain concentration. Your pH probe/sensor works like battery, the type of electrode that we usually see nowadays are combination electrode which a single probe/sensor contains the pH electrode, reference electrode and (if avaliable for the more expensive unit the temperature sensor).
The reference electrode are immersed in a solution (either KCL or AgCL depending on the design) of pH 7, the pH electrode comes into contact with the actual sample (the solution you want to measure) via a glass membrance.
You cannot use distilled water or DI water because the pH value of these are not the same set point as the calibration point of the pH meter. Note that every pH meter has it own set point and you usually perform two point calibration (pH4 and pH7, some pH7 and pH9) or 3 point calibration (pH4, 7 and 9)if you're going to very accurate reading.
ah hah... something learnt again...
BC
pH pen still works with the same principle (wet electrode) as the previous message. They measure the potential difference between the reference and pH sensor.----------------
On 3/7/2003 11:53:24 AM
One more point, the pH pen do not measure [H+] directly. I probably measure conductivity or something like that... ie related some electrical property to pH.
Whether it is a straight line or not... i do not know.
BC
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The wet electrode is invented by the founder of my parent company, Mr Horiba.
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