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19 May 2005, 10:01 PM
| #1 (permalink) |
| Senior Member  HSC: 2005 Gender: Male Location: Sydney
Join Date: Sep 2003
Posts: 219
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31 May 2009, 2:28 PM   | reason for differences between pH meter & indicators You can hide this advertisement by registering. Anyone have an scientific (exam-worthy) explanation of why there can often be such a big difference in the pH reading (or range) you get from using indicators compared to using a pH meter?Obviously a pH meter is more accurate, and indicators show just colours which ppl can not see correctly etc, but is there an actual explanation? thanks~ |
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20 May 2005, 10:25 AM
| #2 (permalink) |
| Argentous Fingers  HSC: 2003 Gender: Male
Join Date: Sep 2003
Posts: 428
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18 Sep 2005, 9:18 PM | pH meters => improper calibration, instrument drift, lack of temperature compensation, improper sampling, or a dirty probe. Some indicators have thermochromic properties, though not terribly significant errors here. Remember that most indicators are weak buffers under equilibrium between protonated and ionic forms (hence the colour change). How about the difference between end point and equivelence point. pH meters measure H+ activity not concentration. For low concentrations the difference isn't huge. I will leave this to you to investigate because I know I'll get something wrong. Involves Nernst eqaution. I don't think this is within the scope of HSC though  .
__________________  Last edited by Jumbo Cactuar; 24 May 2005 at 6:56 PM. |
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21 May 2005, 8:32 PM
| #3 (permalink) |
| Argentous Fingers HSC: 2003 Gender: Male
Join Date: Sep 2003
Posts: 428
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18 Sep 2005, 9:18 PM | Following on from my last post.. pH probe errors: agitation temperature matrix effects ionic strength response time conditioning rinsing read for further explaination Also I read that a recent discovery traced that pH probes measure Na+ transport rather than H+. I don't know if I believe that, but if anyone knows any more I'd be interested!
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22 May 2005, 7:24 PM
| #4 (permalink) |
| Senior Member HSC: 2005 Gender: Male Location: Sydney
Join Date: Sep 2003
Posts: 219
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31 May 2009, 2:28 PM | thanks Jumbo_Cactuar I'm not even sure if this type of thing is in the syllabus but I have a prac test which has a part of 'measuring the pH of an acid using a pH meter and indicator/s" so i'm guessing in the conclusion i'll need something on why there was a difference in the readings thanks again~ |
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22 May 2005, 7:47 PM
| #6 (permalink) |
| Argentous Fingers HSC: 2003 Gender: Male
Join Date: Sep 2003
Posts: 428
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18 Sep 2005, 9:18 PM | I encourage people to go off syllabus from time to time because not only do you get a deeper understanding of the topic, but it makes other elements come more intuitively. 
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24 May 2005, 6:32 PM
| #7 (permalink) | |
| duckie's REBORN!!!!! ^^  HSC: 2003 Gender: Male Location: pond... where the ducks are
Join Date: Jun 2003
Posts: 5,742
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17 May 2009, 2:11 PM  | Quote:
__________________ DUCKIE IS REBORN!!!!! only 3 wks too earlie =S "I am willing to give up any thing for you... even maths!!!!" - anonymous "Don't cry because it ended; smile because it happened." - anonymous | |
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