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Posted by on Tuesday, March 27, 2012 at 9:57pm.

Hi, so I did a lab on acids, bases, salts and buffer solutions. After measuring the pH for a .010 M HCl solution I got a pH of 2.50. After doing a calculated pH of .010 M of HCl the answers is 2.
My question is why do you think my pH from the experimental is slightly higher than that of the calculated? And is this .5 difference really that significant?
Thanks!

  • chemistry lab - , Tuesday, March 27, 2012 at 10:49pm

    Why? There may be several reasons.
    1. The pH meter wasn't standardized properly; i.e., it could have been set at pH 7 or 8 but you were measuring 2. It does happen from time to time;I have done it myself.
    2. The temperature of the solution measured was not the same as the standardizing soln. This robably is not a factor here.
    3. Your calculations are done with concentrations in moles/L whereas the 0.01M does not have an activity of 0.01. This is the most probable reason but would not account for more than about 0.1 (meaning soln with pH 2.0 would measure about 2.1 or so).
    4. The SCE or glass electrode could be faulty. That has happened to me, too.
    Is it significant? That all depends upon what you are doing. Some cases yes and some no.

  • chemistry lab - , Tuesday, March 27, 2012 at 11:15pm

    Thank you for your feed back it helped me out greatly!

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