Colorimetric Determination of Ph
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Date Submitted: July 25, 2013
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EXPERIMENT NO. 4
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COLORIMETRIC DETERMINATION OF pH
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Abstract
This experiment examined the result of the various color indicators combined with different buffer solution, thereby testing the precision and accuracy of determining the pH value colorimetrically. Colorimetric method is a simple and practical procedure with an important advantage: they do not get out of order as from time to time do the pH-meters. Four buffers (Acetate buffer, phosphate buffer, ammonium buffer and an unknown solution) were tested with eight different indicators. The method employs the use of complex organic dyes which change to distinctive colors through a specific pH range of the buffer solutions giving the acid and base color that was used in identifying the pH range. The obtained result of each group is relatively close to the theoretical results. The outcome of this experiment shows that methyl orange, bromphenol blue and bromcresol green are all acidic while methyl red, bromothymol blue, bromocresol purple, thymol blue and phenolphthalein results to being basic.
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Introduction Determination of pH can be used by an indicator, using colorimetric method, or of an unknown solution. An indicator causes the colour of the solution to change depending on the pH, which is how it is read. An acid-base indicator can be a weak acid
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Date Submitted: July 25, 2013
-------------------------------------------------
-------------------------------------------------
-------------------------------------------------
-------------------------------------------------
-------------------------------------------------
-------------------------------------------------
EXPERIMENT NO. 4
-------------------------------------------------
COLORIMETRIC DETERMINATION OF pH
-------------------------------------------------
Abstract
This experiment examined the result of the various color indicators combined with different buffer solution, thereby testing the precision and accuracy of determining the pH value colorimetrically. Colorimetric method is a simple and practical procedure with an important advantage: they do not get out of order as from time to time do the pH-meters. Four buffers (Acetate buffer, phosphate buffer, ammonium buffer and an unknown solution) were tested with eight different indicators. The method employs the use of complex organic dyes which change to distinctive colors through a specific pH range of the buffer solutions giving the acid and base color that was used in identifying the pH range. The obtained result of each group is relatively close to the theoretical results. The outcome of this experiment shows that methyl orange, bromphenol blue and bromcresol green are all acidic while methyl red, bromothymol blue, bromocresol purple, thymol blue and phenolphthalein results to being basic.
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Introduction Determination of pH can be used by an indicator, using colorimetric method, or of an unknown solution. An indicator causes the colour of the solution to change depending on the pH, which is how it is read. An acid-base indicator can be a weak acid
References: • www.files.chem.vt.edu/chem.../buffers/intro.html • http://www.rsc.org/publishing/journals/prospect/ontology.asp?id=CMO:0001748&MSID=b908638b • http://chemwiki.ucdavis.edu/Physical_Chemistry/Acids_and_Bases/Buffers • http://microscopy.berkeley.edu/Resources/instruction/buffers.html • http://wolfson.huji.ac.il/purification/PDF/Buffers/Calbiochem_Buffers_Booklet.pdf • http://www.inc.bme.hu/en/subjects/genchem/phdet2.pdf • http://en.wikipedia.org/wiki/PH_indicator • Book reference: Biochemistry 3rd edition by Mathews, Van Holde & Ahern pg. 41