Bromothymol blue pH indicator dye used in titration?
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I know that dyes are not good for giving accurate pH measurement as they can be affected by components of a solution but... I used this dye in a titration of NaOH into HCl (in equimolar concentrations). It only took 21.6 cm3 of NaOH added to 25cm3 of HCl to reach the endpoint (colour change to blue) and I don't know why Does the actual presence of the dye affect the pH slightly? or could the formation of NaCl salt have affected the pH and therefore the stage at which an endpoint was reached????? Does anyone agree or disagree with this or have any alternative suggestions? ( - I have lots of human error reasons ie. in measurement, preparation etc)
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Answer:
No surprise at all, the transition does not take place at an pH of exactly 7 but already before. Take a look here for a graph: http://antoine.frostburg.edu/chem/senese/101/acidbase/faq/indicating-strong-or-weak.shtml
Ronnie at Yahoo! Answers Visit the source
Other answers
Are the solutions made up correctly and with sufficient accuracy? Bromothymol blue should work very well for a strong acid and base, and it's a very distinct colour change. It only takes a very small amount of indicator to see a colouration so it does not change the concentrations.
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