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pka

Postby 2468 » Fri Nov 30, 2012 10:45 pm

Hey, :)

need help working this out:

pH: 4
molar extinction coefficient: 0.0187142857 m-1cm-1
absorbance at 500nm: 1.492

[Acid form]?? (work out using molar extinction coefficient)
[base form]?
lg([acid]/[base])?
pKa?

If someone can guide me on how to do this especially the acid form....i'd greatly appreciate it...so i can use the basics fr it to work out the rest of my ques...

thank you
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Postby JackBean » Sat Dec 01, 2012 5:44 pm

don't you need more values?
http://www.biolib.cz/en/main/

Cis or trans? That's what matters.
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Re:

Postby 2468 » Sat Dec 01, 2012 5:58 pm

JackBean wrote:don't you need more values?


oh yeah sorry and methyl red concentration was 12.5um....3ml of buffer used and 1ml of stock methyl red..if that helps?...really cant get my head round this..i've tried searching
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Postby JackBean » Sat Dec 01, 2012 6:18 pm

LOL, you're really expert.

From Lambert-Beer law (A = e.c.l) calculate concentration of the color form. Concentration of colorless form is c(total) - c(color)
http://www.biolib.cz/en/main/

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Re:

Postby 2468 » Sat Dec 01, 2012 6:25 pm

JackBean wrote:LOL, you're really expert.

From Lambert-Beer law (A = e.c.l) calculate concentration of the color form. Concentration of colorless form is c(total) - c(color)



'Love' the sarcasm.. :/

Elaborate? Dont undertsand it.
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Postby JackBean » Sat Dec 01, 2012 11:46 pm

This could be of use for you
http://www.usca.edu/chemistry/spectra/methlred.htm (if you can open *.spc files)
http://www.colby.edu/chemistry/PChem/la ... hylRed.pdf (especially picture on p. 3 where you can see that the extinction coefficient is around 8000 M-1 cm-1)
http://www-ec.njit.edu/~grow/Methylred.pdf
http://www.biolib.cz/en/main/

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Postby 2468 » Tue Dec 04, 2012 1:06 am

Thank you! :D
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