Chemistry/Excel experts, quick question

[Devanshu]

Alright, I need help figuring out what to do on my chem lab. The experiment required us to do a titration of a weak acid w/ a strong base and now we need to estimate the equivalence point. I plotted the data in excel and this is what i get...



Now, my lab TA said that when you figure out the equation to the graph, take the first derivative of the equation, plot the new eq. and the tip of the curve will be the equivalence point. I realized I dont know how to figure out the equation so I emailed her and she sent me this link:

http://www.uky.edu/~holler/che226/titrations/titration_curve.html#data

I cant make any sense out of it...so I figured someone here might have some experience in this field.

Thanks

[ps2daddy]

Dont figure out the formula for the graph just follow the example on the differntiate page (click on bottom of page in link to get the differentiate section)
This is the link for the file
http://www.uky.edu/~holler/download/acid_base_curve_fit.xls

1. Take the value for each point and fill in each spot on the spreadsheet that corresponds from the example above
Ex your first point is ~ vol=0, ph=2.3
point 2 is vol=2.6, ph=3.9.......
Last point vol=29, ph=12

Then copy and paste the formulas and the values will fill in automatically to make your first derivative graph automatically for the rest of the values DV(change in V), Dph(change in ph), Vavg....ect ect

The spiked point will be your equivalence value

[Devanshu]

Sweet...I'm blind and didnt see the differentiate thing on the spreadsheet. Thanks man

[eag182]

I would've put the values in my calculator gotten a cubic regression equation and taken the derivative of that and gotten the derivatives y values with the listed x values .

[ps2daddy]

I would've put the values in my calculator gotten a cubic regression equation and taken the derivative of that and gotten the derivatives y values with the listed x values .

Yep that would have worked fine he just had that perfect example there I figured it would be easy to use that

[Devanshu]

I would've put the values in my calculator gotten a cubic regression equation and taken the derivative of that and gotten the derivatives y values with the listed x values .

Thats what I did in lab while we were doing the experiment to see if i was doing ok but the experiment required us to excel and the lab report wanted a printed graph of all 3 trials. The chem dept at my school is really anal about every little thing so it has to be "perfect".