Hello everyone, I am new to this page, so I hope I can find some friendly people to help me.
I am not sure if the error I am experiencing is a chemistry, math, formula or process error so if there is anyone good at chemistry and excel I desperately need your help because I have been trying for 4 days to figure this out.
In the attached sheet I am trying to use a quadratic formula to determine the pH of in this example Sodium Hydroxide.
Yes I know that you can do the simplified version however the simplified version does not work very accurately for PolyProtic Acids and bases.
This is just a small section of a much larger project I am working on. and Yes I know that some text books state that the PKA of sodium hydroxide is 15.7 however more recent books have stated a pka value of 13.8 when the water disassociation is factored in so 13.8 is the value I am using in this example.
So I got the formula to work in the top example to find the H+ but I can not for the life of me to get it to work for the OH- in the bottom formula which is an exact duplicate of the top one but instead of using Pka/Ka it uses Pkb/Kb
So here is what I did
The pk value of NaOH is 13.8
NaOH is a base, so the 13.8 SHOULD be the PKB value
so to get the PKA value it would be 14-13.8 which = a PKA of .2 (G3)
Now to get the KA values it is the =10^-(of the PKA) which in this case gives me 0.630957344 (J3)
Then in S5 you take the total moles (-.19g*40 (molar mass)) which equals -0.002997047 (s5)
So now you have A, B, and C to solve for X in the quad formula which in the first example is +x1=0.004714769 (V3) or -x2=0.635672114 (V4)
Now to calculate the pH it is the -log of the H+ value (V3), or (V4), in our case it is (V3) which gives us a pH of 2.32653955 in cell (X3) which is correct.
Now to verify the second formula, if we take 14 - 2.32653955 = a pOH of 11.67346045 now to figure out the OH- Value, we take the
11.67346045 and go 10^-11.67346045 we should get 2.12099E-12 in the S13 cell
Now if we run the same formula, but use the PKB and PKB values, we should see in cell (S7)the 2.12099E-12, but we dont, we get -7.52824E-17 at (cell X11) a pH of 8.06 instead of 11.67346045
Now I am 100% sure that the quad formula is correct and functional, and I am sure that the values in C11, C12 are correct, and I am pretty sure the formulas in the PKA/KA, PKB/KB are correct, but I can not figure out for the life of me WHY this is not returning the correct values in the second formula.
I have spent 4 days trying to trouble shoot this, to no avail, what am I missing???
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