Okay well I suddenly got confused for a lab I did We took pH meter than we calibrate it. Then we measure the pH of the acetic acid solution, which was used to determine the Ka of the acetic acid using the first method.
We made a 1M solution of NaOH which was used to titrate 50 ml of acetic acid solution, the data which was collected was volume of NaOH versus pH of the solution. The data was ploted and we use second method to find Ka of the solutions.
2.72=-log [H+];
[H+]=0.043M=[Ac-];
To find [HAc] we used the equation
[HAc]ix Va= [NaOH]I x Vb
[HAc]I x 50ml= 0.20M x 25.00ml
[HAc]=0.1 M
Ka for acetic acid (book value) is
Ka= 1.83 x 10^-5
In this method we used Handerson-Hasselbach equation to calculate the Ka of the acetic acid.
pH= pKa + log[Ac-]/[HAc]
BUT NOW I GOT CONFUSED @ FINDING THE pKa is this right? 4.5= pKa
NOW AFTER I FIND THE pKa HOW DO I CALCULATE Ka AGAIN?
pKa = -logKa.
Just enter pKa value, change to - sign, then hit 10x key.
For pKa = 4.75 you will get Ka of 1.778E-5 if you do it right. I just picked a number for you to check your procedure.
how is it that on my calculator I am getting -0.676
pressing -sign then log 4.75 = -0.676
even after I have found the pKa, I don't understand how would I findthe Ka.
Do it this way.
enter 4.75 (that is the pKa.)
change sign to negative to read -4.75. Then PRESS 10X key (not the log key). That would then read 1.75E-5.
sorry. it will read 1.778E-5.
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I apologize for the confusion in my previous responses. Let me clarify the steps to find Ka given the pKa value.
To calculate Ka from the pKa, follow these steps:
1. Take the negative logarithm (base 10) of the pKa value to get -log(pKa). In your case, it would be -log(4.75).
2. Enter the value -log(pKa) into your calculator. Make sure you are using the logarithm function (log) and not the negative sign (-) followed by the log function.
3. Press the "10^x" key on your calculator. This will raise 10 to the power of the result from step 2.
By following these steps correctly, you should calculate the value of Ka.
In your case, to find Ka for acetic acid, you need to use the pKa value of 4.75. So, enter -4.75 into your calculator and then press the "10^x" key. This should give you the Ka value.
The correct calculation should yield a Ka value of 1.778E-5 (or 1.778 x 10^-5). This value is close to the book value of Ka for acetic acid, which is 1.83 x 10^-5.
I apologize again for any confusion caused earlier.