My initial reading on a buret (reads down) was 0.81 mL. As I titrated, I recorded the reading each time.

I have a list of these readings. In order to find the volume added each time, do I subtract 0.81 from ALL readings or just the first reading?

Question

My initial reading on a buret (reads down) was 0.81 mL. As I titrated, I recorded the reading each time.

I have a list of these readings. In order to find the volume added each time, do I subtract 0.81 from ALL readings or just the first reading?

aaronq · Answer

you wanna find how much base or acid you had, right?

so you're only interested in the total volume, so only the final and initial readings are of importance.

anonymous · Answer

I'm recording the pH for every amount added (~1-2 mLs) and plotting the curve, so all readings are of importance.

aaronq · Answer

oh okay, different experiment. What exactly are you looking for? you've plotted your data on excel?

anonymous · Answer

Yes, I'm looking for where the buffer is and then the point of inflection.

anonymous · Answer

I'm just wondering if I need to subtract each of my readings by the initial reading of 0.81 mL so I can find the exact amount added at the time I read the pH.

aaronq · Answer

so you wanna plot the first derivative (i.e. the slope) so yes, you need to subtract the readings from the last. so $\dfrac{\Delta pH}{\Delta V}=\dfrac{pH_2-pH_1}{V_2-V_1}$

anonymous · Answer

When I did subtract my initial buret readings from values recorded, the inflection point is the same in terms of mL added & pH across all trials. Without doing the subtractions, the data is only the same in terms of pH.

I think I need to subtract the readings, but my partner disagrees.

aaronq · Answer

i'm not sure what you mean. Did you do what i mentioned above or did you do something different?

anonymous · Answer

I plotted each trial in excel and marked off the inflection points. I understand the remaining part of the procedure, but am having an issue with whether or not I should subtract 0.81 from the readings made during each trial of the experiment.

For example:
initial buret reading for Trial 1: 0.81 mL
Reading           pH
1.01 mL           3.30
2.03 mL           3.44
3.53 mL           3.71

Should I subtract each reading by 0.81 mL to account for the missing 0.81 mL at the beginning of the titration thus giving me:

Amt added           pH
0.20 mL           3.30
1.22 mL           3.44
2.72 mL           3.71

Before graphing the trials.

aaronq · Answer

we'll since you're only interested in the change, whether you subtract 0.81 from each reading - or not - doesn't make a difference (because the subtraction is constant). In other words, it doesn't your result.

aaronq · Answer

doesn't change*