[student8607]

I'm trying to make sense of my lab data....



LOOK AT THE RATIO OF HCL/NAOH AND THE VOLUME OF NAOH/HCL. WHICH ONE MATCHES THE RATIO OF HPO4/H2PO4 FROM THE CALCULATIONS? WHY?

For Group 1, the ratio of HCl/NaOH matches the ratio of HPO4/H2PO4 better than the ratio of NaOH/HCl. But, for Group 2, the ratio of NaOH/HCl matches the ratio of HPO4/H2PO4 better than the ratio of HCl/NaOH.

But I can't think of why?

[Borek]

I have no idea what all these numbers are about, and I am not going to try to guess. You have to explain what you did before anyone will be able to help.

[student8607]

My bad....

Making Buffers & Buffer Strength:
1.   Using equation 1 from the lab manual, calculate the amount of H2PO4- & HPO42- are needed to make your assigned buffer
2.   Collect desired amounts of H2PO4- & HPO42- in a 100mL flask and fill it to the line with DI water
3.   Calibrate the pH meter using instruction card given and samples of pH 7 and pH 10
4.   Record the initial pH of your buffer solution and compare it with the desired pH in the manual
5.   Titrate 40mL of created buffer with 0.04M HCl
*One mL at a time, recording the pH after each 1mL addition
6.   Continue adding HCl until endpoint is reached (steepest drop of the pH VS volume curve)
7.   Titrate another 40mL of created buffer with 0.04M NaOH
*One mL at a time, recording the pH after each 1mL addition
8.   Continue adding NaOH until endpoint is reached (steepest rise of the pH VS volume curve)
9.   Calculate and share the total amount of NaOH and HCl required to reach the equivalence points, along with the ratio of NaOH volume to HCl volume and the ratio of HCl volume to NaOH volume

[student8607]

Just got a reply back from my lab instructor saying that she must have made a typo.

She said: In theory, the ratio of HCl/NaOH should have matched up with the ratio of HPO4/H2PO4.

But why is this the case....ratio of acid to base VS ratio of conjugate base to acid?

[Borek]

Think about the reaction taking place during titration.

[student8607]

Oh I see.
Acid neutralizing base and vise versa.