December 04, 2020, 02:52:34 AM
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Topic: How to increase pH  (Read 268 times)

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bluecalculator

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How to increase pH
« on: June 16, 2020, 11:47:41 AM »
Hi everyone, I'm stuck in solving this problem. I have two solution of H2SO4 5M that needs two consequential pH increasing: the first from the natural pH of H2SO4 5M (around zero) to pH 2 and then from pH 2 to pH 7. The second solution from the natural pH of H2SO4 5M to pH 2 and then from pH 2 to pH 7. I would like to understand how can I calculate the volume of NaOH (let's say 5M) I have to add for each step.
at the beginning, to calculate the Volume from pH 0 (as you said) to 2 I was considering this formula:

But somebody told me this calculation is wrong because I have to consider that H2SO4 is diprotic.

The value I used are:
V(H2SO4)= 1L
[H2SO4](initial)= 5 M

Thank you !
« Last Edit: June 16, 2020, 01:22:59 PM by bluecalculator »

AWK

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Re: How to increase pH
« Reply #1 on: June 16, 2020, 01:03:32 PM »
1. Read the Forum Rules carefully

The pH calculations for such high concentrations are very approximate because they cannot be done accurately - the actual pH of 5 M H2SO4 is around -0.7.
AWK

bluecalculator

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Re: How to increase pH
« Reply #2 on: June 16, 2020, 01:11:47 PM »
Yes, I'm sorry my fault.
Anyway at the beginning, to calculate the Volume from pH 0 (as you said) to 2 I was considering this formula:

But somebody told me this calculation is wrong because I have to consider that H2SO4 is diprotic.

The value I used are:
V(H2SO4)= 1L
[H2SO4](initial)= 5 M

AWK

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Re: How to increase pH
« Reply #3 on: June 16, 2020, 01:40:56 PM »
Quote
But somebody told me this calculation is wrong because I have to consider that H2SO4 is diprotic.
This "somebody" was right.
You should use K2 of sulfuric acid.
AWK