December 01, 2021, 12:42:10 AM
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### Topic: Concentration of HBr solution whose pH is < 0 (how do you measure negative pH?)  (Read 325 times)

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#### Monoamine

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##### Concentration of HBr solution whose pH is < 0 (how do you measure negative pH?)
« on: March 22, 2021, 04:01:15 AM »
Hi, so I made this solution of HBr, but its pH is less than 0 (tested ectronically and with pH strips). So then how am I supposed to determine the concentration of the HBr solution? (I was going to calculate the HBr concentration from its pH...

One thing I was thinking was to take a small amount of the solution and add known quantities of NaOH to it until its pH is = 7. I think that would mean that there are the same amount of moles of HBr in the solution as moles of Na. This would give me a mol/mL value of the HBr in solution.

From this I could also determine how pure the solution is, since once I know the HBr concentration, I could calculate how the solution should weigh, and if it matches up, then this would suggest that the HBr solution is pure and doesn't contain residual H2SO4 or something...

Would this work? Or is there a simpler way of doing this?

Cheers.

#### Borek

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##### Re: Concentration of HBr solution whose pH is < 0 (how do you measure negative pH?)
« Reply #1 on: March 22, 2021, 06:06:02 AM »
pH is a very poor measure of the acid concentration.

Simple titration with a base gives much more better results (which is more or less what you are thinking about doing): http://www.titrations.info/acid-base-titration

Checking the solution purity requires meticulous tests of contaminants, every other approach will give just an approximate answer which is typically useless.
ChemBuddy chemical calculators - stoichiometry, pH, concentration, buffer preparation, titrations.info, pH-meter.info

#### Monoamine

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##### Re: Concentration of HBr solution whose pH is < 0 (how do you measure negative pH?)
« Reply #2 on: March 22, 2021, 06:16:22 PM »
Thank you for the tip and for the link. I'll try to do it by titration in that case.