[herrhansen]

Hello everybody.

I have a really easy general question about Tris-HCl buffers. I found the outcome odd, but its probably a stupidity from my side 

Today one of my collegues should prepare a Tris HCl buffer by first taking around 11 kg of Tris and dissolve it in around 30 kg of water. The pH should then be adjusted to pH 3.4 or something similar. It should be done with 10 kg HCl 10 % approximatly.

After 5 kg 10 % HCl the pH fell quickly down to 3 or similar. I know for buffers I have to use the Henderson Hasselbalch equation, but viewing this from a normal neutralization reaction I cant see how an amount this small could neutralize 11 kg Tris.

11 kg tris is 90 moles (11.000 g/ 121 g/mol = 91 moles)

91 moles of HCl: 91 moles x 35 g/mol = 3185 g

10 % HCl = 100 g/l

3185 g /100 g/l = 31 l

In this assumption the pH should first drop after the titration point and would then fall quickly.

Am I totally viewing this wrong? Know there is a bit roundoffs as this is a quick calculation.

Thanks in advance.

[Borek]

Strange things you are saying.

Adding 1 kg of HCl to 11 kg of TRIS will give solution with pH around 8.4. No way it could go down to pH 3.

Perhaps when you write 3 you mean 8, and when you write 3.4 you mean 8.4?

If so, the obvious answer is that your colleague added not 10% HCl, but stock solution (around 36%). That would move pH much further down. Then, it is always the simplest approach to blame someone else

[herrhansen]

Thx for answering. I was totally wrong. But I did not blame somebody else though, but since it wasnt me watching the pH meter the confusion came. I just heard wrong. So I couldnt see how that was possible.

Thx.