pKa calculations for H2S

Hi Marvin developer,

while preparing student courses next week I found a severe bug in pKa calculation for hydrogen sulfide H2S.

1) The concentration in the basic region is up to 150 %, see attached screen shot.

And by the way some points more:

2) Please use semicolons to seperate more than one pKa values, see screen shot.

3) And delete the option "Decimal places - infinite". It cannot be "infinite" (and using it shows only 10 ) and exceeding 2 decimal places does not make any sense. How precise is the simulation Marvin uses ?

Best regards, Hans-Ulrich

Hi,

The "H2S" distribution bug fixed.

The fix will be available in the 5.11.5 version.

The "semicolon" and the "infinite" problem also will be fixed in the 5.11.5 version.

 

Thanks for reporting bugs.

Jozsi

Hi Joszi,

now I have a new problem: What is the meaning of the blue value "-8.97" ?

Blue means normally "pKa of the corresponding acid", but here ?

Best regards, Hans-Ulrich

Hi,

It means that  the cationic form "H₃S⁺ "  is present in the solution in fifty percent at  "pH = -8.97".

Jozsi

Hi Jozsi,

OK, it's meant as the basic pKa of H₂S. But in the display the order of the acids is:

H₂S - HS^- - H₃S⁺

This is not usable in student courses, it's illogical. It should be in the order:

H₃S⁺ - H₂S - HS^-

And in this context some more suggestions: Please change the default options of MarvinSketch for simulating pKa values as shown in the attached screenshot. We must set these options in each student course to reasonable values.

Best regards, Hans-Ulrich

Hi,

 

Ok, it is logical what you propose in respect of ordering the pKa values according to their "acidc" strength. We will do this changes. 

Changing of the default setting on the graphical user interface is also Ok. It will be available asap.

 

Jozsi

Hi Joszi,

these are very good news. I've changed the title of this topic.

Thank you.

Best regards, Hans-Ulrich