I was doing a question in which we were required to find the oxidation state of $\ce{H3PO3}$. I knew the structure that is:

Phosphorous  acid

Now, phosphorus being less electronegative than oxygen gets $+2,+1,+1$ charge from respective oxygens. Now we see that in case of hydrogen, it is taught that phosphorus being more electronegative than hydrogen thus it gets $-1$ charge from it, and finally adding all the charges we get Oxidation state of Phosphorus $=+3$.

Now my doubt is that I found on the internet that hydrogen is more electronegative than phosphorus that is, electronegativity of hydrogen$=2.2$ whereas electronegativity of phosphorus$= 2.19$.

Therefore, phosphorus must get $+1$ from hydrogen thus oxidation state of phosphorus $=+5$ but I know this is wrong and the probable reason I could figure out is that hydrogen is more stable in $+1$ form. Therefore, oxidation state of phosphorus is $-1$.

Please tell me if this reason is correct or please add to it.

  • 6
    $\begingroup$ People usually tend to assume that hydrogen is less electronegative than phosphorus (at least for the purposes of this question), which makes the latter's oxidation state +3. Don't overthink it. They are all arbitrary anyway. $\endgroup$ Oct 10 '19 at 19:35
  • $\begingroup$ Generally we consider their electronegativity equal If you go in such depths then you will have a very hard time in thinking about oxidation states of phosphorus sulphur nitrogen in their oxy acids In competitive exams you need to remember all these structures as there are not any generalizations there $\endgroup$
    – Wake
    Oct 12 '19 at 15:47

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Browse other questions tagged or ask your own question.