3
$\begingroup$

I am in class 11th and I am having trouble solving the question.

Calculate the oxidation number of sulphur in $\ce{H2SO5}$?
(The answer is given as as $+6$.)

$\ce{H2SO5}$ exists it is named as "peroxy sulfuric acid".

How tried it: \begin{align} 2(+1) + 1(x) + 5(-2) &= 0\\ 2 + x - 10 &= 0\\ x&=\pm8 \end{align}

$\endgroup$
  • $\begingroup$ en.wikipedia.org/wiki/Peroxymonosulfuric_acid It has oxygen on higher ox state as all peroxyacids have $\endgroup$ – Mithoron Dec 13 '15 at 12:45
  • $\begingroup$ @hackwarewright Also called Caro's acid. $\endgroup$ – Pritt says Reinstate Monica May 12 '17 at 2:30
  • $\begingroup$ Structures are more important than chemical formulae while finding oxidation numbers of individual atoms. $\endgroup$ – Eashaan Godbole May 20 '19 at 14:34
  • $\begingroup$ Note that an oxidation number of $+8$ on $\ce{S}$ would require to open up the 2p shell, which does not happen for sulfur. $\endgroup$ – TAR86 May 20 '19 at 16:24
4
$\begingroup$

$\ce {H_2SO_5}$ has an oxygen-oxygen bond. This means that two of the five oxygen atoms have an oxidation number of $-1$. Same case as in $\ce{H2O2}$.

$$2\cdot (+1) + 1\cdot(x) + 3\cdot(-2) + 2\cdot (-1) = 0\\2 + x - 6 - 2 = 0\\ x = +6$$

You have 3 oxygens with oxidation number $-2$ and 2 oxygen atoms with $-1$.

|improve this answer|||||
$\endgroup$
1
$\begingroup$

$\ce{H2SO5}$ has the Lewis structure shown below: enter image description here It is possible to assign the oxidation # of each atom by considering the electronegativities of the two atoms involved in each bond and assigning the bonding electrons to the more electronegative atom in each case. Oxygen atoms 3 and 4 are bonded to each other, so the bonding electrons are assigned one to each atom.

After assigning bonding electrons to the more electronegative atom in each bond, splitting the O-O bonding electrons and assigning lone pair electrons to the atom they are on, the oxidation # of each atom is found by the following formula: $$ oxidation~number = group~number~of~element - assigned~electrons~in~the~structure$$ e.g. Oxygen 1: group # 6 (for oxygen) - assigned electrons 8 = -2 oxidation #

using these rules, the assigned oxidation #'s are:

Both H's: +1 each

Oxygens 1,2: -2 each

Oxygens 3,4: -1 each

S: +6

Note: there are no formal charges in the Lewis structure shown. There is another contributing form with single (dative) bonds to the two oxygens (# 2). This does not change the assigned oxidation numbers, but it does put 1- formal charges on the oxygens numbered 2, and a 2+ formal charge on the S.

|improve this answer|||||
$\endgroup$

Your Answer

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

Not the answer you're looking for? Browse other questions tagged or ask your own question.