Question

Which statement about $Cr{O_5}$ wrong?
A.Oxidation number of $Cr$ in $Cr{O_5}$ is six
B.$Cr{O_5}$has butterfly structure
C.It has one oxygen atom attached with double bond with $Cr$ and four oxygen atoms attached with single bond with chromium
D.It has four peroxide bonds.

Answer 1

Hint: Chromium (VI) peroxide is an unstable compound with a molecular formula $Cr{O_5}$ . It is a good oxidising agent and oxidizes ketones and primary alcohols to aldehydes and carboxylic acids. It forms a butterfly structure due to one double bonded oxygen atom and four single bonded oxygen atoms.

Complete answer:
Chromium (VI) peroxide has a molecular formula of $Cr{O_5}$ and is a very unstable compound that decomposes even when left undisturbed to form $Cr{O_3}$ . $Cr{O_5}$ is a very good oxidizing agent as it has two reactive peroxo ligands and it oxidizes ketones and primary alcohols to form aldehydes and carboxylic acids while it itself is reduced to $C{r^{3 + }}$ . But due to its unstable behaviour, the peroxo ligands do not participate in organic reactions. $Cr$ is hard metal which is used in alloys to increase strength and corrosion resistance.
Let x be the oxidation number of $Cr$ in $Cr{O_5}$
We know that the sum of all the oxidation states of the elements present in a compound are neutral and equal to zero. Therefore,
We know that in $Cr{O_5}$
$ \Rightarrow 0 = x + ( - 2) + 4( - 1)$
$ \Rightarrow x = + 6$
Thus, the oxidation state of $Cr$ in $Cr{O_5}$ is +6
$Cr{O_5}$ has a butterfly structure as it has one oxygen atom double bonded to $Cr$ and four oxygen atoms single bonded to $Cr$ and it has two peroxide bonds. Due to the attraction and angle between the different atoms and bonds $Cr{O_5}$ has a butterfly structure.
Thus, according to the given question, $Cr{O_5}$ does not have four peroxide bonds and

Therefore, The answer is option (D).

Note: Chromium is abundantly present in Earth’s crust. Chromium is added to iron and nickel and they form ferrochromium which is used to make alloys with high resistance to corrosion and oxidation. Stainless steel is also an alloy of chromium and iron and chromium is also used to harden steel.