Question

Chemistry question?

a) Draw Lewis structure for hydrogen peroxide, H2O2.
b) What is the weakest bond in hydrogen peroxide?
c) Hydrogen peroxide is sold commercially as an aqueous solution in brown bottles to protect it from light. Calculate the longest wavelength of light that has sufficient energy to break the weakest bond in hydrogen peroxide.

Answer 1

Here's what I get.

Explanation:

a) Lewis structure

You put the two `"O"` atoms in the centre, add an `"H"` atom to each `"O"`, distribute the 14 valence electrons to get the Lewis structure.

b) The weakest bond

The weakest bond in hydrogen peroxide is the `"O-O"` bond.

c) Longest wavelength to break the `"O-O"` bond

`"HO-OH" → "HO·" + "·OH"; ΔH = "142 kJ·mol"^"-1"`

This is the energy for 1 mol of molecules.

For 1 molecule,

`E = "142 000 J"/(1 color(red)(cancel(color(black)("mol")))) × (1 color(red)(cancel(color(black)("mol"))))/(6.022 × 10^23 "molecules") = 2.358 × 19^"-19"color(white)(l) "J"`

`E = (hc)/λ`, so

`λ = (hc)/E = (6.626 × 10^"-34" color(red)(cancel(color(black)("J·s"))) ×2.998 × 10^8 "m"·color(red)(cancel(color(black)("s"^"-1"))))/(2.358 × 19^"-19" color(red)(cancel(color(black)("J")))) = 8.42 × 10^"-7"color(white)(l) "m" = "842 nm"`

The longest wavelength that will break the `"O-O"` bond is 842 nm.