Question

Question #fc060

Answer 1

The energy required to separate the ion pair = `4.297xx10^(-19)"J"`

I have assumed a copper(II) ion and an electrostatic model.

Explanation:

For 2 charges `q_1` and `q_2` separated by a distance `r` the force of attraction is given by Coulomb's Law:

`F=(1)/(4piepsilon_0).(q_1q_2)/(r^2)`

The constant `(1)/(4piepsilon_0)` can be written as `k` and has the value `9xx10^(9)"m/F"`

The work done in separating the 2 charges from `r` to infinity is given by:

`W=-k.(q_1q_2)/(r) " "color(red)((1))`

I will assume a wholly electrostatic model where we have discrete ions in contact.

The ionic radii are:

`r^+=87"pm"` for `Cu^(2+)`

`r^(-)=126"pm"` for `O^(2-)`

This means the total distance between the centre of the 2 ions is:

`126+87=213"pm"=r`

The electronic charge = `-1.602xx10^(-19)"C"`

So the charge on the `Cu^(2+)` ion =

`+2(1.602xx10^(-19))=+3.204xx10^(-19)"C"`

The charge on the `O^(2-)` must therefore be:

`-3.204xx10^(-19)"C"`

Putting these values into `color(red)((1))rArr`

`W=-(9xx10^(9)xx(3.204xx10^(-19))xx(-3.204xx10^(-19)))/(215xx10^(-12))color(white)(x)J`

`W=4.297xx10^(-19)"J"`