Question

How many electrons are in 0.990 oz of a pure gold coin?

Answer 1

Atomic number of gold,
`Au` = 79 means there are 79 electrons in per atom of gold.

Atomic mass of gold = 196.967 gm

0.990 oz of gold is given.

Now, converting
`oz to gm`

`1 oz = 28.3495 gm`

So,
`0.990 oz = 0.990* 28.3495 gm = 28.066 gm`

Now, for determining the number of moles, the formula for number of moles is:

`number of moles = (given mass)/(Molar mass)`

Substituting the values:

`number of moles = (28.066)/(196.967) = 0.1425 mole`

1 mole of
`Au = 6.022* 10^(23) atoms of Au`

So, for 0.1425 mole of
`Au = 6.022* 10^(23)* 0.1425 atoms of Au = 0.8581 * 10^(23) atoms of Au`

Since 1 atom of gold has 79 electrons so,

Number of electrons =
`0.8581 * 10^(23)* 79 = 67.7899* 10^(23) electrons`

So, number of electrons in 0.990 oz of pure gold coin is
`67.7899* 10^(23)`.