Question

How many cu atoms are present in a piece of sterlingsilver jewelry weighing 33.24 g ? (sterling silver is a silver–copper alloy containing 92.5% ag by mass.)?

Answer 1

The mass of piece of sterling silver jewelry is 33.24 g. It contains 92.5% silver Ag by mass. Since, sterling silver is an alloy of Ag-Cu thus, percentage of Cu will be:

% Cu=100-92.5=7.5%

Thus, mass of copper will be:

`m_(Cu)=(7.5)/(100)* 33.24 g=2.493 g`

Molar mass of Cu is 63.546 g/mol, thus, number of moles of Cu can be calculated as follows:

`n=(m)/(M)`

Here, m is mass and M is molar mass.

Putting the values,

`n=(2.493 g)/(63.546 g/mol)=0.03923 mol`

Now, in 1 mole of Cu there are
`6.303* 10^(23)atoms` thus, in 0.03923 mol, number of Cu atoms will be:

`0.03923 mol* 6.303* 10^(23)atoms=2.363* 10^(22) atoms`

Thus, number of atoms of Cu will be
`2.363* 10^(22) atoms`.