Question

An alloy is 11.1% copper by mass in tin. Copper makes up what percentage of the atoms in this sample?

Answer 1

Answer 2

To solve this problem, we need to use the atomic masses of copper and tin, which are 63.55 g/mol and 118.71 g/mol, respectively.

Let's assume we have a 100 g sample of the alloy. Then, the mass of copper in the sample would be 11.1 g (since the alloy is 11.1% copper by mass).

We can now calculate the number of moles of copper in the sample:

moles of copper = mass of copper / atomic mass of copper moles of copper = 11.1 g / 63.55 g/mol moles of copper = 0.175 moles

Similarly, we can calculate the number of moles of tin in the sample:

moles of tin = (100 g - 11.1 g) / 118.71 g/mol moles of tin = 0.743 moles

The total number of atoms in the sample is equal to the sum of the number of atoms of copper and tin:

total number of atoms = (moles of copper x Avogadro's number) + (moles of tin x Avogadro's number) total number of atoms = (0.175 mol x 6.022 x 10^23/mol) + (0.743 mol x 6.022 x 10^23/mol) total number of atoms = 4.27 x 10^23

The percentage of atoms that are copper is given by:

percentage of atoms that are copper = (number of atoms of copper / total number of atoms) x 100% percentage of atoms that are copper = (0.175 mol x 6.022 x 10^23/mol / 4.27 x 10^23) x 100% percentage of atoms that are copper = 23.1%

Therefore, copper makes up 23.1% of the atoms in this alloy.