Question

Calculate the mass of gold(III) chloride (Au,C16) that contains a million (1.000 x 10°) gold atoms. Be sure your answer has a unit symbol if necessary, and round it to 4 significant digits. x I ?

Answer 1

1 molecule of Au2Cl6 has 2 atoms of Au

So,
Number of Au2Cl6 = number of Au / 2
= (1.000*10^6) / 2
= 5.000*10^5

use:
number of mol = number of molecules / Avogadro’s number
number of mol = 5*10^5 / 6.022*10^23 mol
number of mol = 8.303*10^-19 mol

Molar mass of Au2Cl6,
MM = 2*MM(Au) + 6*MM(Cl)
= 2*197.0 + 6*35.45
= 606.7 g/mol

use:
mass of Au2Cl6,
m = number of mol * molar mass
= 8.303*10^-19 mol * 6.067*10^2 g/mol
= 5.037*10^-16 g
Answer: 5.037*10^-16 g