Calculate the valence of gold in a compound that contains 64.9% gold and 35.1% chlorine.

Given:

w% (Au) = 64.9%

w% (Cl) = 35.1%

To find:

Formula -?

Valence of gold -?

Decision:

1) Find the molecular weight of the compound using the following formula:

w% (element) = Ar (element): Mr (substance), where Ar is the relative atomic mass of the element, then:

Mr (substance) = Ar (element): w% (element), – let’s take the gold data into account:

Mr (substances) = 127: 0.649 = 195.7

2) Knowing the mass fraction of gold, we find its molecular weight in the composition and the number of atoms:

195.7 – 100%

x – 64.9%,

then x = 64.9% * 195.7: 100% = 127.

N (Au) = 127: Mr (Au) = 127: 127 = 1 atom

3) Then the molecular weight of chlorine accounts for 195.7 – 127 = 68.7

N (Cl) = 68.7: Mr (Cl) = 68.7: 35.5 = ~ 2 atoms.

We got a substance with the formula AuCl2. Since the chlorine ion has a charge of -1, and in the gold chloride compound there are 2 chlorine ions, then the valence of gold is 2.

Answer: gold in gold chloride is in a bivalent state.