Question

What is the name of the compound with 77.3% silver, 7.4% phosphorous and 15.3% oxygen?

Answer 1

`"Silver phosphate"`, `Ag_3PO_4`.

Explanation:

As with all of these problems, we assume there are `100*g` of compound, and proceeed on this basis to derive the empirical formula by calculating the individual molar quantites. And given `100*g` of stuff, there are:

`"Moles of silver"=(77.3*g)/(107.9*g*mol^-1)=0.716*mol`

`"Moles of phosphorus"=(7.4*g)/(31.00*g*mol^-1)=0.239*mol`

`"Moles of oxygen"=(15.3*g)/(16.00*g*mol^-1)=0.956*mol`

For each element we have divided by the atomic mass of the given element to give a molar quantity of that element.

We now divide thru by the SMALLEST molar quantity, that of phosphorus:

`"Equivs of silver"` `=` `(0.716*mol)/(0.239*mol)` `=` `3`

`"Equivs of phosphorus"` `=` `(0.239*mol)/(0.239*mol)` `=` `1`

`"Equivs of oxygen"` `=` `(0.956*mol)/(0.239*mol)` `=` `4`

And thus the empirical formula, the simplest whole number ratio representing equivalent quantities in a species is:

`Ag_3PO_4`