Asked by Kim K

How many grams of Au2S can be obtained from 1017 mol of Au? The answer is 249. How did they get that?
Answered by bobpursley
I don't know how they got that, there could have been a number of ways. One way is to find the percent of Au in Au2S

percentAu= atomicmassAu/molemassAu2S


Then, 1017moleAu/percentAu * atomicmassAu/1 mole

Answered by Dr Russ
I must admit that I didn't understand the question and had to work it backwards.

Start from a balanced equation

2Au + S -> Au2S

if we are starting with 1.17 mol Au (rather than 1017 mol Au which is rather a lot!)

then as 2 moles of Au give 1 mole of Au2S from the equation, 1.17 mol Au will yield 0.585 mol Au2S.

The molar mass for Au2S is 426 g mol^-1, then the mass obtained is

0.585 mol^-1 x 426 g mol^-1 = 249 g




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