How many moles of copper are present in a sample of tennantite with a mass of 2670 grams?
Answers
ANSWER
You know that one mole of tennantite contains
12
moles of copper, as given by the chemical formula of the ore
C
12
As
4
S
13
so the first thing to do here is to figure out how many moles of tennantite you have in that sample.
To do that, use the molar masses of copper, arsenic, and sulfur to find the molar mass of the ore. You will have
12
moles Cu
⋅
molar mass of Cu
63.546 g
1
mole Cu
=
762.552 g
→
from copper
4
moles As
⋅
molar mass of As
74.92 g
1
mole As
=
299.68 g
→
from arsenic
13
moles S
⋅
molar mass of S
32.065 g
1
mole S
=
416.845 g
→
from sulfur
The mass of one mole of tennantite, which is essentially what its molar mass is, will thus be
762.552 g
+
299.68 g
+
416.845 g
=
1479.08 g
Now that you know the mass of one mole of tennantite, use this to find how many moles you have in your sample
2450
g ore
⋅
1 mole ore
1479.08
g ore
=
1.6564 moles ore
Finally, use the fact that one mole of tennantite contains
12
moles of copper to find how many moles of copper it contains
1.6564
moles ore
⋅
12
a
moles Cu
1
mole ore
=
¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯¯
∣
∣
a
a
19.9 moles Cu
a
a
∣
∣
−−−−−−−−−−−−−−−−−
The answer is rounded to three sig figs.