This problem is an example of a gram-to-gram stoichiometry problem. You are given the mass of
Al
Al
in grams and you are asked to find the mass of
Al
2
O
3
Al
2
O
3
in grams. For questions such as this, the strategy is to convert from grams of
Al
Al
to moles of
Al
Al
, then to moles of
Al
2
O
3
Al
2
O
3
, and finally to grams of
Al
2
O
3
Al
2
O
3
.
grams Al⟶moles Al⟶moles
Al
2
O
3
⟶grams
Al
2
O
3
grams
Al
⟶
moles
Al
⟶
moles
Al
2
O
3
⟶
grams
Al
2
O
3
To convert grams of
Al
Al
to moles of
Al
Al
, you use the molar mass of
Al
Al
,
26.98 g/mol
26.98
g/mol
. The balanced chemical equation is used to relate the moles of
Al
Al
to the moles of
Al
2
O
3
Al
2
O
3
. There are 2 moles of
Al
2
O
3
Al
2
O
3
formed for every 4 moles of
Al
Al
that react. To convert moles of
Al
2
O
3
Al
2
O
3
to grams of
Al
2
O
3
Al
2
O
3
, you use the molar mass of
Al
2
O
3
Al
2
O
3
,
101.96 g/mol
101.96
g/mol
. This can be done one conversion at a time, or you can string the conversions together.
30.6 g Al×
1 mole Al
26.98 g Al
×
2 moles
Al
2
O
3
4 moles Al
×
101.96 g
Al
2
O
3
1 mole
Al
2
O
3
=57.8 g
Al
2
O
3
Hopefully the picture will show up this time.