Answer:
You are on the right track.
Explanation:
Indeed, your approach here will be to use the molar mass of aluminium hydroxide to convert the mass of the sample to moles and the mole ratio that exists between the two reactants to find the number of moles of hydrochloric acid consumed.
Al
(
OH
)
3
(
s
)
+
3
HCl
(
a
q
)
→
AlCl
3
(
a
q
)
+
3
H
2
O
(
l
)
The balanced chemical equation tells you that the reaction consumes
3
moles of hydrochloric acid and produces
3
moles of water for every
1
mole of aluminium hydroxide that takes part in the reaction.
So you can say that you have
0.75
g
⋅
the molar mass of Al
(
OH
)
3
1 mole Al
(
OH
)
3
78
g
⋅
the 1:3 mole ratio
3 moles HCl
1
mole Al
(
OH
)
3
=
0.029 moles HCl
−−−−−−−−−−−−−−
Since you know that the reaction produces the same number of moles of water as the number of moles of hydrochloric acid it consumes--the two chemical species have a
3
:
3
mole ratio in the balanced chemical equation--you can use the molar mass of water to say that the reaction will produce
0.029
moles H
2
O
⋅
18.015 g
1
mole H
2
O
=
0.52 g
−−−−−
The answers are rounded to two sig figs, the number of sig figs you have for the mass of aluminium hydroxide.
Explanation:
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