mass of aluminium in 306 gram of aluminim oxide Al2O3
a/ 81 gram
b/ 162 gram
c/ 200 gram
d/ 243 gram
and the reason please
Answers
Explanation:
1 mole of Al
2
O
3
=2×27+3×16
=102g
Moles of Al
2
O
3
=
102
0.051
=5×10
−4
moles
1 mole contains 6.02×10
23
molecules
∴5×10
−4
g of Al
2
O
3
contains = 5×10
−4
×6.02×10
23
=3.011×10
20
molecule
no. of Al
3+
ions in 1 molecules of Al
2
O
3
is 2.
∴ No. of aluminium ions will be:-
2×3.011×10
20
=6.022×10
20
.
Answer:
The molar mass of aluminium is 26.98 g/mol; the molar mass of (atomic) oxygen is 16.00 g/mol.
1 mole of Al₂O₃ therefore has a mass of 2(26.98) + 3(16.00) = 101.96 g.
Divide this into the given mass, to find the number of moles here:
(204 g)/(101.96 g/mol) = 2.001 mol.
There are 2 moles of aluminium per mole of aluminium oxide, so there are
2(2.001) = 4.002 moles of aluminium in the sample.
Then there are (4.002 mol)(26.98 g/mol) = 107.97 g of Al. Since the given mass has only 3 significant figures, round this answer to 108 g.
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