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Question

What is meant by chemical formula? Calculate the number of aluminium ions present in 0.051 g of aluminium oxide.
(Hint: The mass of an ion is the same as that of an atom of the same element. Atomic mass of Al = 27 u)
[5 MARKS]


Solution

Each point: 1 Mark

1. The chemical formula of a compound is a symbolic representation of its composition.

2. Mole of aluminium oxide (Al2O3) = 2 x 27 + 3 x 16

= 102 g

3. i.e., 102 g of Al2O3= 6.022 x 1023 molecules of Al2O3

4. Then, 0.051 g of Al2O3 contains = 6.022×1023102×0.051 molecules

= 3.011 x 1020 molecules of Al2O3

5. The number of aluminium ions ((Al3+) present in one molecule of aluminium oxide is 2.

Therefore, the number of aluminium ions (Al3+) present in 3.011 x 1020 molecules (0.051 g ) of aluminium oxide (Al2O3) = 2 x 3.011 x 1020

= 6.022 x 1020


Chemistry

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