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26 July, 16:05

Al2O3 occurs in nature as a mineral called corundum, which is noted for its hardness and resistance to attack by acids. Its density is 3.970 g cm-3. Calculate the number of atoms of Al in 25.00 cm3 of this mineral.

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  1. 26 July, 16:21
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    1.17*10²⁴ atoms of Al

    Explanation:

    Compound: Aluminum oxide (Al₂O₃)

    Molar mass = 101.96 g/mol

    Density of compound = 3.970 g/cm³ = Mass of compound / Volume of compound

    Density. volume = mass → 3.970 g/cm³. 25 cm³ = 99.25 g

    Let's make this relation

    1 mol of Al₂O₃ has 2 moles of Al and 3 moles of O it is the same to say that:

    101.96 g of Al₂O₃ has 2 moles of Al and 3 moles of O

    Our mass of Al₂O₃ is 99.25 g so let's make a rule of three:

    101.96 g of Al₂O₃ have 2 moles of Al

    Then, 99.25 g of Al₂O₃ must have (99.25 g. 2) / 101.96g = 1.95 moles of Al

    Let's count the atoms:

    1.95 moles of Al. 6.02*10²³ atoms / 1 mol = 1.17*10²⁴ atoms of Al
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