Chem homework help?

I need help with both of these questions and how to get the answers 

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    Lv 7
    4 weeks ago
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    3)

    4 Al(s) + 3 O₂(g) ⟶ 2 Al₂O₃(s)

    aluminum oxide Al₂O₃ :

    The charge of an aluminum ion is +3, and the charge of an oxygen ion is -2, so you need 2 Al³⁺ ions and 3 O²⁻ ions to balance the charges.

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    4)

    number of moles of silver in the sample:

    (7.55 g Ag) x (1 mole Ag / 107.87 g Ag) = 0.0700 mole Ag

    number of moles of sulfur in the sample:

    (1.12 g S) x (1 mole S / 32.07 g S) = 0.0350 mole S

    Find mole ratio by dividing each of those results by the smallest number of moles:

    Ag: (0.0700 / 0.0350) = 2

    S: (0.0350 / 0.0350) = 1

    empirical formula is Ag₂S

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