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Mass of an element in a compound from its formula (percentage composition)

This type of question, asked 2 times: 15 May 2023 S1, 16 Apr 2026 S1. All 2 questions below, oldest first.

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  1. Question 1

    15 May 2023 S1

    52
    What is the percentage by mass of oxygen in NaOH? (Atomic mass of Na=23u, O=16u, H=1u)

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  2. Question 2

    16 Apr 2026 S1

    1
    Calculate the amount of aluminium present in Al2(SO4)3\mathrm{Al_2(SO_4)_3} if the compound contains 4 g of sulfur. [Molar mass of sulfur = 32 g/mol , Molar mass of Al =27 g/mol ]

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