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5 September, 09:22

The compound XF3 containts 65% F (mass percentage). Mw (x) = ?

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  1. 5 September, 09:32
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    The compound XF3 has a molar mass of 87.7 g/mol

    The element x has an atomic mass of 30.7 u

    This element can be P (phosphorus) and the compound will be PF3

    Explanation:

    Step 1: Data given

    Compound XF3 has a mass % of 65% F

    Step 2:

    The sample has 65% mass percent, this is the ratio of the element (F) it's mass compared to the mass of the compound.

    (Mass of F / mass of compound) * 100% = 65 %

    Step 3: Calculate molar mass of the compound

    F has an atomic mass of 19u (Since there are 3x F the atomic mass is 3*19 = 57 u)

    The compound XF3 has a molar mass of (X+57) g/mol

    ⇒ with X = the molar mass of compound x

    Mass % of F = 65% = (3*19g/mol) / (X+57) g/mol

    0.65 = (57 / (X+57))

    57 = 0.65 * (X+57)

    57 = 0.65X + 37.05

    19.95 = 0.65X

    X = 30.7 g/mol

    This means the atomic mass of the element x is 30.7 u

    To control this we can calculate the mass % of F

    ((3*18) / (30.7 + 3*18)) * 100% = 65%

    The compound XF3 has a molar mass of 87.7 g/mol

    The element x has an atomic mass of 30.7 u

    This element can be P (phosphorus) and the compound will be PF3
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