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    A has percentage composition by mass, 43.7% of P and 56.3% of O
    Mr is 284


    Mark scheme

    P : O = 43.7/31 : 56.3/16 / 1.41 : 3.52
    Ratio P:O = 2 : 5 / Empirical formula = P2O5
    Molecular formula = P4O10 (from Mr value)
    Ca3(PO4)29

    I get the answer 1.41 : 3.52
    But Where has the 2:5 come from?
    I know you divide by the smallest value, but when I do that, I get
    1.41/1.41 = 1 and 3.52/1.42 = 2.3
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    (Original post by ILoveUSA)
    Question
    A has percentage composition by mass, 43.7% of P and 56.3% of O
    Mr is 284


    Mark scheme

    P : O = 43.7/31 : 56.3/16 / 1.41 : 3.52
    Ratio P:O = 2 : 5 / Empirical formula = P2O5
    Molecular formula = P4O10 (from Mr value)
    Ca3(PO4)29

    I get the answer 1.41 : 3.52
    But Where has the 2:5 come from?
    I know you divide by the smallest value, but when I do that, I get
    1.41/1.41 = 1 and 3.52/1.42 = 2.3
    3.52/1.41 = 2.496
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    (Original post by charco)
    3.52/1.41 = 2.496
    That still doesn't give the 2:5 ratio, like the mark scheme has
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    (Original post by ILoveUSA)
    That still doesn't give the 2:5 ratio, like the mark scheme has
    It does. You have the ratio 1:2.49... which is essentially, 1:2.5

    Multiply by 2 and you get 2:5
 
 
 
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