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    I can't seem to work this out?
    Can someone guide me step by step?


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    (Original post by DatSmartGuy)
    I can't seem to work this out?
    Can someone guide me step by step?


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    Hey,

    Firstly you work out the moles which is mass divided by Mr

    So Fe: 6.21/207 = 0.03 moles
    Oxygen: 0.72/16 = 0.045 moles

    Therefore, you have a ratio of:
    0.03 : 0.045

    Then, you divide by the smallest number of moles - in this case you will divide both numbers by 0.03. Leaving you with:

    1 : 1.5

    You can't have 1.5 of an element so you X2 on the right to get a whole number of 3. But what you do on the right you do to the left. So you times 1 by 2 leaving you with:

    2 : 3

    Pb203 (the 2 & 3 are below the letters)


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    First, take the the experimental masses you are given:

    Oxygen - 0.72 grams, Lead - 6.21 grams

    Then, divide these by the relative atomic mass:

    0.72 divided by 16 = 0.045
    6.21 divided by 207 = 0.03

    Then, arrange them into a ratio:

    0.045:0.03, which is 45:30, which is 3:2

    So 3 Oxygen atoms and 2 Lead atoms.

    Make sure to put them into the right order, the formula asks for PbO, so the answer is Pb203 (2 and 3 should be small numbers)
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    DatSmartGuy


    1) For lead:
    6.21/207 = 0.03

    For oxygen:
    0.72/16 = 0.045

    2) Divide the values for these two by the smallest one:
    Lead: 0.03/0.03 = 1
    Oxygen: 0.045/0.03 = 1.5

    3) Pb2O3 - get this when you get the ratios into whole numbers.
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    Moles of Pb = 6.21/207 = 0.03 moles
    Moles of O = 0.72/16 = 0.045
    Divide by smallest = Divide both by 0.03

    0.03/0.03 = 1 Pb
    0.045/0.03 = 1.5 O
    However empirical formula is the smallest WHOLE NUMBER ratio of atoms of each element in a compound.
    Therefore multiply both by 2

    = 2 Pb and 3 O
    = Pb2O3
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    (Original post by z1820)
    Hey,

    Firstly you work out the moles which is mass divided by Mr

    So Fe: 6.21/207 = 0.03 moles
    Oxygen: 0.72/16 = 0.045 moles

    Therefore, you have a ratio of:
    0.03 : 0.045

    Then, you divide by the smallest number of moles - in this case you will divide both numbers by 0.03. Leaving you with:

    1 : 1.5

    You can't have 1.5 of an element so you X2 on the right to get a whole number of 3. But what you do on the right you do to the left. So you times 1 by 2 leaving you with:

    2 : 3

    Pb203 (the 2 & 3 are below the letters)


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    Thank you very much

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    Thank you to everyone that responded it really helped me out.

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