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What are your mock exam revision tips?! Share them with our year 10 & 11 students! 19-11-2014
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    I dont understand the markscheme where i've put the part i don't understand in red.

    Specifically i dont get where 40 comes from?
    Click image for larger version. 

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    Thanks in advance .
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    Moles of H2O2 in 250cm3 diluted is the same as the moles of H2O2 in 25cm3 of the original undiluted.

    The 40 comes from calculating the concentration (in dm3) of the H2O2 in 25cm3 by dividing by 25/1000.
    Dividing by 25/1000 is of course the same as multiplying by 40.

    When you have conc in mol per dm3 you multiply by the molar mass to find the mass per dm3.
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    (Original post by Killjoy-)
    Moles of H2O2 in 250cm3 diluted is the same as the moles of H2O2 in 25cm3 of the original undiluted.

    The 40 comes from calculating the concentration (in dm3) of the H2O2 in 25cm3 by dividing by 25/1000.
    Dividing by 25/1000 is of course the same as multiplying by 40.

    When you have conc in mol per dm3 you multiply by the molar mass to find the mass per dm3.
    Oh i see how silly of me , thanks for your help .
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    (Original post by ch0wm4n)
    Oh i see how silly of me , thanks for your help .
    Is this OCR A? (Looks like it.)
    A lot of people have been talking about '40.'

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