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Calculating Mr from density??

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    • Thread Starter

    Attachment 527339527341Name:  image.jpg
Views: 88
Size:  503.4 KBSo I've worked out what the precipitate is Fe(OH)3 but I don't get how to work out the gas is oxygen using a calculation?
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    (Original post by Puddles the Monkey)
    • Thread Starter

    Anyone pls

    You know that the density is 1.333x10^-3 grams for every cm^3.
    The mass can then be calculated by multiplying this by 24000 because 1 mol of gas occupies 24000cm3.
    This gives you 31.992g in 1 mol, or in other words 31.992g.mol^-1. This is the same units as Mr so it is very likely given the context that the gas is O2. (sorry dunno how to do subscripts etc lol)

    Okay, so you need to find the Mr to prove that the gas released is oxygen. You have the density which is 1.333*10-3, density is the mass over the volume right okay

    the gas is released at room temperature and pressure which means that number of moles= V of gas / 24000

    number of moles= mass/Mr , okay so mass= number of moles*Mr

    Substitute these two equations into the density formula, so denisty= (mass) number of moles*Mr / (volume) number of moles*24000, number of moles cancel each other so you're left with Mr/2400=density ................... so Mr/2400= 1.333*10-3 which equals 32 which equals the Mr of oxygen

    AqsaMx Heya, I've popped this in Chemistry for you
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