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help with chemistry! [Solved]

blue powderblue powder Registered User regular
edited February 2008 in Help / Advice Forum
Hey guys, i've come here for help wiht physics and the like before and you've all been great so I thought it'd be okay to post here again. I'm starting a chemistry course next week at uni and i've been doing some study to be prepared.

I'm not sure what's going on here, I think i'm right and there mite be a typo in the question.. The question is:

5.50g of a compund of mercury and chlorine contained 4.67g mercury. Calculate the empirical formula. The molecular weight was found to be 470. Calculate the molecular formula.

So I started off...

Hg 4.67g

Cl 0.83g

then i divided the respective percentages by the atomic masses which got me 0.42 Hg and 0.42 Cl, which would be one part Mercury and one part Chlorine. But this is confusing as the quesitons states they have a molecular mass of 470amu. But this only gets me a mass of 236.04. I'm really confused and feel i've taken a wrong turn somewhere, so if you guys could shine any light on this i'd be really greatful, thanks in advance!

blue powder on

Posts

  • blue powderblue powder Registered User regular
    edited February 2008
    Oh shit, I just read through this and realised, do i just need to adjust the formula so that it's Hg2Cl2 (the 2's should be sub script). That's right isn't it?

    blue powder on
  • Dark MoonDark Moon Registered User regular
    edited February 2008
    To go from empirical formula to molecular formula you take the molecular weight given and divide by the hypothetical weight of the compound you have calculated the formula for. Whatever this works out to is a multiplier with which you multiply all the subscripts in your empirical formula.

    This is required because the initial data gives you only enough information to determine the ratios within the formula, meaning that what is in reality a 2:2 ratio will look the same as a 1:1 ratio when you're working with the first bit of info. In this case, 470/236~2, so your molecular formula would be Hg2Cl2.

    Edit: Yup.

    Dark Moon on
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  • blue powderblue powder Registered User regular
    edited February 2008
    Awesome, thanks for the response, man!

    blue powder on
  • PlutoniumPlutonium Registered User regular
    edited February 2008
    Also, quick tip:

    Mercury ions come in two oxidation states: Hg(I) and Hg(II), also known as mercurous or mercuric.

    The tricky part is that Hg(I) actually means Hg22+, while Hg(II) is just Hg2+

    So yeah, it always comes with a charge of 2, though on the Hg(I), it's in fact an atom with a charge of 1+ that's always diatomic.

    Plutonium on
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