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Chemistry!!
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phoebe_ka
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Joined: 15/12/2008 - 18:28
Posts: 2
Chemistry!!
phoebe_ka
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Joined: 15/12/2008 - 18:28
Posts: 2
Chemistry!!

Does anyone know a good way how they can remember all the moles equations?? This is for the ocr exam in jan 2009!

chemistrysubjec...
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Joined: 10/06/2007 - 22:31
Posts: 347

If you mean things like

No of moles = mass / Mr and that sort of thing, my advice would be to try to understand what the equation is trying to do. Learn the basic definition and then think...

eg The Relative formula mass of a substance (sometimes shortened to Mr or RFM) is the number of grams you need for one mole.

So... for CaCO3, Mr = 100

If I have 12g of CaCO3, how many moles do I have.

Well, 1/100 of a mole would be 1g so 12g must be 12/100 ths of a mole.

This is quite easy with CaCO3 because of the rfm = 100, but what about with NaCl (58.5)? Can we find how many moles are in 26.875 g?

Use the same idea...58.5 g is one mole and so 1g is 1/58.5 moles.

But we want 26.875g so it must be 26.875 / 58.5 moles.

If this helps, good. If not, get back on the discussion page and give some specific problems and I will try to help you.