Homework Help: chemistry

Posted by dr bob's number one fan on Thursday, November 15, 2012 at 12:37am.

How to find moles given oxidation numbers and chemical formula?
Trying to do my chemistry lab but i'm super duper stuck. please help me i'm gonna die. this is the part i'm stuck on:

The overall charge on the complex, [Ni(en)(H2O)]^2+ * SO4^2- * H2O is zero; the charge on sulfate ion is 2-;en and water ligands both have a charge of zero; and nickel has a charge of 2+. Using this information and your previous experimental results, calculate the number of moles of SO4^2- in 100 grams of your complex and the mass percent of SO4^2- in your complex.

previous experimental results:
Molarity of Ni^2+ in unknown sample: 0.0647M
Moles of Ni^2+ in 100 g of complex: 0.475 moles
Mass % of Ni^2+ in complex: 27.86%

chemistry - DrBob222, Thursday, November 15, 2012 at 12:43am
From your formula there is 1 mol Ni in 1 mol of the complex AND 1 mol SO4; therefore, mols Ni from your experimental result in 100 g of complex = mols SO4^2- in 100 g commplex. Right?
And if mass %Ni is 27.86 then mass %SO4^2- is 27.86 x (molar mass SO4/atomic mass Ni) = ?
chemistry - dr bob's number one fan, Thursday, November 15, 2012 at 1:05am
thanks for answering! when we found the moles of en (ethylenediamine) in a previous step, it wasnt a 1 to 1 mole ratio with Ni, it was .283 moles in 100g of complex. i think we're supposed to use the oxidation numbers along with the moles of nickel to find the moles of SO4, but i'm not sure how to do that

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