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For this I keep getting c Idid n(hcl) used=0.19606=n(MgO) and then c1v1=c2v2 to get n(MgO)*4*mm(MgO)/40.6
Where am i going wrong?

 

[Hhhduihsuid]

Did you rmb to balance your equation? It should be:
2HCl + MgO --> MgCl2 + H2O

So n(MgO) = 1/2 * n(HCl) used
= 1/2 * 0.19606mol
= 0.09803mol (instead of 0.19606mol which is what you got)

From there,
since n(MgO) in the 100mL aliquot = 0.09803mol,
then n(MgO) in the original 1L solution should be 0.9803 mol.
0.9803mol * (24.31+16.00)g/mol = 39.5...g
%MgO = 39.5../40.6 * 100%
= 97.3%
therefore D
Hope that helps

 

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ahh i forgot too lol thank you