Chemistry
posted by Bradley .
How many milliliters of 0.0850 M Na3PO4(aq) will react with 22.00 mL of 0.0800 M MgCl2(aq)?
3 MgCl2(aq) + 2 Na3PO4(aq) ==> Mg3(PO4)2(s) + 6 NaCl(aq)
V x M = V x M
(22.00mL)(0.0800M) = (0.0850M)(x)
Is this the correct setup? Does it have 4 sigfigs, or am I wrong?

No. V x M = V x M works ONLY when the reactions coefficients are the same; i.e., 1:1, 2:2 etc.
How many moles MgCl2 do you have? That is M x L = ?moles MgCl2.
Now, using the coefficients in the balanced equation, convert moles MgCl2 to moles Na3PO4.
moles Na3PO4 = ?moles MgCl2 x (2 moles Na3PO4/3 moles MgCl2) = xmoles Na3PO4.
Finally, M Na3PO4 = moles Na3PO4/L Na3PO4. YOu have moles and M, solve for L, then convert to mL. 
Thank you SO much.
Not only did you help me get the correct answer, but you helped increase my understanding of these problems.
Cheers to you. 
what does the 'M' mean?