Question

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 set-up? Does it have 4 sigfigs, or am I wrong?

Answer 1

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.

Answer 2

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.

Answer 3

what does the 'M' mean?