Question

What NaCl concentration results when 209 mL of an 0.660 M NaCl solution is mixed with 492 mL of a 0.270 M NaCl solution?

__ mol/.209 L = 0.660 M
__ mol/.492 L = 0.270 M

.. I have no idea how to solve this. I have no idea why I even set up the equation above when it's asking me to solve for molarity and not mols.. Do i just add 0.660 + 0.270 together since it's mixed together? Can it be that simple? Please help!

Answer 1

No, you can't add molarities but you can add mols. mols = M x L =
mols soln 1 = 0.209 x 0.660 = ?
mols soln 2 = 0.492 x 0.270 = ?
Total mols = mols soln 1 + mols soln 2.
Total volume = L soln 1 + L soln 2.
Then M NaCl = total mols/total L.

Answer 2

thanks Dr. Bob!