Which has the higher concentration of Cl- ion?

What is the Cl ion concentration in a solution obtained by mixing 200mL of 0.605M KCl and 620mL of 0.395M MgCl?

• Assuming the volumes are additive. Need this answered before Monday September 22nd, 2008.

• Answer:

  First, I have to correct the second chemical compound: it is MgCl2 (important to the moles of Cl!!! The moles of Cl from KCl are just the volume times the molarity = 0.200 L x 0.605 mole/L = 0.121 The moles of Cl from MgCl2 are the volume times the molarity times 2 mole Cl/mole MgCl2 =0.620 L x 0.395 M x 2 = 0.490 The total volume is 820 mL = 0.820L, so Final Cl- concentration is (0.121 + 0.490)/0.820 = 0.745 M. In case your teacher is a stickler for significant figures, you may have to reduce the number of decimal places. Since the 200 mL is really only one sig fig, its initial product could strictly be 0.1, etc., leading to an answer of 0.7 M. You might want to report both, letting your teacher know that you understand sig figs, in addition to how to solve this problem! Hope this helped!