Why is K+ larger than Ca^2+?

HI- Why is the Qsp = [Ca2+][F-]^2 ... specifically, why is the [F-} raised to the 2nd power?

• If 30 mL of 5.0 x 10-4 M Ca(NO3)2 are added to 70 mL of 2.0 x 10-4 M NaF, will a precipitate occur? If 30 mL of 5.0 x 10-4 M Ca(NO3)2 are added to 70 mL of 2.0 x 10-4 M NaF, will a precipitate occur? (Ksp of CaF2 = 4.0 x 10-11) 1 year ago Report Abuse Dr.A Best Answer - Chosen by Voters moles Ca2+ = 0.030 L x 5.0 x 10^-4 M=1.5 x 10^-5 moles F- = 0.070 L x 2.0 x 10^-4 M=1.4 x 10^-5 total volume = 0.100 L [Ca2+]= 1.5 x 10^-5 / 0.100 L= 1.5 x 10^-4 M [F-]= 1.4 x 10^-5 / 0.100 L= 1.4 x 10^-4 M Qsp = [Ca2+][F-]^2 = 1.5 x 10^-4 x ( 1.4 x 10^-4)^2 = 2.9 x 10^-12 < Ksp precipitation sholud not occur

• Answer:

  When you combine Ca(NO3)2 and NaF together...the resulting molecule is CaF2. The NO3 and Na are spectator ions and do no participate in the final reaction equation. Well you might wonder why it is CaF2 instead of CaF and heres why. If you look at the molecule Ca(NO3)2...you can see that it is an ionic compound so the charges must have been switched...if you undo the switch you can conclude that Ca would have a charge of +2 and NO3 would have a charge of +1. Same thing with NaF...Na has charge of +1 and F has charge of +1. So now you can see....Ca has +2 and F has +1. Since you are combining them into an ionic compound...you must switch the signs again. It becomes CaF2. The 2 is from the ionic charge of Ca. This is actually a rather simple concept, but my explanation became a bit lengthy, my apologies.