Question

3. A solution containing sodium fluoride is mixed with one containing calcium nitrate to form a solution that is 0.015 M in NaF and 0.010 M in Ca(NO₃)₂.

Ksp (CaF₂)= 1.46 x 10 ^-10

Does a precipitate form in the mixed solution? If so, identify the precipitate.

Please show the steps to reaching the solution or why it is so. Thank you.

Answer 1

molarity of [F-] from NaF = 0.015 M

molarity of Ca+2 from Ca(NO3)2 = 0.010 M

CaF2---------------> Ca+2 + 2F-

Q = [Ca+2] [F-]^2

Q = (0.010) (0.015)^2

Q = 2.25 x 10^-6

Ksp value is given

Ksp = 1.46 x 10^-10

Q > Ksp . so there will be precipitate formed

the precipitate = CaF2

note :

1) if Q > Ksp --------------> precipitate will form

2) if Q < Ksp ------------> no precipitate

3) if Q = Ksp -------------> saturated solution and ready to form precipitate