Calculate the minimum concentration of mg2+ that mustbe added to 0.10 m naf in order to initiate a precipitate ofmagnesium fluoride. (for mgf2, ksp = 6.9 x10-9.)a. 1.4 x 107m
b. 6.9 x 10-9m
c. 6.9x 10-8 md. 1.7 x 10-7m
e. 6.9 x 10-7 m

E. 6.9 E-7 M

Explanation:

      0.10M   0.10M    0.10M

eq:     S             S          2S + 0.1

∴ Ksp = 6.9 E-9 = [Mg2+][F-]² = (S)(2S+0.1)²

if we compared the concentration ( 0.1 M ) with the Ksp ( 6.9 E-9 ); then we can neglect the solubility as adding:

⇒ Ksp = 6.9 E-9 = (S)(0.1)² = 0.01S

⇒ S = 6.9 E-9 / 0.01 = 6.9 E-7 M

it's c. elements are placed in rows based on how may valencies electrons have.