Barrons SAT Subject Test Chemistry, 13th Edition

64. (E) Ksp = [Pb2+] [S2–]. Since [Pb2+] is given at 5.0 × 10–14 and because the

formula is a 1:1 ratio, the [S2–] must also be that value, the Ksp can be

calculated by

Ksp = [5.0 × 10–14] [5.0 × 10–14] = 25 × 10–28

Putting the answer in scientific notation, i.e., one digit to the left of the

decimal point in the first factor, the answer is 2.5 × 10–27.