5g of AuBr3 (Ksp = 4.0 x 10^-36) are placed in 25 ml of water, how many grams of Au ions are dissolved in the 25 ml? My instructor used the conversion factor (6.2 x 10^-10 mol Au ions) to get from 25 ml H2O to grams Au. I believe the conversion from ml of H2O to grams of Au is: 25ml H2O x (6.2 x10^-10 mol Au / 1000ml) (197 g Au / 1 mol Au) = 3.05 x 10^-9 g Au. I'm confused about the conversion factor 6.2 x 10^-10 though, can anyone explain to me where this number comes from? Thank you.