urgent pls help

drset Question: 1. At what pH will a solution containing 0.020 M Hg+2 and 0.020 M Ni+2 have to be buffered at to selectively precipitate out the Ni-2 ions when saturated with Hys. Construct a plot that shows the entire range at which this ion can be precipitated based on the pH when saturated with H2S. (Hint, find the highest pH, lowest pH and somewhere in between and plot this against the % of precipitate that would form.)