1. You have a 0.087565 M solution of a weak acid, HA, pH=4.18177. How many grams of NaA (molar mass = 62.476 g/mol) would you have to add to this solution (assume that there is no change in volume) to have a solution with a pH of 7.40000. Would this new solution be a good buffer? Please explain.
2. You have a mixture of calcium nitrate and magnesium nitrate with each salt being 0.0575 M. To 100.00 ml of this solution you are going to add a 0.0125 M NaF. Which flouride will precipitate first (KspCaF2 = 3.2 x 10-11 and KspMgF2 = 7.4 x 10-9? How much NaF solution must you add to precipitate the least soluble flouride before there is a significant amount of the most soluble flouride precipitate? What will be the concentrations of Ca2+ and Mg2+ ions just as the most soluble flouride starts to precipitate?
You only have 100 ml of solution that I forgot to put in the problem. So you will need to determine the mass of NaA you will add to the 100 ml to get the desired pH.
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The solution is attached below ...
Solution clearly and comprehensively explains how to find out if a solution is a good buffer as well as concentration and determining if a significant amount of precipitate will emerge from a given solution. Attached as Word and PDF.