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# Out-of-class Assignment #6

1. Write mass and charge balances for each of the following solutions.
1. 0.05 mole of ammonium chloride diluted to 500 mL with water.
2. 0.020 mole of ammonium chloride and 0.010 mole of HCl diluted to 250 mL with water.
3. 0.03 mole of potassium hydrogen phthalate and 0.01 mole of sodium hydroxide diluted to 500 mL with water.
4. 0.010 mole of sodium dihydrogen phosphate diluted to 1.0 liter with water.
2. Will a precipitate form if 25 ml of 0.010 M silver(I)nitrate is mixed with 25 ml of 0.0010 M sodium phosphate and the pH is adjusted to 5?
3. One way to separate two substances is to selectively precipitate one in the presence of the other.  Is it possible to selectively precipitate 99.9% of one or more (you could potentially precipitate one ion, filter it off, and then precipitate another) of Cu(II), Pb(II), and Tl(I) as their sulfide salts?  The salts will be precipitated by adding a solution of sodium sulfide.  The concentrations of the metal ions in the initial solution are all 0.050 M.
4. Calculate the solubility of silver arsenate in a solution buffered at pH 6.The buffered solution to which the silver arsenate is added also contains potassium iodide at a concentration of 0.10 M.

NOTE: Silver ion is capable of forming soluble complexes with two different ligands in this problem.

NOTE: Silver ion can also form a precipitate with iodide.

5. Calculate the concentration of all copper species in a solution prepared by mixing 25 mL of 0.020 M copper(II)nitrate with 25 mL of 0.20 M salicylic acid (the complex that forms in this case is somewhat unusual in that it occurs with the HA- form of the ligand).The final solution is buffered at pH 3.