1. An aqueous solution contains 0.350 M nitrous acid. How many mL of 0.391 M sodium hydroxide would have to be added to 250 mL of this solution in

1. An aqueous solution contains 0.350 M nitrous acid.  

How many mL of 0.391 M sodium hydroxide would have to be added to 250 mL of this solution in order to prepare a buffer with a pH of 3.320?

2. How many grams of solid ammonium chloride should be added to 2.00 L of a 0.272 M ammonia solution to prepare a buffer with a pH of 8.710 ?  3. How many grams of solid potassium nitrite should be added to 0.500 L of a 0.222 M nitrous acid solution to prepare a buffer with a pH of 2.442 ? 

It's due within 10 minutes can anyone help?