[newuser]

1. How many mL of 2.0 M HCl must be added to 1.00 L of a 0.100 M solution of sodium formate to produce a buffer with pH 4.00? (Ka formic acid = 1.9 × 10?4)

2. A solution is made by adding 25.0 mL of a 0.123 M solution of the weak base CH3NH2 to 35.0 mL of
a 0.213 M solution of HCl. What is the resulting pH?

3. What is the pH of a solution made by mixing 500 mL of 1.00 M HCN and 1.50 L of 0.250 M NaOH, and then diluting the entire solution to 3.00 L? (Ka HCN = 4.0 × 10?10)

[Borek]

Please read forum rules.

[newuser]

Thank you for sending me the rules of this forum...they were helpful, but how can I get the help with these questions...Is there any specific link on this forum and can you give me a good example of a good title instead of my title that I have had for this topic? Thank you again for help   

[Borek]

First of all - you have to try by yourself.

In case you have no idea where to start (your notes or course workbook are a good idea) visit pH calculation lectures. See the questions link in the left menu, there are some examples similar to questions you have posted.

[newuser]

thank you 

[english]

Start with the Henderson-Hasselbalch equation.