Please help!!! 1. A buffer solution is 1.50 M in HF and 1.20 M in NaF. If 0.110
ID: 809412 • Letter: P
Question
Please help!!!
1. A buffer solution is 1.50 M in HF and 1.20 M in NaF. If 0.110 moles of HCl are added to 1.00 L of the buffer, what is its pH? Assume the volume remains constant. Ka of HF = 7.2 ? 10-4.
2. A buffer solution is 1.10 M in HF and 1.20 M in NaF. If 0.210 moles of NaOH are added to 1.00 L of the buffer, what is its pH? Assume the volume remains constant. Ka of HF = 7.2 ? 10-4.
3. Find the pH of a buffer that consists of 0.54 M methylamine (CH3NH2) and 0.73 M CH3NH3Cl (pKb of methylamine (CH3NH2 = 3.35).
Explanation / Answer
1) pH = pKa + log[salt/acid]
on addition fo 0.11 M/lit acid to this buffer salt con decrease acid conc increase
pH = pKa + log[salt-C/acid+C]
= 3.14 +log [1.2-0.11/1.1+0.11]
=3.09
pH decrease
2) on addition of base to acidic buffer acid conc decrease and salt conc increase
pH = pKa + log[salt+C/acid-C]
=3.14 + log[salt+C/acid-C]
= 3.14 + log[1.2+0.21/1.1-0.21]
= 3.33
pH increase
3) pOH = pKb + log [salt/base]
= 3.35 + log (0.73/0.54)
=3.48
pH = 14- pOH
= 10.52