1. The initial pH can be calculated using the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
First, calculate the initial concentration of HF and NaF after mixing:
- Initial moles HF: (0.3 mol/L) x 0.05 L = 0.015 mol
- Initial moles NaOH: (0 mol/L) x 0 L = 0 mol
Next, calculate the moles of NaF and HF after reacting with NaOH:
- Moles NaOH added: (0.3 mol/L) x 0 L = 0 mol
- Moles NaOH reacted: (0 mol + 0.3 mol/L x 0.01 L) = 0.003 mol
- Moles NaOH remaining: 0.015 mol - 0.003 mol = 0.012 mol
- Moles NaF: 0.003 mol
Now, calculate the concentrations of HF and NaF after reacting with NaOH:
- HF concentration: (0.015 mol - 0.003 mol) / (0.05 L + 0.01 L) = 0.24 mol/L
- NaF concentration: (0.003 mol) / (0.05 L + 0.01 L) = 0.048 mol/L
Lastly, calculate the pH using the Henderson-Hasselbalch equation:
pH = -log(6.6x10^-4) + log(0.048/0.24) = 3.07
2. After adding 10 mL of 0.3 M NaOH:
- Moles NaOH added: (0.3 mol/L) x 0.01 L = 0.003 mol
- Moles NaOH reacted: (0.003 mol) = 0.003 mol
- Moles NaOH remaining: 0.012 mol - 0.003 mol = 0.009 mol
- Moles NaF: 0.003 mol
- HF concentration: (0.015 mol - 0.003 mol) / (0.05 L + 0.01 L) = 0.24 mol/L
- NaF concentration: (0.003 mol) / (0.05 L + 0.01 L) = 0.048 mol/L
- pH = -log(6.6x10^-4) + log(0.048/0.24) = 3.07
3. After adding 25 mL of 0.3 M NaOH:
- Proceed with the same calculations as above to determine the pH
4. After adding 50 mL of 0.3 M NaOH:
- Proceed with the same calculations as above to determine the pH
5. After adding 50 mL of 0.4 M NaOH:
- Proceed with the same calculations as above, but utilize the new NaOH concentration to determine the pH.
Find the pH at each of the following points in the titration of 50 mL of 0.3 M HF with 0.3 M NaOH. The ka value is 6.6×10−4 .
1. The initial pH
2. After adding 10 mL of 0.3 M NaOH
3. After adding 25 mL of 0.3 M NaOH
4. After adding 50 mL of 0.3 M NaOH
5. After adding 50 mL of 0.4 M NaOH
1 answer