Should 25 ml of 0.15 M HCL solution be added to 250 mL of buffer solution containing 0.25M HF Ka-7.1 x 10, and 0.40 M NaF at a pH of 3.15 what is the new pH?
To find the new pH after adding the HCl solution, we need to calculate the change in concentration of H+ ions in the buffer solution. We can then use this change to determine the new pH using the Henderson-Hasselbalch equation.
1. Calculate the moles of HCl added:
Moles of HCl = volume of HCl (in L) * concentration of HCl (in M)
Moles of HCl = 0.025 L * 0.15 M = 0.00375 moles
2. Calculate the initial moles of HF and NaF in the buffer solution:
Moles of HF = volume of buffer solution (in L) * concentration of HF (in M)
Moles of HF = 0.25 L * 0.25 M = 0.0625 moles
Moles of NaF = volume of buffer solution (in L) * concentration of NaF (in M)
Moles of NaF = 0.25 L * 0.40 M = 0.1 moles
3. Determine the change in moles of HF and NaF due to the reaction with HCl:
Moles of HF remaining = initial moles of HF - moles of HCl
Moles of HF remaining = 0.0625 moles - 0.00375 moles = 0.05875 moles
Moles of NaF remaining = initial moles of NaF
Moles of NaF remaining = 0.1 moles
4. Calculate the new concentration of HF and NaF in the buffer solution:
New concentration of HF = moles of HF remaining / volume of buffer solution (in L)
New concentration of HF = 0.05875 moles / 0.25 L = 0.235 M
New concentration of NaF = moles of NaF remaining / volume of buffer solution (in L)
New concentration of NaF = 0.1 moles / 0.25 L = 0.4 M
5. Calculate the new pH using the Henderson-Hasselbalch equation:
pH = pKa + log10([A-] / [HA])
Where:
- pKa is the logarithmic constant for the weak acid (HF), which is -log10(Ka) = -log10(7.1 x 10^-4)
- [A-] is the concentration of the conjugate base (F-) = 0.4 M (new concentration of NaF)
- [HA] is the concentration of the weak acid (HF) = 0.235 M (new concentration of HF)
Calculate the new pH:
pH = -log10(7.1 x 10^-4) + log10(0.4 / 0.235)
By plugging in the numbers, you can calculate the new pH using the equation.