What is the pH of a buffer solution that is made by adding 21.0 grams of sodium fluoride to 1.00 Liter of 0.15M hydrofluoric acid? (see the Table above for the Ka of hydrofluoric acid; calculate the pH to 2 decimal places) hint: you will have to find the molarity of NaF in this solution.
Acid Dissociation Constant:
HF 6.6 x 10-4
To find the pH of the buffer solution, we first need to calculate the molarity of sodium fluoride (NaF) in the solution.
1. Calculate the moles of sodium fluoride:
Moles of NaF = Mass of NaF / Molar mass of NaF
The molar mass of NaF (sodium fluoride) is 22.99 g/mol for sodium (Na) + 18.99 g/mol for fluorine (F), which gives a total of 41.98 g/mol.
Moles of NaF = 21.0 g / 41.98 g/mol
2. Calculate the molarity of sodium fluoride:
Molarity of NaF = Moles of NaF / Volume of solution in liters
The volume of the solution is given as 1.00 Liter.
Molarity of NaF = Moles of NaF / 1.00 L
Now that we have the molarity of sodium fluoride, we can calculate the pH of the buffer solution using the Henderson-Hasselbalch equation:
pH = pKa + log ([A-] / [HA])
Where:
- pH is the desired pH
- pKa is the negative logarithm of the acid dissociation constant (Ka)
- [A-] is the concentration of the conjugate base (NaF in this case)
- [HA] is the concentration of the acid (HF in this case)
In this case, the acid is hydrofluoric acid (HF), and the conjugate base is sodium fluoride (NaF). The pKa value is given as 6.6 x 10^-4.
3. Calculate the concentration of the acid (HF):
The concentration of the acid is given as 0.15M.
4. Substitute the values into the Henderson-Hasselbalch equation and calculate the pH:
pH = -log(6.6 x 10^-4) + log ([NaF] / [HF])
Substitute the molarity of NaF and HF into the equation and solve for pH.
pH = -log(6.6 x 10^-4) + log ([NaF] / 0.15)
Finally, calculate the logarithm and solve for pH, rounding to 2 decimal places.