One buffer solution used to calibrate a pH electrode was made by dissolving 2.24g of potassium propanoate, C2H5COOK, in 250cm3 of 0.20 mooll-1 propanoic acid.
I assume you want the pH of the solution.
pH = pKa + log(base)/(acid)
Substitute and solve or pH.
To calculate the pH of this buffer solution, we first need to determine the concentration of both the conjugate acid (propanoic acid, C2H5COOH) and the conjugate base (potassium propanoate, C2H5COOK).
Step 1: Calculate the moles of potassium propanoate (C2H5COOK) dissolved:
We can use the formula:
moles = mass / molar mass
The molar mass of potassium propanoate (C2H5COOK) can be calculated by adding the molar mass of each element involved:
Molar mass of C = 12.01 g/mol
Molar mass of H = 1.01 g/mol
Molar mass of O = 16.00 g/mol
Molar mass of K = 39.10 g/mol
Molar mass of C2H5COOK = (2 * 12.01) + (6 * 1.01) + 16.00 + 39.10 = 98.16 g/mol
Now, we can calculate the moles of C2H5COOK:
moles of C2H5COOK = 2.24 g / 98.16 g/mol = 0.0228 mol
Step 2: Calculate the concentration of propanoic acid (C2H5COOH):
We are given that the propanoic acid has a concentration of 0.20 mol/L. This means that there are 0.20 moles of propanoic acid in 1 liter of solution.
To determine the concentration of propanoic acid in 250 cm3 (0.250 L) of solution, we use the following formula:
concentration = moles / volume
concentration of propanoic acid = 0.20 mol / 0.250 L = 0.8 mol/L
Step 3: Calculate the concentration of potassium propanoate (C2H5COOK):
Since C2H5COOH and C2H5COOK are involved in a 1:1 ratio based on their balanced equation, the concentration of C2H5COOK will also be 0.8 mol/L.
Step 4: Calculate the total concentration of the buffer (C2H5COOH + C2H5COOK):
The total concentration of the buffer is determined by summing the concentrations of the conjugate acid and the conjugate base:
total buffer concentration = concentration of C2H5COOH + concentration of C2H5COOK
total buffer concentration = 0.8 mol/L + 0.8 mol/L = 1.6 mol/L
Step 5: Calculate the pH of the buffer solution:
To determine the pH, we need to use the Henderson-Hasselbalch equation:
pH = pKa + log([conjugate base] / [conjugate acid])
The pKa value of propanoic acid (C2H5COOH) can vary, but let's assume it is 4.87 for this example.
Now, substitute the known values into the equation:
pH = 4.87 + log(0.8 mol/L / 0.8 mol/L)
pH = 4.87 + log(1)
pH = 4.87 + 0
pH = 4.87
Therefore, the pH of the buffer solution is 4.87.