I did an experiment on Buffers:
In a polystyrene beaker, mix 20 ml of 0.1M Acetic acid ad 25 ml of 0.1 M sodium acetate and immediately measure the pH. Remove the electrode and add 5 ml of 0.1 M HCL to this buffer. Stir the solution and measure the pH.
This is my data:
Conc.of acetic acid 0.1 M- volume 20mL
Conc.of sodium acetate 0.1M-volume 25ml
Conc. of Hydrochloric acid 0.1M-volume 5 ml
Buffer Solution- pH measured- 4.65
pH calculated ?
Buffer solution + HCL -pH measured- 4.43
pH calculated-?
A. So basically i need to show calculation for the calculated pH before the addition of HCl
B. Show the calculations for the calculated pH after the addition of HCl
The equilibrium in both mixtures is:
HC2H3O2(aq) <=> H+(aq) + C2H3O2^-(aq)
For the first mixture use the Henderson-Hasselbalch Equation to get the pH:
pH = pKa + log{[C2H3O2^-]/[HC2H3O2]}
NOTE: [C2H3O2^-] = molarity of NaC2H3O2
pH = pKa + log{1}
In the second mixture, reaction between HCl and NaC2H3O2 converts half of the C2H3O2- ions to acid, HC2H3O2, so,
pH = pKa + log{1/2}
Look up the pKa of HC2H3O2 and complete the calculations
only to correct that conce of acetate is not equal to that of acetic acid molatrity of HC2H3O2=2 molarity of NaC2H3O2=2.5 so pH=pKa+log2/2.5 . =pKa+log0.8
A. To calculate the pH of the buffer solution before the addition of HCl, you can use the Henderson-Hasselbalch equation. This equation relates the pH of a buffer solution to the pKa of the acid and the ratio of the concentrations of the acid and its conjugate base:
pH = pKa + log([conjugate base]/[acid])
In this case, acetic acid is the weak acid and sodium acetate is its conjugate base. The pKa of acetic acid is known to be around 4.76 (at 25°C).
Given:
Concentration of acetic acid = 0.1 M
Volume of acetic acid = 20 mL
Concentration of sodium acetate = 0.1 M
Volume of sodium acetate = 25 mL
Step 1: Calculate the moles of acetic acid:
moles of acetic acid = concentration of acetic acid x volume of acetic acid
moles of acetic acid = 0.1 M x 0.02 L (20 mL converted to liters)
Step 2: Calculate the moles of sodium acetate:
moles of sodium acetate = concentration of sodium acetate x volume of sodium acetate
moles of sodium acetate = 0.1 M x 0.025 L (25 mL converted to liters)
Step 3: Calculate the ratio of conjugate base to acid:
ratio = moles of sodium acetate / moles of acetic acid
Step 4: Calculate the pH using the Henderson-Hasselbalch equation:
pH = pKa + log(ratio)
Substitute the known values:
pH = 4.76 + log(ratio)
Calculations for the pH before the addition of HCl:
moles of acetic acid = 0.1 M x 0.02 L = 0.002 moles
moles of sodium acetate = 0.1 M x 0.025 L = 0.0025 moles
ratio = 0.0025 moles / 0.002 moles ≈ 1.25
pH = 4.76 + log(1.25)
pH = 4.76 + 0.0969
pH ≈ 4.8569
Thus, the calculated pH of the buffer solution before the addition of HCl is approximately 4.86.
B. To calculate the pH of the buffer solution after the addition of HCl, we need to consider the additional moles of HCl and how it affects the buffer system.
Given:
Concentration of HCl = 0.1 M
Volume of HCl = 5 mL
Step 1: Calculate the moles of HCl:
moles of HCl = concentration of HCl x volume of HCl
moles of HCl = 0.1 M x 0.005 L (5 mL converted to liters)
Step 2: Determine the new moles of acetic acid and sodium acetate:
moles of acetic acid = original moles of acetic acid
moles of sodium acetate = original moles of sodium acetate
Step 3: Calculate the new total moles of the buffer system:
total moles = moles of acetic acid + moles of sodium acetate + moles of HCl
Step 4: Calculate the new ratio of conjugate base to acid:
new ratio = moles of sodium acetate / moles of acetic acid
Step 5: Calculate the new pH using the Henderson-Hasselbalch equation:
pH = pKa + log(new ratio)
Evaluating these calculations will provide the pH of the buffer solution after the addition of HCl.