Calculate the pH of a solution container 0.20m ch3cooh and 0.30m ch3coona
To calculate the pH of a solution containing CH3COOH and CH3COONa, we need to understand the acid-base properties of these compounds.
CH3COOH is acetic acid, a weak acid that dissociates partially in water, represented by the following equation:
CH3COOH ⇌ CH3COO- + H+
CH3COONa is the sodium salt of acetic acid, which dissociates completely in water, resulting in the formation of CH3COO- ions:
CH3COONa → CH3COO- + Na+
Knowing this, we can calculate the pH of the solution using the Henderson-Hasselbalch equation:
pH = pKa + log([A-]/[HA])
Where:
- pH is the measure of the acidity or basicity of a solution.
- pKa is the logarithmic expression of the acid dissociation constant (Ka) of the weak acid (CH3COOH).
- [A-] is the concentration of the conjugate base (CH3COO-) of the weak acid.
- [HA] is the concentration of the weak acid (CH3COOH).
The pKa value for acetic acid (CH3COOH) is approximately 4.75.
To calculate [A-] and [HA], we need to consider the concentrations of CH3COOH (0.20 M) and CH3COONa (0.30 M) in the solution.
Since CH3COONa dissociates completely, the concentration of the acetate ion (CH3COO-) is equal to the concentration of CH3COONa, which is 0.30 M.
The concentration of CH3COOH (HA) will be the initial concentration (0.20 M) minus the concentration of CH3COO- (A-), which is 0.30 M.
[HA] = 0.20 M - 0.30 M = -0.10 M
Substituting these values into the Henderson-Hasselbalch equation:
pH = 4.75 + log([0.30 M]/[-0.10 M])
When taking the logarithm of a negative concentration, we need to indicate the negative sign using parentheses:
pH = 4.75 + log([0.30 M]/([-0.10 M]))
Performing the division and logarithm calculation:
pH = 4.75 + log(3)
Using a calculator, the logarithm of 3 is approximately 0.48:
pH = 4.75 + 0.48
pH ≈ 5.23
Therefore, the pH of the solution containing 0.20 M CH3COOH and 0.30 M CH3COONa is approximately 5.23.
To calculate the pH of a solution containing both a weak acid (CH3COOH) and its conjugate base (CH3COONA), you can use the Henderson-Hasselbalch equation. This equation relates the pH of a solution to the pKa (acid dissociation constant) of the weak acid and the ratio of the concentrations of the weak acid and its conjugate base.
Here are the steps to calculate the pH:
1. Find the pKa value of CH3COOH. The pKa can usually be found in reference books or online resources. For CH3COOH, the pKa is approximately 4.75.
2. Calculate the ratio of the concentration of CH3COOH to CH3COONA. In this case, the concentration of CH3COOH is 0.20 M, and the concentration of CH3COONA is 0.30 M. Therefore, the ratio is:
[CH3COOH]/[CH3COONA] = 0.20/0.30 = 0.667
3. Take the logarithm (base 10) of the ratio calculated in step 2. In this case, the logarithm of 0.667 is approximately -0.175.
4. Substitute the pKa value and the logarithm of the ratio into the Henderson-Hasselbalch equation:
pH = pKa + log([CH3COOH]/[CH3COONA])
= 4.75 + (-0.175)
= 4.575
Therefore, the pH of the solution with 0.20 M CH3COOH and 0.30 M CH3COONA is approximately 4.575.
home work
pH=pka+log[Ac/HAc]
HAc=0.20M CH3COOH=acetic acid
Ac=0.30M CH3COONa=sodium acetate
Use your text to find the pka of CH3COOH (acetic acid)