Propose buffer components to hold a pH of 3.5, let the acid have a concentration of 0.1 M show all work
To propose buffer components that can maintain a pH of 3.5 with an acid concentration of 0.1 M, we need to choose a weak acid and its conjugate base. The buffer system will help resist changes in pH when small amounts of acid or base are added.
Here's how we can find the appropriate buffer components:
Step 1: Choose a weak acid (HA) with a pKa value close to the desired pH. The pKa is the negative logarithm of the acid dissociation constant (Ka), and it indicates the strength of the acid.
In this case, we want a pH of 3.5. The corresponding pKa can be determined using the Henderson-Hasselbalch equation:
pH = pKa + log ([A-]/[HA])
Since we want to maintain a pH of 3.5, we can assume that [A-] (conjugate base) and [HA] (weak acid) will have approximately equal concentrations.
So, pH ≈ pKa + log (1/1)
Therefore, pKa ≈ 3.5.
Step 2: Find a weak acid with a pKa close to 3.5. Acetic acid (CH3COOH) has a pKa of 4.76, which is reasonably close. We will use acetic acid as our weak acid component.
CH3COOH (acetic acid) ⇌ CH3COO- (acetate ion) + H+ (proton)
Step 3: Determine the concentration of the weak acid (acetic acid) and its conjugate base (acetate ion) required to prepare the buffer.
Since the acid concentration (HA) is given as 0.1 M, we will use this concentration for acetic acid.
Step 4: Prepare the buffer solution by combining the weak acid (acetic acid) and its conjugate base (sodium acetate, NaCH3COO), both at the desired concentrations.
So, the proposed buffer components are:
- 0.1 M acetic acid (CH3COOH)
- Sodium acetate (NaCH3COO) at a concentration equivalent to 0.1 M
The final buffer solution will consist of acetic acid and its conjugate base in equal concentrations, helping maintain the pH at 3.5 when small amounts of acid or base are added.
Please note that the calculations assume the acid dissociates completely and ignore any interaction with water or other factors that may affect the pH.