mixing 100ml of 0.015M Nah2PO4 and 100ml of NA2HPO4. What is the pH?
This has got to be simple but why am I having trouble with it?
Use the Henderson-Hasselbalch equation.
pH = pKa + log (base)/(acid)
Your two big problems.
1. What pKa do you use?
2. which is the acid and which the base.
3. (Actually, it doesn't matter which is the acid and which the base because the concentrations are equal which means log 1 = 0 and pH = pKa.
SO your only problem is know which pka to use; i.e.k, pka1, pka2, pka3.
Soo, can you walk through the problem w final answer?
To find the pH of the mixture, you need to consider the dissociation of the acid (NaH2PO4) and the base (Na2HPO4) and their respective conjugate base and acid forms.
NaH2PO4 is a weak acid that can donate a proton (H+) to form its conjugate base H2PO4-. It can be represented by the following equilibrium reaction:
NaH2PO4 ⇌ H+ + HPO42-
Na2HPO4 is a weak base that can accept a proton (H+) to form its conjugate acid H2PO4-. It can be represented by the following equilibrium reaction:
Na2HPO4 + H2O ⇌ HPO42- + OH-
To calculate the pH of the mixture, we need to consider the concentrations of H+ ions and OH- ions in the solution resulting from the reactions of NaH2PO4 and Na2HPO4.
Here's an approach to finding the pH:
Step 1: Calculate the concentrations of H+ and OH- ions from the reactions.
For NaH2PO4:
- Since it is a weak acid, you can assume that it dissociates to a small extent, and the initial concentration can be considered as the equilibrium concentration.
- The initial concentration of NaH2PO4 is given as 0.015 M.
For Na2HPO4:
- Since it reacts with water as a base, it generates OH- ions. The initial concentration of Na2HPO4 is also given as 0.015 M.
Step 2: Use the equilibrium concentrations of H+ and OH- ions to calculate the pH.
Since NaH2PO4 and Na2HPO4 are present in equal volumes and equal concentrations, the concentrations of H+ and OH- ions will be the same.
The equation for water dissociation is: H2O ⇌ H+ + OH-
Since water is neutral, the concentration of H+ ions equals the concentration of OH- ions.
To determine the concentration of these ions, you will need to use the water dissociation constant (Kw), which is typically 1.0 x 10^-14 at 25°C.
Kw = [H+][OH-]
Since [H+] = [OH-], we can assume the concentration of each ion to be x.
So:
Kw = x * x = x^2
x = sqrt(Kw) = sqrt(1.0 x 10^-14) ≈ 1.0 x 10^-7 M
Since the concentration of H+ ions equals the concentration of OH- ions in the solution, the pH can be calculated using the formula: pH = -log[H+].
Thus:
pH = -log(1.0 x 10^-7) ≈ 7
Therefore, the pH of the mixture is approximately 7.
If you have any further questions, feel free to ask!