What is the pH of H3PO4?
* pH is a measure of acidity or alkalinity: It's defined as the negative logarithm (base 10) of the hydrogen ion concentration ([H+]) in a solution.
* Phosphoric acid is a weak acid: It doesn't fully dissociate (break apart) into hydrogen ions (H+) and phosphate ions (PO4^3-) in solution. The extent of dissociation depends on the concentration.
* Higher concentration, lower pH: A higher concentration of H3PO4 means more hydrogen ions are released, making the solution more acidic and resulting in a lower pH.
To calculate the pH of a specific H3PO4 solution, you need to know its molarity (moles per liter).
Here's a general approach:
1. Write the dissociation equations for H3PO4:
H3PO4 ⇌ H+ + H2PO4-
H2PO4- ⇌ H+ + HPO4^2-
HPO4^2- ⇌ H+ + PO4^3-
2. Use the Ka values for each dissociation step:
* Ka1 =7.5 x 10^-3
* Ka2 =6.2 x 10^-8
* Ka3 =4.8 x 10^-13
3. Set up an ICE table (Initial, Change, Equilibrium) for each dissociation step.
4. Solve for the hydrogen ion concentration ([H+]) at equilibrium.
5. Calculate the pH using the formula:pH =-log[H+]
Σημαντική σημείωση: The calculations for a weak acid like H3PO4 can get quite complex, especially at higher concentrations. You may need to use an iterative method or approximation techniques to solve for the pH.
