* Ammonia Concentration: The pH of ammonia solution depends on the concentration of ammonia (NH₃) in the water. "Pounds per gallon" describes weight, not concentration.
* Equilibrium: Ammonia in water exists in equilibrium with its conjugate acid, ammonium ion (NH₄⁺):
* NH₃ (aq) + H₂O (l) ⇌ NH₄⁺ (aq) + OH⁻ (aq)
* pH and Equilibrium: The position of this equilibrium determines the concentration of hydroxide ions (OH⁻), which in turn determines the pH.
Here's what you need to know:
* Higher Ammonia Concentration: A higher concentration of ammonia in water will shift the equilibrium to the right, increasing the hydroxide ion concentration and resulting in a higher pH (more basic).
* Lower Ammonia Concentration: A lower concentration of ammonia will shift the equilibrium to the left, decreasing the hydroxide ion concentration and resulting in a lower pH (less basic).
To calculate the pH of ammonia solution:
1. You need to know the concentration of ammonia (NH₃) in the solution. This is usually expressed in molarity (moles per liter) or percent by weight.
2. Use the equilibrium constant (Kb) for ammonia to calculate the hydroxide ion concentration.
3. Calculate the pH using the formula pH = -log[H⁺] or pOH = -log[OH⁻] and the relationship pH + pOH = 14.
Example:
Let's say you have a solution that is 10% ammonia by weight (approximately 1.4 M ammonia). Using the Kb of ammonia and the equilibrium reaction, you can calculate the pH, which would be around 11.6.
In summary:
* You can't directly convert ppg to pH.
* The pH of ammonia solutions depends on the *concentration* of ammonia, not just its weight.
* You need to know the concentration of ammonia to calculate the pH.
