What Is The PH Of Household Ammonia? If You Were To Dilute It 100 Times With Distilled Water Would You Expect Its PH To Increase, Decrease Or Not Change? Explain Your Answer Based On The Definition Of PH.
The correct answer and explanation is :
Household ammonia typically has a pH between 11 and 12, making it quite alkaline. This is because ammonia (NH₃) is a weak base and dissolves in water to form ammonium hydroxide (NH₄OH), which dissociates partially to produce hydroxide ions (OH⁻) and ammonium ions (NH₄⁺). The presence of hydroxide ions increases the solution’s pH, giving it its basic character.
When household ammonia is diluted with distilled water, its concentration of ammonia molecules (and subsequently hydroxide ions) decreases. As the concentration of hydroxide ions decreases, the pH of the solution also decreases. This happens because the pH is a measure of the concentration of hydrogen ions (H⁺) or, more directly in basic solutions, the concentration of hydroxide ions (OH⁻). Specifically, pH is defined as:
[
\text{pH} = -\log[\text{H}^+]
]
or, equivalently, for basic solutions:
[
\text{pOH} = -\log[\text{OH}^-]
]
And since pH and pOH are related by:
[
\text{pH} + \text{pOH} = 14
]
When you dilute a basic solution like ammonia, the concentration of hydroxide ions (OH⁻) decreases. This leads to an increase in pOH, which in turn causes the pH to decrease because pH and pOH are inversely related.
In other words, diluting ammonia decreases the number of OH⁻ ions in the solution, reducing its alkalinity and, consequently, lowering the pH. Therefore, when you dilute ammonia 100 times with distilled water, you would expect its pH to decrease, not increase or remain unchanged. This is because the concentration of hydroxide ions decreases, resulting in a lower pH value.