Understanding pH and Hydrogen Ion Concentration

The pH scale is a measure of how acidic or basic a solution is, defined as the negative logarithm of the concentration of hydrogen ions
([H⁺]). It is calculated using the formula:

[ \text{pH} = -\log[H^+] ]

This concept is crucial in various fields, including chemistry, biology, and environmental science. Below are three practical examples that demonstrate how to determine pH from the concentration of hydrogen ions.

Example 1: Determining the pH of a Lemon Juice Solution

Lemon juice is known for its acidity and has a significant concentration of hydrogen ions. Let’s calculate the pH of a lemon juice solution with a hydrogen ion concentration of 0.01 M (molar).

To find the pH:

1. Identify the concentration of hydrogen ions: [H⁺] = 0.01 M
2. Apply the pH formula: [ ext{pH} = -\log(0.01) ]
3. Calculate the logarithm: [ ext{pH} = -(-2) = 2 ]

Thus, the pH of the lemon juice solution is 2, indicating it is quite acidic.

Notes:

• Lemon juice typically ranges between pH 2 and 3.
• The pH can vary slightly based on the concentration of citric acid and other components present.

Example 2: pH of a Household Cleaning Product

Many household cleaning products, such as vinegar, contain acetic acid, which contributes to their acidity. Suppose we have a vinegar solution with a hydrogen ion concentration of 0.05 M.

To determine the pH:

1. Identify the concentration of hydrogen ions: [H⁺] = 0.05 M
2. Apply the pH formula: [ ext{pH} = -\log(0.05) ]
3. Calculate the logarithm: [ ext{pH} = -(-1.3) \approx 1.3 ]

Hence, the pH of the vinegar solution is approximately 1.3, confirming its strong acidity.

Notes:

• Typical pH values for vinegar range from 2.4 to 3.4.
• The acidity can be adjusted by diluting the vinegar with water.

Example 3: Calculating pH from a Diluted Hydrochloric Acid Solution

Hydrochloric acid (HCl) is a strong acid commonly used in laboratories. If we dilute hydrochloric acid to achieve a hydrogen ion concentration of 0.001 M, we need to calculate the new pH.

To find the pH:

1. Identify the concentration of hydrogen ions: [H⁺] = 0.001 M
2. Apply the pH formula: [ ext{pH} = -\log(0.001) ]
3. Calculate the logarithm: [ ext{pH} = -(-3) = 3 ]

Therefore, the pH of the diluted hydrochloric acid is 3, indicating that it is still acidic, though less so than concentrated solutions.

Notes:

• The pH of strong acids like HCl remains low even at lower concentrations.
• Safety precautions should be taken when handling strong acids, even in diluted forms.