Understanding the pH scale is key to determining whether a substance is acidic, neutral, or alkaline (basic). The pH scale ranges typically from 0 to 14.

• A pH less than 7 indicates acidity.
• A pH of 7 indicates neutrality.
• A pH greater than 7 indicates alkalinity or basicity.

The lower the pH (below 7), the stronger the acid. The higher the pH (above 7), the stronger the base.

Lemon juice is well-known for its sour taste, which is a characteristic property of acids. The acidity of lemon juice is primarily due to the presence of citric acid.

Let's look at the typical pH range of lemon juice.

Typical pH Range of Lemon Juice

Lemon juice is considered a weak acid. Its typical pH value falls within a range that signifies acidity. Studies and common knowledge indicate that the pH of lemon juice is usually between 2 and 3.

Now let's examine the given options in the context of the pH scale and the known properties of lemon juice:

• Option 1: pH 2. This value is less than 7, indicating acidity. It falls within the typical pH range of lemon juice.
• Option 2: pH 9. This value is greater than 7, indicating alkalinity. Lemon juice is not alkaline.
• Option 3: pH 12. This value is significantly greater than 7, indicating strong alkalinity. Lemon juice is not strongly alkaline.
• Option 4: pH 7. This value indicates neutrality. Lemon juice is not neutral; it is acidic.

Based on the typical pH of lemon juice, which is acidic and falls between 2 and 3, a pH of 2 is the most appropriate answer among the given options.

Understanding Acidity and pH

The pH value is a measure of the concentration of hydrogen ions (H⁺) in a solution. Mathematically, pH is defined as:

\(\text{pH} = -\log_{10}[\text{H}^{+}] \)

A higher concentration of H⁺ ions results in a lower pH and thus greater acidity. Lemon juice has a relatively high concentration of hydrogen ions compared to neutral water, hence its low pH.

Here is a table showing the approximate pH values of some common substances for comparison:

As shown in the table, lemon juice falls in the acidic range with a typical pH between 2 and 3. Therefore, a pH of 2 is a characteristic value for lemon juice.

Revision Table: pH Concepts

Additional Information on Acids and Bases

Acids are substances that donate hydrogen ions (H⁺) when dissolved in water, or accept electron pairs. Bases are substances that accept hydrogen ions or donate electron pairs. The strength of an acid or base depends on how completely it dissociates (breaks apart) in water.

• Strong Acids: Dissociate almost completely in water (e.g., Hydrochloric Acid - HCl). They have very low pH values (typically 0-1).
• Weak Acids: Only partially dissociate in water (e.g., Citric Acid in lemon juice, Acetic Acid in vinegar). They have pH values typically ranging from 2 to 6.
• Strong Bases: Dissociate almost completely in water (e.g., Sodium Hydroxide - NaOH). They have very high pH values (typically 13-14).
• Weak Bases: Only partially dissociate in water (e.g., Ammonia - NH₃). They have pH values typically ranging from 8 to 12.

Lemon juice, containing citric acid, is classified as a weak acid, which aligns with its pH being in the 2-3 range, and specifically pH 2 as given in the options.