Problem 18 - A Complete Resource Book in Chemistry for JEE Main

Question

At \(25^{\circ} \mathrm{C}\) the \(\mathrm{pH}\) value of a solution is 6 , the solution is (a) neutral (b) acidic (c) alkaline (d) basic

Step-by-Step Solution

Answer

(b) acidic

Step 1: Understanding pH Scale

The pH scale ranges from 0 to 14. It indicates how acidic or basic a solution is. A pH of 7 is considered neutral, below 7 is acidic, and above 7 is basic or alkaline.

Step 2: Analyzing the Given pH Value

The problem states that the pH value of the solution at 25°C is 6. We compare this value with 7 to determine the nature of the solution.

Step 3: Classifying the Solution

Since the given pH value of 6 is less than 7, the solution is categorized as acidic. Acidity is indicated by pH values below 7.

Key Concepts

Acidic Solution

An acidic solution is characterized by a pH value less than 7. When substances dissolve in water, they can release hydrogen ions (H⁺) into the solution. The presence of these hydrogen ions gives the solution its acidic nature.
The more hydrogen ions present, the stronger the acid, and the lower the pH value will be. Common examples of acidic solutions include:

• Lemon juice, which typically has a pH of around 2.
• Vinegar, often with a pH of about 3.
• Stomach acid, with an extremely acidic pH of about 1-2.

Acids are not always harmful. Many have significant roles in daily life, like in digestion or in food preservation.

pH Value Interpretation

The pH scale is a tool used to measure the acidity or basicity of a solution. It ranges from 0 to 14, with each number representing a tenfold change in acidity or basicity. A pH of 7 is considered neutral, meaning it is neither acidic nor basic. The pH scale can be interpreted as follows:

• 0 to 6: Acidic solutions
• 7: Neutral solutions
• 8 to 14: Basic or alkaline solutions

Interpreting pH values is crucial in many fields, such as chemistry, biology, and medicine. For example, when testing the pH of soil, gardeners can determine if it's suitable for growing certain plants. Similarly, in the human body, the pH of blood is tightly regulated to stay around 7.4, crucial for proper physiological functioning.

Neutral, Acidic, and Basic Solutions

Understanding the distinctions between neutral, acidic, and basic solutions is fundamental in science. A neutral solution has a pH of 7, meaning it has a balance between hydrogen ions (H⁺) and hydroxide ions (OH⁻). Pure water is the most common example. An acidic solution, on the other hand, has more hydrogen ions than hydroxide ions. This is why its pH is lower than 7. Such solutions are typically found in the foods we consume, like citrus fruits. Basic or alkaline solutions have more hydroxide ions than hydrogen ions, giving them a pH above 7. Examples include:

• Household ammonia, with a pH around 11.
• Baking soda, which often has a pH of about 9.

These concepts help us understand how substances interact in water, influencing numerous processes such as digestion, environmental science, and even product development in industries.