Question

What color will litmus be in a solution of \(\mathrm{pH}\) 9? A solution of pH 3?

Short answer

Litmus will be blue in pH 9 and red in pH 3.

Step-by-step solution

Understanding Litmus Behavior

Litmus is a dye used to determine whether a solution is acidic or basic. It changes color depending on the pH of the solution. In acidic solutions (pH < 7), litmus turns red, and in basic solutions (pH > 7), it turns blue.

Analyzing pH 9

With a pH of 9, the solution is basic because its pH is greater than 7. Therefore, when litmus is introduced to this solution, it will change to blue.

Analyzing pH 3

With a pH of 3, the solution is acidic because its pH is less than 7. Therefore, when litmus is introduced to this solution, it will change to red.

Key concepts

Acidic Solution

An acidic solution is one where the concentration of hydrogen ions (H⁺) is higher than the concentration of hydroxide ions (OH⁻). This typically occurs when the pH value is less than 7. When a substance dissolves in water and increases the concentration of H⁺ ions, it creates an acidic solution. Common examples include vinegar and lemon juice.

In the context of litmus testing, an acidic solution will cause the litmus paper to turn red. This color change is a clear indicator of the acidic nature of the solution.

• Acidic solutions have a sour taste.
• They can be corrosive and reactive, particularly with metals.
• They conduct electricity due to the presence of ions.

Understanding how acidic solutions interact with different substances can help in identifying them in various practical scenarios.

Basic Solution

A basic solution, in contrast to an acidic one, has a higher concentration of hydroxide ions (OH⁻) compared to hydrogen ions (H⁺). This happens when the pH value exceeds 7. Basic solutions result from substances that release OH⁻ ions when dissolved in water, like baking soda or ammonia.

When litmus paper is submerged in a basic solution, it turns blue, providing a straightforward visual confirmation of its basic nature. This color shift forms the basis of using litmus as a reliable test.

• Basic solutions often have a bitter taste.
• They feel slippery to the touch, a trait shared by many soaps.
• These solutions can neutralize acids, resulting in the formation of water and salt.

Basic solutions play an important role in numerous cleaning and industrial applications.

pH Scale

The pH scale is a numerical representation that measures the acidity or basicity of a solution. Ranging from 0 to 14, it helps identify how acidic or basic a solution is. The scale is logarithmic, which means each whole number change on the pH scale represents a tenfold change in hydrogen ion concentration.

- **Neutral solutions** have a pH of 7, which indicates an equal concentration of H⁺ and OH⁻ ions. Pure water is a common example. - **Acidic solutions** have a pH less than 7, indicating higher hydrogen ion concentration. - **Basic solutions** exceed a pH of 7, showing higher concentrations of hydroxide ions.

Using the pH scale is essential in fields like chemistry, biology, and environmental science to monitor acidity and alkalinity. Proper understanding of the pH scale aids in ensuring that substances are used safely and efficiently in various chemical processes.