Question

Given the following \(\mathrm{pH}\) values for solutions containing a drop of methyl red indicator, state the color of each solution: (a) \(\mathrm{pH} 3\) (b) \(\mathrm{pH} 7\)

Short answer

(a) Red, (b) Yellow

Step-by-step solution

Understand Methyl Red Indicator Range

Methyl red is a pH indicator that changes color based on the acidity or basicity of the solution. It is red in acidic solutions with pH below 4.4 and turns yellow in basic solutions with pH above 6.2. The transition range of methyl red is approximately from pH 4.4 to 6.2 where it gradually changes color from red to yellow.

Evaluate pH 3

For solution (a) with pH 3, this value is below the methyl red transition range of 4.4. This means the solution is acidic, and within this range, methyl red displays a red color.

Evaluate pH 7

For solution (b) with pH 7, this value is above the methyl red transition range of 6.2. This means the solution is basic, and methyl red shows a yellow color in basic solutions.

Key concepts

Exploring Methyl Red as a pH Indicator

Methyl red is a fascinating and widely used pH indicator, known for its ability to reveal the nature of a solution through a vivid color change. This organic compound is especially useful in determining whether a solution is acidic or basic.
Many science enthusiasts and students might wonder what makes methyl red special. Here’s why: it changes color distinctively in a narrow pH range, making it a precise indicator. Let's explore the details of its operation:

• In strongly acidic conditions (with a pH less than 4.4), methyl red is red.
• In neutral and basic conditions (with a pH greater than 6.2), it turns yellow.
• Within the transition range of pH 4.4 to 6.2, the color shifts from red to orange and finally yellow.

This sharp color transition helps chemists and students alike to discern the pH level of solutions just by observing the color changes. Methyl red’s reliable transition makes it particularly valuable in titrations and other chemical analysis methods.

How Color Change Indicates Solution pH

One of the remarkable abilities of pH indicators like methyl red is the visible color change they undergo in response to different pH levels of a solution. This happens due to the change in the chemical structure of the indicator molecule when it gains or loses protons.
In the case of methyl red:

• In acidic solutions with pH less than 4.4, the indicator remains in its protonated form, exhibiting a clear red color.
• As the pH increases and surpasses 4.4, methyl red starts losing protons, gradually shifting to an orange hue.
• Once the pH exceeds 6.2, the indicator is fully deprotonated, displaying a bright yellow color.

This transformation from red to yellow through the intermediate orange stage vividly demonstrates the acid-base nature of the solution. Such clear indications make it practical for identifying the endpoint in titrations and for educational demonstrations of acid-base interactions.

Understanding Acidic and Basic Solutions

Acidic and basic solutions form the cornerstone of many chemical reactions and processes. Recognizing whether a solution is acidic or basic is fundamental in chemistry, and indicators like methyl red play a pivotal role in this identification.
Here are some key characteristics:

• An acidic solution has a high concentration of hydrogen ions (H⁺). It's often associated with a pH value less than 7. Such environments are perfect for methyl red to show its red color.
• Basic solutions, on the other hand, have a higher concentration of hydroxide ions (OH⁻) and a pH value greater than 7. In these solutions, methyl red will appear yellow.
• Neutral solutions have balancing levels of H⁺ and OH⁻, with a pH of around 7, which would lie beyond the methyl red transition range.

The ability to distinguish between these solutions using indicators like methyl red is crucial for tasks ranging from everyday titrations to complex industrial processes. Understanding the fundamentals of acidic and basic solutions aids not only in academic studies but also in practical chemical applications.