Question

An universal indicator (1) consists of a single indicator which changes colour at different \(\mathrm{pH}\) ranges (2) consists of a number of indicators which give different colours at different \(\mathrm{pH}\) ranges (3) is used only in the \(\mathrm{pH}\) range of 0 to 7 (4) is used only in the \(\mathrm{pH}\) range of 7 to 14

Short answer

Option (2)

Step-by-step solution

Understand the question

The question is asking about the properties and use of an universal pH indicator. There are four options given, and only one of them accurately describes an universal indicator.

Evaluate Option 1

Option (1) states that an universal indicator consists of a single indicator which changes colour at different pH ranges. This is incorrect since an universal indicator is a mixture of several indicators, not just a single one.

Evaluate Option 2

Option (2) states that an universal indicator consists of a number of indicators which give different colours at different pH ranges. This is correct because an universal indicator is indeed a mixture of several indicators that display a variety of colors at different pH levels.

Evaluate Option 3

Option (3) states that an universal indicator is used only in the pH range of 0 to 7. This is incorrect because an universal indicator is used across the entire pH spectrum, from 0 to 14.

Evaluate Option 4

Option (4) states that an universal indicator is used only in the pH range of 7 to 14. This is also incorrect for the same reason as Option (3) - an universal indicator covers the full pH range from 0 to 14.

Conclusion

Upon reviewing all options, Option (2) is the correct answer.

Key concepts

pH range

A universal pH indicator provides a visual representation of pH levels across the entire spectrum, which ranges from 0 to 14. It helps measure the acidity or basicity of a solution.

The pH scale:

• Ranges from 0 to 14
• 0 to < 7: Acidic
• 7: Neutral
• > 7 to 14: Alkaline (Basic)

Universal pH indicators cover this complete range, making it easier to determine how acidic or basic a solution is.

color change

Universal pH indicators reveal different colors at various pH levels. This variation in color allows for easy identification of a solution's pH.

Here’s how it works:

• Red/Orange: Strongly acidic (pH 0-3)
• Yellow: Weakly acidic (pH 4-6)
• Green: Neutral (pH ≈ 7)
• Blue: Weakly basic (pH 8-11)
• Purple: Strongly basic (pH 12-14)

The accuracy and ease of using a color spectrum make universal indicators perfect for quickly gauging pH levels.

mixture of indicators

Unlike a single indicator that shows a specific color change at a particular pH, a universal indicator is a blend of multiple indicators. Each of these individual indicators responds to different pH levels, creating a wide range of color changes.

Why Use a Mixture?

• Covers the full pH range from 0 to 14
• Provides more nuanced and accurate color changes
• Enables quick and visually interpretable results

This mixture approach enhances the utility of the pH indicator across a broader array of chemical environments.

acid-base indicators

Acid-Base indicators play a crucial role in identifying the pH of solutions. These indicators change color based on the acidity or basicity of a solution.

Types of Acid-Base Indicators:

• Single Indicators (e.g., Litmus, phenolphthalein, methyl orange)
• Universal Indicators (a combination of multiple indicators)

While single indicators are useful for specific pH ranges, universal indicators offer the advantage of a broad pH range detection. This makes them invaluable in varied scientific contexts, from classrooms to industrial labs.