Predict whether litmus paper will turn red or blue when dipped in:
a. washing powder (containing sodium carbonate)
b. orange juice (containing citric acid)
c. lemonade (containing H₂CO₃)
d. cleaner (containing NH₃)
The Correct Answer and Explanation is:
Litmus paper is a common indicator used to determine the pH level of a solution. There are two types of litmus paper: red and blue. Red litmus paper turns blue in basic (alkaline) solutions, while blue litmus paper turns red in acidic solutions. Here’s the prediction for each of the substances you mentioned:
a. Washing powder (containing sodium carbonate): Blue
Sodium carbonate (Na₂CO₃) is a basic compound. When dissolved in water, it dissociates to form sodium ions (Na⁺) and carbonate ions (CO₃²⁻), resulting in an alkaline solution. Therefore, blue litmus paper will remain blue, and red litmus paper will turn blue.
b. Orange juice (containing citric acid): Red
Orange juice contains citric acid, which gives it an acidic pH (usually around 3 to 4). When dipped in orange juice, blue litmus paper will turn red, indicating the acidic nature of the solution.
c. Lemonade (containing H₂CO₃): Red
Lemonade typically contains citric acid as well, which is acidic. If carbonic acid (H₂CO₃) is formed when carbon dioxide is dissolved in the lemonade, it further contributes to the acidity. Thus, blue litmus paper will turn red in lemonade due to its acidic properties.
d. Cleaner (containing NH₃): Blue
Ammonia (NH₃) is a weak base. When dissolved in water, it forms ammonium hydroxide (NH₄OH), which increases the pH of the solution, making it alkaline. As a result, blue litmus paper will remain blue, while red litmus paper will turn blue.
In summary:
- Washing powder: Blue
- Orange juice: Red
- Lemonade: Red
- Cleaner: Blue
Understanding the pH level of different substances is crucial in various fields, including chemistry and environmental science, as it helps predict the behavior of compounds in reactions and their effects on the environment and biological systems.