Blue litmus paper is dipped in vinegar. What will be the change in color and why?
The correct answer and explanation is:
Correct Answer:
The blue litmus paper will turn red when dipped in vinegar.
Explanation (300 words):
Litmus paper is a common chemical indicator used to test the acidity or basicity of a substance. There are two types of litmus paper: blue and red. Blue litmus paper is used to test for acids, while red litmus paper is used to test for bases (alkalis).
Vinegar is a weak acid. It contains acetic acid (CH₃COOH) as its active ingredient, which releases hydrogen ions (H⁺) when dissolved in water. This increase in hydrogen ion concentration is what gives vinegar its acidic properties.
When blue litmus paper comes into contact with an acidic solution like vinegar, it undergoes a chemical reaction due to the presence of excess hydrogen ions (H⁺). These hydrogen ions interact with the dye molecules in the blue litmus paper, altering their structure. As a result, the paper changes from blue to red, indicating that the solution is acidic.
This color change is a qualitative test, meaning it tells us that the substance is acidic but does not measure how acidic it is. Blue litmus turning red is a clear and straightforward sign of an acidic environment with a pH less than 7.
In summary:
- Vinegar contains acetic acid, which is an acid.
- Acids have a pH below 7 and release hydrogen ions (H⁺).
- Blue litmus paper turns red in the presence of hydrogen ions.
- Therefore, dipping blue litmus paper in vinegar causes it to turn red.
This experiment is a basic but effective demonstration of acid-base chemistry often used in schools to teach students about indicators and the pH scale.