Review the key concepts, formulae, and examples before starting your quiz.
🔑Concepts
Acids are chemical substances characterized by a sour taste. They turn blue litmus paper red. Examples include acetic acid found in vinegar and citric acid in lemons.
Bases are substances that taste bitter and feel soapy to the touch. They turn red litmus paper blue. Examples include sodium hydroxide () and magnesium hydroxide ().
Indicators are special substances used to test whether a substance is acidic or basic. They change color when added to a solution containing an acidic or a basic substance.
Litmus is the most commonly used natural indicator. It is extracted from lichens. In distilled water, it has a mauve (purple) color. It is available in the form of a solution or as strips of paper (Red and Blue litmus).
Neutral substances are those which are neither acidic nor basic. These substances do not change the color of either red or blue litmus paper. Examples include distilled water (), sugar solution, and common salt () solution.
Neutralization is the reaction between an acid and a base. It results in the formation of salt and water, accompanied by the evolution of heat. The general word equation is:
📐Formulae
💡Examples
Problem 1:
A drop of a liquid was put on the blue litmus paper. It changed to red. What is the nature of the liquid?
Solution:
The liquid is acidic in nature.
Explanation:
Acids have the characteristic property of changing the color of blue litmus paper to red. Since the blue litmus turned red, the substance must contain an acid, such as dilute or lemon juice.
Problem 2:
What happens when you test a solution of baking soda () with red and blue litmus paper?
Solution:
The red litmus paper turns blue, while the blue litmus paper remains blue.
Explanation:
Baking soda is basic in nature. Bases turn red litmus paper blue and do not change the color of blue litmus paper.
Problem 3:
State the effect of distilled water on red and blue litmus paper.
Solution:
There is no change in color for either red or blue litmus paper.
Explanation:
Distilled water is a neutral substance. Neutral substances do not react with indicators like litmus to change their color.