Question

Litmus is made from plant pigment.

it is red when placed in an acidic solution.

it is blue when placed in an alkaline solution.

it is purple when neutral.


a) what do we call substance that change colour like this?
b) what colour would litmus be in a solution of pH 10?
c) what colour would you expect litmus to be in pure water?

Answer 1

For (a): The substances are known as acids and bases.

For (b): The color of the litmus for pH = 10 will be blue.

For (c): The color of the litmus for pure water will be purple.

Step-by-step explanation:

pH determines the acidity or basicity of a solution. There are three types of solution classified based on the pH:

• If pH<7 then the solution is acidic in nature
• If pH>7 then the solution is basic/alkaline in nature
• If pH=7 then the solution is neutral in nature

Litmus paper is used as an indicator to know the type of solution. There are 2 types of litmus paper:

1. Red litmus paper: It turns blue when placed in a basic/alkaline solution.
2. Blue litmus paper: It turns red when placed in an acidic solution.

(a):

An acid is defined as the chemical species that produces hydrogen ions in the solution while a base is defined as the chemical species that produces hydroxide ions in the solution.

(b):

Given pH value = 10

The solution is basic in nature, thus the color of litmus will be blue.

(c):

Pure water is neutral in nature and has a pH of 7.

Thus, the solution of litmus would be purple.