16 Questions
What is the primary function of an indicator?
To change its colour in the presence of an acid or a base
What is the most common indicator used for testing acids and bases in the laboratory?
Litmus
What happens when an acid is added to blue litmus?
It turns blue litmus to red
What is the neutral colour of methyl orange?
Orange
What is the purpose of using litmus paper in the laboratory?
To detect the presence of an acid or a base
What is the term for a water-soluble base?
Alkali
What is the characteristic of litmus?
It is a natural indicator
What is the colour of methyl orange indicator in basic solution?
Yellow
What happens when a base is added to red litmus?
It turns red litmus to blue
What is the colour of phenolphthalein indicator in acid solution?
Colourless
What is litmus extracted from?
A type of plant
What is the colour of litmus paper when it comes in contact with a basic solution?
Blue
What happens to the colour of turmeric when it comes in contact with a basic solution?
It turns red
Why does the yellow stain of curry on a white cloth turn reddish-brown when soap is scrubbed on it?
Because soap solution is basic
What happens to the colour of the stain when the cloth is rinsed with plenty of water?
It turns yellow again
What is the general term for substances like litmus and turmeric that change colour in response to changes in acidity or basicity?
Acid-base indicators
Study Notes
Acid-Base Indicators
- An indicator is a substance that changes color when it comes into contact with an acid or a base, indicating whether the substance is acidic or basic.
- Litmus, Methyl Orange, and Phenolphthalein are three common indicators used to test for acids and bases.
Litmus Indicator
- Litmus can be used in the form of litmus solution or litmus paper.
- It has two types: Blue Litmus and Red Litmus.
- Acid turns Blue Litmus to Red, while a Base (or Alkali) turns Red Litmus to Blue.
- Litmus is a natural indicator with a neutral color of purple.
Methyl Orange Indicator
- Methyl Orange is a synthetic indicator with a neutral color of orange.
- It turns red in acid solution and yellow in basic solution.
Phenolphthalein Indicator
- Phenolphthalein is a synthetic indicator with a neutral color of colorless.
- It is colorless in acid solution and turns pink in basic solution.
Universal Indicator
- The universal indicator is another acid-base indicator that will be discussed later.
Natural Indicators
- Litmus is extracted from a type of plant called lichen, belonging to the division Thallophyta.
- Turmeric is also a natural indicator, containing a yellow dye that turns red in basic solutions.
- Turmeric is found in curry and can change color when coming into contact with soap solution, which is basic in nature.
Learn about indicators and how they change color to identify acids and bases. Discover the three most common indicators: Litmus, Methyl orange, and Phenolphthalein.
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