Acid–Base Indicators: Types, Examples, and Uses
Key Concepts
- Indicators
- Natural Indicators
- Synthetic Indicators
- Olfactory Indicators
- Action of Indicators on Acids and Bases
Introduction: Indicators – Acids and Bases
By now, we know that substances like tomatoes, lemon, pineapples taste sour because they contain acids. In contrast, substances like detergents and soaps feel bitter and slippery because they contain the substance known as base.
How do we find it acidic or basic if we cannot taste every substance? Special types of substances are used to determine whether a given substance is acid or base. These substances are known as indicators. Indicators change colors when they contact an acid or a base.
Let us learn more about these indicators, types and how they are used to identify the nature of substances.
INDICATORS
Definition: Indicators are the substances used to determine whether an aqueous solution is acidic, neutral, or basic.
There are three types of indicators.
NATURAL INDICATORS AROUND US
- Natural indicators are generally found in nature.
- They are mostly derived from plants.
- Examples : Litmus, China rose, red cabbage, turmeric, beetroot are all examples of natural indicators around us.
1. LITMUS AS AN INDICATOR
- The most commonly used indicator is litmus.
- It is extracted from a plant known as lichen(belonging to the thallophyte family)
- Litmus is purple in color in neutral solution.
- There are two types of litmus paper used.
a. Blue Litmus Paper
Action of Acid: When blue litmus paper is dipped inside the acid solution, it changes color from blue to red.
Action of Base: When blue litmus paper is dipped inside the base solution, it remains blue only. (colorless)
b. Blue Litmus Paper
Action of Acid: It has no effect when red litmus paper is dipped inside the acid solution.
Examples of acids: HCl, H2SO4, citric acid
Action of Base: When dipped in basic solution (like NaOH, KOH), it turns red to blue.
Litmus Test
2. TURMERIC AS AN INDICATOR
Turmeric is another good natural indicator.
Turmeric is bright yellow color and is obtained from turmeric plants.
However, when mixed with a basic solution, it turns red in color.
Action of turmeric on Acids: It remains yellow only. No change in color.
Action of turmeric on Bases: Turmeric turns red when in contact with basic solutions.
On Salts: No change in color.
Sometimes, when you have stains of curry on your clothes, applying soap turns out too red. Have you ever wondered why it happens?
It is because of turmeric. Turmeric is a natural indicator, as soap is basic in nature, so the action of turmeric changes the color of stain into red.
However, when it is added to lemon juice or vinegar, the color remains the same. The turmeric paper is not effective to identify the acidic solution. However, it is very effective to identify the basic solution.
3. CHINA ROSE AS AN INDICATOR
- China rose indicator is a solution that is pink color.
- It is extracted from the red flower of the hibiscus plant (China rose) and mixed with water.
Action on Acids:
when it is added to acid, the color changes to magenta (deep pink).
Action on Base:
When added to a solution of the base (e.g., baking soda), the color of the indicator changes from light pink to green.
(4) RED CABBAGE AS AN INDICATOR
- Red cabbage was originally purple in color.
- However, it changes the color when added to acid or basic solution.
- The pigment molecule flavin or anthocyanin present in the cabbage is responsible for changes in color. This pigment molecule changes color when an acid or base is added to it.
Action on Acid:
When red cabbage solution is mixed with acid solution, the color changes from violet to red.
Action of Base:
When base is added to red cabbage solution , the solution turns blue-green in color
Natural Indicators With Their Characteristic’s Colors
SYNTHETIC INDICATORS
- Synthetic indicators are those indicators that are made from artificial substances.
- They were synthesized in the lab by chemical reactions.
- Some commonly used synthetic indicators are Phenolphthalein and methyl orange.
1. Phenolphthalein as a Synthetic Indicator
- Phenolphthalein is colorless solution.
- In an acidic medium, it does not change color.
- When added to basic medium, the color of solution changes to pink.
- It also does not change the color when salt solution is added.
Phenolphthalein:
2. Methyl Orange as a Synthetic Indicator
- Methyl orange is another most common synthetic indicator.
- It is orange in color.
- In acids: When added to acid, it turns red-orange.
- In bases: It turns yellow in the basic medium.
- Salt: It turns out to be a yellow-coloured solution.
Olfactory Indicators
Olfactory indicators are those indicators that change their smell in the acidic or basic solution.
For example, an onion acts as an olfactory indicator and has a sharp smell.
Some common Olfactory Indicators
Summary
- Indicators are the substances used to distinguish between acid and bases. They change colors when mixed with acids or bases.
- Indicators are classified into three types:
- (a) Natural Indicator.
- (b) Synthetic Indicators.
- (c) Olfactory Indicators
- Natural Indicators: Obtained from natural sources.
- Synthetic Indicators: These are prepared in the lab.
- Olfactory Indicators: These indicators change their smell in the acidic or basic solution.
FAQs
What are acid–base indicators?
Acid-base indicator are special substances. It helps you know if something is an acid or a base. You can see this by their changing color. When an indicator touches an acid or a base, its color changes. This color change tells us the nature of the substance. These indicators are very useful because you cannot taste or touch every substance safely. So this helps you know whether you can use it or not. This is why indicators of acid and base are important. They help you use things safely and correctly.
What is an indicator in chemistry?
An indicator in chemistry is a substance you can use to test a solution. It tells you if it is acidic, basic or neutral. Many of you may wonder what are indicators. The simple answer is that indicators are tools that show you results using color or smell. They are mostly used in labs, schools and experiments. It helps you understand the nature of liquids.
What are the different types of indicators?
There are three main types of indicator used in chemistry:
Natural indicators
Synthetic indicator
Olfactory indicators
All these indicators work in different ways, but they help you with the same task. They help you to find acids and bases easily.
What are natural indicators?
Natural indicators are indicators that come from nature. They are usually taken from plants. These indicators change color when they touch an acid or a base. A natural indicator example is easy to find around us. It is safe for you to use. Natural indicators are simple and very useful for basic experiments.
What are some examples of natural indicators?
Some common natural indicators are:
Litmus
Turmeric
China rose
Red cabbage
Beetroot
Each of these is an indicator example that changes color in acids and bases. These examples are often shown in an acid-base indicators list that you see in schools. You can find these indicators easily and use them for your experiments.
What are synthetic indicators?
A synthetic indicator is an indicator that is made in a lab. You cannot find these indicators in nature. They are made by scientists using chemicals. In synthetic indicators, you can see that they give clear and strong color changes. It makes them very useful in experiments.
Common synthetic indicators are:
Phenolphthalein
Methyl orange
How do indicators show acids and bases?
Indicators show acids and bases by changing color or smell.
When you add an indicator to an acidic solution, it shows one color
When you add an indicator to a basic solution, it shows another color
For example, litmus turns red in acids and blue in bases.
This simple change helps you quickly understand the nature of the solution. You will get to know whether it is acidic or basic. This is how indicators of acid and base work in a simple way.
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