Red Cabbage Indicator Notes: Chemical substances called indicators can be added to an acidic, basic, or neutral solution. A purple-coloured solution called the red cabbage indicator determines if a product is acidic or basic. Red cabbage, commonly found in homes, can make a pH indicator solution. The pigment molecule flavin or anthocyanin found in cabbage changes colour based on the solution’s acidity. When the purple solution reacts with something acidic, it turns red, and when it reacts with something basic, it turns green. If a substance does not change its colour, it is neutral. Let’s try a red cabbage indication experiment to see what happens.

In this article, we have provided detailed notes on the red cabbage indicator. Students can read the notes and learn all important topics included in the red cabbage indicator. Continue reading this article to learn about red cabbage indicators, olfactory indicators examples etc.

Red Cabbage Indicator Notes: Indicators

An indicator is a ‘dye’ that changes colour when put into an acid or a base. An indicator gives different colours in acid and base. Thus, an indicator tells us whether the substance we are testing is an acid or a base by its colour change.

There are three types of indicators:

• i. Natural indicators
• ii. Synthetic indicators
• iii. Olfactory indicators

CLEAR YOUR CONCEPTUAL DOUBTS ON RED CABBAGE INDICATOR

Natural Indicators

Natural indicators are indicators derived from natural sources such as vegetables and fruits. Litmus, turmeric, red cabbage, China rose, and other natural indicators are commonly used to determine whether a product is acidic or basic.

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The hydrogen ions \(\left({{{\text{H}}^ + }} \right)\) and hydroxyl ions \(\left({{\text{O}}{{\text{H}}^ – }} \right)\) in a solution are detected using these natural indicators. Some changes in the natural indicator are given as below:

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Synthetic Indicators

Synthetic indicators are those that have been created in a laboratory. Phenolphthalein, methyl orange, and other synthetic markers are synthetic indicators. Another example of a synthetic indicator is litmus paper.

Methyl orange shows red colour in acidic solution and yellow colour in basic solution. Phenolphthalein turns colourless in acidic solution and pink in the basic solution.

Olfactory Indicators

Olfactory indicators help identify whether the given solution is acidic or basic by changing its smell instead of colour.

Onion, vanilla and cloves are examples of olfactory indicators.

Importance of Indicators

The nature of a material is important in Biology, Chemistry, Engineering, Water Purification, Agriculture, Forestry, Food Industry, Environment, Water Treatment, Medicine, Nutrition, and other fields.

Practice Exam Questions

Red Cabbage Indicator

The natural pH indicator in red cabbage juice changes colour based on the solution’s acidity. Flavin is the pigment in red cabbage that produces the red colour shift (an anthocyanin). Apple skins, plums, and grapes contain flavin, a water-soluble pigment. The indicator turns red when exposed to very acidic solutions, purple when exposed to neutral solutions, and greenish-yellow when exposed to basic solutions.

Red Cabbage Experiment

Let’s perform the Red Cabbage experiment now

Materials Required for Red Cabbage Experiment

• i. A red cabbage
• ii. A sharp knife
• iii. A pot of boiling water
• iv. Household liquids to test (vinegar, baking soda, juices, soaps, bleach, ammonia)
• v. Glass bowl 
• vi. Something to stir

The aim is to create a natural indicator using red cabbage.

Red Cabbage Experiment Procedure

• 1. Cut around \(2 – 3\) cups of red cabbage.
• 2. Boil the red cabbage pieces in a kettle of water for a few minutes. Turn off the heat and let it sit for \(10\) minutes after it has boiled.
• 3. Strain the water and set it aside to cool in a glass bowl.
• 4. Pour some into transparent cups or glasses once it has cooled and experimented with different liquids.
• 5. Gently stir or swirl the solution to see how it changes.
• 6. It will be noticed that the colour of the substance will change depending on whether it is acidic or basic.

Observation

Acidic chemicals turn the solution purple to red or pink in appearance. The purple solution becomes blue when neutral chemicals are added. The purple solution turns green or yellow when basic chemicals are added.

Conclusion

Hence, red cabbage is a natural indicator.

Making \({\text{pH}}\) paper

Red cabbage can also be used to make \({\text{pH}}\) paper strips in addition to the solution. We can use a filter paper (or a coffee filter) dipped in the concentrated red cabbage solution.

Soak it for a while, then remove the paper and dry it. After it has dried, cut the paper into little strips, which can then be used to test the \({\text{pH}}\) of various liquids; see what colour you get by putting a drop of liquid on the test strip. Depending on whether the strip is acidic or basic, it turns red or green.

Red Cabbage \({\text{pH}}\) Indicator Colour Chart

Below given is the table which indicates the colour according to the \({\text{pH}}\) of the liquids:

\({\text{pH}}\)	Colour
\(2\)	Red
\(4\)	Purple
\(6\)	Violet
\(8\)	Blue
\(10\)	Blue-Green
\(12\)	Greenish Yellow

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Disadvantages of Using Red Cabbage Juice as an Indicator

• i. Slower than litmus paper.
• ii.It contaminates the solution.
• iii.It does not tell acid strength.
• iv. It requires more solutions than litmus paper.
• v. If the solution is dark, the colour change is not visible.

Summary

This article studied how indicators change their colour or characteristic smell to detect that the given substance is acidic or basic. We also studied that the red cabbage indicator is a natural indicator and changes to red in acidic solutions, purple in neutral solutions and greenish-yellow in basic solution. We now know how to execute an experiment to make red cabbage a natural indication.

PRACTICE QUESTIONS RELATED TO RED CABBAGE INDICATOR

FAQs on Red Cabbage Indicator

Q.1: How does the red cabbage indicator work?
Ans: When red cabbage is treated with an acid or a base, it produces anthocyanin, a water-soluble pigment that changes colour. In acidic situations with a \({\text{pH}}\) less than \(7,\) the pigment turns red, and in alkaline (basic) environments with a \({\text{pH}}\) of more than \(7,\) the pigment turns bluish-green.

Q.2: Is red cabbage a good indicator?
Ans: Red cabbage is a good indicator, but it has its disadvantages which are as follows:
It is slower than litmus paper, it contaminates the solution, it does not tell about the acidic or basic strength, it requires more solutions than litmus paper, and if the solution is dark, the colour change is not visible.

Q.3: How long does the red cabbage indicator last?
Ans: Over time, the red cabbage indicator solution will acquire an odour and mould. Red cabbage indicator solution that has not been used can be kept refrigerated for up to one week in a stoppered flask.

Q.4: Why is the red cabbage indicator called an acid-base indicator?
Ans: The red cabbage indicator is called an acid-base indicator because in acidic situations with a \({\text{pH}}\) less than \(7,\) the pigment turns red, and in alkaline (basic) environments with a \({\text{pH}}\) of more than \(7,\) the pigment turns bluish-green.

Q.5: How to make the red cabbage a \({\text{PH}}\) indicator?
Ans: The red cabbage can be made a \({\text{pH}}\) indicator by following these steps:
i. Take a red cabbage and cut off about \(2 – 3\) cups.
ii. Boil the pieces of red cabbage in a pot of water for a couple of minutes. After it is boiled, turn the heat off and let it sit for ten minutes.
iii. Strain the water in a glass bowl and let it cool.
iv. Once it is cooled, pour some into clear cups or glasses and experiment with different liquids.
v. Stir or swirl the solution gently and observe the changes. It will be observed that the colour of the substance will change according to its acidic or basic characteristics.

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