How to make a universal indicator from cabbage

The universal indicator is one of the most commonly used substances to check whether a substance is acidic or basic. This chemical compound is sensitive to the pH of each solution where it is found, and will indicate whether the substance is acidic or alkaline. Today, we will see how to make a universal cabbage-based indicator.

purple cabbage

Materials

- 250 g purple cabbage.

- A pot with a capacity of one litre.

- A metal bracket.

- One burner.

- A sieve.

- A glass jar.

- Water

Creating our universal indicator

The first thing we are going to do is cut the cabbage into pieces, the darker they are, the better. Next, place the cabbage pieces in the pot.

Once the cabbage pieces are in the pot, it is time to add about half a litre of water and let the pot boil on the cooker for about 10 minutes.

After boiling our mixture for the estimated time, we turn off the cooker and let our solution cool down. Once our solution is cool, we strain it through a strainer, recover the liquid in a glass bottle, identify it and we have our indicator ready to use.

Testing our indicator

Universal indicator

To test our indicator, we must place three different flasks with the same volume of acidic and alkaline solutions, such as lemon juice, coffee, soapy water, milk, etc.

In these containers, we add the same amount of indicator as we have done (about 20 drops) and observe how each of the solutions inside the containers change colour, indicating the acidity or alkalinity of each of the solutions.

How it works

When purple cabbage is boiled, it releases a substance called anthocyanin into the water, which is nothing more than an organic compound that is very sensitive to the pH levels of various aqueous media. Thus, when in acidic or alkaline solutions, it changes colour, indicating the degree of acidity or pH of the solutions, functioning in a similar way to phenolphthalein, one of the most common compounds in water. indicators most common in laboratories.

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