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Homemade indicators. Chemical experiments

Entertaining experiences at home / Chemistry experiments for children

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In chemical laboratories, indicators are used every now and then - sometimes to determine certain substances, and mostly to find out the acidity of the medium, because both the behavior of substances and the nature of the reaction depend on this property. We will need indicators more than once, and since it is not always possible to buy them, we will try to cook them ourselves. Plants will serve as the raw material: many flowers, fruits, berries, leaves and roots contain colored substances that can change their color in response to a particular impact. And, getting into an acidic (or, conversely, alkaline) environment, they clearly signal this to us.

It is not difficult to collect plant "raw materials" in the summer - in the forest, in the field, in the garden or vegetable garden. Take bright flowers - iris, dark tulips and roses, pansies, mallow; dial raspberries, blackberries, blueberries, blueberries; stock up on a few leaves of red cabbage and young beets.

Since indicator solutions are obtained by boiling (a decoction is something like a broth), they, of course, quickly deteriorate - turn sour, moldy. They must be prepared immediately before the experiment. Take some stocked raw materials (the exact amount does not matter), put in a test tube, pour water, put in a water bath and heat until the solution is colored. After cooling, filter each solution and pour into a clean bottle prepared in advance with a label.

To provide yourself with indicators for the whole year, dry the petals and berries in the summer, put them in separate boxes, and then, in the same way as mentioned above, prepare decoctions from them, separately from each plant.

To find out which decoction serves as an indicator for a particular environment and how its color changes, it is necessary to conduct a test. Take a few drops of a homemade indicator with a pipette and add them alternately to an acidic or alkaline solution. Table vinegar can serve as an acidic solution, and a solution of washing soda, sodium carbonate can serve as an alkaline solution. If, for example, you add a bright blue decoction of iris flowers to them, then under the influence of vinegar it will turn red, soda - green-blue.

Record the results of all these experiments carefully, preferably in a table; we present a sample of it here.

Not only leaves and berries can serve you as indicators. Some juices (including those from red cabbage, cherries, black grapes, black currants) and even compotes clearly react to a change in acidity with a change in color. Ordinary borscht can serve as an indicator. Mistresses have noticed this for a long time and use this property of beetroot broth, but not for analysis. To make the borscht bright red, a little food acid - acetic or citric acid - is added to it before the end of cooking; The color changes right before your eyes.

The phenolphthalein indicator is widely used in laboratories. Let's prepare it from pharmaceutical tablets of the same name. Rub one or two tablets and dissolve in about 10 ml of vodka (in extreme cases, just in warm water). In any case, the tablets will not dissolve completely, because in addition to the main substance, phenolphthalein, they also contain talc or chalk filler. Filter the resulting solution through absorbent paper and transfer to a clean bottle labeled "phenolphthalein indicator". This colorless solution does not deteriorate over time. It will come in handy, and more than once, to determine the alkaline environment: in it, it instantly turns red. To test, add a drop or two of phenolphthalein to the washing soda solution.

And here is a sample table that will serve as a guide for you when choosing an indicator:

Indicator	Mortar color
	parent	in an acidic environment	in an alkaline environment
Grape juice	Dark red	Red	Green
blue iris	Bright blue	Red	green-blue