We paint without paint. Fun chemistry experience at home

ENTERTAINING EXPERIENCES AT HOME
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We paint without paint. Chemical experiments

Entertaining experiments in chemistry

Entertaining experiences at home / Chemistry experiments for children

Without paint, many metal surfaces can be painted if they are coated (chemically or electrochemically) with a thin layer of colored oxides or salts firmly adhered to the surface. The last condition is not so easy to fulfill. For example, iron in moist air quickly (and without our help) becomes covered with a red-brown coating of oxidation products, simply put, with rust, but this method of painting is no good, because the rust barely sticks and gets dirty when touched.

Here we will give several recipes for coloring non-ferrous metals. Only some of them are suitable for a home experiment, the rest require chemicals that you can’t buy either in a pharmacy or in a photo store. However, we hope you have already signed up for a chemistry circle.

Copper and brass tarnish rather quickly in air. But they will retain their shine if they are chemically dyed. The preparation of the parts will take some time, because the surface must be completely clean, without traces of dirt and grease. Carefully wipe the polished part with a cloth soaked in gasoline, and then with wet chalk or tooth powder. After rinsing the item in running water, hang it on a harsh thread or fishing line and do not touch it with your hands anymore so as not to leave grease stains (even if the skin looks completely dry, there is still at least a little grease on it). Dip the part in a dilute solution of nitric acid (no more than 5-10 ml per 100 ml of water) and rinse again, preferably with hot water. Preparation completed

What happens next depends on what color you decide to paint the copper. If it is black, then hold the part for five minutes in a solution in which 100 g of sodium hydroxide and 0,9 g of ammonium persulfate (NH₄)₂SO₈ (it is used in photography). Solution temperature 90-100 °C

In a solution of potassium chloride, nickel sulfate NiSO₄ and copper sulfate CuSO₄ (respectively 4,5, 2 and 10,5 g per 100 ml of water) at the same temperature, copper and brass will acquire a pleasant chocolate tint. Brass will become azure after a short exposure to a mixture consisting of 3 g of lead acetate (lead lotion can be used), 6 g of sodium thiosulfate (hyposulfite), 5 g of acetic acid and 100 ml of water. The temperature of such a solution is about 80 ° C

Copper can also be green. To do this, it must be lowered into such a solution: for 100 ml of water, 20 g of copper nitrate Сu (NO₃)₂, 30 g of ammonia and 40 g of ammonium chloride (ammonia) and sodium acetate; a solution of the latter substance is easy to obtain from soda and vinegar. Please handle copper nitrate with care, avoiding contact with the face and especially the mouth.

With the exception of the blackening experience, we do not state reaction times anywhere. Choose it yourself by experience, taking into account that the longer the processing time, the more intense the color.

The next metal that lends itself to chemical coloring is zinc. It is used infrequently, but everyone is well acquainted with galvanized objects - buckets, basins, troughs. The object of the experiment can be any old, unusable galvanized object. Wash its surface with a solution of soda or wipe it with a cloth soaked in gasoline, wash with hot water and soap and rinse several times. On a galvanized surface, we will apply mixtures of substances that will react with zinc; giving colored compounds. Here are the color recipes

Black: 2 parts copper nitrate, 3 parts copper oxide, 8 parts hydrochloric acid and 64 parts water; after the appearance of color, rinse the surface with water and dry

Green: 10 parts of copper sulfate and tartaric acid, 12 parts of water and 24 parts of sodium hydroxide solution in water (1:15); as soon as the color appears, immediately rinse the surface with water, otherwise there will be a brown tint

Blue: for 100 ml of water - 6 g of any nickel salt and the same amount of ammonium chloride

Golden: mix a solution of 1 part tartaric acid, 2 parts soda and 1 part water with pure clay; rub the surface with the mixture, and when it dries, rinse with water

Brown-bronze: a mixture of 1 part verdigris and 5 parts acetic acid; rub the surface with the mixture, rinse with water and dry

Copper; since zinc is more active than copper, it means that it is enough to moisten it with a solution of copper salt, for example, copper sulfate

By the way, with such paints you can draw a picture on a zinc surface.

Let's move on from zinc to aluminum. It is somewhat more difficult to color it: there are more operations, and you cannot do without electric current. Oxide and aluminum salts are inconspicuous, so another method of staining is needed. It is known: it is anodizing. Its essence is that a current is passed through an aluminum part immersed in an electrolyte; in this case, an oxide film with a thickness of less than 0,1 mm is formed on the surface. Since the aluminum parts in the electroplating bath serve as the anode, the process is called anodizing. The oxide film is permeated with microscopic branched pores, in which dyes are well retained. It is possible to paint the anodized surface with organic dyes, including natural ones, but it is better with inorganic substances. Usually, the part is processed alternately in two coloring solutions, and brightly colored reaction products remain in the pores.

Polish the aluminum part, degrease it with gasoline or acetone, rinse it in hot water and hang it on a wire. Dip the part for two to three minutes in a 5% sodium hydroxide solution, rinse again and immerse in a weak solution of nitric acid (20-30 ml of acid per 100 ml of water). Of course, it is no longer possible to touch the part, and if it is inconvenient to work with the suspension, help yourself with tweezers

Rinse the parts again in hot and cold water and hang on a wire in a glass. You can put a stick or pencil on the edges of the glass and wrap the wire around it once or twice, picking up such a height that the part is a few centimeters above the bottom. Connect the workpiece to the positive pole of the current source. Cathodes - steel plates - hang in the same way. Batteries can serve as a current source, but they will "sit down" very quickly; battery or transformer with rectifier is preferred

Pour a solution of sulfuric acid into the glass with the part (20 ml of acid per 100 ml of water; be careful!). Include a key or switch and a rheostat in the circuit to regulate the current. To measure it, you need a milliammeter, but a tester that many radio amateurs have is also suitable. Close the circuit and set the current at the rate of 20-25 mA per 1 cm² surfaces. The part will immediately be covered with gas bubbles - this releases oxygen, which oxidizes aluminum. At room temperature, the process takes about an hour.

We paint without paint

Rinse the anodized part in running water and start painting. Immerse the part alternately in two coloring solutions, holding in each for 5-10 minutes and rinsing each time in running water. Rinse and dry painted parts again.

Here are the compositions of coloring solutions and their possible concentration (in grams per 100 ml of water):

blue or blue color - potassium ferrocyanide (1-5) and iron (III) chloride (1-10); brown - potassium ferrocyanide (1-5) and copper sulfate (1-10); black - cobalt acetate (5-10) and potassium permanganate (1,5-2,5); yellow - potassium dichromate (5-10) and lead acetate (10-20); golden yellow - sodium hyposulfite (1-5) and potassium permanganate (1-5); white - lead acetate (1-5) and sodium sulfate (1-5); orange - potassium bichromate (0,5-1) and silver nitrate (5-10)

Author: Olgin O.M.

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▪ Electrification of water

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Scientists from the Cryolife medical corporation in Atlanta (USA) and German doctors are now developing a prosthetic heart valve for children, which is expected to grow with the patient.

If such a valve is implanted in a child, there will be no need for subsequent operations to replace it with a larger valve in a growing heart. Moreover, this prosthesis is gradually overgrown with host cells and becomes completely its own.

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