Experiments with gases

Let's work with gases. Experiments with gases are somewhat more difficult to do than with liquids. Therefore, first of all, we will need plugs with holes and gas pipes. Slide a rubber or polyethylene flexible tube 30 centimeters long over the glass tube, and insert a short glass tube into the other end.

Let's work with gases. Experiments with gases are somewhat more difficult to do than with liquids

Now we can begin our experiments with gases. Prepare lime water by pouring hot water (1/2 cup) with half a teaspoon of chopped slaked lime, stir the mixture and let stand. The transparent sediment over the settled solution is lime water. Drain the sediment carefully; this laboratory technique, as you remember, is called decantation.

Take a chilled bottle of mineral water or lemonade. Open the stopper, quickly insert the stopper with the gas outlet tube into the neck, and lower its other end into a glass of lime water. Place the bottle in warm water. Gas bubbles will be released from it. This is carbon dioxide CO2 (aka carbon dioxide, carbon dioxide). It is added to water to make it tastier.

The gas enters the glass through the tube, it passes through the lime water, and it becomes cloudy before our eyes, because the calcium hydroxide contained in it turns into calcium carbonate CaCO3, and it dissolves poorly in water and forms a white cloud.

Open another bottle, insert the tube stopper, and continue pouring carbon dioxide through the lime water. Some time later, the solution will again become transparent, because carbon dioxide reacts with calcium carbonate, converting it into another salt - Ca(HCO3)2 bicarbonate, and this salt is very soluble in water.

Let's do an experiment with ammonia. It is easy to recognize by its sharp characteristic smell - the smell of pharmacy ammonia.

Pour some boiled saturated washing soda solution into the bottle. Then add ammonia, insert a stopper with a flexible discharge tube into the neck and put the tube upside down on its other end. Heat the bottle in warm water. Ammonia vapors are lighter than air and will soon fill an inverted tube. Still holding the tube upside down, gently dip it into the glass of water. Almost immediately, the water will begin to rise up into the test tube, because ammonia dissolves well in water, making room for it in the test tube.

Second, let's do a good ammonia test. A qualitative reaction is one that allows one or another substance or group of substances to be accurately identified.

Prepare a weak solution of copper sulfate (it should be pale blue) and lower the gas pipe into it. When ammonia NH3 starts to evolve, the solution will turn bright blue at the end of the tube. Ammonia with a copper salt gives a brightly colored complex compound of a rather complex composition [Cu(NH3)4]SO4.

Now try to get a very small piece of calcium carbide - we will get acetylene. Assemble the device, as in the previous experiment, only pour soda, not ammonia, into the bottle. Dip a small pea-sized piece of calcium carbide carefully wrapped in absorbent paper into it and insert the cork with the tube. When the blotting paper is soaked, gas will start to release, which you will continue to collect in an inverted tube. A minute later, turn the tube upside down and bring up a lighted match. The gas will flare up and burn with a smoky flame. This is the same acetylene used by gas welders.