Kneel down for a few interesting, obvious junior high school chemistry demonstration experiments

1. Improvement of combustion condition experiments.

When teaching the section on combustion and slow oxidation in Chapter 1, Section 4 of the compulsory education chemistry textbook, it is easy for students to understand that insulating air can extinguish fires, but they are always skeptical that lowering the temperature below the ignition point of combustibles can also extinguish fires. In order for students to truly understand the principle of fire extinguishing, we added an experiment to lower the temperature to extinguish the fire.

The experimental process is as follows: add about 150ml of water to a 250ml beaker, and then add an appropriate amount of NH4NO3 to the water, and stir constantly to reduce the temperature of the water sharply; Then pour a small amount of soybean oil into a small tin box and light it; Then use the crucible pliers to place the small iron box on the cold water surface of the beaker, and the students can see that the flame is extinguished due to the decrease in temperature. In order to make the observed phenomenon more comprehensive, we took out the small tin box and re-ignited it, and the soybean oil remaining in the tin box burned again in the air.

So far, the students have been convinced that lowering the temperature can extinguish the fire, and at the same time, they have deepened their understanding of the principle of fire extinguishing.

2. Improvement of hydrogen gas flow blowing experiment.

According to the compulsory textbook demonstration experiment 3 4 device to do hydrogen bubble blowing experiment, the blown bubbles can not be continuous, sometimes the control is not good, the bubbles are also relatively calibrated to make the experimental phenomenon more obvious, we have made the following changes to this device: first replace the glass tip of the rubber head dropper with a glass tube without a sharp mouth, then cut off the top of the rubber head dropper rubber head, and then cut off the porous plastic head of the children's blowing bubble toys sold on the market and insert it into the top of the rubber head that has been cut, dip some washing liquid, and introduce hydrogen gas from the glass tube. Continuous, bulky hydrogen bubbles can be blown out at the porous plastic head.

Egg whites are heated in water --- denaturation of proteins.

The best observation for the preparation of hydrogen is to put a zinc skin (ordinary battery case) in the test tube, add a test tube plug, a thin glass catheter with a pointed mouth, add hydrochloric acid to the test tube, and cover the plug after 3 seconds, then you can ignite hydrogen at the tip of the catheter

Sulfur is burned in oxygen and magnesium is burned in air.

Combustion of magnesium in the air.

The egg will float in the HCI.

1.Blow air to make a fire: wrap sodium peroxide with cotton, blow air against sodium peroxide with a glass tube, and after a while, cotton will burn: 2Na2O2+2CO2===2Na2CO3+O2

2.Fountain experiment: The dry gas collection cylinder is filled with ammonia gas, which initiates a reaction, and the water dripping with phenolphthalein below reacts and turns red in the gas collection cylinder.

3.Thermite reaction: A mixture of iron oxide and aluminium is wrapped in a wetted filter paper, covered with a layer of potassium chlorate, and ignited with magnesium strips.

3al+fe2o3==3fe+al2o3

4.Color reaction: the sodium hydroxide solution of phenolphthalein is red, add hydrochloric acid to become colorless, carefully design the mechanism (hide the sodium peroxide), oscillate and turn red, and then become colorless.

First of all, add vinegar to the egg shell, this reaction du

It's not obvious, and it can be said that there is almost no anti-dao response.

I recommend having a flame reaction.

This one should. The inside is the easiest, needed.

Containing materials alcohol lamps, as well as various powders, the effect is also obvious, the operation is simple, please find the specific way by yourself.

The other is the saponification reaction, homemade soap, the materials are better to obtain, the last one can be observed redox, the material is an apple, the cut green apple is oxidized in the air, and the ferrous ions are oxidized to reddish-brown.

If there is concentrated sulfuric acid (I said if), it is not bad to add concentrated sulfuric acid to sucrose, which is as fun as foaming, oh yes, you can also take quicklime, quicklime with water, release heat, and then find a pipe to blow air into it There will be precipitation.