Experimental principle
Cobalt hydroxide will show different colors when it loses water gradually when heated, so it can be made into a thermometer according to the color change of temperature.
Experimental steps and phenomena
Add 95% ethanol and a small amount of red cobalt chloride crystal (CoCl2 6H2O) into the test tube, shake it evenly and dissolve it. It turns purple at room temperature, and the color changes from blue-purple to pure purple with the increase of temperature when heating.
2. soda-acid fire extinguisher
Experimental steps and phenomena
(a) As shown in the figure below, use a large bottle with a single-hole rubber stopper and insert the glass tube. Add some sodium bicarbonate solution to the bottle, take a test tube that can be put into the bottle, fill it with concentrated hydrochloric acid, slowly put the test tube into the bottle, make the test tube stand upright, and plug it with a rubber stopper with a glass tube. When using the fire extinguisher, turn the bottle upside down and aim the glass nozzle at the flame. Watch out! Don't point the nozzle at others or yourself.
(b) adding a detergent to the acid to produce a covering foam. Aim the bottle at the flame, quickly turn the bottle upside down, and the violent reaction will produce a lot of carbon dioxide, and then the pressure of the gas will press the liquid out of the nozzle to extinguish the fire.
3, wand lighting
Can a glass rod be used instead of a match to light an alcohol lamp?
Experiment: put a small amount of potassium permanganate crystal on the mirror (or glass), drop 2 or 3 drops of concentrated sulfuric acid on potassium permanganate, dip it with a glass rod, and touch the wick of the alcohol lamp, and the alcohol lamp will light up immediately.
4. Build an "underwater garden"
Sodium silicate (Na2SiO3) was dissolved in water to make water glass with 40% solute mass fraction. When salt particles, such as chlorides of cobalt, iron, copper, nickel and lead, sulfates of aluminum, iron, copper and nickel, and nitrates of cobalt, iron, copper and nickel are gently added to water glass (be careful not to mix them), colorful "flowers" will slowly grow.
Step 5 paint
Experimental principle
FeCl3 _ 3 _ 3 solution is blood red in the presence of potassium thiocyanate (KSCN), blue in the presence of potassium ferrocyanide [K4 [Fe (CN) 6]], green in the presence of potassium ferricyanide [K3 [Fe (CN) 6]] and purple in the presence of phenol. FeCl3 _ 3 solution is yellow when sprayed on white paper.
Experimental supplies
White paper, brush, sprayer, wooden frame, nail clippers.
Ferric chloride solution, potassium thiocyanate solution, concentrated potassium ferrocyanide solution, concentrated potassium ferrocyanide solution, concentrated phenol solution.
experimental procedure
1. Dip potassium thiocyanate solution, concentrated potassium ferrocyanide solution, concentrated potassium ferricyanide solution and concentrated phenol solution with a brush and draw on white paper.
2. Dry the paper and nail it on the wooden frame.
3. Spray FeCl _ 3 solution on white paper with pictures with a sprayer.
6, wood carving or bamboo carving (word) method
Reaction principle: Dilute sulfuric acid turns into concentrated sulfuric acid when heated, which has a strong dehydration effect and makes cellulose (C6H 10O5)n dehydrate and carbonize, so it appears black or brown. Wash away the excess sulfuric acid to get black or brown flowers or characters on the wood (bamboo) ware.
Experimental steps: Draw flowers or write on wood (or bamboo) with a brush dipped in 5% dilute sulfuric acid. After drying, put the wood (bamboo) ware on a small fire for a period of time, and then wash it with water to get black or brown patterns or handwriting on the wood (bamboo) ware. 7. Traces of protein
Take an egg, wash the oil on the surface and dry it. Dip the brush in acetic acid and write on the eggshell. After the acetic acid volatilizes, cook the egg with dilute copper sulfate solution, and peel off the eggshell after the egg cools, leaving clear blue or purple handwriting on the egg white, but leaving no trace on the eggshell.
This is because acetic acid can dissolve a small amount of protein after dissolving eggshells. Egg white is a globulin composed of amino acids, which hydrolyzes under weak acidic conditions to produce peptides and other substances, and the peptide bonds in these substances are complexed with Cu2+ and appear blue or purple.
8. Violet discoloration experiment
-Principle of acid-base indicator
Violets are in full bloom this season. You can use violets as acid-base indicators.
See the new textbook (People's Education Edition) for the experimental operation, which is very interesting. This experiment is simple and clear. It also goes well with chrysanthemums.
Boyle first proposed the concept of acid-base indicator by accident.
9. Check the iodine in iodized salt.
Experimental principle
Iodized salt contains potassium iodate (KIO3), but generally does not contain other oxidizing substances. Under acidic conditions, IO3- can oxidize I- to I2, and it will turn blue when it meets starch test solution. However, salt without iodine cannot have a similar reaction.
Experimental supplies
Test tube, rubber head dropper.
Iodized salt solution, non-iodized salt solution, KI solution, dilute sulfuric acid, starch test solution.
experimental procedure
1. Add a small amount of iodized salt solution and non-iodized salt solution into two test tubes, and then drop a few drops of dilute sulfuric acid and a few drops of starch test solution respectively. Observe the phenomenon.
2. Add an appropriate amount of KI solution and a few drops of dilute sulfuric acid to another test tube, and then add a few drops of starch test solution. Observe the phenomenon.
3. Pour the liquid in the third test tube into the first two test tubes respectively, mix them evenly and observe the phenomenon.
10, homemade soda
Soda water is made of mineral water or drinking water after being boiled and disinfected by ultraviolet radiation and filled with carbon dioxide. Belonging to carbonated drinks containing carbon dioxide. This factory makes soda by dissolving carbon dioxide gas in water under pressure. The more carbon dioxide dissolved in soda, the better the quality. About 1 volume of soda water on the market contains 1 volume to 4.5 volume of carbon dioxide. In addition to carbon dioxide, some soft drinks also contain proper amount of sugar, juice and essence.
When carbon dioxide is excreted, it can take away some calories, so drinking soda can reduce fever and quench thirst. When drinking iced soda, because the temperature of soda is low, more carbon dioxide is dissolved (at 0℃, the solubility of carbon dioxide is higher 1 times than at 20℃), and more carbon dioxide is excreted, which can take more heat away, so the temperature of the stomach can be reduced. Therefore, you must not drink a lot of iced soda to avoid strong cold stimulation to the stomach, causing stomach cramps, abdominal pain and even gastroenteritis. In addition, excessive soda will dilute gastric juice, reduce its digestive ability and bactericidal effect, affect appetite, and even increase the burden on the heart and kidneys, causing physical discomfort. Soda can also be made in the laboratory and at home. Take a clean soda bottle, add 80% cold boiled water into the bottle, then add sugar and a small amount of fruity essence, then add 2 g of sodium bicarbonate, stir and dissolve, and then quickly add 2 g of citric acid. Immediately press the bottle cap tightly, so that the generated gas cannot escape, but dissolves in water. Put the bottle in the refrigerator to cool. After taking it out, open the bottle cap and you can drink it.
1 1, urine sugar test
[experimental principle]
Diabetes patients have more glucose in their urine, which makes them seriously ill. To detect the sugar content in urine, we can use a liquid medicine called Fehling reagent, which is made up of copper sulfate, potassium sodium tartrate and sodium hydroxide solution. The reaction principle is the same as that of detecting aldehyde groups with copper hydroxide suspension.
[experimental operation]
Preparation of (1) Flynn test solution
Take 100 mL distilled water and add 3.5 g copper sulfate crystal (CuSO4 5H2O) to make solution I; Take 100 mL distilled water, add 17.3 g potassium sodium tartrate (NaKC4H4O6 4H2O) and 6 g sodium hydroxide to make solution II. The solution I and the solution II are divided into two clean reagent bottle with sealed plugs, and are mixed in equal volume when in use to obtain the Fening test solution.
② check
Suck a small amount of urine (1mL~2 mL) with a straw and inject it into a clean test tube, then add 3 ~ 4 drops of Fehling reagent into the test tube with another straw and heat it to boiling on the flame of an alcohol lamp. After heating: (1) If the solution is still blue, there is no sugar in the urine, which is indicated by "-"; (2) If the solution turns green, it means that the urine contains a small amount of sugar, which is indicated by "+"; (3) If the solution is yellow-green, it means that there is a little more urine sugar, which is indicated by "++"; (4) If the solution is khaki, it means that there is more urine sugar, which is represented by "+++"; (5) If the solution is brick red and turbid, it means that there is a lot of urine sugar, which is represented by "++++".
Determination of Vitamin C in Vegetables
Experimental principle
Starch solution will turn blue-purple when it meets iodine, which is the characteristic of starch. Vitamin C can react with iodine in blue-purple solution, making the solution colorless. Through this principle, it can be used to detect vitamin C in some vegetables.
Experimental steps and phenomena
Put a small amount of starch in the glass bottle, pour some boiling water and stir with a stick to form a starch solution. Drop 2 ~ 3 drops of iodine, you will find that the milky white starch liquid turns blue-purple. Find 2 ~ 3 pieces of green vegetables, remove the leaves, leave the petiole, squeeze out the juice from the petiole, and then slowly drip the juice into the blue-purple liquid in the glass bottle, stirring while dripping. At this time, you will find that the blue-purple liquid has become milky white again. It shows that vegetables contain vitamin C.