What is the practice of alum crystallization? Why can t alum evaporate and crystallize

Principle: There are two ways to make crystals from a saturated solution, for solubility.

Solid solutes that are not greatly affected by temperature are commonly used to evaporate solvents.

Supplies] beaker.

Surface dishes, iron stands, alcohol lamps.

Asbestos nets, funnels, graduated cylinders.

Glass rods, tweezers, filter paper, fine wires, copper sulfate crystals (CuSO4·5H2O).

Operation] 1. Prepare small crystals In a beaker containing 100ml of water, add 10g of finely ground copper sulfate powder, and add 1ml of dilute sulfuric acid at the same time.

prevents the hydrolysis of copper sulfate) and heats to completely dissolve the crystals. Continue to heat to 80-90, filter while hot, and the filtrate flows into a beaker that has been washed and warmed with hot water, and the lid is allowed to stand. After a few hours or overnight, you will notice the formation of several small crystals at the bottom of the cup.

2. The growth of small crystals Pick a crystal with a relatively complete crystal shape, tie it with a thin wire, and hang it in a saturated copper sulfate solution.

beaker and cover and let stand. Add a small amount of slightly hot saturated copper sulfate solution to the beaker every day, and the small crystal will gradually grow into a large crystal.

1) The reagent used must be pure, and it is difficult to obtain a complete crystal form if it contains impurities.

2) Control the concentration of the solution, if the solution is too concentrated, the crystallization rate is too fast, and it is not easy to form crystals with complete crystal shape; If the concentration of the saturated solution is not large, the crystallization rate is too slow, and the small crystals grow slowly. When preparing small crystals, use a saturated solution 20 -30 above room temperature; The saturated solution added later should be a solution higher than room temperature 15 -20, the amount of each addition is about 1 10 of the original solution, the crystals should be taken out when added, and the crystals should be immersed after the temperature of the solution is uniform.

3) Pay attention to the change of ambient temperature, the saturated solution should be cooled slowly, and the beaker can be wrapped with cloth or cotton. The crystals can be removed during the day when the temperature is high and put back into the solution at night.

4) The container used must be clean and covered to prevent dust from falling in.

3. Preparation of small crystals Once crystallized, if the precipitated crystals are too small, a few crystals with complete crystal shape can be picked up, and then cultivated with a saturated solution higher than room temperature, so that they can be tied with a thin wire. You can also hang a fine line in the filtrate, and when the solution cools, small crystals will be precipitated on the fine line, and one crystal shape will be kept intact (the rest will be peeled off) to make the crystal seed, and it will grow according to step 2.

1. Alum. Crystal. Target. Experiment.

Preparation. Take 50ml of 2mol·l-1

KOH solution, add 2g in multiple doses

Aluminum scrap. Goods.

Aluminum toothpaste shell, aluminum alloy.

Cans. etc.), after the reaction is completed, use a Brinell funnel. Suction filtration. Take.

Liquid. Dilute to l00 ml and add dropwise 3 with constant stirring

mol·l-1

H2SO4 solution (Press.

Chemistry. Reactive metering). Heat until the pellet is completely dissolved, and concentrate the solution appropriately, then use.

Tap water. Cooling.

Crystallized. The resulting crystal is kal(SO4)2·12H2O.

2. Cultivation of transparent single crystals of alum.

kal(SO4)2·12H2O.

Regular octahedron. Crystal form.

In order to obtain a single crystal with intact edges and corners and transparent corners, it should be allowed.

Seed crystals. Seed.

There is enough time to grow, and the premise for the crystal seeds to grow is solution.

Concentration. in a state of appropriate supersaturation. This experiment will be done by willing.

Saturated solution. At.

Room temperature. Under the standstill, lean. Solvent. Target.

Nature. Volatilization creates a quasi-stable state of the solution, and the crystal seed is artificially injected to gradually grow into a single crystal.

Growth and selection of seed crystals.

According to KAL (SO4) 2·12H2O.

Solubility. Weigh l0g of homemade alum, add an appropriate amount of water, heat and dissolve, and then put it in a place that is not easy to vibrate, a beaker.

Mouth on the shelf one. Glass rods.

Then cover a piece over the beaker mouth.

Filter. Lest.

Dust. Drop, leave for a day, the bottom of the cup.

There will be small crystals precipitated, from which the complete crystalline crystals will be selected for later use, and the solution will be filtered for later use.

The growth of crystals (can be operated under class) Tie the seed crystals with a fine polyester thread for sewing, cut off the remaining heads, wrap them around the glass rod and hang them in a filtered saturated solution, and observe the slow growth of the crystals. After a few days, you can get large crystals with intact edges and corners, and crystal clear.

In the process of crystal growth, it should be observed frequently, and if small crystals are found to grow on the seed crystals, they should be removed in time. If there is crystal precipitation at the bottom of the cup, it should also be filtered out in time to avoid affecting the crystal growth.

Summary. Alum (chemical formula kal(SO4)2·12H2O) has a high solubility in water, so it is difficult to separate from aqueous solution by evaporation crystallization. Even if the aqueous solution of alum is evaporated to dryness, only an amorphous white powder will be obtained, not crystals.

This is because a relatively stable hydrogen bond is formed between the water molecule and the alum molecule in the alum molecule, which makes it difficult for the alum molecule to form a regular crystal structure. Therefore, other methods, such as cooling crystallization or adding other chemicals for precipitation, are often used to separate from the aqueous solution of alum.

Alum (chemical formula kal(SO4)2·12H2O) has a high solubility in water, so it is difficult to separate it from aqueous solution by evaporation and crystallization. Even if the aqueous solution of alum is evaporated to dryness, only an amorphous white powder will be obtained, not crystals. This is because a relatively stable hydrogen bond is formed between the water molecule and the alum molecule in the alum molecule, which makes it difficult for the alum molecule to form a regular crystal structure.

Therefore, other methods, such as cooling crystallization or adding other chemicals for precipitation, are often used to separate from the aqueous solution of alum.

Fellow, I really didn't understand, I can be more specific.

Hydrogen bonds are formed between the water molecules in the alum molecule and the alum disturbance rock locust molecule, which makes it difficult for the alum molecule to form a regular crystal structure. In water, alum molecules form hydrogen bonds with water molecules, which increases the interaction between alum molecules and water molecules, making it more difficult for alum molecules to form crystals. When the aqueous solution of alum evaporates, the water molecules will gradually evaporate, while the alum molecules will gradually condense.

However, due to the strong hydrogen bonding force between the alum molecule and the water molecule, it is difficult for the alum molecule to form a regular crystal structure. Therefore, even if the aqueous solution of alum is evaporated to dryness, only an amorphous white powder will be obtained, not crystals. Therefore, other methods, such as cooling crystallization or adding other chemicals to precipitate jujube cryptosome, are usually used to slow down the separation of alum from the aqueous solution of alum.

For example, an aqueous solution of alum can be cooled to a certain temperature so that the alum molecules gradually coalesce to form crystals. Alternatively, alum can be separated by adding other chemicals, such as copper sulphate or potassium chloride, to form a precipitate with alum molecules.

Summary. In response to this problem, the reason why ammonium sulfate cannot evaporate and crystallize is because its boiling point is too low, and the boiling point is lower than room temperature, so it cannot evaporate and crystallize. The solution to this problem is to use the heating evaporation method, that is, the ammonium sulfate is heated above the boiling point, evaporated, and then cooled to crystallize.

In addition, solvent crystallization can also be used, that is, ammonium sulfate is dissolved in a solvent and then the solvent is slowly evaporated to crystallize. In addition, solvent extraction can be used, in which ammonium sulfate is dissolved in a solvent and then the solvent is slowly evaporated to crystallize. Finally, solvent extraction can also be employed, in which ammonium sulfate is dissolved in a solvent and then the solvent is slowly evaporated to crystallize.

These methods can effectively solve the problem that ammonium sulfate cannot evaporate and crystallize.

In response to this problem, the reason why ammonium sulfate cannot evaporate and crystallize is because its boiling point is too low, and the boiling point is lower than room temperature, so it cannot be evaporated and crystallized. The solution to this problem is to use the heating evaporation method, that is, the ammonium sulfate is heated above the boiling point, evaporated, and then cooled to crystallize. In addition, solvent crystallization can also be used, that is, ammonium sulfate is dissolved in a solvent and then the solvent is slowly evaporated to crystallize.

In addition, solvent extraction can be used, either by dissolving ammonium sulfate in a solvent imitation state, and then slowly evaporating the solvent to crystallize. Finally, solvent extraction can also be employed, in which ammonium sulfate is dissolved in a solvent and then the solvent is slowly evaporated to crystallize. These methods can effectively solve the problem that ammonium sulfate cannot evaporate and crystallize.

Can you add, I don't quite understand it.

In response to this problem, we can say that the reason why alum cannot evaporate and crystallize is that its boiling point is too low. The boiling point of alum is only about 50, which is much lower than the boiling point of water, so it cannot evaporate and crystallize. Also, the solubility of alum is also very low, it can only be dissolved in a very small amount in water, so it cannot evaporate and crystallize.

The solubility of alum is only about that, which is much lower than that of water, so it cannot evaporate and crystallize. Alum has a low boiling point and solubility, so it cannot evaporate and crystallize. However, alum has many other useful properties, such as it can be used to clean metal surfaces as it dissolves dirt, and it can also be used to eliminate chloride ions in water, thus improving the taste and quality of water.

It is a crystal formed by potassium aluminum sulfate and water. Daily life is used to precipitate water magazines, also known as alum, potassium alum, potassium alum, potassium alum. It is a double salt of potassium sulfate and aluminum sulfate containing crystalline water.

Chemical formula KAL(SO4)2·12H2O, formula, colorless cube, monoclinic or hexagonal crystal, with glass luster, density, melting point.

9 molecules of crystal water are lost, and 12 molecules of crystal water are lost at 200, soluble in water, insoluble ethanol. Alum has a sour taste, is cold, and poisonous. Therefore, it has antibacterial effect, astringent effect, etc., and can be used as traditional Chinese medicine.

Storage and transportationStore in a cool, dry and ventilated warehouse. Keep away from fire and heat sources. It should be stored separately from the oxidizing agent.

The lighting, ventilation and other facilities in the storage room should be explosion-proof, and the switch should be located outside the warehouse.

Equipped with the corresponding variety and quantity of fire-fighting equipment. It is forbidden to use mechanical equipment and tools that are prone to sparks.

Pay attention to personal protection in sub-packing and handling operations.

When handling, it is necessary to load and unload lightly to prevent damage to the packaging and containers.

Homemade crystals.

It must be fun to keep the crystals on the windowsill. If you add some food coloring, it can also make it grow any color you want.

One of the keys to making your own crystals is to find the right chemistry. You may have seen copper sulphate and potassium permanganate in school. Both of these reagents are highly toxic, so neither is easily available at a nearby pharmacy.

If you ask very politely, maybe your natural science teacher will give you a little sample.

In this chapter, we decided to use potassium aluminium sulfate, commonly known as alum. It is non-toxic and is commonly used in bread making to increase the whiteness of bread. Although almost every family has it, you still have to be careful not to get it in your eyes.

100 grams of alum is enough to make crystals. Alum can also be used to prevent fire and tan ** in the sun, which we will discuss in other chapters. It can also be used as a hemostatic agent when ** is scratched, or it can be used to make crystals as a deodorant under the armpits.

Material preparation: 10 g of potassium aluminum sulfate (alum).

A large tumbler.

A well-washed lollipop stick.

Warm water line. Some small stones, preferably with raw edges.

Method: 1 Be sure to wash the stone – preferably under running water.

2 Fill the cup with enough warm water – cover the stone (about 1 3 points in the cup), but don't put the stone in it yet.

3 Add the alum to the cup and stir with a lollipop stick until the alum is no longer easily dissolved. There may be some alum particles left at the bottom of the cup at this point, so you can just put the stone into the cup, or the more classic method as shown in the picture below: tie a thread to a small stone, and wrap the other end of the thread around the lollipop stick.

We used both.

4 If you want to add food coloring, this is the stage. Then, you can proudly show it to your parents and surprise the mom and dad who always pat you on the head and call you baby.

Evaporation is the key to making these little crystals well, so be sure to keep the cup in a warm place. It will take a few days for the first crystals to appear, and it will take a few weeks to see all the crystals. If you want to get a large crystal, you need to tie the small pieces of crystal that you started to make like a small stone at the beginning, and then repeat the above process.

The crystal you see in the picture above** is one of the crystals we cultivate: the one on the left is smaller, and the one on the right is large and round, which we made at the bottom of the cup in a variety of ways, and it looks more impressive than natural crystals. It took 6 weeks before and after making this crystal, and we kept adding alum to the cup.