Goal of the work:observation of the growth process of a sodium chloride crystal and comparison of the resulting crystals with models of crystal lattices, checking the anisotropy of strength by splitting.
Progress:
To grow crystals at home, you need to prepare a supersaturated salt solution. The starting substance was salt, which people use very often, this is table salt.
She poured hot water into a glass and sprinkled table salt into it, stirring all the time. She poured until the salt stopped dissolving and a sediment formed at the bottom, which did not disappear with stirring. Then she took a piece of thin wire and wrapped it with a woolen thread. On the glass I put a stick on top and hung a wrapped wire on a thread from it. The brine gradually cooled, then the water from it began to evaporate. After three days (as long as possible), I pulled the wire out. The salt settled on the hairs in small, regular cubes.
It is necessary to periodically measure the sizes of some faces. The faces of the crystals change their sizes, they grow, the angles between the corresponding faces remain constant.
The shapes of the obtained crystals were compared with the shapes of crystal lattice models. NaCl table salt should have faces that are square and crystals that are cubes. The grown crystal meets these requirements
Conclusion
I chose the most convenient, acceptable method of growing crystals at home and grew table salt crystals. As the crystals grew, I observed. I compared the shapes of the resulting crystals with the shapes of their crystal lattices; they correspond to the shapes of cube crystals.
The attractive forces arising between planes consisting of only one type of Na+ or Cl- ions (forming the faces of the octahedron) are five times greater than between planes parallel to the faces of the cube, each of which contains both ions, both Na+ and Cl-. That is why it is much easier to split a NaCl crystal along the planes of a cube than along the planes of an octahedron. That is why it crystallizes, forming cubes. The crystal actually consists of ions of opposite signs.
Conclusion
Single crystals are solids whose particles form a single crystal lattice.
The external shape of single crystals of the same type may be different, but the angles between
their corresponding faces remain constant. This law of constancy of angles was formulated by the French naturalist J.B. Romeu de Lisle. He made an important conclusion: the correct shape of crystals is associated with the regular placement of the particles that form the crystal. Most minerals are single crystals. However, large natural single crystals are quite common rarely. Currently, many single crystals are grown artificially.
Crystals are characterized by the presence of significant forces of intermolecular interaction. The forces of interaction between atoms in crystals in different directions are not the same. The forces of attraction that arise between the planes forming the faces of the octahedron in table salt crystals consisting of ions of the same type are five times greater than the forces between the planes parallel to the faces cube, each of which contains both ions, Na+, and Cl-. In this we can trace the action of the law of anisotropy.. Its essence is that many properties solids depend on the direction in which these properties are measured. We studied the anisotropy of strength on table salt. If crystals of table salt, which have a cubic shape, are split, then the small fragments will have predominantly the shape rectangular parallelepipeds. This means that in directions parallel to the faces, the strength of a table salt crystal is much less than in diagonal and other directions. We were unable to study other physical properties due to the limitations of instruments and materials. For example, the thermal conductivity of a crystal measured in different directions may not be the same. It will be the same only in parallel and symmetric directions. The same can be said about electrical conductivity, hardness, and other properties. In other words, the symmetry of the external form is accompanied by symmetry physical properties crystals.
Laboratory work
Subject:"Observation of crystal growth from solution"
Target: learn to create crystals, watch the growth of a crystal
Theoretical information
There are two simple ways growing crystals from solution: cooling a saturated salt solution and evaporating it. The first step in any of the two methods is to prepare a saturated solution. In a school physics classroom, the easiest way is to grow potassium alum crystals. At home, you can grow a crystal of copper sulfate or regular table salt.
The solubility of any substance depends on temperature. Typically, solubility increases with increasing temperature and decreases with decreasing temperature.
When a hot (about 40°C) saturated solution is cooled to 20°C, it will contain an excess amount of salt per 100 g of water. In the absence of crystallization centers, this substance can remain in solution, i.e. the solution will be supersaturated.
With the appearance of crystallization centers, an excess of the substance is released from the solution; at each given temperature, the amount of substance that corresponds to the solubility coefficient at this temperature remains in the solution. Excess substance from the solution precipitates in the form of crystals; The more crystallization centers there are in the solution, the greater the number of crystals. The centers of crystallization can be dirt on the walls of the container with the solution, dust particles, and small salt crystals. If you give the fallen crystals the opportunity to grow within a day, then among them there will be specimens that are pure and perfect in shape. They can serve as seeds for growing large crystals.
To grow a large crystal, you need to add a crystal - a seed, pre-attached to a hair or thin fishing line, pre-treated with alcohol - into a carefully filtered saturated solution.
It is possible to grow a crystal without a seed. To do this, the hair or fishing line is treated with alcohol and dipped into the solution so that the end hangs freely. Crystal growth may begin at the end of the hair or fishing line.
If a large seed crystal is prepared for growing, it is better to add it to a slightly warmed solution. A solution that was saturated at room temperature will be unsaturated at a temperature 3-5°C above room temperature. The seed crystal will begin to dissolve in it and will lose its upper, damaged and contaminated layers. This will lead to an increase in the transparency of the future crystal. When the temperature drops to room temperature, the solution will become saturated again and the crystal will stop dissolving. If the glass with the solution is covered so that the water from the solution can evaporate, then the solution will soon become supersaturated and crystal growth will begin. During crystal growth, it is best to keep the glass with the solution in a warm, dry place where the temperature remains constant throughout the day. Depending on the experimental conditions, growing a large crystal can take from several days to several weeks.
Progress
1. Wash the glass and funnel thoroughly and hold them over steam.
2. Pour 100. g of distilled (or twice boiled) water into a glass and heat it to 30°C-40°C. Using the solubility curve shown in Figure 1, determine the mars salt required to prepare a saturated solution at 30°C.
Prepare a saturated solution and pour it through a cotton filter into a clean glass. Cover the glass with a lid or piece of paper. Wait until the solution cools to room temperature. Open the glass. After some time, the first crystals will begin to fall out.
3. After a day, drain the solution through a cotton filter into a clean, newly washed and steamed glass. Among the many crystals remaining at the bottom of the first glass, choose the cleanest crystal of the correct shape. Attach a seed crystal to a hair or fishing line and lower it into the solution. First wipe the hair or fishing line with cotton wool soaked in alcohol. You can also place the seed crystal at the bottom of the glass before pouring the solution into it. Place the glass in a warm, clean place. Do not touch the crystal or move the glass for several days or weeks. At the end of the growing period, remove the crystal from the solution, dry it thoroughly with a paper towel and place it in a special box. Do not touch the crystal with your hands, otherwise it will lose its transparency.
Video experience.
Experience 1. Growing a crystal from copper sulfate.
(youtube)461jk7C4Ck8(/youtube)
Experience 2. Growing a crystal from table salt.
(youtube)bGy_XP1rxxQ(/youtube)
Control questions
1. What can serve as a center of crystallization?
2. What explains the unequal growth rate of different faces of the same thing?
is it a crystal?
3. How can a saturated solution be made supersaturated without
adding a solute?
4. Why was the solution filtered?
O.S.GABRIELYAN,
I.G. OSTROUMOV,
A.K.AKHLEBININ
START IN CHEMISTRY
7th grade
Continuation. For the beginning, see No. 1, 2, 3, 4, 5, 6, 7, 8, 9/2006
Chapter 3.
Phenomena occurring with substances
(ending)
§ 17. Distillation or distillation
Obtaining distilled water
Tap water is clean, transparent, odorless... But is this substance pure from the point of view of a chemist? Look into the kettle: scale and brownish deposits that appear on the spiral and walls of the kettle as a result of repeated boiling of water in it are easily detected.
(Fig. 71). What about limescale on taps? Both natural and tap water are homogeneous mixtures, solutions of solid and gaseous substances. Of course, their content in water is very small, but these impurities can lead not only to scale formation, but also to more serious consequences. It is no coincidence that injection medications are prepared only using specially purified water, called distilled.
Where did this name come from? Water and other liquids are purified of impurities through a process called distillation, or distillation. The essence of distillation is that the mixture is heated to a boil, the resulting vapors of the pure substance are removed, cooled and again converted into a liquid that no longer contains contaminants.
A laboratory installation for the distillation of liquids is assembled on the teacher’s desk (Fig. 72).
The teacher pours water tinted into the distillation flask. Orange color soluble inorganic salt (potassium dichromate). So you will see with your own eyes that this substance will not be in purified water. To ensure uniform boiling, 3-4 pieces of porous porcelain or pumice (boiling stones) are thrown into the flask.
Water is supplied to the refrigerator jacket, and the distillation flask is heated until the contents boil using an electric heater. Water vapor entering the refrigerator condenses, and distilled water flows into the receiver.
What temperature does the thermometer show? What outlet do you think cold water is supplied to the refrigerator through, and through which it is drained?
Distilled water is used not only to prepare medicines, but also to obtain solutions used in chemical laboratories. Even motorists use distilled water, adding it to batteries to maintain electrolyte levels.
And if it is necessary to obtain a solid substance from a homogeneous solution, then use evaporation, or crystallization
Crystallization
One way to isolate and purify solids is crystallization. It is known that when heated, the solubility of a substance in water increases. This means that when the solution is cooled, a certain amount of the substance precipitates in the form of crystals. Let's check this experimentally.
Demonstration experiment. Remember the beautiful orange crystals of potassium dichromate that the teacher used to “color” the water for distillation? Let's take about 30 g of this salt and “contaminate” it with several crystals of potassium permanganate. How to clean the main substance from the introduced impurity? The mixture is dissolved in 50 ml of boiling water. When the solution is cooled, the solubility of the dichromate decreases sharply, and the substance is released in the form of crystals, which can be separated by filtration and then washed on a filter with several milliliters of ice water. If you dissolve the purified substance in water, then by the color of the solution you can determine that it does not contain potassium permanganate. Potassium permanganate remained in the original solution.
Crystallization of a solid from a solution can be achieved by evaporating the solvent. This is what the evaporation cups you encountered while learning about chemical glassware are designed for.
If the evaporation of liquid from a solution occurs naturally, then for this purpose special thick-walled glass vessels are used, which are called crystallizers. You also became acquainted with them in practical work No. 1.
In nature, salt lakes are unique pools for crystallization. Due to the evaporation of water on the shores of such lakes, a gigantic amount of salt crystallizes, which, after purification, ends up on our table.
Oil distillation
Distillation is used not only to purify substances from impurities, but also to separate mixtures into separate portions - fractions that differ in boiling point. For example, oil is a natural mixture of a very complex composition. During the fractional distillation of oil, liquid petroleum products are obtained: gasoline, kerosene, diesel fuel, fuel oil and others. This process is carried out in special devices - distillation columns (Fig. 73). If there is an oil refinery in your city, you might have seen these chemical machines that continuously separate oil into those that are important and necessary in life. modern society products (Fig. 74).
Gasoline is the main fuel for passenger cars. Tractors and trucks use another petroleum product as such - diesel fuel (diesel fuel). The fuel for modern aircraft is mainly kerosene. With this small example you can understand how important it is to modern life a process such as oil distillation.
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Rice. 74.
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Fractional distillation of liquid air
You already know that any gases are mixed in any ratio. Is it possible to isolate individual components from a mixture of gases? The task is not easy. But chemists have proposed a very effective solution. The mixture of gases can be turned into a liquid solution and subjected to distillation. For example, air is liquefied by strong cooling and compression, and then individual components (fractions) are allowed to boil away one after another, since they have different boiling points. Nitrogen is the first to evaporate from liquid air (Fig. 75); it has the lowest boiling point (–196 °C). Argon (–186 °C) can then be removed from the liquid mixture of oxygen and argon. What remains is almost pure oxygen, which is quite suitable for technical purposes: gas welding, chemical production. But for medical purposes it needs to be further purified.
The nitrogen obtained in this way is used to produce ammonia, which in turn is used to produce nitrogen fertilizers, medicinal and explosives, nitric acid etc.
The noble gas argon is used in a special type of welding, which is called argon.
1. What is distillation or distillation? What is it based on?
2. What kind of water is called distilled? How do you get it? Where is it used?
3. What petroleum products are obtained during the distillation of oil? Where are they used?
4. How to separate air into separate gases?
5. How is evaporation (crystallization) different from distillation (distillation)? What are both methods of separating liquid mixtures based on?
6. What is the difference between the processes of evaporation and crystallization? What are both methods of isolating a solid from a solution based on?
7. Give examples from Everyday life, in which evaporation and distillation are used.
8. What mass of salt can be obtained by evaporating 250 g of a 5% solution? What volume of water can be obtained from this solution by distillation?
PRACTICAL WORK No. 4.
Growing salt crystals
(home experiment)
Before you start getting the job done, carefully read its description to the end.
First of all, select the appropriate salt for the experiment. Any salt that is highly soluble in water (copper or iron sulfate, alum, etc.) is suitable for growing crystals. Table salt - sodium chloride - will also work.
Equipment you will need:
A liter jar or small saucepan, in which you will prepare the salt solution;
Wooden spoon or stirring stick;
Funnel with cotton wool for filtering the solution;
A thermos with a wide neck with a capacity of 1 liter (it is needed so that the solution cools slowly, then large crystals will grow).
If you don’t have a funnel or the right thermos, you can make them yourself.
To make a funnel, take a plastic drink bottle and carefully cut off the neck with scissors, as shown in Fig. 76.
Instead of a thermos, an ordinary glass liter jar will do. Place it in a cardboard or foam box. There is no need to take a large box, the main thing is that it completely fits the jar. Seal the gaps between the box and the jar tightly with pieces of rag or cotton wool. To seal the jar tightly, you will need a plastic lid.
Prepare a hot saturated salt solution. To do this, fill the jar halfway with hot water (you don’t need to use boiling water to avoid getting burned). Add salt in portions and stir. When the salt stops dissolving, leave the solution for one or two minutes so that the undissolved crystals have time to settle. Filter the hot solution through a funnel filled with cotton wool into a clean thermos. Close the thermos with a lid and leave the solution to cool slowly for two to three hours.
The solution has cooled down a bit. Now introduce a seed into it - a salt crystal suspended on a thread. After introducing the seed, cover the vessel with a lid and leave for a long time. It will take several days or even weeks for a large crystal to grow.
Usually several crystals grow on the thread. It is necessary to periodically remove the excess ones so that one large crystal grows.
It is important to record the conditions of the experiment and its result; in our case, these are the characteristics of the resulting crystal. If several crystals are obtained, then a description of the largest is given.
Examine the resulting crystal and answer the questions.
How many days did you grow the crystal?
What is its shape?
What color is the crystal?
Is it transparent or not?
Crystal dimensions: height, width, thickness.
Crystal mass.
Sketch or photograph the resulting crystal.
PRACTICAL WORK No. 5.
Cleaning table salt
The purpose of this work is to purify table salt contaminated with river sand.
The contaminated table salt offered to you is a heterogeneous mixture of sodium chloride crystals and sand. To separate it, it is necessary to take advantage of the difference in the properties of the components of the mixture, for example, different solubility in water. As you know, table salt dissolves well in water, while sand is practically insoluble in it.
Place the contaminated salt provided by the teacher into a beaker and add 50–70 ml of distilled water. Stir the contents with a glass rod until the salt is completely dissolved in the water.
The salt solution can be separated from the sand by filtration. To do this, assemble the installation as shown in Fig. 77. Using a glass rod, carefully pour the contents of the glass onto the filter. The transparent filtrate will flow into a clean glass, while the insoluble components of the original mixture will remain on the filter.
The liquid in the glass is an aqueous solution of table salt. Pure salt can be isolated from it by evaporation. To do this, pour 5–7 ml of the filtrate into a porcelain cup, place the cup in the tripod ring and carefully heat it over the flame of an alcohol lamp, constantly stirring the contents with a glass rod.
Compare the salt crystals obtained after evaporation of the solution with the original contaminated salt. List the techniques and procedures you used to clean contaminated salt.
Before starting work, carefully read its description to the end. First of all, choose the right salt for the experiment. Any salt that is highly soluble in water (copper or iron sulfate, alum, etc.) is suitable for growing crystals. Table salt - sodium chloride - will also work.
Equipment you will need:
- a liter jar or a small saucepan, in which you will prepare the salt solution;
- wooden spoon or stirring stick;
- funnel with cotton wool for filtering the solution;
- thermos with a wide neck with a capacity of 1 liter (it is needed so that the solution cools slowly, then large crystals will grow).
If you don’t have a funnel or the required thermos, you can make them yourself.
To make a funnel, take a plastic drink bottle and use scissors to carefully cut off the top 1/3 of the way as shown in Figure 92.
Rice. 92.
Making a funnel from a plastic bottle
Instead of a thermos, an ordinary glass liter jar will do.
Place it in a cardboard or styrofoam box. There is no need to take a large box, the main thing is that it completely fits the jar. Seal the gaps between the box and the jar tightly with pieces of rag or cotton wool. To seal the jar tightly, you will need a plastic lid.
Prepare a hot saturated salt solution. To do this, fill the jar halfway with hot water (you don’t need to use boiling water to avoid getting burned). Add salt in portions and stir. When the salt stops dissolving, leave the solution for one or two minutes so that the undissolved crystals have time to settle. Filter the solution through a funnel filled with cotton wool into a clean thermos. Close the thermos with a lid and leave the solution to cool slowly for two to three hours.
The solution has cooled down a bit. Now introduce a seed into it - a salt crystal glued to the tip of the thread. After introducing the seed, cover the vessel with a lid and leave for a long time. It will take several days for a large crystal to grow.
Usually several crystals grow on the thread. It is necessary to periodically remove the excess ones so that one large crystal grows.
It is important to record the conditions of the experiment and its result; in our case, these are the characteristics of the resulting crystal. If several crystals are obtained, then a description of the largest is given.
Draw or photograph the resulting crystal (Fig. 93, 94). Examine your crystal and answer the questions.
Rice. 93. Table salt crystal
Rice. 94. Copper sulfate crystals
- How many days did you grow the crystal?
- What is its shape?
- What color is the crystal?
- Is it transparent or not?
- What are the dimensions of the crystal: height, width, thickness?
- What is the mass of the crystal?
Cleaning table salt
The purpose of this work is to purify table salt contaminated with river sand.
The contaminated table salt offered to you is a heterogeneous mixture of sodium chloride crystals and sand. To separate it, it is necessary to take advantage of the difference in the properties of the components of the mixture, for example, different solubility in water. As you know, table salt dissolves well in water, while sand is practically insoluble in it.
Place the contaminated salt given by the teacher into a beaker and pour in 50-70 ml of distilled water. Stir the contents with a glass rod until the salt is completely dissolved in the water.
The salt solution can be separated from the sand by filtration. To do this, assemble the installation as shown in Figure 95. Using a glass rod, carefully pour the contents of the glass onto the filter. The transparent filtrate will flow into a clean glass, while the insoluble components of the original mixture remain on the filter.
Rice. 95.
Filtration installation
The liquid in the glass is water solution table salt. Pure salt can be isolated from it by evaporation. To do this, pour 5-7 ml of the filtrate into a porcelain cup, place it in the ring of a tripod and carefully heat it over the flame of an alcohol lamp, constantly stirring the contents with a glass rod until the liquid has completely evaporated. Compare the salt crystals obtained after evaporation of the solution with the original contaminated salt. List the techniques and operations you used to clean contaminated salt.
Municipal educational institution "MITROFANOVSKAYA SOSHI WITH CADET CLASSES"
Secrets of growing crystals
Research
Performed:
8th grade student
Nikitina Lada Alexandrovna.
Supervisor:
Teacher: chemistry "MOU
"Mitrofanovskaya SOSHI
With cadet classes"
Viktorova Raisa Rashitovna
2017-2018
Introduction ………………………………………………………………………….3
1. Theoretical part…………………………………………………………5-
1.1. What are crystals........................................................ ....................................5-6
1.2.Crystal shapes
1.3. From the history of crystals
1.4. Formation of crystals in nature 6
1.5. Crystals in our lives……………………. 7
1.6. 8 methods of growing crystals
2. Practical part……………………………………………………….9-11
2.1. Growing copper sulfate crystals…………………………9-10
2.2. Growing potassium dichromate crystals 12
2.4. Research results, analysis and conclusions
3.Conclusion ………………………………………………………… 4. Literature
5. Application
Introduction
I once had a chance to visit the geological and mineralogical museum of the Transbaikal State University, where more than 20 thousand mineral samples are presented. After this excursion, a love for stone arose in a corner of my soul. A small crystal or a large druse of crystals, but how much perfection, grace and harmony they contain. It seems that they were created by nature precisely in order to attract human attention and love. But crystals are created not only by nature; crystals are widely obtained in industry. Many crystals are products of the vital activity of living organisms. They can also be obtained in the laboratory. I decided to try to grow a crystal of some substance myself. The available substances were table salt, copper sulfate, and potassium dichromate. I found literature on a topic that interested me, studied it and got to work. Like any researcher, I was faced with questions: What is a crystal? What shapes are there and how are they formed? And of course where are they used?
Purpose of the study:Grow crystals of copper sulfate and potassium dichromate in the laboratory.
Tasks:
1.Select and study literature on the research topic. 2.Grow crystals in laboratory conditions. 3. Determine the favorable conditions necessary for growing crystals. 4. Find out the role of crystals in our lives 5. Make practical recommendations for growing crystals.
Hypothesis:
I guess thatcrystals grown different ways and under different conditions will be different from each other.
Object of study: crystals.
Subject of study:crystallization process.
Research methods:work with sources, experiment, observation, photography, comparison, generalization.
Practical significanceresearch is that the results can be used in physics, chemistry, geography lessons, extracurricular activities, in circle work in career guidance. During the work, such qualities as observation, patience, and the ability to compare and generalize experimental data are formed.