In the reactions of connection from several substances, one is formed. Give the reaction equations of the compound, in which the sum of the coefficients is equal to: a) 5; b) 7; c) 9. Recall that the coefficients must be integers.
What is the minimum possible sum of the coefficients in the compound reaction equation? Give an example.
Can this sum be an even number? If yes, please provide an example.
Solution:
a) 2Cu + O 2 = 2CuO or 2H 2 + O 2 = 2H 2 O
b) 4Li + O 2 = 2Li 2 O
c) 4Al + 3O 2 = 2Al 2 O 3 or 4Fe + 3O 2 = 2Fe 2 O 3
The minimum possible sum of coefficients is 3 (two reagents and one product), for example
C + O 2 \u003d CO 2 or S + O 2 \u003d SO 2
Of course, the sum of the coefficients can be even, for example:
Na 2 O + H 2 O \u003d 2NaOH or H 2 + Cl 2 \u003d 2HCl
N 2 + 3H 2 = 2NH 3 or 3Fe + 2O 2 = Fe 3 O 4
Evaluation criterion: 2 points each for each equation (only one equation is counted in each paragraph). Any reasonable equation that satisfies the condition of the problem is accepted.
Total 10 points
Problem 2. Substance from hydrogen and oxygen
A complex substance, in the molecule of which there is one hydrogen atom per oxygen atom, is an unstable liquid that is infinitely miscible with water. A dilute (3%) solution of this substance is used in medicine. Write the molecular and structural formula of this substance. What happens if a pinch of manganese(IV) oxide is added to an aqueous solution of this substance? Write down the reaction equation.
Solution
The substance in question is hydrogen peroxide. Its molecular formula is H 2 O 2 . (3 points). To compose it, it is enough to know that oxygen has a constant valency equal to 2. Structural formula
4 points
When manganese oxide is introduced, hydrogen peroxide decomposes:
2H 2 O 2 \u003d 2H 2 O + O 2: 3 points
(1 point, if the wrong equation of expansion into simple substances is written).
Manganese oxide acts as a catalyst.
Total 10 points
Task 3. Fluorides in nature and in everyday life
The natural mineral fluorite has interesting properties. It has a wide range of colors from shades of pink to purple. The color of the mineral is given by impurities of compounds of various metals. After heating or irradiation with ultraviolet light, the mineral begins to glow in the dark. The chemical composition of the mineral: calcium content - 51.28%, fluorine content - 48.72% by weight.
- Using data about chemical composition, derive the formula for the mineral fluorite. Write down the calculations.
- What hygiene products contain fluoride compounds? In what cases should this hygiene product be used? What disease do they prevent?
Solution
1) Ca: F \u003d (51.28 / 40) : (48.72: 19) \u003d 1: 2.
The simplest formula of fluorite is CaF 2 .
Definition of a formula with calculations - 5 points
Definition of a formula without calculations, by valency - 1 point
2) Fluorine compounds are part of toothpastes (2 points), such pastes are used with a lack of fluorine (1 point). With a lack of fluorine compounds in the body, dental disease develops - caries (2 points).
Total 10 points
Task 4. New rocket fuel
The new experimental rocket fuel is a mixture of finely divided ice and aluminum powder, the particles of which are 500 times smaller than the thickness of a hair. When ignited, a chemical reaction occurs in which an oxide and a simple substance are formed. Write an equation for this reaction.
- In what mass ratio should the reactants be mixed in order for them to react completely?
- What do you think makes it possible jet thrust?
- The new fuel is called ALICE. Why?
Solution
As a result of the reaction, aluminum oxide and hydrogen are formed. Reaction equation:
2Al + 3H 2 O \u003d Al 2 O 3 + 3H 2 4 points
For 2 aluminum atoms with a mass of 2 27 \u003d 54 a. e.m. there are 3 water molecules with a mass of 3 18 = 54 a.m. e. m. Mass ratio 1: 1. 4 points
The reaction proceeds at high speed, jet thrust is created by the released hydrogen. 1 point
AL + ICE = ALICE 1 point
Total 10 points
Task 5. Combustion reaction
The combustion of a complex substance in air produced nitrogen, carbon dioxide and water. Write the formula of this substance if it is known that it contains a carbon atom, a nitrogen atom and the maximum possible number of hydrogen atoms. Remember that the valency of carbon is 4, nitrogen is 3, and hydrogen is 1. Write an equation for the combustion reaction.
Solution
The formula of a substance, compiled according to valence, is CH 5 N
(5 points for any correct formula - molecular or structural).
(if the solution contains the HCN formula - 2 points out of 5)
Combustion reaction equation:
4CH 5 N + 9O 2 \u003d 4CO 2 + 2N 2 + 10H 2 O 5 points
(if the correct HCN combustion equation is given - 5 points)
Total 10 points
Problem 6. Experiments with gases
The empty flask was closed with a cork with a gas outlet tube, the end of which was lowered into a glass of water (see Figure 1). When the flask was tightly grasped by hand, gas bubbles began to emerge from the opening of the tube (see Figure 2).
- Why are gas bubbles given off when the flask is held in the hand? What gas is released?
- Is the release of gas from the gas outlet pipe in this case a physical or chemical phenomenon? Explain the answer.
- The student assembled the device described in the condition of the problem (a flask with a stopper and a gas outlet tube). However, no matter how hard he tried to wrap his hand around the flask, no gas bubbles emerged from the vent tube. Suggest a possible explanation for this result.
- Is it possible to carry out the experiment in such a way that water from the glass begins to be sucked through the tube into the flask? If yes, please describe how this can be done. It is not allowed to disassemble the device and fill it with any special gas.
- If the flask is first filled with some gas, and then a stopper with a gas outlet tube is inserted, the end of which is lowered into water, then a “fountain” can be observed. Water under pressure will rise into the flask and at the end of the experiment will almost completely fill it. Suggest a variant of such a gas and explain the formation of a "fountain" inside the flask.
Solution
1) From the heat of the hand, the walls of the flask and the gas inside the flask are heated. When heated (if the pressure practically does not change), the gases expand, their volume increases. 2 points
Air bubbles are released, i.e. of the gas with which the flask (and gas outlet tube) was filled before the experiment. 1 point
2) This is a physical process, because the gases that make up the air do not undergo any chemical transformations. Only the volume of air increases. 1 point
3) The student may have assembled a leaky instrument. Air could pass through a loose connection between the flask and the stopper or the stopper with the gas outlet tube.
Another possible explanation is that the flask was preheated. The warmth of the hand was not enough.
2 points for any reasonable and justified explanation
4) Yes, it is possible. To do this, the flask must be cooled, for example, with ice or cold water. Also, the flask can be preheated, and then lower the end of the gas outlet tube into a glass of water.
/Page 1
The venting glass tube is connected with a rubber tube with a screw clamp to a glass tee, the longest end of which is bent at a right angle and inserted into a cork that closes the upper opening-throat of the gasometer, which is a 3-4 liter bottle with a tube. The third end of the tee is connected to one end of a U-tube, half filled with tinted water and serving as a pressure gauge. A graph paper is fixed behind the tube to observe and read the difference in the position of the meniscus of water in both elbows of the tube.
Some time after the start of heating, the retorts periodically bring the flame to the outlet of the gas outlet glass tube and try to ignite the gas. As soon as it ignites, the heating of the retort is regulated in such a way that the height of the flame of the burning gas is not less than 1 and not more than 1 5 cm. By the end of the experiment, the flame becomes smaller and smaller, despite increased heating, and finally goes out. After that, the heating of the retort is continued for another half an hour, after which the experiment is considered finished; its total duration is from 4 to 6 hours. In order to avoid cracking of the retort, its heating is reduced gradually, again transferring the flame to smoking and gradually reducing it. Then the receiving flask is taken away, the cork is removed from the throat of the retort, and by carefully heating the latter, the remnants of the resin frozen in the throat are allowed to drain into the receiving flask.
Bunsen to secure it; 3 - rubber plug with a hole; 4 - G - shaped gas outlet glass tube; 5 - test tube with lime water to detect outgoing carbon dioxide; 6 - burner.
Chlorine water is obtained by passing chlorine through water. The gas outlet glass tube is lowered to the bottom of a test tube or a glass of water and chlorine is bubbled through the water for some time.
Determination of yields of semi-coking products in an aluminum retort is sometimes carried out without gas collection. In this case, the gas outlet glass tube, which removes gas from the receiving flask, is not connected to the tee and through it to the gasometer, but serves to release the gas, for which its end is pulled. The escaping gas is ignited as described above in the first method.
A test tube with a stopper equipped with a gas outlet glass tube (Fig. 41), a device for obtaining sulfur dioxide gas (Fig. 42), a 100 ml glass, a 50 ml cone, porcelain - a lid, a spoon or a spatula.
In a flask mounted on a tripod, pour up to half a 3% solution of hydrogen peroxide. To the side tube of the flask, attach a gas outlet glass tube lowered into a crystallizer with water, where a small cylinder filled with water and overturned is placed.
The upper open end of the left burette is connected to the test tube with a gas outlet glass tube and two plugs. To test the device for tightness, connect the upper end of the left burette with a test tube, lower the right burette by 15–20 cm, fix it in the tripod holder and observe the position of the water level in it for 3–5 minutes. If the device is sealed, then the water level in the buret does not change during this time.
The tube, placed horizontally in the furnace, is tightly closed at both ends with cork plugs through which glass tubes pass. One of them is connected with a rubber tube to a vaporizing flask, and a vented glass tube is connected to the other, lowered into a crystallizer with water. The latter also contains glass cylinder, filled with water, turned upside down and fixed in the foot of the tripod.
The latter is very important, since the cork closing the flask must be wide enough to allow two holes to be drilled in it: one for the outlet tube of the retort, the other for the glass tube that removes the gases that are not condensable in the flask. The outlet tube of the retort should enter the receiving flask as deep as possible (without touching, however, the condensate) so that the vapor does not escape into the gas outlet glass tube without having time to cool and condense in the flask.
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Cation. |
Impact or reagent |
Observed response |
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Li + | ||
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Na + | ||
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To + | ||
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Sa 2+ | ||
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Sr 2+ | ||
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Wa 2+ | ||
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Cu 2+ | ||
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Pb 2+ | ||
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Fe 2+ | ||
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Fe 3+ | ||
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Al 3+ | ||
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NH 4 + | ||
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H + (acid environment) | ||
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Anion |
Impact or reagent |
Observed response |
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SO 4 2- | ||
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NO 3 - | ||
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RO 4 3- | ||
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CrO 4 2- | ||
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S 2- , | ||
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SO 3 2- | ||
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CO 2 | ||
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SO 3 2- | ||
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F - | ||
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Cl - | ||
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Br - | ||
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I - | ||
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HE - (alkaline environment) |
Laboratory work No. 5 general techniques for working with gases
Objective: learn how to obtain and collect simple and complex gaseous substances, depending on the properties of these substances.
Reagents and materials: zinc, aluminum, copper, sodium chloride, potassium permanganate, ammonium chloride, calcium hydroxide, concentrated solutions of sodium hydroxide, hydrochloric, sulfuric and nitric acids, splint.
Equipment: test tubes, funnels, crystallizer, Kipp apparatus, test tube with vent tube, Wurtz flask, dropping funnel, gasometer, wash bottles, mortar and pestle.
Safety precautions: observe the basic rules of work in the chemical laboratory and when working with the Kipp apparatus.
Getting gases
Substances in the gaseous state in the laboratory receive:
a) the interaction of a mixture of several solids when heated;
b) calcination of one solid substance;
c) the interaction of a solid with a liquid when heated and without heating (chlorine, hydrogen chloride, etc.).
To obtain gases, various devices are used (Fig. 1-2). The simplest of these is the device shown in Fig. 2, a, representing a test tube with a gas outlet tube. When using this device, it is necessary to take into account the conditions of the reaction. So, if the reaction proceeds only when heated, then it can be stopped by stopping heating. If heating is not required for the reaction, then it goes on until the initial substances (or one of them) are used up. The advantage of such a device is its simplicity. The disadvantage is the need to disassemble the device after each experiment to obtain gas.
On fig. 2b shows a device consisting of a Wurtz flask and a dropping funnel. It is convenient for obtaining gases when at least one of the reactants is liquid or is contained in solution. The evolution of gas in such a device can be controlled by adding a liquid reagent. Such a device for obtaining gas can be used repeatedly and, therefore, it is not necessary to dismantle it after each experiment.
Devices for obtaining gases (Fig. 2) must be checked for leaks before use. To do this, the end of the gas outlet tube from the device is lowered into a vessel with water and the reaction vessel is slightly heated. If the device is sealed, then air bubbles will go into the water, and when the heating stops, water from the vessel will begin to be sucked into the device.
In practice, automatic devices are often used.
One of these devices is Kipp apparatus (Fig. 1). This is a glass device, consisting of two parts: a vessel 1 with a narrowing in the middle part and a spherical funnel 2 , the end of which does not reach the bottom of the vessel by 1-2 cm. The funnel is inserted into the vessel on a thin section, which ensures the tightness of the device. The middle ball has a tube closed with a stopper with a gas outlet tube and a tap 3 . At the bottom of the device there is a tube 4 , through which the waste liquid is poured. Kipp's apparatus is made of thick-walled glass for greater strength, since it must withstand the high pressure of the gas contained in it. Using the Kipp apparatus, carbon monoxide (IV), hydrogen, hydrogen sulfide and some other gases can be obtained.
When charging the Kipp apparatus, a solid substance (marble for CO 2 production, zinc for H 2 production) is placed in the middle part of the device (in the assembled form) through the tube. Then the tube is closed with a cork with a gas outlet tube and, with the tap open, the acid solution is poured into the funnel. The acid enters the bottom of the device. Then it rises into the middle ball and comes into contact with a solid substance - a chemical reaction begins, gas is released. Once the acid has covered the solid, the acid infusion is stopped and the faucet is closed. After closing the tap, the acid is forced out under the pressure of the formed gas into the lower part of the device and into the funnel. The reaction stops.
The device is put into action by opening the tap. In this case, the resulting gas exits through the gas outlet tube. The acid comes into contact with the solid, the reaction begins. When discharging the Kipp apparatus, the acid is poured out through the lower tube, the solid is extracted through the upper tube. In order to avoid violation of the tightness of the device, the separation of the funnel and the vessel is carried out only when absolutely necessary.
Gathering gases
The methods of collecting gases are determined by their properties: solubility and interaction with water, air, poisonousness of the gas. There are two main methods of gas collection: air displacement and water displacement. Air displacement collect gases that do not interact with air.
According to the relative density of gas in air, a conclusion is made on how to position the vessel for collecting gas (Fig. 3, a and b).
On fig. 3a shows the collection of a gas with an air density greater than unity, such as nitric oxide (IV), whose air density is 1.58. On fig. 3b shows the collection of gas with an air density of less than unity, such as hydrogen, ammonia, etc.
By displacing water, gases are collected that do not interact with water and are poorly soluble in it. This method is called collecting gas above the water , which is carried out as follows (Fig. 3, c). The cylinder or jar is filled with water and covered with a glass plate so that no air bubbles remain in the cylinder. The plate is held by hand, the cylinder is turned over and lowered into a glass bath of water. Under water, the plate is removed, a gas outlet tube is brought into the open hole of the cylinder. The gas gradually displaces water from the cylinder and fills it, after which the hole of the cylinder under water is closed with a glass plate and the cylinder filled with gas is removed. If the gas is heavier than air, then the cylinder is placed upside down on the table, and if it is lighter, then upside down on the plate. Gases above the water can be collected in test tubes, which, like the cylinder, are filled with water, closed with a finger and overturned into a glass or glass bath with water.
I 
Toxic gases are usually collected by displacing water, since it is easy to note the moment when the gas completely fills the vessel. If there is a need to collect gas by the method of air displacement, then for this proceed as follows (Fig. 3, d).
A cork with two gas outlet tubes is inserted into the flask (jar or cylinder). Through one, which reaches almost to the bottom, gas is let in, the end of the other is lowered into a glass (jar) with a solution that absorbs gas. So, for example, to absorb sulfur oxide (IV), an alkali solution is poured into a glass, and water is poured into a glass to absorb hydrogen chloride. After filling the flask (jar) with gas, the cork with gas outlet tubes is removed from it and the vessel is quickly closed with a cork or glass plate, and the cork with gas outlet tubes is placed in a gas-absorbing solution.
Experience 1. Obtaining and collecting oxygen
Assemble the installation according to fig. 4. Place 3-4 g of potassium permanganate into a large dry test tube, close with a stopper with a gas outlet tube. Fix the test tube in the rack obliquely with the hole slightly up. Next to the tripod on which the test tube is mounted, place the crystallizer with water. Fill an empty test tube with water, close the hole with a glass plate and quickly turn it upside down into the crystallizer. Then in the water, take out the glass plate. There should be no air in the test tube. Heat potassium permanganate in a burner flame. Dip the end of the gas outlet tube into the water. Observe the appearance of gas bubbles.
H 
A few seconds after the start of bubbles, put the end of the gas outlet tube into the opening of a test tube filled with water. Oxygen displaces water from the tube. After filling the test tube with oxygen, cover its opening with a glass plate and turn it upside down.
AT
Rice. 4. Device for obtaining oxygen
What laboratory methods for obtaining oxygen do you know? Write the corresponding reaction equations.
2. Describe your observations. Explain the location of the test tube during the experiment.
3. Write an equation for the chemical reaction of the decomposition of potassium permanganate when heated.
4. Why does a smoldering splinter flare up in a test tube with oxygen?
Experience 2. Hydrogen production the action of a metal on an acid
Assemble the apparatus, consisting of a test tube with a stopper, through which a glass tube with a retracted end passes (Fig. 5). Place a few pieces of zinc in a test tube and add a dilute solution of sulfuric acid. Firmly insert the stopper with the tube pulled back, fix the test tube vertically in the tripod clamp. Observe gas evolution.
AT
Rice. 5. Device for producing hydrogen
If air is present in a test tube with hydrogen, a small explosion occurs, accompanied by a sharp sound. In this case, the gas purity test should be repeated. After making sure that pure hydrogen comes out of the device, light it at the hole of the drawn tube.
Control questions and tasks:
1. Specify the methods of obtaining and collecting hydrogen in the laboratory. Write the corresponding reaction equations.
2. Write an equation for the chemical reaction to produce hydrogen under experimental conditions.
3. Hold a dry tube over the hydrogen flame. What substance is produced by burning hydrogen? Write the equation for the hydrogen combustion reaction.
4. How to check the purity of the hydrogen obtained during the experiment?
Experience 3. Getting ammonia
Rice.6
. Apparatus for obtaining ammonia
AT
Control questions and tasks:
What hydrogen compounds of nitrogen do you know? Write their formulas and names.
Describe what is happening. Explain the location of the test tube during the experiment.
Write an equation for the reaction between ammonium chloride and calcium hydroxide.
Experience 4. Obtaining nitric oxide (IV)
Assemble the device according to fig. 7. Put some copper shavings into the flask, pour 5-10 ml of concentrated nitric acid into the funnel. Pour acid into the flask in small portions. Collect the escaping gas in a test tube.
Rice. 7. Device for receiving
nitric oxide(IV)
Control questions and tasks:
1. Describe what is happening. What is the color of the escaping gas?
2. Write an equation for the reaction of the interaction of copper with concentrated nitric acid.
3. What properties does nitric acid have? What factors determine the composition of the substances to which it is reduced? Give examples of reactions between metals and nitric acid, as a result of which the reduction productsHNO 3 areNO 2 , NO, N 2 O, NH 3 .
Experience 5. Getting hydrogen chloride
Place 15-20 g of sodium chloride in a Wurtz flask; into a dropping funnel - a concentrated solution of sulfuric acid (Fig. 8). Insert the end of the gas outlet tube into a dry vessel for collecting hydrogen chloride so that the tube reaches almost to the bottom. Close the opening of the vessel with a loose ball of cotton wool.
Place a crystallizer with water next to the device. Pour the sulfuric acid solution from the dropping funnel.
Warm the flask slightly to speed up the reaction. When over
cotton wool, with which the opening of the vessel is closed, fog will appear,
n
Rice. 8. Device for producing hydrogen chloride
Control questions and tasks:
Explain the observed phenomena. What is the reason for the formation of fog?
What is the solubility of hydrogen chloride in water?
Test the resulting solution with litmus paper. What is the pH value?
Write the equation for the chemical reaction of the interaction of solid sodium chloride with concentrated sulfuric acid.
Experience 6. Obtaining and collecting carbon monoxide (IV)
The installation consists of a Kipp apparatus 1 , charged with pieces of marble and hydrochloric acid, two Tishchenko flasks connected in series 2 and 3 (bottle 2 filled with water to clean the passing carbon monoxide (IV) from hydrogen chloride and from mechanical impurities, bottle 3 - sulfuric acid for gas drying) and flasks 4 with a capacity of 250 ml for collecting carbon monoxide (IV) (Fig. 9).
Rice. 9. Device for obtaining carbon monoxide (IV)
Control questions and tasks:
Immerse the lit torch into a flask with carbon monoxide (IV) and explain why the flame goes out.
Write an equation for the formation of carbon monoxide (IV).
Is it possible to obtain carbon monoxide (IV) use concentrated sulfuric acid solution?
Pass the gas released from the Kipp apparatus into a test tube with water, tinted with a neutral solution of litmus. What is observed? Write the equations for the reaction that occurs when a gas is dissolved in water.
Test questions:
List the main characteristics of the gaseous state of matter.
Propose a classification of gases according to 4-5 essential features.
How to read Avogadro's law? What is its mathematical expression?
Explain the physical meaning of the average molar mass of a mixture.
Calculate the average molar mass of air in which mass fraction oxygen is 23%, and nitrogen - 77%.
Which of the following gases is lighter than air: carbon monoxide (II), carbon monoxide (IV), fluorine, neon, acetylene C 2 H 2 , phosphine pH 3 ?
7. Determine the hydrogen density of a gas mixture consisting of argon with a volume of 56 liters and nitrogen with a volume of 28 liters. The volumes of gases are given to n.o.s.
8. An open vessel is heated at a constant pressure of 17 about C to 307 about C. what part of the air (by mass) in the vessel is displaced?
9. Determine the mass of 3 liters of nitrogen at 15 about C and a pressure of 90 kPa.
10. Mass of 982.2 ml of gas at 100 about C and a pressure of 986 Pa is 10 g. Determine the molar mass of the gas.
We have already worked a little, we will deal with gases. This is somewhat more difficult, and first of all we will need plugs with holes and vent pipes.
The tube can be glass, metal or even plastic. It is better not to take a rubber cork - it is difficult to drill holes in it. Take cork or polyethylene stoppers - holes in them can be burned with a heated awl. Insert a tube into this hole - for example, from an eyedropper; it should enter the cork hole tightly, without gaps, so the hole in the cork must first be made slightly smaller than required, and then gradually expand it, fitting it to the diameter of the tube. Put on a glass tube a rubber or polyethylene flexible tube 30 centimeters long, also insert a short glass tube into its other end.
Now the first experience with gases. Prepare lime water, bay hot water(1/2 cup) half teaspoon crushed slaked lime, stir the mixture and let stand.
A transparent precipitate over the settled solution is lime water. Carefully drain the liquid from the sediment; this lab is called decantation.
If you do not have slaked lime Ca (OH) 2, then lime water can be prepared from two solutions sold in a pharmacy: calcium chloride CaCl 2 and ammonia NH 4 OH (aqueous ammonia). When mixed together, clear lime water is also obtained.
Take a chilled bottle mineral water or lemonade. Open the cork, quickly insert the cork 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 come out of it. This is carbon dioxide CO 2 (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 lime water and it becomes cloudy before our eyes, because the calcium hydroxide contained in it turns into calcium carbonate CaCO 3, and it is poorly soluble in water and forms a white turbidity.
To experiment with lime water, it is not necessary to buy lemonade or mineral water. After all, when we breathe, we consume oxygen and release carbon dioxide, the same gas that makes lime water cloudy. Dip the end of any clean tube into a fresh portion of lime water and exhale through the tube several times - the result will not be long in coming.
Open another bottle, insert a stopper with a tube and continue to pass carbon dioxide through the lime water. After some time, the solution will again become transparent, because carbon dioxide reacts with calcium carbonate, turning it into another Ca(HCO 3) 2 bicarbonate salt, and this salt just dissolves very well in water.
The next gas we'll be looking at has been mentioned quite recently: ammonia. It is easy to recognize by its sharp characteristic smell - the smell of pharmaceutical ammonia.
Pour some boiled saturated washing soda solution into the bottle. Then add ammonia, insert a stopper with a flexible outlet tube into the neck and put the test tube upside down on its other end. Warm up the bottle warm water. Ammonia vapor is lighter than air and will soon fill an inverted test tube. Still holding the tube upside down, carefully lower it into the beaker of water. Almost immediately, the water will begin to rise up into the test tube, because ammonia is highly soluble in water, making room for it in the test tube.
At the same time, you can learn to recognize ammonia - and not just by smell. First, make sure the ammonia solution is alkaline (use phenolphthalein or homemade indicators). And secondly, conduct a qualitative reaction for ammonia. Qualitative reaction- this is such a reaction that allows you to accurately identify a particular substance or group of substances.
Prepare a weak solution blue vitriol(it should be pale blue) and lower the gas tube into it. When ammonia NH 3 begins to be released, 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 SO 4 composition.
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 into the bottle not ammonia, but soda. Dip a small, pea-sized piece of calcium carbide, carefully wrapped in blotting paper, into it and insert a cork with a tube. When the blotting paper gets wet, gas will begin to be released, which you will collect in an inverted test tube as before. After a minute, turn the test tube upside down and bring a lit match. The gas will ignite and burn with a smoky flame. This is the same acetylene that gas welders use.
By the way, not only acetylene is obtained in this experiment. An aqueous solution of calcium hydroxide, i.e. lime water, remains in the bottle. It can be used for experiments with carbon dioxide.
The next experiment with gases can only be done with good ventilation, and if it is not, then fresh air. We will get a sharp smelling sulfur dioxide (sulphurous gas) SO 2 .
Pour dilute acetic acid into a bottle and add some sodium sulfite Na 2 SO 3 wrapped in blotting paper (this substance is sold in photo stores). Close the bottle with a cork, dip the free end of the gas outlet tube into a glass with a pre-prepared dilute solution of potassium permanganate KMpO 4 (this substance is known in everyday life as potassium permanganate). The solution should be pale pink. When the paper gets wet, sulfur dioxide will start to come out of the bottle. It reacts with potassium permanganate solution and discolors it.
If you can't buy sodium sulfite, then replace it with the contents of a large cartridge of a conventional photodeveloper. True, in this case there will be an admixture of carbon dioxide in sulfur dioxide, but this will not interfere with the experiment.
O. Olgin. "Experiments without explosions"
M., "Chemistry", 1986
SMOKE WITHOUT FIRE
Much has been described various options entertaining experiences based on the reactions of interaction of gaseous ammonia and hydrogen chloride with the formation of an aerosol of ammonium chloride. We present one of them. Pour 3-5 ml of a concentrated solution into a clean, dry, wide-mouthed flask with a volume of 200 ml. of hydrochloric acid. By rotating the flask, the walls of the vessel are moistened with acid, the excess solution is poured out and tightly closed with a cork. In another, exactly the same, flask, a solution of ammonia (25%) is collected in a similar way.
During the experiment, the flasks are opened and connected with their necks one to the other, turning them in this position by 180 °. The flasks fill with thick white smoke.
COLORED FLAME
Saturated solutions of Bertolet salt in water (about 8 g of salt per 100 ml of water) are prepared, with the addition of various other salts.
Various shapes are cut out of filter paper (circles, triangles, squares, etc.) small size, immersed in an appropriate solution and dried, repeating this operation several times, so that crystals of Bertolet salt appear in the pores of the paper. Well-dried paper figures, when ignited, quickly burn out, forming a flame of different colors.
As additives to the solution of Berthollet salt, 2-3 g of sodium chloride (yellow flame), strontium nitrate, lithium chloride (red flame), copper chloride (emerald flame), barium nitrate (greenish flame) are taken. Part of the paper figures are impregnated with a solution of Bertolet salt without additives, the flame acquires a purple hue.
"WATER" LIGHTS A FIRE
A small porcelain cup (a watch glass can be used) with a small amount of a mixture of potassium permanganate and sulfuric acid is placed on the asbestos mesh. Dry splinters imitating a fire are placed on the porcelain cup and around it.
To ignite the resulting fire, moisten the cotton wool with "water" (ethyl alcohol) and squeeze it over it so that the drops fall into the cup. Alcohol (you can take denatured alcohol) ignites, then setting fire to the splinters.
ASH - CATALYST
If a piece of sugar is brought into the flame of a burner with tweezers, it will begin to melt and char, but will not ignite.
If, on the sugar, pour a little ashes from the burnt bay leaf and bring into the flame, then the sugar will ignite and will burn even outside the flame of the burner.
IGNITION OF ALCOHOL
An alcohol lamp can be ignited with strong oxidizers. One of these is manganese (VII) oxide. To obtain it, pour 0.5 g of potassium permanganate in a pile into a porcelain cup and pour 2-3 drops of concentrated sulfuric acid on the side of a pile of salt. The resulting slurry is collected on the tip of a glass rod, which is touched with the wick of an alcohol lamp (the wick must be well moistened with alcohol). The flask immediately ignites. Note. Should be avoided large quantities permanganate and acid to prepare the mixture.
DISAPPEARANCE OF COLOR
Three glasses are filled with colored aqueous solutions, in the first - with violet ink, in the second - with blue litmus, in the third - with red litmus (lakmoid).
From a flask into which a colorless liquid is poured (whiteness bleach solution with a few drops of hydrochloric acid), the solution is poured into glasses. Colored solutions become colorless. The experience can be diversified by using other organic dyes to prepare colored solutions that become colorless under the action of chlorine.
GETTING "MILK"
Mixtures imitating milk can be obtained by mixing 10% solutions of barium nitrate and sodium sulfate; calcium chloride and sodium bicarbonate.
"Milk", obtained by the second method, can be turned into carbonated "water" by adding small portions of concentrated hydrochloric acid to it until calcium carbonate is completely dissolved.
QUESTIONS AND TASKS
Which of the above games, verbal forms of entertainment and entertaining experiences, in your opinion, are the most effective?
Make up options didactic games, verbal forms of entertainment and entertaining experiences to your topic.
8. Unification chemical experiment. Under the unification of a chemical experiment in education, we mean a rational reduction in the types of instruments and installations with which experiments are carried out. In the proposed device (sometimes with additions or changes), it is possible to successfully carry out various chemical reactions both during the demonstration experiments and during the student experiment.
The basis of the device is a flask or flask with a capacity of 50-200 ml, a stopper with a separating funnel (respectively, the flask) for 25-100 ml, the device must have a gas outlet tube. A variety of modifications of a unified device are possible (using Wurtz, Bunsen flasks, etc.) (Fig. 1).
The use of this installation ensures the safety of the chemical experiments, since the release of gaseous and volatile toxic substances it is possible to regulate them quantitatively and send them either directly for carrying out reactions involving these gases, or for trapping by absorption devices.
Another advantage of this device is the ability to quickly and accurately dose the initial substances used for the experiment. Substances and solutions are placed in flasks and separating funnels in advance, before the start of classes, in required quantity, and not by eye, as is usually the case when demonstrating experiments in test tubes or glasses, when substances and solutions are collected directly in the lesson during the demonstration of experiments.
When using the device, the perception of experience is achieved by all students, and not only by those who sit at the first desks, as is the case when conducting experiments in test tubes. The recommended device allows you to carry out qualitative and quantitative experiments in chemistry at school, as well as in secondary special and higher educational institutions. Let us illustrate the fundamental application of the device on the example of some experiments, grouping them according to similar features.
Getting gases. The production of most gases studied at school is based on heterogeneous reactions between solid and liquid phases. The solid phase is placed in a flask, which is closed with a stopper with a funnel and a gas outlet tube. An appropriate solution or liquid reaction reagent is poured into the funnel, the addition of which to the flask is dosed using a separating funnel tap. If necessary, the flask with the reaction mixture is heated, adjusting the volume of the evolved gas and the reaction rate.
Using the device and appropriate reagents, it is possible to obtain oxygen, ozone, chlorine, hydrogen, carbon dioxide, carbon monoxide and sulfur dioxide, hydrogen halides, nitrogen and its oxides, nitric acid from nitrates, ethylene, acetylene, bromoethane, acetic acid from acetates, acetic anhydride, complex ethers and many other gaseous and volatiles.
Naturally, at the same time when receiving gases with the help of the device, it is possible to demonstrate their physical and Chemical properties.
Reactions between solutions. In this device it is convenient to carry out experiments in which the addition of a liquid reagent must be carried out in small portions or dropwise, when the course of the reaction is affected by an excess or deficiency of one of the starting substances, etc., for example:
Dissolution of sulfuric acid in water and compliance with safety rules during this operation;
Experiments illustrating the diffusion of substances in liquids or gases;
Determination of the relative density of mutually insoluble liquids and the formation of emulsions;
Dissolution of solids, the phenomenon of flotation and the formation of suspensions;
Salt hydrolysis reactions, if it is important to show the change in the degree of hydrolysis depending on the volume of water added to the salt solution;
Experiments illustrating the color of indicators in various media and neutralization reactions;
Reactions between electrolyte solutions;
Reactions, long in time;
Reactions organic matter(bromination and nitration of benzene, oxidation of toluene, production of soap and aniline, hydrolysis of carbohydrates).
Demonstration of the characteristic properties of the studied substance. With the help of the device, you can consistently and clearly, with minimum cost time to demonstrate the characteristic physical and chemical properties of the substance under study. At the same time, reagents are saved, the necessary safety of the experiment is achieved (the emitted harmful gases and volatile substances are captured by the appropriate absorption solutions), and a better perception of the experiment by all students of the class is ensured.
Consider the preparation and conduct of an experiment in demonstrating the properties of hydrochloric acid. Teacher prepares before class required number flasks (according to the number of reactions studied) and one stopper with a separating funnel and a gas outlet tube in it. Substances or solutions (zinc, copper, copper oxide (P), copper hydroxide (P), sodium hydroxide solution with phenolphthalein, sodium carbonate, silver nitrate solution, etc.) are placed in the flasks in advance. About 30 ml of a solution of 10-20% hydrochloric acid is poured into a separating funnel. During the lesson, the teacher only needs to rearrange the cork with a separating funnel filled with acid from one flask to another, spending 3-5 ml of solution for each reaction.
If toxic volatile compounds are formed during the reactions, then the gas outlet tube of the device is immersed in the appropriate solutions to absorb these substances, and the reaction mixture in the flask is neutralized after the end of the experiment.
Solubility of gases in water. Let us consider the demonstration experiment of the solubility of gases in water using the example of sulfur oxide (IV). Two devices are required for the experiment. In the first device (in the flask - sodium sulfite, in the separating funnel - concentrated sulfuric acid) sulfur oxide (IV) is obtained, which is collected in the flask of the second device by the method of air displacement. After filling this flask with gas, water is poured into the funnel, the gas outlet tube is lowered into a glass of water, tinted with purple litmus or another indicator (Fig. 2).
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If we now open the clamp or valve of the gas outlet tube, then due to the small contact surface (through the inner opening of the tube) of sulfur oxide (IV) and water, a noticeable dissolution of the gas with subsequent fountaining of liquid into the flask does not occur immediately, but after a rather long period of time, until the flask will not create sufficient vacuum.
To speed up this process, 1-2 ml of water is poured from the funnel into the flask (with the clamp on the gas outlet tube closed) and shaken gently.
This volume of water is quite enough for the pressure in the flask to decrease, and the water tinted with the indicator, when the clamp is removed from the gas outlet tube, rushes into the flask with a fountain, changing the color of the indicator. To enhance the effect, the flask can be turned upside down, having previously closed the separating funnel with a stopper and without removing the gas outlet tube from the glass of water.
Discoloration of dyes. About 0.5 g of potassium permanganate is placed in the flask of the device. Two needles are injected into the lower part of the cork, on which a piece of dyed fabric or strip is pricked. litmus paper. One of the samples is moistened with water, the second is left dry. The flask is closed with a stopper, several milliliters of concentrated hydrochloric acid are poured into the separating funnel, the gas outlet tube is lowered into a sodium thiosulfate solution to absorb the excess chlorine released (Fig. 3).
During the demonstration of the experiment, the faucet of the separating funnel is slightly opened and the acid is poured dropwise into the flask, then the faucet is closed again. In the flask, a reaction takes place between substances with the release of chlorine, a wet cloth or a strip of litmus paper discolors quickly, and a dry sample - later, as it is moistened.
Note. Many fabrics are dyed with chlorine- and other bleach-resistant dyes, so pre-testing and pre-selecting appropriate fabric samples is essential. In the same way, the discoloration of dyes by sulfur dioxide can be shown.
Adsorption properties of coal or silica gel. About 0.5 g of powder or shavings of copper is placed in the flask. A piece of metal wire with a bent end is injected into the lower part of the plug, to which a small mesh is attached to hold the activated sorbent weighing 5–15 g (Fig. 4).
The flask of the device is closed with a stopper prepared in this way, and nitric acid is poured into the funnel. A gas outlet tube equipped with a clamp (the clamp is open before the start of the experiment), dropped into a glass with colored water. After assembly, the device is checked for leaks. At the time of the demonstration of the experiment, the faucet of the separating funnel is slightly opened and a few drops are poured out acid into a flask in which a reaction occurs with the release of nitric oxide (IV). Do not add an excess of acid, it is necessary that the volume of the released gas corresponds to the volume of the flask.
After the end of the reaction, which is determined by the cessation of the release of bubbles of air displaced from the flask through the gas outlet tube, the clamp on it is closed. The device is installed in front of a white screen. The adsorption of nitric oxide (IV) in the flask is judged by the disappearance of the color of the gas. In addition, due to the formation of a certain vacuum in the flask, liquid from the glass is sucked into it if the clamp is opened on the gas outlet tube.
Experiments on the study of the electrical conductivity of substances and solutions. If an additional two metal or better two are passed through the cork of the device graphite rod(electrode), the lower ends of which almost touch the bottom of the flask, and connect them through a light bulb or galvanometer to a current source, then we get an installation for determining electrical conductivity solutions of substances and the study of the provisions of the theory electrolytic dissociation(Fig. 5).
Quantitative experiments based on reactions occurring with the release of gases. If you bring the gas outlet tube of the device under a graduated cylinder with water installed in a crystallizer with water, and collect the gas released during the reaction by displacing water, then by the volume of the resulting gas, you can carry out quantitative calculations to establish the molar masses of substances, confirm the laws of chemical kinetics and thermochemistry, determining the formula of ethanol and others
substances, etc. (Fig. 6). If the gas released during the reaction dissolves or reacts with water, then other liquids and solutions must be used in the experiments.
Rice. 6. Installation for carrying out quantitative experiments.
The examples given do not exhaust all the possibilities of the proposed unified device in the educational chemical experiment. If you have stoppers with two gas outlet tubes or two separating funnels in stock, as well as other installation options, then the number of experiments using a unified device can be significantly increased, which will contribute to the scientific organization of the work of a chemistry teacher.
Component parts of the instrument: flasks, graduated separating funnels, stoppers, clamps, etc. - should be included in standard sets of utensils and equipment for school chemistry classrooms and educational chemical laboratories of pedagogical higher educational institutions.
9. Home experiment. Without denying the possible use at home of the use of various computer programs"Virtual Labs", yet the real home experiment gives students more value. It is impossible to imagine chemistry without chemical experiments. Therefore, it is possible to study this science, understand its laws and, of course, fall in love with it only through an experiment. Naturally, chemical reactions are best carried out in specially equipped chemical rooms and laboratories under the guidance of a teacher, in the classroom or in the classes of a chemical circle and electives.
Unfortunately, not all schools have chemistry circles, not all students interested in chemistry have the opportunity to attend additional classes at school. Therefore, only a home chemical experiment can fill the gap in teaching chemistry in modern conditions, when the programs are oversaturated with theoretical material, teachers refuse to conduct practical work, and laboratory experiments have generally become a rarity in school practice. Those authors of textbooks and workbooks who include in the texts of paragraphs certain experiments and observations that students must perform outside the lesson, at home, should be welcomed and supported.
It is difficult to overestimate the importance of such an experiment on the formation of interest in chemistry and motivation to study this subject. A home experiment is of great importance in deepening and expanding knowledge, improving special skills and abilities, in general development students.
In this regard, a chemistry teacher should help students organize a home chemical experiment. In doing so, several factors should be taken into account. Firstly, the teacher should talk with parents on all issues of organizing a home experiment in chemistry, primarily on the problem of arranging a place for conducting experiments at home. Secondly, students must firmly know and strictly follow the safety rules laboratory work. Thirdly, the teacher of chemistry must methodically and practically help the student in acquiring necessary equipment for conducting experiments, preparing solutions and obtaining certain substances from food products, funds household chemicals etc. Fourth, it is necessary to outline a program for conducting educational experiments and a plan for a research experiment on a specific topic. Fifth, we must teach young chemists conduct appropriate observations and document the results of experiments in a laboratory journal.
Here are some variants of experiments for schoolchildren's home experiment.
Experiences with iron. 1. Pour a few drops of salt solution (5%) into two test tubes, add a few drops of alkali solution to one. Pick up stoppers for test tubes. Clean an iron nail 10-15 cm long to a shine and insert it through both stoppers so that the part of the nail with the head is closed with a stopper in one test tube, and the tip of the nail is closed in another test tube. Part of the nail (middle) should remain between the vessels and be in contact with the surrounding air. Place the test tubes with the nail in the supine position. Thus, you will simultaneously conduct three variants of the iron corrosion test: first, normal conditions; secondly, a humid, salty atmosphere; thirdly, a humid alkaline atmosphere. Observe the state of the surface of the three sections of the nail for several days and draw conclusions . (draw)
2. Pour the common salt solution acidified with acetic acid into three test tubes. In the first test tube, add a urotropine tablet ( medicinal product) and dissolve it; in the second - add a few drops of iodine tincture until a yellow color appears. Insert a polished iron nail into each test tube so that one end protrudes from the solution. Track how additives affect the corrosion of iron under experimental conditions, and draw conclusions.
3. Place a few small nails (pins, paper clips) in a test tube and add 3-5 ml of hydrochloric acid (1:1). What did you observe? Write down the reaction equation. Add a few crystals of copper sulfate to the reacting mixture. What did you observe? Give an explanation.
4. Pour 4-6 ml of copper sulfate solution into a test tube, add iron powder to the solution. What did you observe? Write down the reaction equation. After the end of the reaction, pour the iron (II) sulfate solution into another test tube and save it for the next experiment. Iron powder coated with a loose layer of copper, rinse 2 times clean water, dry on a sheet of paper and separate the copper powder.
5. Add a few drops of an alkali solution to a solution of iron (II) sulfate (experiment 4). Shake the resulting mixture. What did you observe? Write down the reaction equations.
6. Heat a small portion of the sediment from experiment 5 on a tin scoop. What did you observe? Write down the reaction equation.
Iodine and its properties. 1. Pour a few drops of iodine tincture into a test tube and carefully evaporate. Insert a glass rod into the test tube and continue heating gently. Pay attention to the color of the vapors in the test tube and to the crystals deposited on the stick. Describe your observations.
2. How does the sublimation of iodine differ from the sublimation of ammonium chloride?
3. Dilute 2-3 ml of iodine tincture to 10-15 ml with water and pour the resulting solution into several penicillin vials or 3 ml test tubes. To each portion of the solution, add some metal in the form of powder or small sawdust (prepare with a file), such as iron, aluminum, copper, tin, etc. Describe the observed changes and write down the corresponding reaction equations.
4. Clean the metal plate from dirt and cover with a thin layer of nail polish (ask your mom). With a darning needle, scratching the varnish, make an inscription or drawing on the plate. Moisten the plate with iodine solution and leave for a while. After the reaction, rinse the plate in water, dry it with a cloth and remove the varnish with a special liquid. An etched pattern will remain on the plate. Describe what you did. Write down the reaction equation.
5. Pour up to 1/3 of the volume of water into the test tube and add a few drops of iodine tincture. Pour half the volume of gasoline or thinner to the solution to oil paints and shake the mixture well. What do you see after the separation of liquids into two layers? Is it possible, on the basis of this experiment, to judge the different solubility of iodine in water and in an organic solvent?
Experiments with glycerin. 1. Solutions of glycerin in water freeze when low temperatures. Pour 0.5 ml of glycerin into four penicillin vials, add the same amount of water to the first, 1 ml of water to the second, 1.5 ml of water to the third, and 2 ml of water to the fourth. Put the solutions in the cold or in the freezer, note the temperature and determine which solutions are not frozen.
2. Wet the end of an iron wire or a glass rod with glycerin and bring it into the flame. The glycerin will ignite. Note the nature of the flame and give an explanation. Write down the reaction equation.
3. Pour 2 ml of sodium hydroxide solution, 2-3 drops of copper sulfate solution into a test tube, then add glycerin drop by drop until the precipitate dissolves. Write down the reactions carried out and your observations.
4. A little (1-2 ml) of glycerin purchased at a pharmacy, heat (carefully!) In a spoon to remove water from it. After cooling, add a pinch of potassium permanganate to the glycerin. After 1-2 minutes, glycerin flashes and burns with a bright flame. (If you have anhydrous glycerin at your disposal, preheating is unnecessary.) Describe your observations.
QUESTIONS AND TASKS
What is your opinion about the method of unification of a chemical experiment?
Develop a version of a demonstration experiment using a unified device for your topic.
Develop options for a chemical experiment to be carried out at home on your topic.
10. Test technologies in teaching chemistry. The process of accounting and control of students' knowledge is one of the most responsible and complex types learning activities for both students and teachers. The control of mastering the knowledge of students performs a number of functions in the learning process: evaluative, diagnostic, stimulating, developing, teaching, educational, etc.
To determine the quality of knowledge, skills and abilities, various techniques, means and methods are used, among which in last years testing has become essential in school practice.
