Chemical equations with sodium thiosulfate. Sodium hyposulfite (sodium thiosulfate)
Lesson motto:
“Just knowing is not everything, knowledge must be used.”
Lesson Objectives:
Educational:
- expand students' understanding of the speed of chemical reactions;
- to understand the essence of the law of mass action (LMA);
- introduce students to new concepts (homogeneous and heterogeneous reactions);
- experimentally investigate the dependence of the rate of a chemical reaction on the concentration of reactants.
Developing:
- continue the formation of experimental skills of students;
- develop the ability to work in groups and individually;
- continue the formation of chemical thinking, the development of speech, memory, cognitive interest in the subject, independence, the ability to draw conclusions.
Educational:
- to cultivate the ability to work in pairs, communication skills.
Equipment:
- For the teacher : porcelain bowl, porcelain pestle, computer, video projector.
- On the student's desktop : four test tubes, test tube stand, clock with a second hand, black paper.
Reagents: Sodium thiosulfate, sulfuric acid, water, aluminum, iodine.
During the classes
1. Introductory part: the message of the topic of the lesson, the mood of the students for the lesson.
Teacher. Kinetics is a branch of chemistry that includes the study of such topics as the reversibility of chemical reactions, the thermal effect of reactions, the rate of chemical reactions, and chemical equilibrium. We start with a topic whose name you need to guess (the topic on the board is closed; I show an experiment demonstrating the dependence of the reaction rate of the interaction of aluminum and crystalline iodine on a catalyst).
Question to the class. Why do we start the study of chemical kinetics with this topic?
The topic of the rate of chemical reactions is relevant, since various processes are constantly taking place around us and their speed is different. These processes are important and occur in all corners of nature, human life. (Picture 1). Discussion among the guys - comparing the rates of the proposed reactions. The class comes to conclusion: All processes run at different speeds.
Questions to the class:
1. What is the reaction rate? Which of the following formulas corresponds to the speed chemical reactions?
2. In what units is the rate of chemical reactions measured?
It is important not only to know the rate of a chemical reaction, but also to learn how to control it. What for? To speed up the desired reaction and slow down the unwanted. As Goethe said: "Just knowing is not everything, knowledge must be used." Let's look at the screen: the figure shows the dependence of the reaction rate on certain external factors (Figure 2).
3. What factors affect the rate of chemical reactions?
The guys name the temperature, the catalyst, the nature of the substances, the area of contact of the reacting substances, give examples in which the influence of these factors is observed.
2. The main part.
Teacher. And what factor is not here, but affecting the rate of chemical reactions?
This is the concentration of reactants, it increases the rate of reactions in a liquid and gaseous medium. Therefore, in this lesson, we experimentally study the effect of the concentration of substances on the rate of chemical processes. In the 9th grade it was the experience of the interaction of zinc with dilute and concentrated hydrochloric acid, and in the 10th grade we use the reaction of the interaction of sodium thiosulfate with sulfuric acid.
A little about sodium thiosulfate: the chemical formula is Na 2 S 2 O 3, it is widely used in medicine. In photography, it is known as fixing salt. With its help, undecomposed silver bromide is removed from plates, paper or film. This process is based on the ability of sodium thiosulfate to form a water-soluble compound with silver bromide. Films treated with it and thoroughly washed with water become insensitive to the further action of light.
The meaning of the chemical reaction underlying the experiment: when sodium thiosulfate interacts with sulfuric acid, turbidity is observed - the appearance of pure sulfur (a sign of a chemical reaction). This reaction proceeds in two stages.
Stage I: Na 2 S 2 O 3 + H 2 SO 4 = Na 2 SO 4 + H2S2O3(thiosulfuric acid)
Stage II: H 2 S 2 O 3 \u003d H 2 SO 3 + S v
Sulfur is insoluble in water, which is why it precipitates. Before starting the experiment, let's look at the table that is on your tables - the instructions for conducting the experiment (Figure 3). It indicates the concentration of sodium thiosulfate in drops (conditional concentration). We will change it with water. The concentration of sulfuric acid remains unchanged - 1 drop. In the next column, write down the reaction time with a pencil. What is considered the start time of the reaction? The moment of draining solutions of sodium thiosulfate, water and sulfuric acid is considered zero, then you count the time until cloudiness appears. To better see the formation of sulfur in the reaction, use black paper.
Let's do a preliminary experience of the interaction of sodium thiosulfate with sulfuric acid and note the reaction time (second hand).
After the experiment, we plot the dependence of the reaction time on the concentration of sodium thiosulfate (Figure 4). We build a chart on half a page. We set aside the concentration in drops, the time in seconds. You have 10 minutes to work. Get started.
Let's look at the results of the experiment. On the board, the student enters his data in a pre-prepared table. I compare with my data (experiment spend the day before). I note which of the pairs conducted the experiment more accurately. The student then draws a graph of reaction time versus sodium thiosulfate concentration. class does conclusion:
The rate of a chemical reaction depends on the concentration. The larger it is, the faster the reaction rate.
Questions to the class:
1. Why does the rate of a chemical reaction increase, because with an increase in concentration, the reaction time decreases? (the answer is an inverse relationship between speed and time - see the formula).
2. What does a graph of reaction rate versus time look like? The guys build a graph (Figure 5). Why?
The dependence of the rate of a chemical reaction on the concentration of substances is expressed by the law of mass action (LMA), discovered in the 19th century. For example, for a conditional response
the rate of a chemical reaction is equal to the product of the rate constant of the chemical reaction k on the molar concentrations of the reactants raised to the power of their stoichiometric coefficients, if necessary: ? = k C A C B 2
where S A and M B– molar concentration of substances A and B, mol/l.
physical sense k : when C A \u003d C B \u003d 1 mol / l, then k=v.
But here it is important to take into account in what medium the reaction proceeds: in homogeneous or heterogeneous. According to ZDM, the concentrations of substances in the dissolved and gaseous state are recorded in the expression for the reaction rate. If the substance is in the solid state, then its concentration is neglected (two students go to the blackboard to write down the expression for the reaction rate in a homogeneous and heterogeneous medium):
| 2SO 2 + O 2 \u003d 2SO 3 | C + O 2 = CO 2 |
| v= k With O2 With 2 SO2 | v= k With O2 |
That is, ZDM is valid for homogeneous reactions. And what does the expression for the rate of a chemical reaction look like for a homogeneous and heterogeneous reaction?
For a homogeneous reaction:
For a heterogeneous reaction:
Control. To consolidate the topic, students answer the test questions (Figure 6).
Then, students check all the answers with the screen where the answers are projected for verification (Figure 7).
The result of the lesson: deepened knowledge on the topic of the rate of chemical reactions, experimentally investigated the effect of the concentration of substances on the reaction rate. I think that you have acquired new knowledge, skills that will be useful to you in the future. And, finally, a small wish in chemical language.
IV. Reflection.
I wish you not with loud words,
So that they do not explode like hydrogen, in case of failures
What's behind you
And were not inert, like neon, on the way,
What you haven't seen yet.You be patient like fate
Don't oxidize like a group of alkali metals
hardworking always
For long, long years.Let there be fewer inhibitors
Like a burden, slowing down the path at times.
Let there be more individuals
Talented and creative of you.Be active in our mad life,
Like a free radical.
Catalysts on your way are promised
Love, patience and kindness.
Product description
Sodium hyposulfite externally looks like colorless crystals, which are readily soluble in water. It is widely used in industry and medicine. It is considered a strong reducing agent.
Hyposulfites (thiosulfates) are unstable, therefore they do not occur in nature.
Chemical formula: Na2S2O3 or Na2SO3S
Synonyms: sodium thiosulfate, antichlorine, sodium sulfidotrioxosulfate, sodium sulphate.
The use of sodium hyposulfate (thiosulfate).
It is used to remove traces of chlorine after bleaching fabrics, to quickly extract silver from ores, a fixer in photographs, as a reagent in iodometry, an antidote for poisoning with toxic mercury, as well as other heavy metals, cyanides.
During the First World War, gauze bandages and gas mask filters were impregnated with hyposulfite to protect the respiratory organs from poisonous chlorine. It is also used as a reagent in analytical and organic chemistry, they neutralize strong acids, neutralize heavy metals and their toxic compounds. The interaction reactions of thiosulfate with various substances are the basis of iodometry and bromometry.
In medicine sodium hyposulfite is used to disinfect the intestines, treat scabies, as an anti-inflammatory and anti-burn agent. Also used as an optimal medium for determining molecular weights by freezing point depression.
In the food industry sodium hyposulfite is registered as food additive E539. Especially often it is used in bakery production. Sodium hyposulfite makes the dough more plastic, and the bread becomes more friable and voluminous. Cracks do not form on the surface of the product, and baking acquires a more attractive appearance. The amount of input into the composition depends on the type of bread and ranges from 0.001 to 0.002 percent of the total flour weight.
In photography The use of sodium hyposulfite (thiosulfate) as a fixative is based on the ability of the thiosulfate ion to convert light-sensitive silver ions insoluble in water into soluble non-light-sensitive complexes.
Fixers are conventionally divided into neutral, acidic, tanning and fast.
A neutral fixer is a solution of sodium thiosulfate in water. To strengthen the emulsion layer of photography, tanning fixers are used.As tanning 
substances in different formulations can be used sodium tetraborate, boric acid, potassium chromium or potassium alum and formalin.
In the leather industry the property of tanning fixatives is successfully used in the manufacture of semi-finished leather and fur products at the tanning stage. Such tanning is called sulfur. Hyposulfite, under the influence of the acid added to the composition of the solution, releases sulfur, which envelops the collagen structure of the fibers in the thickness of the skin. As a result, the core is soft and plastic. Skins tanned with sodium gyrosulfate (thiosulfate) are not inferior in quality to products tanned with aluminum or chromium.
In the textile industry hyposulfite is used to remove traces of chlorine after bleaching fabrics.
Specifications
| Mass fraction, % |
Sodium hyposulfite (photo) |
Sodium hyposulfite (technical) |
|---|---|---|
| Sodium thiosulfate (Na 2 S 2 O 3 5H 2 O), min. | 99,0 | 98,5 |
| substances insoluble in water, max. | 0,01 | 0,03 |
| iron (Fe), max. | 0,001 | 0,002 |
| sodium sulfide (Na 2 S), max. | 0,001 | 0,001 |
| calcium, magnesium and substances insoluble in ammonium solutions, max. | 0,02 | not the norm. |
| heavy metals (Pb), max. | 0,001 | not the norm. |
| pH of aqueous solution at 20°C, max. | 6,5-9,5 | not the norm. |
| appearance of the aqueous solution | colorless, transparent. | not the norm. |
Where to buy sodium hyposulfite (thiosulfate)?
Sodium hyposulfite (sodium thiosulfate) in 100g, 250g, 500g, 1kg packages. for sale in Novosibirsk in the online store "For business". During business hours, you can pick it up by self-delivery or use the services of a courier. For buyers from other regions, these products are sent by Russian Post or transport companies.
We take sodium thiosulfate and three acids (sulfuric, hydrochloric and orthophosphoric):
Na2S2O3 + H2SO4 = Na2SO4 + SO2 + S + H2O
Na2S2O3 + 2 HCl = 2 NaCl + SO2 + S + H2O
3 Na2S2O3 +2 H3PO4 = 2 Na3PO4 + 3 SO2 + 3 S + 3 H2O
Pour into three test tubes 8 ml of sodium thiosulfate solution. Pour 8 ml of sulfuric acid into the first test tube with a solution of sodium thiosulfate, mix quickly and note the time in seconds from the start of the reaction to the cloudiness of the solution. To better notice the end of the reaction, glue a strip of black paper on the opposite side of the test tube wall. We finish the time report at the moment when this strip is not visible through the cloudy solution.
Similarly, we carry out experiments with other acids. The results are entered in the table (Appendix 1, table 1). The reaction rate is defined as a value inversely proportional to time: υ = 1/ t. Based on the table, we build a graph of the dependence of the reaction rate on the nature of the reactants (Appendix 2, graph 1).
Conclusion: thus, the nature of acids affects the rate of a chemical reaction. And, since the strength of acids is determined by the concentration of hydrogen ions, the reaction rate also depends on the concentration of the reactants.
B. Consider the reaction of the interaction of various metals with hydrochloric acid. The reaction rate will be determined by the volume of released hydrogen, which is collected by the method of water displacement (Appendix 3, Figure 1).
In four test tubes we place 0.05 g of metals: magnesium, zinc, iron and copper. In turn, pour equal volumes of hydrochloric acid (1:2) into each test tube (a). Hydrogen, which will be rapidly depleted, will enter the test tube (b). Note the time it takes for the tube to fill with hydrogen. Based on the results (Appendix 4, Table 2), we build a graph depending on the nature of the reactants (Appendix 4, Chart 2).
Conclusion: not all metals can interact with acids by removing hydrogen. Metals that displace hydrogen from acid solutions are located in the series N.N. Beketov to hydrogen, and metals that do not displace hydrogen - after hydrogen (in our case, this is copper). But the first group of metals also differ in the degree of activity: magnesium-zinc-iron, therefore, the intensity of hydrogen evolution is different.
Thus, the rate of a chemical reaction depends on the nature of the reactants.
2. Dependence of the rate of a chemical reaction on the concentration of interacting substances.
Target. Establish a graphical dependence of the effect of concentration on the reaction rate.
For the experiment, we use the same solutions of sodium thiosulfate and sulfuric acid that were used in the first experiment (A).
Pour the indicated amounts of milliliters of sodium thiosulfate solution and water into numbered test tubes. Pour 8 ml of sulfuric acid solution into the first test tube, mix quickly and note the time from the beginning of the reaction to the cloudiness of the solution (see experiment 1 A). We carry out similar experiments with the rest of the test tubes. We enter the results in a table (Appendix 6, Table 3), on the basis of which we build a graph of the dependence of the rate of a chemical reaction on the concentration of reactants (Appendix 7, Chart 3). We obtained a similar result by keeping the concentration of sodium thiosulfate constant, but changing the concentration of sulfuric acid.
Conclusion: thus, the rate of a chemical reaction depends on the concentration of the reacting substances: the higher the concentration, the greater the reaction rate.
3. Dependence of the rate of a chemical reaction on temperature.
Purpose: To test whether the rate of a chemical reaction depends on temperature.
We carry out the experiment with solutions of sodium thiosulfate and sulfuric acid (see experiment 1), additionally we prepare a beaker, a thermometer.
Pour 8 ml of sodium thiosulfate solution into four test tubes, 8 ml of sulfuric acid solution into 4 others. We place all test tubes in a glass of water and measure the temperature of the water. After 5 minutes, we take out two test tubes with solutions of sodium thiosulfate and sulfuric acid, drain them, mix and note the time until the solution becomes cloudy. We heat a glass with water and test tubes by 10 ° C and repeat the experiment with the next two test tubes. We carry out the same experiments with the rest of the test tubes, each time increasing the water temperature by 10°C. The results obtained are recorded in a table (Appendix 8, Table 4) and we plot the dependence of the reaction rate on temperature (Appendix 9, Chart 4).
Conclusion: this experiment led to the conclusion that the rate of a chemical reaction increases with an increase in temperature for every 10°C by 2–4 times, i.e. proved the validity of Van't Hoff's law.
4. Effect of a catalyst on the rate of a chemical reaction.
Purpose: to check whether the rate of a chemical reaction depends on the catalyst, and whether the catalysts have specificity.
A. To test the specificity of the catalyst, we used the decomposition reaction of hydrogen peroxide: 2H2O2 = 2H2O + H2. They took a 3% solution, the decomposition of hydrogen peroxide is very weak, even a smoldering splinter dropped into a test tube does not flare up. We used silicon dioxide SiO2, manganese dioxide MnO2, potassium permanganate KMnO4, and sodium chloride NaCl as catalysts. Only when manganese (IV) oxide powder was added did a rapid evolution of oxygen occur, a smoldering splinter, lowered into a test tube, flared up brightly.
Thus, catalysts are substances that speed up a chemical reaction, and, most often, a particular reaction requires its own catalyst.
5. Kinetics of the catalytic decomposition of hydrogen peroxide.
Purpose: to find out the dependence of the reaction rate on the concentration of substances, temperature and catalyst.
The decomposition of a very weak solution of hydrogen peroxide begins under the influence of a catalyst. With the course of the reaction, the concentration of hydrogen peroxide decreases, as can be judged by the amount of oxygen released per unit time. We carry out the experiment in the device (Appendix 10, Figure 2): put 0.1 g of manganese dioxide powder into a test tube, attach it to a rubber tube, pour 40 ml of a 3% hydrogen peroxide solution into the flask, connect it with a test tube using a rubber tube. We fill the cylinder (burette) with water, lower it into the crystallizer, fix it vertically in the clamp of the tripod, and bring the gas outlet tube from the Wurtz flask under it. Without a catalyst, oxygen evolution is not observed. After adding manganese dioxide, every minute for 10 minutes we note and write down in the table the volume of released oxygen (Appendix 11, Table 5). Based on the data, we build a graph of the dependence of the volumes of released oxygen on time (Appendix 12, graph 5)
6. Influence of the contact surface of reactants on the rate of a chemical reaction.
Target. Find out whether the contact surface of the reactants affects the rate of a heterogeneous chemical reaction.
The same amount (0.5 g) of chalk (CaCO3) in the form of a piece and powder was weighed on a balance, the weighed portions were placed in two test tubes, into which the same amount of hydrochloric acid (1:2) was poured. We observe the release of carbon dioxide, and in the first test tube (chalk in the form of a piece) the reaction is less vigorous than in the second (chalk in the form of powder) (Appendix 13, photos 1.2): CaCO3 + 2 HCl = CaCl2 + CO2 + H2O
Topic: RATE OF CHEMICAL REACTIONS AND
CHEMICAL EQUILIBRIUM
Temperature dependence of the reaction rate
(checking the van't Hoff rule)
The regularity is studied on the example of the interaction of sodium thiosulfate with sulfuric acid
The reaction proceeds in two stages:
The first stage - ion exchange - occurs instantly, so that in fact the monitoring is carried out over the rate of the second monomolecular stage, a sign of the course of which is the appearance of turbidity as a result of the formation of elemental sulfur. Therefore, the concentration of sulfuric acid does not actually affect the rate of the reaction, as long as it is taken in an amount sufficient for the complete interaction of thiosulfate, and is the same in all experiments.
Therefore, the velocity equation can be written as:
Experience 1. Prepare a simple thermostat: a 200 ml glass with a lid that has 3 holes. Insert a thermometer fixed on a thread into the first hole, into the second - a conical test tube with a -2 N solution of H 2 SO 4 with a pipette lowered into it, into the third - a conical test tube, into which 10 drops of 0.1-N sodium thiosulfate solution are added with a clean pipette. Fill the glass with water aged at room temperature so that the bulb of the thermometer and the solution are immersed in it. The mercury ball of the thermometer and the solutions of the reactants should be at the same level in the middle part of the water filling the glass - the thermostat.
After waiting 5 minutes - the time required to equalize the temperature of the water in the thermostat and the solutions in the test tubes, record the thermometer readings. Without removing the test tubes from the thermostat, add 1 drop of sulfuric acid solution to the sodium thiosulfate solution with a pipette. At this moment, turn on the stopwatch (measure the time on a clock with a second hand), without removing the test tube from the thermostat, observe the course of the experiment until a cloudiness that is noticeable to the eye appears in the test tube and, if it is detected, turn off the stopwatch. Record the duration of the experiment in seconds.
Experience 2. It is carried out at a temperature increased by 10 °. To do this, replace the test tube in the thermostat in which the experiment was carried out with a clean one and add 10 drops of 0.1 N sodium thiosulfate solution into it again. Adding hot water to the glass, raise its temperature by 14 - 15 ° above the temperature of the first experiment and observe its cooling with a thermometer. When the temperature is 10° higher, carry out the experiment in exactly the same way as the first.
Experience 3. Carrying out the experiment at a temperature increased by 20 °. The experiment is carried out in the same way as in the previous case, but the temperature of the water in the thermostat initially rises by 24 - 25 ° above room temperature, and the addition of sulfuric acid to hyposulfite is carried out at the moment when it is exactly 20 ° above the temperature of the first experiment. All experimental data and calculation results are recorded in the form of a table. Instead of indices, indicate the actual temperatures.
Calculate:
A) the relative rate of the reaction.
Let's take the reaction rate at room temperature
in the first experience. Since the speed and magnitude, the reciprocal of time,
from this proportion we find
Similarly, we make a proportion and calculate
B) thermal velocity coefficient according to van't Hoff. It is calculated from the results of two experiments, independently of one another.
The performance of the work is satisfactory if the results of these two calculations differ slightly. Then you can take their average values. In case of a sharp discrepancy, the work must be repeated.
The rate of chemical reactions in homogeneous and
HETEROGENEOUS SYSTEMS
Experience 1. The influence of the size of the interface of reactants on the reaction rate in a heterogeneous system
Dissolution of calcium carbonate in hydrochloric acid
Completing of the work. Take two small, if possible identical, pieces of chalk. Put one of them on a piece of filter paper and grind it into powder with a glass rod. Place the resulting powder into a conical test tube. The second piece of chalk is completely lowered into another conical test tube. In both test tubes simultaneously add the same amount (10-20 drops) of hydrochloric acid with a density of 1.19 g/cm 3 . (To maintain the simultaneous addition of acid, the experiment can be carried out by two students together). Note the time of complete dissolution of the chalk in each case.
Recording experience data. Write the equation for the corresponding
reactions. Why is the dissolution rate of chalk in these two cases
different?
Experience 2. The effect of a catalyst on the reaction rate
Catalytic reduction of iron (III) Performance of work. Add 10 drops of 0.5 N to two test tubes. potassium thiocyanate solution and 1 drop of 0.5 n. solution...Experience 3. Shifting the chemical equilibrium of reversible reactions
Influence of the concentration of reacting substances on the equilibrium shift Performance of work. Add 5-7 drops of 0.0025 N to four conical tubes. solutions of iron chloride (III) and ...TOPIC: SOLUTIONS
Experience 1 Determination of the density of the solution with a hydrometer.
Figure 1 - Hydrometer for determining the density of the solutionExperience 2 Preparation of solutions of various concentrations
A) Preparation of a 0.1N solution of sulfuric acid.
2. How many ml of a 10% sulfuric acid solution (ρ, see experiment No. 1) must be taken to prepare 250 ml of a 0.1N sulfuric acid solution. 3. How many ml of a 15% sulfuric acid solution (ρ, see experiment No. 1) is necessary ... 4. How many ml of a 15% sulfuric acid solution (ρ, see experiment No. 1) must be taken to prepare 250 ml of a 0.1 n solution ...B) Preparation of a solution of a given concentration by mixing solutions of a higher and lower concentration
2. Prepare 150 ml of 12% sodium hydroxide solution, having at your disposal 5% and 25% NaOH solutions. 3. Prepare 500 ml of 20% sodium hydroxide solution, having in your own, ... 4. Prepare 250 ml of 15% sodium hydroxide solution, having in your disposal 8% and 25% solutions ...Experience 3 Determination of the concentration of solutions
Rinse a burette with a capacity of 10 ml (Figure 2c) with a small volume of 0.1 N NaOH solution, then pour it through the lower end of the burette, equipped with ... Add a dry pipette to a conical flask with a capacity of 30-50 ml (Figure 2b) ... Repeat the titration three more times. A sharp change in the color of phenolphthalein from one drop of alkali is an indicator ...TOPIC: THE THEORY OF ELECTROLYTIC DISSOCIATION
Experience 1. Comparison of the electrical conductivity of solutions of some electrolytes.
Pour 20-30 ml of distilled water into a glass with electrodes. Does the lamp light up? Does water conduct electricity? Add 4-5 to a glass of water ... Explain why a salt solution is a current conductor, although pure water and ... Pour 20-30 ml of 0.1 n into four glasses with a capacity of 50 ml each. solutions: in the first - hydrochloric acid, in ...Experience 2. The nature of the dissociation of hydroxides
Completing of the work. Number 5 tubes and add 4-5 drops of 0.5 N. solutions: in the first test tube MgCl2, in the second - AlCl3, in the third ... Similarly, investigate the properties of hydroxides of aluminum, silicon, nickel (II) and zinc. What do they dissolve into?Experience 3. Comparison of the chemical activity of acids
a) Interaction of hydrochloric and acetic acids with marble. Performance of work. Introduce 3-4 drops of 2n into one test tube. acetic acid solution, in another - the same amount of 2 n. solution...Experience 4. Shifting the equilibrium of dissociation of weak electrolytes
a) Influence of a salt of weak acids on the dissociation of this acid Performance of work. In two test tubes, 5-7 drops of 0.1 N. acetic acid solution. Add one to each tube...Experience 1. The reaction of the medium in solutions of various salts
Stir the solutions (do not transfer glass rods from one solution to another). By changing the color of litmus, draw a conclusion about the reaction of the medium in a solution of each ... Which of the studied salts undergo hydrolysis? Write the ionic and molecular equations for the reactions of their hydrolysis and ...Experience 2. Formation of basic and acidic salts during hydrolysis
A) Hydrolysis of sodium sulfite
The presence of which ions in the solution is indicated by the found pH value? As a result of what process did these ions appear? By the absence of the smell of sulfur dioxide, make sure that sodium sulfite ... Write the molecular and ionic equations for the hydrolysis of sodium sulfite. Which salts are hydrolyzed to produce...Experience 3. Factors affecting the degree of hydrolysis of salts
A) The effect of the strength of an acid and a base forming a salt on the degree of its hydrolysis
Write the ionic equations for the hydrolysis of sodium sulfite and sodium carbonate (in the first stage). In a solution of which salt, the color of phenolphthalein is more ... The degree of hydrolysis of which salt at the same concentrations and temperatures should ... Make a general conclusion about the effect of the strength of the acid and base that form the salt on the degree of its hydrolysis.TOPIC: REDOX
PROCESSES
HYDROGEN
Experience 1 Obtaining hydrogen
Open the valve of the gas outlet pipe. Watch how the acid pours into the apparatus, fills its lower part and rises to the middle, where it is ... Familiarize yourself with the automaticity of the operation of the Kipp apparatus. To do this, turn off the tap... NEVER ignite the hydrogen at the end of the Kipp's gas outlet tube without checking it for cleanliness and without being...HYDROGEN PURITY CHECK
Experience 2 Transfusion of hydrogen.
Check the purity of hydrogen and fill a large test tube with it, holding it upside down, place next to it, also upside down, another test tube so that their holes are next to each other. Without moving the test tubes with hydrogen, turn it upside down so that the empty test tube covers the test tube with hydrogen. After separating the test tubes, bring each of them to the flame of an alcohol lamp. In which test tube is the outbreak observed?
Experience 3 Formation of water during combustion.
CHECK HYDROGEN for purity. If it is clean, light it at the end of the gas tube and, holding the tube up, cover the flame with a glass jar, stopping the process of hydrogen evolution. What needs to be done for this? What is observed on the walls of the bank? Write down the reaction equation.
OXYGEN
OBTAINING OXYGEN AND BURNING SUBSTANCES IN IT
1. Familiarize yourself with the device of the gasometer. 2. Place potassium permanganate in a test tube, close with a stopper with a gas outlet ...Experience 2. Combustion of sulfur in oxygen.
Experience 3. Combustion of magnesium in oxygen.
Fill the jar with oxygen, as in the previous experiment. Take shavings or a ribbon of magnesium with crucible tongs, heat it in the flame of an alcohol lamp until it lights up and quickly add it to a jar of oxygen. What is magnesium oxide? Test the nature of magnesium oxide. To do this, as in the previous experiment, pour a little solution of purple litmus into the jar and shake. How did the color of the litmus change? Make a conclusion about the nature of the resulting hydroxide.
Experience 4. Combustion of iron in oxygen.
The influence of the medium on the course of redox processes The influence of the pH of the medium on the nature of the reduction of potassium permanganateH2O2 + 2H+ + 2e- = 2H2O
for the oxidation reaction of hydrogen peroxide (H 2 O 2 - reducing agent):
H 2 O 2 - 2e - \u003d O 2 + 2H +
b) Interaction of hydrogen peroxide with potassium iodide
Completing of the work. To a solution of potassium iodide, acidified with sulfuric acid, add 1 - 2 drops of a solution of hydrogen peroxide. For what type of substance did the color of the solution appear?
Write the reaction equation. Is hydrogen peroxide an oxidizing or reducing agent?
c) Interaction of hydrogen peroxide with mercury oxide (II)
Completing of the work. Place 3-4 drops of mercury nitrate solution in a test tube Hg(NO 3) 2 and add the same amount of 2 n. alkali solution until precipitation of mercury oxide (II). Note the color of the precipitate. Add 4 - 5 drops of hydrogen peroxide solution and observe the color change of the precipitate due to the formation of suspended particles of metallic mercury. What gas is released?
Write the reaction equation. Is hydrogen peroxide the oxidizing and reducing agent in this reaction? Draw appropriate conclusions.
DETERMINATION OF ELECTRODE POTENTIALS. DIRECTION
REDOX
PROCESSES
Performing the work. Fill one of the microcups 1 (figure) to the top with a 1M solution of zinc sulfate (more precisely, a solution in which the activity of ions ... Record the data of the experiment. Depict a double electric layer at the interface between the metal - a solution of its salt on zinc and ...ELECTROLYSIS OF AQUEOUS SOLUTIONS
The experiments described below are carried out in the apparatus shown in the figure.B) Electrolysis of potassium iodide solution
Note the color change of the solution near the cathode and anode. Write the equation of the cathode and anode processes. Why did the solutions in the cathode and ...C) Electrolysis of sodium sulfate solution
Completing of the work. In a beaker with a volume of 100 ml, mix a solution of sodium sulfate with a neutral solution of litmus and pour the resulting solution into ...D) Electrolysis of aqueous solutions of salts with soluble anodes
Completing of the work. Pour into the electrolyzer 0.5 N. copper sulfate solution, lower the graphite electrodes into it and pass an electric current through the solution. After a few minutes, stop the electrolysis and mark the red copper coating on the cathode. Write the equations of the cathode and anode processes. What gas is released in small quantities at the anode?
Without disconnecting the electrolyzer from the battery, swap the electrodes in the knees of the electrolyzer, as a result of which the electrode, which was first covered with copper, will turn out to be the anode. Pass the electric current again. What happens to the copper at the anode? What substance is released at the cathode? Write the equations of the cathodic and anode processes occurring during the electrolysis of copper sulfate with a copper anode.
Carry out a similar experiment with 0.5 n. nickel(II) sulfate solution. What is released at the cathode? Write an equation for the cathodic reduction of nickel. What substance is oxidized at the anode during the electrolysis of nickel sulfate with a carbon anode? With a nickel anode? Write the equations of the corresponding anodic processes.
TOPIC: COMPLEX COMPOUNDS
Experience 1. Obtaining and properties of some ammonias
Dilute the solution with an approximately equal volume of alcohol and centrifuge the resulting crystals of [Сu(NH3)4]SO4 ·H2O - complex ... Write the equations of all reactions carried out in this experiment.Experience 2. Study of tetraamine cupro (׀׀) sulfate
Pipette 10 drops of the test solution of the complex salt into four numbered test tubes. a) Test for the Cu2+ ion by the action of alkali. Add a few drops to test tube No. 1 ... b) Test for Cu2+ ion by the action of sodium sulfide. Add a few drops of Na2S solution to test tube No. 2. Is it observed...TOPIC: CHEMISTRY OF THE ELEMENTS
HALOGENS
Experience 1. Obtaining chlorine
Completing of the work. Put 3-4 crystals of various oxidizing agents into three test tubes: in the first, manganese dioxide MnO2 or lead dioxide PbO2, in ... a) obtaining chlorine, given that the oxidation numbers of manganese change from +4 to ... b) the interaction of chlorine with sodium thiosulfate with the participation water; the reaction proceeds with the formation of free sulfur, ...Experiment 2. Obtaining chlorine water and studying its properties
A) Obtaining chlorine water
Write the reaction equation for the production of chlorine by oxidation of hydrochloric acid with potassium permanganate, given that the oxidation number of manganese varies from ...B) Study of the composition and properties of chlorine water
Cl2 + H2O ↔HClO + HCl. (1) In this case, the equilibrium is strongly shifted to the left. Therefore, chlorine water can be ... HClO \u003d HCl + O (2)Experience 3. Obtaining bromine
Completing of the work. Place 2-3 crystals of potassium or sodium bromide and the same amount of manganese dioxide into a dry cylindrical test tube. Gently shake the test tube and add 2-3 drops of concentrated sulfuric acid (pl. 1.84 g/cm3) to the mixture. What are the prominent brown vapors? Write the reaction equation for the production of bromine.
Experience 4. Obtaining iodine
Experiment 5. Oxidizing properties of free halogens (oxidizing number is ...A) Comparison of the oxidative activity of free halogens.
By the color of the benzene ring, determine which halogen is released in the free state in each case. Write the equations for the reactions of mutual ...B) Oxidation of magnesium or zinc with bromine.
Contribute in a test tube 3 - 5 drops of bromine water and a little powder of magnesium or zinc. Stir with a glass rod. Note the discoloration of solutions with bromine water and indicate the cause of this phenomenon. Write the corresponding reaction equation.
Experiment 6. Obtaining hydrogen compounds of halogens (hydrogen halides).
Hydrogen halides can be produced by the action of non-volatile and non-oxidizing acids on metal halides.
B) The action of hydrofluoric acid on glass.
C) Obtaining hydrogen chloride and its dissolution in water.
After filling the test tube with hydrogen sulfide, close it tightly with a stopper. Disconnect the capillary from the tube, quickly close it with your index finger and, turning it over ...D) Production of hydrogen bromide and hydrogen iodide.
Put 2-3 microspatulas of cadium or sodium bromide into one test tube, and the same amount of any iodide into another. Add 5-10 drops of a concentrated solution of orthophosphoric acid to both tubes. Heat the solutions on a small burner flame. Observe the evolution of hydrogen bromide and hydrogen iodide in the form of white smoke. Does this release free bromine and iodine? To conclude, does phosphoric acid oxidize hydrogen bromide and hydrogen iodide? Write reaction equations.
Experience 7. Reducing properties of hydrogen halides and halide ions.
A) Recovery of sulfuric acid.
Note in the second test tube the release of brown vapors of bromine and sulfur dioxide SO2, in the third - violet vapors of iodine, sulfur and hydrogen sulfide formed ... Write the reaction equation for the interaction of chloride, bromide and potassium iodide or ...B) Recovery of iron trichloride.
Can negative halogen ions be oxidizing agents? Justify the answer. Experience 8. Interaction of bromine with aluminum. Pour bromine into a demonstration tube fixed in a rack over a tray with sand. Drop an aluminum...Experience 1. Obtaining ammonia and studying its properties
Experience 2. Obtaining oxides of nitrogen and nitric acid
a) obtaining nitric oxide (II) by the interaction of dilute nitric acid with copper; b) oxidation of nitric oxide (II) to nitric oxide (IV) and oxide polymerization ... c) interaction of nitrogen dioxide with water, proceeding with the formation of nitric and nitrous acids;Experience 3. Obtaining nitrous acid and its decay
a) interaction of potassium nitrite with sulfuric acid; b) decomposition of nitrous acid; c) decomposition of nitrous anhydride.Experience 4. Redox properties of nitrites
1. Add 2-4 drops of potassium iodide solution and the same amount of 2N sulfuric acid to the test tube. Add 2-4 drops of potassium or sodium nitrite solution. Than… 2. Interaction of potassium nitrite with permanganate. Add 2-3 drops to the test tube...Experience 5. Oxidizing properties of nitric acid
Reaction of dilute nitric acid with copper and tin
2. Interaction with concentrated nitric acid with copper and tin. Place a small piece of copper and tin into 2 test tubes. Add them to...Experience 6 . Salts of nitric acid
Place 2-3 microspatulas of dry potassium nitrate into a cylindrical tube. Having strengthened it obliquely in a tripod, heat until the salt melts. Contribute…Experience 1. Allotropy of phosphorus
P+CuSO4+H2O H3PO4+H2SO4+CuExperience 2. Salts of orthophosphoric acid
Find the dissociation constants of orthophosphoric acid and determine whether alkali metal orthophosphates undergo hydrolysis. Check your…SULFUR AND ITS PROPERTIES
Experience 1. Sulfur allotropy
1. Obtaining plastic sulfur. In a 10 ml test tube. pour on ¼ of the volume of small pieces of cutting sulfur. Fix the test tube in the holder and…Experience 2. Obtaining sulfur dioxide and sulfurous acid
Fill the micro flask to 1/3 of its volume with sodium sulfate crystals, add 6-8 drops of 4 and sulfuric acid solution and quickly close with a stopper about ... Experiment 3. Oxidizing and reducing properties of sulfur (IV)Experience 5. Dehydrating properties of sulfuric acid
Experience 6 Theosulfuric acid and theosulfates
1. Study of thiosulfuric acid. Add 5-6 drops of sodium thiosulfate Na2S2O3 solution and 3-4 drops of sulfuric acid solution to the test tube. Note… 2. Interaction of sodium thiosulfate with chlorine and bromine. In two test tubes with… 3. Interaction of sodium thiosulfate with iodine. In a test tube with iodine water (5-6 drops), add dropwise a solution ...APPENDIX
Table 1 - Instability constants of some complex ions
| complex ion | K nest |
| - | 1 ∙ 10 -21 |
| + | 7 ∙ 10 -8 |
| 3- | 1 ∙ 10 -13 |
| 2- | 9 ∙ 10 -3 |
| 2- | 8 ∙ 10 -7 |
| 2- | 1 ∙ 10 -17 |
| 2+ | 8 ∙ 10 -8 |
| 2+ | 8 ∙ 10 -6 |
| 3+ | 6 ∙ 10 -36 |
| 2+ | 2 ∙ 10 -13 |
| 3- | 5 ∙ 10 -28 |
| 4- | 1 ∙ 10 -37 |
| 3- | 1 ∙ 10 -44 |
| 2+ | 1 ∙ 10 -3 |
| 2- | 1 ∙ 10 -21 |
| 2- | 8 ∙ 10 -16 |
| 2- | 1 ∙ 10 -30 |
| 2- | 1 ∙ 10 -22 |
| 2- | 3 ∙ 10 -16 |
| 2+ | 2 ∙ 10 -9 |
| 2- | 2 ∙ 10 -17 |
| ] 2+ | 4 ∙ 10 -10 |
Table 2 - Density of solutions of some acids, alkalis and ammonia at 20 0 C (in g / cm 3, g / ml).
Thiosulfuric acid. sodium thiosulfate. Obtaining, properties, application.
Sulfuric acid esters include dialkyl sulfates (RO2)SO2. These are high-boiling liquids; the lower ones are soluble in water; in the presence of alkalis, they form alcohol and salts of sulfuric acid. Lower dialkyl sulfates are alkylating agents.
Diethyl sulfate (C2H5)2SO4. Melting point -26°C, boiling point 210°C, soluble in alcohols, insoluble in water. Obtained by the interaction of sulfuric acid with ethanol. It is an ethylating agent in organic synthesis. Penetrates through the skin.
Dimethyl sulfate (CH3)2SO4. Melting point -26.8°C, boiling point 188.5°C. Let's dissolve in alcohols, it is bad - in water. Reacts with ammonia in the absence of a solvent (explosively); sulfonates some aromatic compounds, such as phenol esters. Obtained by interaction of 60% oleum with methanol at 150°C. It is a methylating agent in organic synthesis. Carcinogen, affects the eyes, skin, respiratory organs.
Sodium thiosulfate Na2S2O3
Salt of thiosulfuric acid, in which two sulfur atoms have different oxidation states: +6 and -2. Crystalline substance, highly soluble in water. It is produced in the form of Na2S2O3 5H2O crystalline hydrate, commonly called hyposulfite. Obtained by the interaction of sodium sulfite with sulfur during boiling:
Na2SO3+S=Na2S2O3
Like thiosulfuric acid, it is a strong reducing agent. It is easily oxidized by chlorine to sulfuric acid:
Na2S2O3+4Сl2+5Н2О=2H2SO4+2NaCl+6НCl
The use of sodium thiosulfate to absorb chlorine (in the first gas masks) was based on this reaction.
Sodium thiosulfate is oxidized somewhat differently by weak oxidizing agents. In this case, salts of tetrathionic acid are formed, for example:
2Na2S2O3+I2=Na2S4O6+2NaI
Sodium thiosulfate is a by-product in the production of NaHSO3, sulfur dyes, in the purification of industrial gases from sulfur. It is used to remove traces of chlorine after bleaching fabrics, to extract silver from ores; is a fixer in photography, a reagent in iodometry, an antidote for poisoning with arsenic, mercury compounds, an anti-inflammatory agent.
Thiosulfuric acid- an inorganic compound, a dibasic strong acid with the formula H 2 SO 3 S. A colorless viscous liquid that reacts with water. Forms salts - inorganic thiosulfates. Thiosulfuric acid contains two sulfur atoms, one of which has an oxidation state of +4, and the second is electrically neutral.
Receipt
The reaction of hydrogen sulfide and sulfur trioxide in ethyl ether at low temperatures:
The action of gaseous hydrogen chloride on sodium thiosulfate:
Physical Properties
Thiosulfuric acid forms a colorless viscous liquid that does not freeze even at very low temperatures. Thermally unstable - decomposes already at room temperature.
Quickly, but not instantly, decomposes in aqueous solutions. In the presence of sulfuric acid, it decomposes instantly.
Chemical properties
Thermally very unstable:
Decomposes in the presence of sulfuric acid:
Reacts with alkalis:
Reacts with halogens:
Forms esters - organic thiosulfates.
Sodium thiosulfate (antichlor, hyposulfite, sodium sulfidotrioxosulfate) - Na 2 S 2 O 3 or Na 2 SO 3 S, a salt of sodium and thiosulfuric acid, forms a crystalline Na 2 S 2 O 3 5H 2 O.
Receipt
Oxidation of Na polysulfides;
Boiling excess sulfur with Na 2 SO 3:
The interaction of H 2 S and SO 2 with NaOH (a by-product in the production of NaHSO 3, sulfur dyes, in the purification of industrial gases from S):
Boiling excess sulfur with sodium hydroxide:
then, according to the above reaction, sodium sulfide adds sulfur, forming sodium thiosulfate.
At the same time, during this reaction, sodium polysulfides are formed (they give the solution a yellow color). For their destruction, SO 2 is passed into the solution.
Pure anhydrous sodium thiosulfate can be obtained by reacting sulfur with sodium nitrite in formamide. This reaction proceeds quantitatively (at 80 °C in 30 minutes) according to the equation:
Dissolution of sodium sulfide in water in the presence of atmospheric oxygen:
Physical and chemical properties
Colorless monoclinic crystals. Molar mass 248.17 g/mol (pentahydrate).
Soluble in water (41.2% at 20°C, 69.86% at 80°C).
At 48.5 °C, the crystalline hydrate dissolves in its water of crystallization, forming a supersaturated solution; dehydrated at about 100°C.
When heated to 220 ° C, it decomposes according to the scheme:
Sodium thiosulfate is a strong reducing agent:
With strong oxidizing agents, such as free chlorine, it oxidizes to sulfates or sulfuric acid:
Weaker or slower acting oxidizing agents, for example, iodine, are converted into salts of tetrathionic acid:
The above reaction is very important, as it serves as the basis of iodometry. It should be noted that in an alkaline medium, sodium thiosulfate can be oxidized with iodine to sulfate.
It is impossible to isolate thiosulfuric acid (hydrogen thiosulfate) by the reaction of sodium thiosulfate with a strong acid, since it is unstable and immediately decomposes:
Molten hydrated Na 2 S 2 O 3 ·5H 2 O is very prone to supercooling.
Application
for removing traces of chlorine after bleaching fabrics
for the extraction of silver from ores;
fixer in photography;
Reagent in iodometry
antidote for poisoning: As, Br, Hg and other heavy metals, cyanides (translates them into thiocyanates), etc.
for intestinal disinfection;
for the treatment of scabies (together with hydrochloric acid);
Anti-inflammatory and anti-burn agent;
can be used as a medium for determining molecular weights by freezing point depression (cryoscopic constant 4.26°)
Registered in the food industry as a food additive E539.
admixtures for concrete.
for cleansing tissues from iodine
· Gauze bandages impregnated with sodium thiosulfate solution were used to protect the respiratory organs from the poisonous substance chlorine during the First World War.
