Reactions that change the oxidation state of elements are called redox reactions. Properties of potassium and its interaction with water Interaction of potassium with complex substances

Using a funnel and a glass rod, pour aluminum filings into the reactor canister, then lye, close the hole with a piece of adhesive tape and shake the contents. Next, attach the receiver. Its lower hole (for the release of hydrogen) must be closed with a nail. Gently lubricate the junction of the reactor and the receiver with alabaster gruel (take it quite a bit). After waiting 5 minutes, dry the connection with a hair dryer for about 4-5 minutes.

Now we carefully wrap the wet cotton wool on the tin of the receiver, stepping back from the edges of 5-8 mm, and fix it with a thin wire.

First, remove the nail plug. Then we gradually warm up the can with the reaction mixture with a burner (you can use a blowtorch to save money).

For heating, I used a butane can and the large burner nozzle mentioned above. The combustible gas inside the can cools down, and over time the flame decreases slightly, so I had to warm the butane can by hand.

Make sure that half of the "retort" is heated to an orange heat, the throat of the receiver must be heated to the beginning of a red heat. Heat for about 13-14 minutes. The reaction is initially accompanied by the appearance of a violet flame coming out of the receiver, then it gradually decreases and disappears, then you can reduce the hole by inserting a nail (loose and with a gap). During the reaction, gradually wet the cotton with a pipette, preventing water from entering the joints.

After stopping the heat, firmly insert the plug. Let the appliance cool down to room temperature! I just took it out into the cold. Then we remove the cotton wool, and erase the traces of water.

Prepare in advance the place where you will scrape potassium from the receiver. Be aware of the risk of fire! You should have gasoline, tweezers, a homemade scraper, a potassium storage container with an inert liquid like kerosene or oil. It is desirable that the liquid be dried. We scrape off the plaster and separate the receiver. We immediately put a piece of polyethylene on the throat of the receiver and press it down with plasticine (or make a cork in advance). We open the halves of the receiver, the main part of the potassium condensed in the left side (which was attached to the reactor with a neck), inside the right side there were only traces of potassium (the structure of the receiver is shown in the photograph). Pour gasoline into the left side (I used hexane). This is done to protect the metal from oxidation (gasoline is good because then it will evaporate without a trace, and it will be possible to use the refrigerator again without disturbing the gypsum putty). The operation is carried out in protective glasses!

Use a spatula to scrape the metal from the walls, then place it in a storage container with tweezers. Remember, small chips of potassium oxidize so quickly in air that they can ignite. This is easy to see if you carefully flatten a dried piece of potassium with a knife on a piece of paper (preferably filter or toilet paper) - potassium usually ignites. Part of the metal will turn out in the form of small chips and grains. They can be collected by flushing with gasoline in a storage container or a dry cup. They are useful for reaction with water: even small grains burn with beautiful purple lights.

I managed to collect about 1.1 g of potassium in a bottle (0.7-0.8 g in the form of a compact mass). In total, about 1.3 g of metal was formed. I did not collect part of the potassium in the form of residues, I blotted it with paper from hexane and transferred it to water with tweezers (it’s convenient to just shake off the grains from the paper). After the reaction, you need to remove traces of metal from the receiver, just throw the right half ("bottom") into the water on an outstretched arm and immediately move away. Let the left half lie in the air until traces of potassium are partially oxidized, then remove them with damp cotton wool on the wire (without damaging the plaster putty). Then rinse the receiver with a pipette and dry it with a tissue (be careful not to point the opening at yourself).

Potassium - the nineteenth element of the periodic table of Mendeleev, belongs to the alkali metals. This is a simple substance that under normal conditions is in a solid state of aggregation. Potassium boils at a temperature of 761 °C. The melting point of the element is 63 °C. Potassium has a silvery-white color with a metallic sheen.

Chemical properties of potassium

Potassium - which has a high chemical activity, therefore it cannot be stored in the open air: alkali metal instantly reacts with surrounding substances. This chemical element belongs to group I and period IV of the periodic table. Potassium has all the characteristic properties of metals.

He interacts with simple substances, which include halogens (bromine, chlorine, fluorine, iodine) and phosphorus, nitrogen and oxygen. The interaction of potassium with oxygen is called oxidation. During this chemical reaction, oxygen and potassium are consumed in a 4:1 molar ratio, resulting in the formation of potassium oxide in the amount of two parts. This interaction can be expressed by the reaction equation:

4K + O₂ \u003d 2K₂O

During the combustion of potassium, a flame of bright purple color is observed.

Such an interaction is considered a qualitative reaction to the determination of potassium. The reactions of potassium with halogens are named according to the names of the chemical elements: these are fluorination, iodination, bromination, chlorination. Such interactions are addition reactions. An example is the reaction between potassium and chlorine, which produces potassium chloride. To carry out such an interaction, two moles of potassium and one mole are taken. As a result, two moles of potassium are formed:

2K + СІ₂ = 2КІ

Molecular structure of potassium chloride

When burning in the open air, potassium and nitrogen are consumed in a molar ratio of 6:1. As a result of this interaction, potassium nitride is formed in the amount of two parts:

6K + N₂ = 2K₃N

The compound is green-black crystals. Potassium reacts with phosphorus in the same way. If you take 3 moles of potassium and 1 mole of phosphorus, you get 1 mole of phosphide:

3K + P = K₃P

Potassium reacts with hydrogen to form a hydride:

2K + N₂ = 2KN

All addition reactions occur at high temperatures

The interaction of potassium with complex substances

Complex substances with which potassium reacts include water, salts, acids, and oxides. Since potassium is an active metal, it displaces hydrogen atoms from their compounds. An example is the reaction between potassium and hydrochloric acid. For its implementation, 2 moles of potassium and acid are taken. As a result of the reaction, 2 moles of potassium chloride and 1 mole of hydrogen are formed:

2K + 2HCI = 2KSI + H₂

In more detail, it is worth considering the process of interaction of potassium with water. Potassium reacts violently with water. It moves on the surface of the water, it is pushed by the released hydrogen:

2K + 2H₂O = 2KOH + H₂

During the reaction, a lot of heat is released per unit time, which leads to the ignition of potassium and the released hydrogen. This is a very interesting process: upon contact with water, potassium instantly ignites, the violet flame crackles and quickly moves along the surface of the water. At the end of the reaction, a flash occurs with splashing of drops of burning potassium and reaction products.

Reaction of potassium with water

The main end product of the reaction of potassium with water is potassium hydroxide (alkali). The equation for the reaction of potassium with water:

4K + 2H₂O + O₂ = 4KOH

Attention! Do not try to repeat this experience yourself!

If the experiment is carried out incorrectly, you can get a burn with alkali. For the reaction, a crystallizer with water is usually used, in which a piece of potassium is placed. As soon as the hydrogen stops burning, many want to look into the crystallizer. At this moment, the final stage of the reaction of potassium with water occurs, accompanied by a weak explosion and splashing of the resulting hot alkali. Therefore, for safety reasons, it is worth keeping some distance from the laboratory table until the reaction is complete. you will find the most spectacular experiences you can have with your kids at home.

The structure of potassium

The potassium atom consists of a nucleus containing protons and neutrons, and electrons revolving around it. The number of electrons is always equal to the number of protons inside the nucleus. When an electron is detached or attached to an atom, it ceases to be neutral and turns into an ion. Ions are divided into cations and anions. Cations have a positive charge, anions have a negative charge. When an electron is attached to an atom, it becomes an anion; if one of the electrons leaves its orbit, the neutral atom turns into a cation.

The serial number of potassium in periodic table Mendeleev - 19. So, protons in the nucleus chemical element there are also 19. Conclusion: there are 19 electrons around the nucleus. The number of protons in the structure is determined as follows: subtract the serial number of the chemical element from the atomic mass. Conclusion: there are 20 protons in the potassium nucleus. Potassium belongs to the IV period, has 4 "orbits", on which electrons are evenly distributed, which are in constant motion. On the first "orbit" there are 2 electrons, on the second - 8; on the third and on the last, fourth "orbit", 1 electron rotates. This explains high level chemical activity potassium: its last "orbit" is not completely filled, so the element tends to combine with other atoms. As a result, the electrons of the last orbits of the two elements will become common.

Topic 1.6. Redox reactions.

Questions on a previously studied topic:

1. In what cases during the electrolysis of aqueous solutions of salts:

a) hydrogen is released at the cathode;

b) oxygen is released at the anode;

c) is there a simultaneous reduction of metal cations and water hydrogen cations?

1. What processes occurring on the electrodes are combined common name""electrolysis""?
2. What is the difference between the electrolysis of caustic soda melt and the electrolysis of its solution?
3. Which pole of the battery - positive or negative - should the metal part be connected to when it is chrome plated.
4. Reveal the meaning of electrolysis; concept - electrolysis.
5. What chemical processes occur at the cathode and anode during the electrolysis of a solution of potassium iodide? A melt of potassium iodide?
6. Make electrolysis schemes using carbon electrodes of melts and solutions of the following salts: KCl.
7. In what sequence will cations be reduced during the electrolysis of their salts of the same concentration (anode insoluble) of the following composition: Al, Sn, Ag, Mn?
8. Explain why metallic potassium cannot be obtained on carbon electrodes by electrolysis aqueous solution potassium chloride, but can be obtained by electrolysis of a melt of this salt?
9. During the electrolysis of an aqueous solution of silver nitrate at the cathode, the following is formed:

a) Ag b) NO 2 c) NO d) H 2 ?

know basic concepts and essence of oxidative reducing reactions, the rules for compiling redox reactions by the method electronic balance;

be able to classify reactions in terms of oxidation state; define and apply the concepts: “oxidation state”, “oxidizers and reducers”, “oxidation and reduction processes”; draw up an electronic balance for redox reactions and use it to arrange the coefficients in a molecular equation.

Changing the properties of elements depending on the structure of their atoms

Having previously studied the types chemical reactions, the structure of molecules, the relationship of the main classes chemical compounds, we can say that most reactions - addition, decomposition and substitution, proceed with a change in the oxidation state of the atoms of the reacting substances, and only in exchange reactions this does not occur.

Reactions that change the oxidation state of elements are called redox reactions.

There are several ways to write equations for redox reactions. Let us dwell on the electronic balance method based on the definition total number moving electrons. For example:

MnO 2 + KClO 3 + KOH \u003d K 2 MnO 4 + KCl + H 2 O

We determine the atoms of which elements have changed the oxidation state:

Mn → Mn Cl → Cl

Determine the number of lost (-) and gained (+) electrons:

Mn - 2 e→ Mn Cl + 6 e→ Сl

The number of lost and gained electrons should be the same. Both processes of half-reactions are depicted as follows:

reducing agent Mn - 2 eˉ → Мn 3 3Мn – 6 eˉ → 3Mn oxidation

oxidizing agent Cl + 6 eˉ → Сl 1 Сl + 6 eˉ → Сl recovery

The main coefficients for the oxidizing agent and reducing agent are transferred to the reaction equation

3MnO 2 + KClO 3 + 6KOH \u003d 3K 2 MnO 4 + KCl + 3H 2 O

The process of transformation of manganese +4 into manganese +6 is the sag of recoil (loss) of electrons, i.e. oxidation; the process of converting Cl(+5) into Cl(-1) is the process of obtaining electrons, i.e. recovery process. In this case, the MnO 2 substance is a reducing agent, and KClO 3 is an oxidizing agent.

Sometimes one of the substances involved in the reaction performs two functions at once: an oxidizing agent (or reducing agent) and a salt former. Consider as an example the reaction

Zn + HNO 3 \u003d Zn (NO 3) 2 + NH 4 NO 3 + H 2 O

Compose the half-reactions for the oxidizing agent and reducing agent. Zinc loses two electrons, and nitrogen N(+5) gains eight electrons:

Zn-2 eˉ → Zn 8 4

N+8 eˉ → N 2 1

Thus, the oxidation of four zinc atoms requires eight HNO 3 molecules and two HNO 3 molecules for salt formation.

4Zn + 2HNO 3 + 8HNO 3 \u003d 4Zn (NO 3) 2 + NH 4 NO 3 + 3H 2 O

4Zn + 10HNO 3 \u003d 4Zn (NO 3) 2 + NH 4 NO 3 + 3H 2 O

Types of equations of redox reactions.

Basic oxidizing and reducing agents.

Redox reactions are divided into three groups: intermolecular, intramolecular and disproportionation reactions.

Reactions in which one substance is the oxidizing agent and the other is the reducing agent are called intermolecular reactions, for example:

2KMnO 4 + 16HCl \u003d 2MnCl 2 + 5Cl 2 + 2KCl + 8H 2 O

Intermolecular reactions also include reactions between substances in which interacting atoms of the same element have different oxidation states:

2H 2 S + SO 2 \u003d 3S + 2H 2 O

Reactions that occur with a change in the oxidation state of atoms in the same molecule are called intramolecular reactions, for example:

2KClO 3 \u003d 2KCl + 3O 2

Intramolecular reactions include reactions in which atoms of the same element have different oxidation states:

NH 4 NO 3 \u003d N 2 O + H 2 O

Reactions in which the oxidizing and reducing functions are performed by atoms of the same element in the same oxidation state are called disproportionation reactions, for example:

2Nа 2 O 2 + 2СО 2 = 2NаСО 3 + О 2

Oxidizers

The measure of the oxidizing ability of an atom or ion, as already mentioned, is the electron affinity, i.e. their ability to accept electrons.

The oxidizers are:

1. All atoms of non-metals. The strongest oxidizing agents are halogen atoms, since they are able to accept only one electron. With a decrease in the group number, the oxidizing abilities of non-metal atoms located in them fall. Therefore, the atoms of non-metals of group IV are the weakest oxidizing agents. In groups from top to bottom, the oxidizing properties of non-metal atoms also decrease due to an increase in the atomic radii.

2. Positively charged metal ions in the state high degree oxidation, for example:

KMnO 4, K 2 CrO 4, V 2 O 5, MnO 2, etc.

In addition, oxidizing agents are metal ions with a low oxidation state, for example:

Ag, Hg, Fe, Cu, etc.

3. Concentrated HNO 3 and H 2 SO 4 acids.

Restorers

Restorers can be:

1. Atoms of all elements except He, Ne, Ar, F. The atoms of those elements that have one, two, three electrons on the last layer lose electrons most easily.

2. Positively charged metal ions in a low oxidation state, for example:

Fe, Cr, Mn, Sn, Cu.

3. Negatively charged ions, for example: Сlˉ, Вгˉ, Iˉ, S 2 ˉ.

4. Weak acids and their salts, for example: H 2 SO 3 and K 2 SO 3; HNO 2 and KNO 2.

Questions on the topic studied:

1. What reactions are called redox reactions? How are redox reactions different from other chemical reactions?

1. Why do metals in compounds show only positive oxidation states, while non-metals show both positive and negative ones?
2. Which substances are called oxidizing agents and which are reducing agents?
3. How can relative electronegativity be used to judge the nature of the bond between atoms in a molecule?
4. What is the relationship between the energy of electron affinity and the oxidizing power of a chemical element?
5. What complex substances are characterized only by oxidizing properties? In what cases can complex substances act as oxidizing and reducing agents?
6. In the following reaction equations, determine the oxidizing agent and reducing agent, their oxidation state, arrange the coefficients:

a) HgS + HNO 3 + Hcl → HgCl 2 + S + NO + H 2 O

b) SnCl 2 + K 2 Cr 2 O 7 + H 2 SO 4 → Sn (SO 4) 2 + SnCl 4 + Cr 2 (SO 4) 3 + K 2 SO 4 + H 2 O

c) AsH 3 + AgNO 3 + H 2 O → H 3 AsO 4 + Ag + HNO 3

1. In the following reactions, in which the oxidizing agent and reducing agent are in the same substance (reactions of intramolecular oxidation - reduction), arrange the coefficients:

a) NH 4 NO 3 → N 2 O + H 2 O

b) KClO 3 → KCl + O 2

c) Ag 2 O → Ag + O 2

1. For disproportionation reactions (self-oxidation - self-healing), write electronic circuits and arrange the coefficients:

a) K 2 MnO 4 + H 2 O → KMnO 4 + MnO 2 + KOH

b) HclO 3 → ClO 2 + HclO 4

c) HNO 2 → HNO 3 + NO + H 2 O

1. Which of the following reactions are intramolecular and which are disproportionation reactions:

a) Hg (NO 3) 2 → Hg + NO 2 + O 2

b) Cu (NO 3) 2 → CuO + NO 2 + O 2

c) K 2 SO 3 → K 2 SO 4 + K 2 S

d) (NH 4) 2 Cr 2 O 7 → N 2 + Cr 2 O 3 + H 2 O

Select the coefficients for each reaction.

Literature: 1, 2,3.