What is the electronic balance scheme?
Given the task: "According to the schemes, draw up electronic balance schemes." How can I do it? What is required for this? Let's try to figure it out together.
The essence of the method
To begin with, let's look at what this method is. If the electronic balance scheme is correctly formed, it is possible to put in the proposed reaction all the stereochemical coefficients.
The essence of this technique is to determinedegrees of oxidation of individual elements that participated in the reaction. If in the left and right parts of the equation the element retains a constant degree of oxidation, then the electronic balance scheme is compiled without it.
For elements that have changed their degree of oxidation during the interaction, the values obtained are taken into account in the calculations of the least common multiple.
How to make a balance
To begin with, you will have to put in eachelement of its oxidation state, using certain rules. If a simple substance has entered into the interaction, it does not accept, nor does it give the other element electrons, hence its degree of oxidation is zero. Examples of compounds with a zero degree of oxidation are halogen molecules, metals.
In the binary compound of the second element, the degreeoxidation has a negative, and in the first - a positive value. In the sum (taking into account the number of atoms) should be zero. In calcium oxide, for example, in the first element the degree of oxidation is +2, and in the second (oxygen) -2. Their total value is zero, since the molecule is neutral.
If it is necessary to arrange the degree of oxidation inmore complex substance, then first determine the indicators for the first and last elements. Then, using mathematical calculations, determine the degree of oxidation of the central element. The sum of all indicators must be zero.
Algorithm of actions
How is the electronic balance scheme drawn up? In the left part of it, together with the degrees of oxidation, the elements that are involved in the oxidation-reduction process are recorded.
Further signs "plus" and "minus" indicatethe number of electrons taken and delivered in the course of chemical interaction. Between the number of electrons, the smallest common multiple is determined. Recall that by it is meant a positive number, which will be divided without a remainder into both figures concerning electrons.
The electronic balance scheme is considered complete in thatThe case where the coefficients are also defined in it. How to find them? The smallest common multiple must be divided into the electrons received and delivered in the process. The figures obtained will be the stereochemical coefficients.
It is also important to determine the reductant andoxidizer, as well as processes occurring during the interaction (oxidation and reduction). The obtained scheme of the electronic balance of the oxidation-reduction process will allow you to arrange the missing coefficients in the reaction.
OBD assignments in the final attestation
Based on this method, graduates are invited to complete a job from the "C" level. Success depends on the level of practical skills of the student, the degree of mastery of theoretical fundamentals.
For example, the task says: according to these schemes, draw up electronic balance schemes. In addition, some of the reactants, as well as certain interaction products, can be missed. This issue is considered a task of increased complexity, therefore, it assumes a certain sequence of reasoning.
To begin with, all the elements in known substances are determined by oxidation states, then substances that are missing in both parts of the reaction are recorded.
Then a balance is drawn up. According to the obtained scheme of the reaction, arrange the coefficients by the electronic balance method, as described above. The last action will be an indication of all the ongoing processes.
In the tests of the USE on chemistry, a separate record of substances directly participating in the equation is proposed, followed by an indication of the oxidizing agent and reducing agent.
This method is far from the only oneway of placing the coefficients in the equation. You can use the half-reaction method, which allows you to equalize all substances recorded in the equation.