The task is given: "According to these schemes, draw up electronic balance schemes." How to do it? What is required for this? Let's try to figure it out together.
The essence of the method
First, let's dwell on what this method is. If the electronic balance diagram is composed correctly, all stereochemical coefficients can be put in the proposed reaction.
The essence of this technique is to determine the oxidation states of the individual elements that participated in the reaction. If a constant oxidation state is maintained in the left and right sides of the equation for an element , then the electronic balance scheme is compiled without it.
For elements that have changed their oxidation state during the interaction, the values obtained are taken into account in the calculations of the lowest common multiple.
How to balance
To begin with, you will have to put at each element its oxidation state, using certain rules. If a simple substance entered into the interaction, then it does not accept, and also does not give electrons to another element, therefore, its oxidation state is zero. Examples of compounds with zero oxidation state are halogen molecules, metals.
In the binary compound, the second element has a negative oxidation state, and the first one has a positive value. In total (taking into account the number of atoms) should be zero. In calcium oxide, for example, the first element has an oxidation state of +2, and the second (oxygen) -2. Their total value is zero, since the molecule is neutral.
If it is necessary to arrange the degree of oxidation in a more complex substance, then the indicators of the first and last elements are first determined. Then, using mathematical calculations, the oxidation state of the central element is determined. The sum of all indicators should be equal to zero.
Action algorithm
How is the electronic balance sheet compiled? In its left part, together with the oxidation states, the elements that participated in the redox process are recorded.
Next, the plus and minus signs indicate the number of electrons received and given during the chemical interaction. The least common multiple is determined between the number of electrons . Recall that by it is meant a positive number, which will be completely divided by both numbers relating to electrons.
The electronic balance sheet is considered complete when the coefficients are also determined in it. How to find them? The least common multiple must be divided into the electrons received and given in the process. The resulting numbers will be stereochemical coefficients.
It is also important to determine the reducing agent and oxidizing agent, as well as the processes occurring during the interaction (oxidation and reduction). The resulting electronic balance sheet of the redox process will allow you to arrange the missing coefficients in the reaction.
Tasks for the OVR in the final certification
Based on this method, graduates are offered to complete a task from level “C”. Success depends on the level of practical skills of the student, the degree of knowledge of the theoretical foundations.
For example, the assignment says: according to these schemes, draw up electronic balance schemes. In addition, some of the reactants, as well as some reaction products, may be missed. This question is considered a task of increased complexity, therefore, it involves a certain sequence of reasoning.
To begin with, all elements in known substances determine the degree of oxidation, then write down substances that are not enough in both parts of the reaction.
Next, a balance is drawn up. According to the reaction scheme obtained, arrange the coefficients by the electronic balance method, as described above. The last action will be an indication of all ongoing processes.
In tests of the exam in chemistry, a separate record of substances directly involved in the equation is assumed, followed by an oxidizing agent and a reducing agent.
Conclusion
Such a method is far from the only way to arrange the coefficients in the equation. You can use the half-reaction method, which allows you to immediately equalize all substances recorded in the equation.