Chemical chains of transformations are one of the most common in school textbooks, as well as on independent, verification and control types of tasks in chemistry. To successfully solve them, you need to understand exactly how they are arranged and how to approach them. Let's consider how to solve chains of transformations in general and with specific examples.
General principles for solving chemical chains of transformations
First, you need to carefully read the condition of the problem and study the chain. Having clearly understood what is required in the task, you can proceed directly to its solution.
- Writing out a separate chain of chemical transformations, number the number of necessary reactions (they are indicated by arrows from one substance to another).
- Determine which class of substances each member of the chain belongs to and, if necessary, write down each substance from the chain and its class separately in a column on the draft. When there are unnamedsubstances and their class is unknown, analyze which substances can be obtained from the original and which class the substance should act as the source for the next element of the chain after the unnamed substance.
- Analyze how you can get a substance of this class from the original one for each element of the chain. In case a direct reaction is not possible, think about what classes of substances can be obtained from the starting substance and from what resulting substances the final required substance can be synthesized later.
- Make an equation diagram for the first of the necessary reactions. Don't forget to put the coefficients in the equation.
- Sequentially carry out a chain of chemical transformations, considering each reaction separately. Test yourself by paying attention to the design of reactions.
An example of solving a chain of transformations
Assume that the problem has a chemical chain of transformations of the following form:
It is necessary to find substances marked as X1, X2 and X3, and carry out these reactions. Consider what reactions need to be performed to solve this chain after you number the arrows and determine the classes of substances.
- In order to obtain acetylene from 1, 2-dibromoethane, it is necessary to act on it with an alcohol solution of alkali when heated. During this reaction, two molecules of hydrogen bromide are split off from one of the molecules of 1,2-dibromoethane. These molecules will be neutralized with alkali.
- Further, based on the conditionsthe course of the reaction, you conclude that this is the reaction of M. G. Kucherov. It leads to the formation of acetaldehyde.
- Acetaldehyde, reacting in the presence of sulfuric acid with potassium dichromate, gives acetic acid.
- Hydrocarbonate reacts with an acid solution.
- The resulting alkaline earth metal acetate decomposes when heated to form metal carbonate and ketone.
Thus, the step-by-step solution of this chemical chain of transformations will look like this:
Helpful tips
When solving chains of chemical equations, it is important to remember that the final result depends on each sequentially correctly solved reaction in this chain. Therefore, checking yourself at the last stage, you need to double-check the possibility of each reaction and the correctness of the compilation and solution of the equation.
In addition, if you are in doubt whether you have correctly deduced this or that formula of a substance, you can look at the study stage in the reference book of chemicals. At the same time, it is important to remember that one must not only refer to it, but memorize the formulas and try to reproduce them independently in the future.
