Chemical Transformation Chains: Examples and Solutions

Chemical transformation chains is one of the most common in school textbooks, as well as on independent, test and control types of problems in chemistry. To successfully solve them, you need to understand exactly how they are arranged and how to approach them. Consider how to solve the chain of transformations in general and on specific examples.

General principles for solving chemical transformation chains

First you need to carefully read the condition of the problem and study the chain. Having clearly understood what is required in the problem, we can proceed directly to its solution.

1. Having written down separately the chain of chemical transformations, number the number of necessary reactions (they are indicated by arrows from one substance to another).
2. Determine which class of substance each member of the chain belongs to and, if necessary, write out each substance from the chain and its class separately in a draft column. In the case when there are unnamed substances and their class is unknown, analyze which substances can be obtained from the source and which class the substance should be the source for the next element of the chain after the unnamed substance.
3. Analyze how you can get a substance of this class from the source for each element of the chain. If a direct reaction is not possible, consider which classes of substances can be obtained from the starting material and from which obtained substances the final desired substance can be synthesized later.
4. Make a diagram of the equation of the first of the necessary reactions. Do not forget to put the coefficients in the equation.
5. Consistently carry out a chain of chemical transformations, considering each reaction separately. Check yourself, paying attention to the design of reactions.

Transformation Chain Solution Example

Suppose a problem has a chemical chain of transformations of the following form:

You must find the substances designated as X ₁ X ₂ and X ₃ and carry out these reactions. Consider what reactions must be performed to solve this chain after you number the arrows and determine the classes of substances.

1. In order to obtain acetylene from 1,2-dibromoethane, it is necessary to expose it to an alcohol solution of alkali when heated. During this reaction, two hydrogen bromide molecules are split off from one of the 1,2-dibromethane molecules. These molecules will be neutralized with alkali.
2. Further, based on the reaction conditions, you conclude that this is a reaction of M. G. Kucherov. It leads to the formation of acetaldehyde.
3. Acetaldehyde, reacting in the presence of sulfuric acid with potassium dichromate, gives acetic acid.
4. Bicarbonate reacts with an acid solution.
5. The resulting alkaline earth metal acetate decomposes upon heating, forming metal carbonate and ketone.

Thus, the solution of this chemical chain of transformations recorded in stages will look like this:

Useful Tips

When solving a chain of chemical equations, it is important to remember that the final result depends on each successively correctly resolved 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 preparation and solution of the equation.

In addition, if you are in doubt whether a particular formula of a substance is correctly derived, you can look at the chemical reference book at the training stage. It is important to remember at the same time that one should not just check with him, but remember the formulas and try to reproduce them independently in the future.