A clear algorithm for solving a problem in chemistry is a great way to tune in to final tests in this complex discipline. In 2017, significant changes were made to the structure of the exam, questions with one answer were removed from the first part of the test. The wording of the questions is given in such a way that the graduate demonstrates knowledge in various areas, for example, chemistry, and cannot simply put a “tick”.
Main Challenges
Maximum difficulty for graduates is questions on derivation of formulas of organic compounds, they cannot compose an algorithm for solving the problem.
How to deal with such a problem? In order to cope with the proposed task, it is important to know the algorithm for solving problems in chemistry.
The same problem is typical for other academic disciplines.
Sequence of actions
The most common are the problems of determining the compound by known combustion products, so we propose to consider the algorithm for solving problems using an examplethis type of exercise.
1. The value of the molar mass of a given substance is determined using the known relative density for some gas (if present in the condition of the proposed task).
2. We calculate the amount of substances formed in this process through the molar volume for a gaseous compound, through the density or mass for liquid substances.
3. We calculate the quantitative values of all atoms in the products of a given chemical reaction, and also calculate the mass of each.
4. We summarize these values, then compare the obtained value with the mass of the organic compound given by the condition.
5. If the initial mass exceeds the obtained value, we conclude that oxygen is present in the molecule.
6. We determine its mass, subtract for this from the given mass of the organic compound the sum of all atoms.
6. Find the number of oxygen atoms (in moles).
7. We determine the ratio of the quantities of all atoms present in the problem. We get the formula of the analyte.
8. We compose its molecular version, the molar mass.
9. If it differs from the value obtained in the first step, we increase the number of each atom by a certain number of times.
10. Compose the molecular formula of the desired substance.
11. Defining the structure.
12. We write the equation of the indicated process using the structures of organic substances.
The proposed algorithm for solving the problem is suitable for all tasks related to the derivation of the formula of an organic compound. He will help high school studentsadequately cope with the exam.
Example 1
What should algorithmic problem solving look like?
To answer this question, here is a finished sample.
When burning 17.5 g of the compound, 28 liters of carbon dioxide were obtained, as well as 22.5 ml of water vapor. The vapor density of this compound corresponds to 3.125 g/L. There is information that the analyte is formed during the dehydration of tertiary saturated alcohol. Based on the data provided:
1) perform certain calculations that will be required to find the molecular formula of this organic substance;
2) write its molecular formula;
3) make a structural view of the original compound, uniquely reflecting the connection of atoms in the proposed molecule.
Task data.
- m (starting material)- 17.5g
- V carbon dioxide-28L
- V water-22.5ml
Formulas for mathematical calculations:
- √=√ mn
- √=m/ρ
If you wish, you can cope with this task in several ways.
First way
1. Determine the number of moles of all products of a chemical reaction using molar volume.
nCO2=1.25 mol
2. We reveal the quantitative content of the first element (carbon) in the product of this process.
nC=nCO2=, 25 mol
3. Calculate the mass of the element.
mC=1.25 mol12g/mol=15 g.
Determine the mass of water vapor, knowing that the density is 1g/ml.
mH2O is 22.5g
We reveal the amount of the reaction product (water vapor).
n water=1.25 mol
6. We calculate the quantitative content of the element (hydrogen) in the reaction product.
nH=2n (water)=2.5 mol
7. Determine the mass of this element.
mH=2.5g
8. Let's sum up the masses of the elements to determine the presence (absence) of oxygen atoms in the molecule.
mC + mH=1 5g + 2.5g=17.5g
This corresponds to the data of the problem, therefore, there are no oxygen atoms in the desired organic matter.
9. Finding the ratio.
CH2is the simplest formula.
10. Calculate M of the desired substance using the density.
M substance=70 g/mol.
n-5, the substance looks like this: C5H10.
The condition says that the substance is obtained by dehydration of alcohol, therefore, it is an alkene.
Second option
Let's consider another algorithm for solving the problem.
1. Knowing that this substance is obtained by dehydration of alcohols, we conclude that it may belong to the class of alkenes.
2. Find the value M of the desired substance using the density.
M in=70 g/mol.
3. M (g/mol) for a compound is: 12n + 2n.
4. We calculate the quantitative value of carbon atoms in an ethylene hydrocarbon molecule.
14 n=70, n=5, so the molecularthe formula of a substance looks like: C5H10n.
The data for this problem says that the substance is obtained by dehydration of a tertiary alcohol, therefore it is an alkene.
How to make an algorithm for solving a problem? The student must know how to obtain representatives of different classes of organic compounds, owns their specific chemical properties.
Example 2
Let's try to identify an algorithm for solving the problem using another example from the USE.
With complete combustion of 22.5 grams of alpha-aminocarboxylic acid in atmospheric oxygen, it was possible to collect 13.44 liters (N. O.) of carbon monoxide (4) and 3.36 L (N. O.) of nitrogen. Find the formula of the suggested acid.
Data by condition.
- m(amino acids) -22.5 g;
- √(carbon dioxide ) -13.44 liters;
- √(nitrogen) -3, 36 y.
Formulas.
- m=Mn;
- √=√ mn.
We use the standard algorithm for solving the problem.
Find the quantitative value of interaction products.
(nitrogen)=0.15 mol.Write down the chemical equation (we apply the general formula). Further, according to the reaction, knowing the amount of substance, we calculate the number of moles of aminocarboxylic acid:
x - 0.3 mol.
Calculate the molar mass of an aminocarboxylic acid.
M(starting substance )=m/n=22.5 g/0.3 mol=75 g/mol.
Calculate the molar mass of the originalaminocarboxylic acid using the relative atomic masses of the elements.
M(amino acids )=(R+74) g/mol.
Mathematically determine the hydrocarbon radical.
R + 74=75, R=75 - 74=1.
By selection, we identify the variant of the hydrocarbon radical, write down the formula of the desired aminocarboxylic acid, formulate the answer.
Consequently, in this case there is only a hydrogen atom, so we have the formula CH2NH2COOH (glycine).
Answer: CH2NH2COOH.
Alternative solution
The second algorithm for solving the problem is as follows.
We calculate the quantitative expression of the reaction products, using the value of the molar volume.
(carbon dioxide )=0.6 mol.We write down the chemical process, armed with the general formula of this class of compounds. We calculate by the equation the number of moles of the taken aminocarboxylic acid:
x=0.62/in=1.2 /in mol
Next, we calculate the molar mass of the aminocarboxylic acid:
M=75 in g/mol.
Using the relative atomic masses of the elements, we find the molar mass of an aminocarboxylic acid:
M(amino acids )=(R + 74) g/mol.
Equite the molar masses, then solve the equation, determine the value of the radical:
R + 74=75v, R=75v - 74=1 (take v=1).
Through selection it comes to the conclusion that there is no hydrocarbon radical, therefore the desired amino acid is glycine.
Consequently, R=H, we get the formula CH2NH2COOH(glycine).
Answer: CH2NH2COOH.
Such problem solving by the method of an algorithm is possible only if the student has sufficient basic mathematical skills.
Programming
What do the algorithms look like here? Examples of solving problems in informatics and computer technology require a clear sequence of actions.
When the order is violated, various system errors occur that do not allow the algorithm to function in full. Developing a program using object-oriented programming consists of two steps:
- creating a GUI in visual mode;
- code development.
This approach greatly simplifies the algorithm for solving programming problems.
Manually it is almost impossible to manage this time-consuming process.
Conclusion
The standard algorithm for solving inventive problems is presented below.
This is a precise and understandable sequence of actions. When creating it, it is necessary to own the initial data of the task, the initial state of the described object.
In order to highlight the stages of solving problems of algorithms, it is important to determine the purpose of the work, to highlight the system of commands that will be executed by the executor.
The created algorithm mustbe a specific set of properties:
- discreteness (division into steps);
- uniqueness (each action has one solution);
- conceptual;
- performance.
Many algorithms are massive, that is, they can be used to solve many similar tasks.
A programming language is a special set of rules for writing data and algorithmic structures. Currently, it is used in all scientific fields. Its important aspect is speed. If the algorithm is slow, does not guarantee a rational and fast response, it is returned for revision.
The execution time of some tasks is determined not only by the size of the input data, but also by other factors. For example, the algorithm for sorting a significant number of integers is simpler and faster, provided that a preliminary sorting has been carried out.
