school chemistry course is an introductory guide to the complex science.From the beginning, students are trying to understand how to solve the design problem.Suppose that in the early stages they have little practical use, but if the student learned, for example, how to find a lot of unreacted substances, it may qualify for significant achievements.
Consider a simple example of the problem, on the basis of which you can learn to solve more complex.Assume that for complete combustion of carbon monoxide (II) you needed to 11.2 liters.How many grams of CO2 you managed to get it?
1. We form the equation for the reaction.
CO + O2 = CO2
2. equalize oxygen.There are certain rules, which in most cases can help you.Begin to place the coefficients of the substances, the number of atoms which is odd.In this case, the oxygen in the CO molecule.To put it a factor of 2. Since the left formed two carbon atoms, and the right - one in front and then put CO2 2. Thus we get:
2CO + O2 = 2CO2
As you can see, the left and right sides of fouroxygen atom.Carbon also is in balance.Consequently, we equalized right.
3. Next you need to find the amount of O2.The molecular weight determination for students too cumbersome and hard to remember, so we use a different method.Recall that there is a molar amount which is equal to 22.4 l / mole.You must find the number of moles (n) entered into the reaction: n = V / V m. In our case, n = 0.5 moles.
4. Now draw up a proportion.The amount of unreacted oxygen in half n (CO2).This follows from the fact that 0.5 mol / mol x = 1/2.A simple ratio of the two values has helped create the right equation.When we find x = 1, we can get an answer to the question of how to find a lot.
5. True to start the recall have another formula: m = M * n.The last variable found, but what to do with M?Molar mass - is experimentally set relative to hydrogen.That it is designated by the letter M. Now we know that m (CO2) = 12 g / mol * 1 mole = '12 That got a response.As you can see, there is nothing difficult.
This task is very easy on a variety of others.But the main thing - to understand how to find a lot.Imagine a molecule of a substance.It has long been known that the mole has 6 x 10 23 molecules.At the same time in the periodic system, there elements mounted weight per 1 mol.Sometimes it is necessary to calculate the molar mass of the substance.Suppose M (H20) = 18 g / mol.That is, one molecule of hydrogen has M = 1 gram / mol.But the water contains two atoms of H. Also, do not forget about the presence of oxygen, which gives us an additional 16 grams.Summing up, we obtain 18 grams / mole.
theoretical calculation of the mass will subsequently be of practical use.Especially for students who expect chemical workshop.Do not be afraid of this word, if you are studying in non-core school.But if chemistry - your profile subject, it is best not to run the basic concepts.So, now you know how to find a lot.Remember that in chemistry is very important to be consistent and considerate man who not only knows some algorithms, but also knows how to use them.
