Everyone who has already moved a little in studying chemistry, faces the concept of "mole." True, most immediately think about moths, who ate a fur coat in the closet for the summer, but mole in chemistry is a completely different story . And now we'll figure it out.
So, let's look at some chemical reaction. For example, such:
H2 + F2 = 2HF
Here, 1 hydrogen molecule H2 reacts with one fluorine F2 molecule and two hydrogen fluoride molecules is obtained. Let me remind you, the number of molecules or atoms that react or obtained in the reaction is determined by the coefficient, that is, the digit facing the formula of the substance. In our example, there is nothing before hydrogen, but in fact we can deliver a unit here, that is, we need 1 hydrogen molecule. Before Fluoro, it is also worth nothing, it means that we need 1 fluorine molecule. But in front of hydrogen fluoride HF is a twice. This means that we have 2 hydrogen fluoride molecule. I.e:
H2 + F2 = 2HF is the same as
1 H2 + molecule 1 molecule F2 = 2 HF molecules.
But you know that molecules are so small that we cannot see them. How do we consider these molecules that react? To do this, have introduced the concept Mole .
Mol is the amount of substance in which the same particles are contained as atoms are contained in 12 grams of carbon with a atomic unit of mass 12.
This is a rather surrounding definition, but it needs to be remembered. There is a pleasant moment: in one mole of any substance contain Number of Avogadro Particles. Here it is, this is the number:
Such a number is difficult. You just think, a billion is 1,000,000,000. And in one mole of particles 6.02 * 100,000,000,000,000,000,000! (But not to see nightmares at night, just remember 6.02 * 10 in twenty-third degree).
So, In one mole of any substance contains 6.02 * 10 in the twenty-third degree of particles. But we know that atoms of different substances have a different structure, and therefore a different mass. That's why The masses of one praying among different substances vary . To sort out this, let's go to the country and do the experiment.
We remember exactly that 1 mol is always the same number of particles (6.02 * 10 in twenty-third degree). But in the usual life of such numbers there is no, so we take the number less, for example, 100. It will be our conditional experimental mole. Now in one pile we put 100 cherries, in another bunch - 100 pears, in the third - 100 watermelons. A bunch is 1 mol. In every pile, we conscientiously folded the same number of particles, right? But particles of these different types: in one pile of Cherry, in the other - pears, in the third - watermelon. And now we will weigh. What do you think there will be a mass of 100 cherries, 100 pears and 100 watermelons? Of course, it will be. At the same time, please note: the number of particles in each pile is equally, but these piles weigh differently. Why? Because the particles are different!
In chemistry everything is the same. If you take 1 mol of hydrogen, 1 moth oxygen and 1 mol sodium, then mass will be different (remember the trip to the country). And it is important. But now there is a lawsager question: what to find out what is the mass of 1 mol of hydrogen, 1 mol of oxygen and 1 mol sodium and in general any substance? For this introduced the concept molar mass.
Molar mass and there is a mass of 1 praying substance.
How to determine it? Simply. This is an atomic mass or molecular weight of the substance that we expect, using the Mendeleev table. The molar mass is denoted by the letter M and is expressed in g / mol (just because it shows how many grams lead 1 mol). Examples from chemistry textbook.
Find a lot of one pray (it is molar mass ) Aluminum.
We solve chemistry and look at the Mendeleev table. We see that the atomic mass of aluminum 27. The formula is simply aluminum substance - Al, that is, the atom here is one. Consequently, the molar mass of aluminum coincides with the atomic and equal to 27 g / mol.
Find the molar mass of fluoride.
Fluorine under us under normal conditions - gas, so the fluorine molecule consists of two atoms and looks like this: F2. In the periodic table we find fluorine and see that its atomic mass is 19. Therefore, the molar weight of fluorine 2 * 19 = 38 g / mol.
Find the molar mass of calcium oxide.
Formula Calcium oxide Sao. We look again in the table: Calcium atomic mass 40, atomic mass of oxygen 16. Molar mass of calcium oxide 40 + 16 = 56 g / mol.
Find the molar mass of silicon oxide.
SiO2 silicon oxide formula. The Mendeleev Table reports that the atomic mass of silicon 28, oxygen - 16. Be careful, in this matter of the trick! In the oxide formula, two oxygen atoms, be sure to consider this so that the answer is correct. And it will be like this: the molar mass of silicon oxide 28 + 16 * 2 = 60 g / mol. (16 is the mass of one oxygen atom, we have two in the formula, so we multiplied 16 to 2!).
A complex example of chemistry tutor. But I recommend to penetrate and figure out to clarify everything finally. So, answer, what is the molar mass of sulfuric acid.
Here you have to focus not get confused. The formula of sulfuric acid H2SO4, that is, we have:
· 2 hydrogen atoms
· 1 sulfur atom
· 4 oxygen atoms.
We look into the periodic table and determined atomic masses:
· Atomic weight of hydrogen - 1
· Sulfur atomic weight - 32
· Atomic mass of oxygen - 16.
Go to the calculation:
2 hydrogen atom + 1 sulfur atom + 4 oxygen atom
2 * 1 + 1 * 32 + 4 * 16
In this expression in each term, the first factor is the number of element atoms, the second factor is atomic mass. Then just mathematics: 2 * 1 + 1 * 32 + 4 * 16 = 98. And yes, molar mass Sulfuric acid 98 g / mol.
I am sure, now you will distinguish the mole in the closet and mole in chemistry. And then we will understand, how to weigh on ordinary scales these moths .
Please write in the comments that remained incomprehensible, and I will definitely give additional explanations. Be complain about difficulties in learning the school course and say that you have been scared in the textbook of chemistry. And then the next article will tell exactly about this problem.