# How to find the amount of a substance?

How to find the amount of a substance?

So, the amount of matter in chemistry is denoted by the Greek letter "ny".

I remember how in the 9 class my physics teacher Igor Yuryevich taught me to correctly write the letter "nyu". Before that, it was a bit clumsy.

But since BV does not pass Greek letters, I will denote the amount of substance by the Latin letter v. Latin v is very similar to the Greek quot; nuquot ;.

Consider the following cases.

1) If we know the number of particles of a substance, then the amount of matter can be found by the formula:

v = n / NA

where

v amount of substance;

n is the number of particles in the substance. This is a dimensionless quantity, that is, it is simply a number. True, this number is very large, for example, 5 * (10 ^ 24).

NA constant Avogadro. The permanent Avogadro is a

**universal constant**. NA = 6,022 * (10 ^ 23) mole ^ (1).2) If we know the mass of the substance, then the amount of matter is according to the following formula:

v = m / M

where

v amount of substance;

m mass of substance;

M molar mass of the substance is found by the chemical formula of the substance, using the periodic system of DI Mendeleyev, the way of summing the atomic masses of all the atoms entering into a molecule, taking into account the available indices.

3) If we know the volume

**gaseous**substance, then we can find the amount of gas substance according to the following formula:v = V / Vm

where

v amount of substance;

V volume of gas;

Vm is the molar volume of gases. The molar volume of gases is a universal constant. Vm = 22,414 l / mol = 22414 m3 / mol.

I repeat that

**The formula v = V / Vm is valid only for gases**!Finally, consider your case.

According to the condition, you are given volume and volume share.

I'll venture to assume that you have a problem of this kind:

The volume of the gas mixture is 240 l. The bulk fraction of oxygen in the mixture is equal to 45%. Calculate the amount of oxygen in the mixture ".

This task is solved in two actions.

1) Find the volume of oxygen:

V (O2) = V0 * ф / 100 = 240 л * 45 / 100 = 108 л.

(Φ is a voluminous share, it is denoted by the Greek letter "quot ;, instead of writing Russian ph).

2) Find the amount of oxygen. Oxygen is gas, so we have the right to use the formula v = V / Vm.

v (O2) = V / Vm = 108 l: 22,414 l / mol =

**4,818 mole**. Rounding is performed to thousandths.In chemistry

**the amount of the substance is measured in moles**. In one mole the amount of matter is numerically = constant Avogadro (NA = 6,022). If the number of molecules N is NA, then their weight in atomic mass units (amu) is equal to their weight in grams. Therefore, to translate an amu. in grams, just multiply them by NA (6,022 * au = 1).The mass of 1 mole of substance is usually called the molar mass (denoted by the letter M), which is determined by multiplying the molecular weight by the constant Avogadro.

**Molecular weight**find by adding the atomic mass of atoms that are part of the molecule of a particular substance. A classic example of the molecular weight for water molecules: 1 * 2 + 16 = 18 g / mol.**The amount of the substance is calculated by the formula**: n = mM, in which m is the mass of the substance.Number of molecules: N = NA * n

for gases, the following formula is used: V = Vm * n, in which Vm is the molar volume of gas, under normal conditions, equal to 22,4 l / mol.

The general relation is as follows:

n = mM = NNA = VVm

The amount of a substance is a chemical term that is used and in some cases to count the number of similar structural units.

Even at school they teach such material and coma was interesting to remember this information and formulas.

But if anyone has forgotten, can refresh the memory:

We solve the problems using the formula n = mM, where m is taken as the mass of the substance.

The amount of a substance is the number of molecules and is indicated by moles.

1 mol is equal to 6,02.1023 structural particles of the substance.

Here you can see how to solve similar problems.

Finding the amount of a substance is usually used in physics or chemistry. There are several formulas by which you can find the amount of substance, depending on what we are given in the data task condition. These are the formulas:

The amount of substance can be found, the mass divided by the molar mass

Often you can see how to use such a thing as the molar volume - V (m). It is equal to the volume of one mole of substance - has the following formula:

Another possible use is a consequence of one of the basic laws of chemical science - Avogardo's law.

The amount of a substance is a physical quantity characterized by the same type of structural units present in the substance. So, these structural units are understood to mean any particles that make up matter (molecules, ions, atoms, electrons, etc.). The amount of the substance is measured in the SI system in moles.

Here's how you can find the amount of matter:

The most widely used formula for finding the quantity of a substance was the following formula

Where

As you can see, it is necessary to build the calculations based on the input data, then either from the mass or from the volume of the substance.

The unit for measuring the amount of substance is mole. Denoted by letter

**n**. General formulas for finding:In the formula could meet unfamiliar designations, it is necessary to clearly know that:

M molar mass;

NA -

constant Avogadro ;N is the number of molecules;

Vm is the molar volume of gases (constant value equal to 22,414 l / mol).

First of all, let's figure out what is "the amount of substance".

By this term we mean a value that characterizes the number of structural units of the same type of substance. Structural units can be either atoms, molecules, or electrons, ions.

The amount of substance is measured in moles.

One mole contains a certain amount of matter, which is called the permanent Avogadro or the Avogadro number.

This number is NA = 6,022 141 79 (30) 1023 mole1.

So the amount of substance can be found by the following formula:

**n = m / M**where m is the mass of the substance, and M is the molar mass of the substance.

There is one more formula:

**n = V / Vm**where V is the volume of gas under normal conditions, and Vm is the molar volume of gas under normal conditions (it is equal to 22,4 l / mol).