Chemical quantities and mole


Chemical quantities and mole

Quantità chimica e mole

Very often in chemistry you hear of chemical quantities (or amount of substance) and mole, But what are actually ?What makes chemical quantity and amount?
Start off by saying that the chemical quantity is a physical quantity present in the international system of units, While the mole ( symbol: n) is the unit of measurement of chemical quantities.
We could summarize what has been said in the table below.

Measuring Unit Symbol name Symbol u. m
Quantity n Mole moL
Chemistry or
amount of

The mole, Instead it has a precise definition that is shown below: A mole is the amount of substance that contains as many elementary entities as there are elementary entities contained in 12 g of C12 . Elementary principal are atoms, molecules, electrons, protons,…
A mole of substance, by definition it will always contain 6,022 x 1023 elementary entities (Avogadro's number).
One mole of water is formed by 6,022 x 1023 water molecules, While a mole of oxygen substance (dioxygen) consists of 6,022 x 1023 elementary entities of oxygen.
But we must pay attention to one small detail concerning the definition of molar mass, or in concrete terms “how heavy is a mole of a substance”.
For the elements on the periodic table are going to read the relative atomic mass, Therefore the mass of an atom of that substance.
For simple substances (for example or2, H2, N2,…), being composed of molecules formed by atoms of the same element we can derive the molar mass.
To compound substances (for example H2Or), composed of molecules with atoms of different elements we can calculate the molar mass.
We see in detail how to calculate molar mass of a compound substance.
Let us take as an example the CO2 , composed of two molecules of carbon and one of dioxygen. To calculate the molar mass of this substance we must first find the overall molecular mass, so m(CO2 )= 12,01 u + 2 (15,9994 u)= 44, 01u
Therefore to calculate molar mass replace the unit of measurement as follows:
MM (CO2)= 44,01 g/mol

Synthesizing so what are the steps to find the molar mass?

  1. It is necessary to know the chemical formula
  2. Calculate the molecular mass using the periodic table
  3. Replace the unit of measure u with g/mol





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