What is U in chemistry

Mole (molar mass)

Chemists often speak of moles or molar mass. What exactly this is all about and why this unit is used in chemistry at all will now be explained below. This article belongs to the basics of chemistry.

This article is all about the mole or molar mass. I will go into the important fundamentals of chemistry again in a moment in order to explain these relationships in a more understandable way. However, if you have any major gaps in your previous knowledge, I advise you to read the following articles first:


Moles and molar mass

Why don't you just say 1440 minutes instead of 1 day? Quite simply: it is much harder to deal with relatively large or small numbers. It is much easier to imagine something under 1 day than under 1440 minutes. Chemists are not doing much better in the world of atoms and particles. For this reason the terms mol and molar mass were introduced.

A Mole of a substance contains approximately 6,022 x 1023 Particle. So if I take one mole of oxygen or one mole of copper, etc., I always have 6.022 ยท 1023 Particles of this substance. A particle is understood to be a core particle, i.e. protons and neutrons together. According to the Italian scientist Avogadro this got the name Avogadro's constant NA. with the unit 1 / mol (spoken: one per mol).

This number can be used to convert the atomic mass, given in "u", into the mass in grams, which is 6.022 x 1023 Own atoms. To do this, the Avogadro constant is multiplied by the atomic mass (1u = 1.661 10-24g). The result is called the molar mass. A few examples should make this easier to understand. It is best to open the periodic table of the elements (show periodic table in a new window). There is also the necessary information for the elements, as you can see in the following calculations:

  • Oxygen: 6.02 x 1023 / mol x 16 x 1.661 x 10-24 g = 16 g / mol
  • Copper: 6.02 x 1023 / mol x 63.5 x 1.661 x 10-24 g = 63.5 g / mol


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