Friday, 10 April 2015

1d) Relative formula masses and molar of gases

Relative formula mass can be found by adding up the mass numbers

A mole is a precise number. When you get precisely that number of atoms or molecules, of any element or compound, they weight exactly the same number of grams as the relative atomic mass, Ar of the element or compound. One mole of atoms or molecules of any substance will have a mass in grams equal to the relative formula mass for that substance.
Example- Carbon has an Ar of 12 and so the one mole of carbon weighs exactly 12g.

The number 6.023x1023 is called Avogadro's number or the Avogardo constant. So you can think of a mole as the Avogardo number of particles in a substance, where the articles are atoms, molecules, ions or electrons.

Number of moles = Mass in g/ Mr

One mole of any gas always occupies 24dmº (=24000 cmº) at room temperature and pressure (RTP: 25ºc and 1 atmosphere)

Volume (dm3) = moles of gas x 24

Volume (dm3) = (mass of gas/ Mr of gas) x 24



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