The Mole

REVIEW OF TERMINOLOGY

Atomic mass mass of 1 atom in AMUs read from P.T. Atomic Mass C = AMU H = AMU

Formula units represents a number of particles whether they are atoms, molecules or whole ionic compounds. Coefficients in a chemical reaction represent formula units E.g. 2 H C  1 CH 4

Formula mass is mass in AMUs for one formula unit of a compound. Formula Mass of CH 4 = AMUs

However the AMU is not practical because it is TOO small. Also, how do we relate AMUs to units we are familiar with like grams, pounds, liters, etc..

The MOLE

A little history related to the development of the mole

While trying to find Chemical Formulas… Chemists Discovered a way of determining Atomic Masses & the Mole

Chemists discovered that as long as temperature and pressure is kept constant gas rxns had whole number ratio coefficients 2 L Hydrogen + 1 L Oxygen  Steam 1 L Nitrogen + 3 L Hydrogen  Ammonia

This helped determine chemical formulas as follows 2 L Hydrogen + 1 L Oxygen  Water So Water is H 2 O 1 1 L Nitrogen + 3 L Hydrogen  Ammonia So Ammonia is N 1 H 3

Avogadro realized that to find formulas from the volumes of gases used in a chemical reaction you have to assume equal volumes of gasses contain the same number of gas particles H2H2H2H2 Cl 2 O2O2O2O2

In other words, 1 L of any gas has the same number of gas particles no matter what the composition of the gas.

That allowed chemists to find relative atomic masses

Chemists took equal volumes of gases & weighed them to get the relative atomic masses & created a new unit called Atomic Mass Unit (AMU).

So, relative atomic masses were developed: E.g. If Nitrogen weighs 14 times as much as Hydrogen. 1 atom Nitrogen = 14 amu 1 atom Hydrogen = 1 amu

This is where the MOLE is created

Chemists realized that they could keep the already established relative atomic masses, but could change the unit to grams if they had enough volume. All that was needed was to find the volume to that would match the atomic masses measured in grams.

What they found is that 22.4 L of a gas will allow you to keep the numerical value of the atomic weight, but change the unit to grams L He = 4 grams He

The Mole is Born 22.4 L which was termed a MOLE is the amount of gas to make the AMUs convert directly to grams 22.4 L N 2 = 1 mole N 2 = 28 g N 2

22.4 L only works at S.T.P. Standard Temp and Pressure STP is 25 °C and 1 atmosphere

22.4 L H STP = 1 mole H 2 = 2.01 g H L N STP = 1 mole N 2 = 28.0 g N L O STP = 1 mole O 2 = 32.0 g O L CO STP = 1 mole CO 2 = 44.0 g CO L Cl STP = 1 mole Cl 2 = 71.0 g Cl 2

Mole means Molecular Equivalent

NOTE!!: Mole is standing for a certain number of particles (atoms, molecules, formula units). Chemists just did not know how many particles yet.

Through Mathematics & later confirmed by experimentation we found that...

A mole is x of something. It is a name for a number and the number of gas particles in 22.4 L of a gas!!!!

6.022 x is called (N A ) Avogadro’s Number

DO WS – Molar Mass Lab – Molar Mass Methane

Mole Conversions

The Mole is essential to chemical manufacturing because the mole links the atomic scale to the human scale atoms & molecules mass & volume

1 mol of a “X” is equal to … L X = 1 mol X = __ g X = 6.02 x X

You own a New Neon sign store and are making a sign that will take 0.50 L of Ne. You call a gas supplying store and Ne costs $100 for 100 g. The glass and electrical equipment cost $30. You charged $200 for the sign. Did you make or lose money on the sign?

So Again a Mole is ……. 1 mol __ = 6.02 x __ = __ g__ and if it’s a gas the 1 mol ___ = 22.4 L of STP

Helpful reference chart

Moles Volume (Liters) Mass (grams) Molecules F.U.s Atoms 6.02 x mole 22.4 L 1 mole 6.02 x mole grams ? 1 mole ?

Conversion Practice

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