The Mole: It’s a Big Deal in Chemistry! October 2017

Remember: The mole is a chemistry term that represents a crazy big number

Why do we need the mole in chemistry? It is EASIER Just like it is easier to say you want 2 dozen donuts rather than 24 donuts, It is way easier to say that you just drank 28 moles of water (equivalent to a half a litre) than to say that you just drank 16,700,000,000,000,000,000,000,000 molecules of water!

Every time you see the term mole think an unbelievably huge number of things. For example: 2 donuts – I can eat that much! 2 dozen donuts – I can’t eat that much but I can share! 2 moles of donuts – I can’t even share that with every person in the world! That’s 1,200,000,000,000,000,000,000,000 donuts for me OR 158,000,000,000,000 donuts for each person in the world!

Counting by massing In the jelly belly activity, you “counted” the number of jelly bellies by massing them. All you needed to know was the mass of 1 jelly belly and the total mass of all of them. We can do the same thing in chemistry. We just need to know the mass of 1 mole of the substance and the mass of the substance and we can determine how many molecules are in the substance.

How do we know the mass of 1 mole of a substance? It’s easy! It is right on the periodic table. For example: The mass of 1 mole of sodium (remember we are talking about a HUGE number of sodium atoms) is 22.99 g. It is called the molar mass of sodium. It is written as: mmNa = 22.99 g/mole

Molar mass of elements: the mass of 1 mole of atoms of the element (6 Molar mass of elements: the mass of 1 mole of atoms of the element (6.02 x 1023) Look up the molar mass of the following elements: Aluminum Chlorine Oxygen Carbon Hydrogen

Molar mass of compounds: the mass of 1 mole of the compound 1 NaCl is made up of ___ Na and ___ Cl 10 NaCl are made up of ___ Na’s and ___ Cl’s 1 mole of NaCl is made up of _______ of Na and ______ of Cl mmNaCl = mmNa + mmCl =

Here’s another example: 1 AlCl3 is made up of ___ Al and ___ Cl’s 1 mole of AlCl3 is made up of ___ mole of Al and ___ moles of Cl mmAlCl3 = mmAl + 3 x mmCl =

Calculate the molar mass of the following compounds: BaCl2 O2 AgNO3 Ca(OH)2 Al2O3

Changing how many to how much it weighs Moles (n) to mass (m): 1 mole of NaCl has a mass of ___________ g 2 moles should have a mass of ___________ g 0.50 moles should have a mass of _________ g (To do this, you simply multiply the mass of 1 mole (mm) by the number of moles (n) This gives us the formula: m = n x mm

Moles (n) to mass (m): m = n x mm Change the following from moles to mass: 1.5 moles of AgNO3 0.45 moles of Ca(OH)2 2.54 moles of H2O

Changing how much it weighs to how many: Mass (m) to moles (n): 18.02 g of H2O is _______ moles of H2O 36.04 g of H2O should be ________ moles of H2O (To do this, you simply divide the mass (m) by the molar mass (mm)) This gives us the formula: n = m ÷ mm or n = m/mm

Mass (m) to moles (n): n = m/mm Change the following from mass to moles: 16.0 g of NaCl 2.0 g of H2O 14.5 g of O2