THE MOLE Still Unit 5 Chapter 8

Background info We create new units to describe smaller quantities (dozen eggs, reams of paper, carton of milk, etc) The mole is just like those other units, used to help describe the number of particles in chemical processes

MOLES The number equal to the number of carbon atoms in g of carbon. Huh? 1 mole = 6.02 x particles of something THIS IS A HUGE NUMBER!!

Examples of a mole A computer counting atoms at 10 million atoms a second would take 2 billion years to count one mole of atoms. If one mole of marbles were spread over the surface of the Earth, our planet would be covered by a 50-mile-thick layer of marbles.

Why do we need moles? In chemical reactions, it’s the individual particles moving around and reacting. It’s important to know how many particles we have. Counting atoms not easy to do. A lot easier to measure the mass of something, then calculate how many you have. Moles is the connection between mass and number of particles

Molar Mass Grams per 1 mole of a substance. Add up the mass of each atom in a formula from the periodic table with units of g/mol

Calculating molar masses Elemental Hydrogen Hint: hydrogen is diatomic Argon Hydrogen peroxide H 2 O 2 Ammonium carbonate g/mol g/mol g/mol 96.0 g/mol

Practice Problems How many moles of water are in g? How many molecules of water are there? How many grams of iron(III) chloride are there in moles? How many formula units of iron(III) chloride are there?

Mole Diagram Volume of a STP Moles MassParticles (atoms, molecules)

Percent Composition % by mass of each element in a compound **It’s the total mass of the element in the compound, meaning include the subscripts when adding up.

Calculate the % composition of Propane (C 3 H 8 ) What do you know? Molar Mass of Carbon = g/mol Molar Mass of Hydrogen = g/mol Molar Mass of Propane = g/mol

Calculate the mass of carbon in 82.0 g of propane.

Hydrate A Hydrate is a substance that contains water molecules trapped or bound within its crystalline structure. For example, barium chloride typically has 2 water molecules per 1 BaCl 2 We would write this formula, including the water as: BaCl 2 2H 2 O

What is the molar mass of barium chloride dihydrate? (137.33) + 2(35.453) + 2( ) **NOTE, you do not multiply by the number of waters, you add their mass Molar Mass Ba Molar Mass Cl Molar Mass H 2 O