INTRODUCING THE MOLE CHEMICAL QUANTITY

WHAT DO WE MEAN BY MOLE ? The animal with the weird nose? The popular sauce in Mexican cuisine? A dark “spot” on a person’s face or body?

THE MOLE WE ARE TALKING ABOUT The mole is a unit of measurement used in chemistry to express amounts of a chemical substance It is also referred to as Avogadro’s number X or

HOW DO WE MEASURE HOW MUCH? You often measure the amount of something by one of three different methods --- by count, by mass, and by volume When we are dealing with atoms we can’t exactly count the particles, so that method is out…. Chemists, however, came up with a unit that represents a specific number of particles, called the mole. Can you think of other units that represent a specific number of items? Pair Dozen

EXAMPLES A dozen eggs is how many eggs? 12 A dozen boron atoms is how many boron atoms? 12 A mole of eggs would be how many eggs? X A mole of boron atoms would be how many boron atoms? X 10 23

WHAT IS A MOLE ? A mole (mol) is a unit representing 6.02 X representative particles. What do we mean by a representative particle? Representative particle – refers to the species present in a substance: usually atoms, molecules, or formula units. Elements (except diatomics) – atoms Molecular compounds (including diatomics) – molecules

REPRESENTATIVE PARTICLES AND MOLES SubstanceRepresentative Particle Chemical Formula Representative Particles in 1.00 mole Atomic nitrogenAtomN6.02 X Nitrogen gasMoleculeN2N X WaterMoleculeH2OH2O6.02 X Calcium IonIonCa X Calcium fluorideFormula UnitCaF X SucroseMoleculeC 12 H 22 O X 10 23

WHAT IS THE MASS OF ONE MOLE OF AN ATOM OR MOLECULE? To find the mass of one mole of an atom of any element, you can go to the periodic table and find the atomic mass of that element. The atomic mass of an element can also be referred to as that element’s molar mass

PRACTICE What is the mass of one mole of mercury? Answer: g/mol What is the molar mass of chromium? Answer: g/mol

WHAT ABOUT COMPOUNDS? Steps to finding the molar mass of a compound Step 1: List the elements in the compound and the number of atoms you have for each element. Step 2: Write the molar mass of each element and multiply it by the number of atoms. Step 3: Add the masses for each element to get the molar mass (Make sure you are following rules for sig figs)

PRACTICE Water Formula: H 2 O H: (2)( )+ O:(1)( ) = g/mol How many sig figs? Carbon dioxide Formula: CO 2 C: (1)( )+ O:(2)( ) = g/mol How many sig figs?

MORE PRACTICE Calcium sulfate Formula: Ca(SO 4 ) Ca: (1)(40.078)+ S: (1)(32.065)+ O: (4)( ) = answer with sig figs? g/mol Copper(II)perchlorate Formula: Cu(ClO 4 ) 2 Cu: (1)(63.546)+ Cl: (2)(35.453)+ O: (8)( ) = answer with sig figs g/mol

MOLAR CONVERSIONS 1.Write down your given and what you are trying to find 2.Cross out to get what you want 3.Use mole island (p.15 CRM) 4.Significant figures is determined by the given 5.Always include the compound and unit (remember sig figs)

EXAMPLE How many moles of boron are in 25 g of boron? 25 g of B 1 mol of B = 2.3 mol of B g of B

PRACTICE How many moles of NaCl are in 100 g of NaCl?

MORE CONVERSIONS We now can go between mass (grams) and moles How do we go between moles and number of particles or vice versa? Remember that Avogadro’s number is the number of particles in a mole Therefore that will be our conversion factor 1 mol = 6.02 X atoms, molecules, or representative particles

CONVERTING MOLES TO NUMBER OF ATOMS Propane is a gas used for cooking and heating. How many atoms are in 2.12 mol of propane (C 3 H 8 )? KNOWNS: # moles = 2.12 mol C 3 H 8 1 mol C 3 H 8 = 6.02 X molecules C 3 H 8 1 molecule C 3 H 8 = 11 atoms (3 carbon atoms and 8 hydrogen atoms) UNKNOWNS: Number of atoms = ? 2.12 mol C 3 H X molecules C 3 H 8 11 atoms 1 mol C 3 H 8 1 molecule C 3 H 8 = X = 1.40 X atoms

CONVERTING NUMBER OF ATOMS TO MOLES Magnesium is a light metal used in the manufacture of aircrafts, automobile wheels, tools, and garden furniture. How many moles of magnesium is 1.25 X atoms of magnesium? KNOWNS: # of atoms = 1.25 X atoms Mg 1 mol Mg = 6.02 X atoms Mg UNKNOWN: Moles of Mg = ? 1.25 X atoms Mg 1 mol Mg 2.08 X = mol Mg 6.02 X atoms Mg

NOW YOU TRY How many moles is 2.80 x atoms of silicon? How many moles is 2.17 X representative particles of bromine?

YOUR TURN How many atoms are in 1.14 mol SO 3 ? How many moles are in 4.65 X molecules of NO 2 ?

MOLE-VOLUME RELATIONSHIP Volume of a Gas Gases are difficult to weigh (mass) The volume is effected by temperature and pressure Gases must be compared at the same temperature and pressure when finding the amount of moles of gas we have

STP Standard Temperature and Pressure 0 0 and 1 atmosphere (atm) of pressure At STP, 1 mole of any gas occupies 22.4 L This is referred to as molar volume 1 mole = 22.4L of gas at STP

EXAMPLES What is the volume of 4.59 mole of CO 2 gas at STP? 4.59 mol of CO L CO L of CO 2 1 mol CO 2