The MOLE It’s a beauty mark… It’s a small furry garden pest… No, wait… its how we count ATOMS!

The mass of 1 mole of a substance. Molar Mass The mass of 1 mole of a substance.

FORMULAS - review MgCl2 The subscript is the number at the bottom of a formula. There is 1- Mg & 2 - Cl

Calculate the molar mass Calculate the molar mass of 1 mole of magnesium chloride. (first you need a formula)

How to calculate molar mass Identify the # of atoms of each element Multiply # atoms by the atomic mass of that element. (round to 2 #’s after the decimal) Add them all together Grams (g) is the unit

MgCl2 Mg – 1 (24.31) = 24.31 Cl – 2 (35.45) = 70.90 or 95.21 g/mol Molar Mass MgCl2 Mg – 1 (24.31) = 24.31 Cl – 2 (35.45) = 70.90 or 95.21 g/mol 1 mole MgCl2 = 95.21 g MgCl2

Calculate the molar mass: (you MUST write the formula correctly before answering) 1 mole of Ammonium phosphide 1 mole of Trinitrogen pentachloride

What is a percentage mean? How is a percent calculated? What is the percentage of girls in the class? What is the percentage of students in Mrs. Muchnick’s class if she has 10 girls and 12 boys?

Percent Composition The percent BY MASS of each element in a compound – divide the element’s total mass (part) by the molar mass (whole) then multiple by 100 to get the percent. Ex: % composition of MgCl2 Mg – 1 (24.31) = 24.31 / 95.21 x 100 = 25.53% Mg Cl – 2 (35.45) = 70.90 / 95.21 x 100 = 74.47% Cl Molar mass = 95.21 g/mol (PART) (WHOLE) (PART) (WHOLE)

Practice - Calculate the % comp of KMnO4: K – 1 (39.10) = 39.10 / 158.04 x 100 = 24.74% K Mn – 1 (54.94) = 54.94 / 158.04 x 100 = 34.76% Mn O – 4 (16.00) = 64.00 / 158.04 x 100 = 40.50% O molar mass KMnO4 = 158.04

Calculating the amount of an element in a sample Find the % comp of the element in the compound Change the % to a decimal (move decimal 2 times to the left or divide by 100) Multiply that decimal by the amount (g) of the sample. Ex: Calculate amount of chlorine in 203.5 grams of MgCl2. (use the % we found earlier) 74.47% Cl = .7447 x 203.5 = 151.5 grams Cl

Practice: Calculate the amount of oxygen in 15.75 grams of water. H – 2(1.01) = 2.02 O – 1(16.00) = 16.00 Molar mass H2O = 18.02 / 18.02 x100 = 88.79% O 88.79% O = .8879 x 15.75 = 13.98 grams O Complete % comp worksheet

Empirical Formula The lowest whole number ratio (subscripts) of elements in a compound. Cannot be reduced!!! not empirical empirical Ex: C6H12O6  CH2O

Molecular Formula NO3 Actual number of atoms in a chemical compound EX: C12H24O12 Molecular Formulas can be reduced to Empirical Formulas molecular empirical EX: C12H24O12  CH2O Different molecular formulas can have similar empirical formulas molecular empirical EX: N3O9  N12O36  Molecular formula: C76H52O46 Empirical formula: ___________ NO3

PRACTICE: 1. Identify each as empirical (can’t be reduced) or molecular (can be reduced) 2. If its molecular – write the empirical C2H4 NO3 S9Cl12 C3Cl9 N4S9 CH2 - empirical molecular empirical S3Cl4 - empirical molecular CCl3 - empirical molecular empirical

Finding Empirical Formula from Percent Composition Ex: A compound was found to be 54.53% Carbon, 9.15% Hydrogen, and 36.32% Oxygen. Find its Empirical Formula. Steps: Assume a 100g sample (change %  g) Use molar mass to find moles of each Divide all moles by the smallest number of moles Round each to the nearest whole # (sometimes you have to multiply to get a whole number - special) The resulting whole #are the subscripts for that element in the empirical formula

Calculating Empirical Formula 63.5% Silver 8.2% Nitrogen 28.3% Oxygen 63.5 g Ag 8.2 g N 28.3 g O 107.87 14.01 16.00 .589 mole Ag .59 mole N 1.77 mole O .589 .589 .589 1 1 3 AgNO3

Calculating Empirical Formula (special) 60.00%C 4.48%H 35.53%O 60.00g C 4.48g H 35.53g O 12.01 1.01 16.00 4.996 mole C 4.44 mole H 2.221 mole N 2.221 2.221 2.221 2.249 2 1 x4 x4 x4 9 8 4 C9H8O4

Calculating Molecular Formula Find the empirical formula Calculate the molar mass of your empirical formula Identify the molar mass of your molecular (GIVEN in the problem everytime!) Divide the molecular mass / empirical mass Round to the nearest whole # Multiply the whole # by the subscripts in the Empirical formula

Practice If a compound has an empirical formula of NO3 and a molecular mass of 186g – what is the molecular formula? Empirical formula: NO3 molar mass: 62.01g Molecular mass (given) 186g empirical mass 62.01 3 x NO3 = N3O9

What is a mole? For counting matter (quantity) in chemistry we use the mole Moles are used to correctly measure chemicals for reactions in a lab. Problem – no way to “physically” measure a mole. (no lab equipment measures moles) Solution – molar mass (balance)

Using Molar Mass Remember – Molar mass is the mass (grams) of 1 mole 1 mole Fe = _________grams Fe 2.5 mole Fe = ________ grams Fe 113.5 grams Fe = _______ moles Fe Mass to mole = divide by molar mass Mole to mass = moletiply by mole mass 

Using molar mass How many grams are in 15.7 mole MgCl2 How many moles are in 0.75 grams of silver? What is the mass of 30.7 mole water?

Using molar mass In the lab, Mrs. Mathieson needs 2.57 moles of NaCl to do an experiment. How many grams would be needed to equal 2.57 moles of NaCl? After doing the experiment, Mrs. Mathieson has 1.02 moles of NaCl remaining – how many grams does that equal?

What is a mole? For counting matter (quantity) in chemistry we use the mole 1 mole = 6.02 x 1023 representative particles (particles are very tiny) This value is called Avogadro’s Number

What are REPRESENTATIVE PARTICLES? ie. the smallest particle that retains chemical and physical properties 3 types depending on the compound: Atoms: Single element Molecules: covalent compound Formula Units: Ionic Compounds or ions

Using Avagadro’s Number Remember there are 6.02 x 1023 particles (atoms, molecule, f.u) in 1 mole How many atoms are in 1 mole? How many atoms are in 2.10 moles of Copper? How many moles are in 4.21 x 1026 atoms of aluminum?

What is a mole? For counting matter (quantity) in chemistry we use the mole 1 mole = 22.4 L of any gas This value is called Molar Volume

Using molar volume How many liters are in 1 mole of any gas? How many liters are in 12.95 L of oxygen gas? How many moles are in 0.758 moles of nitrogen gas?