Unit 6 - Chapter 12 The Mole

The Mole – a word that means a # Other words that mean #s: One dozen = 12 One gross = 144 One score = 20 One ream = 500 One MOLE = 6.02 x 1023 602000000000000000000000

Atoms are too small/light Atoms are too small and too light to count or mass as individuals One Carbon-12 atom = 1.99 x 10-23 grams We use this as the basis for atomic mass units 1 Carbon atom is 12 amu. 6 protons + 6 neutrons = 12 “things” that make up the mass of a carbon atom

Atomic Mass & Molecular Mass Atomic mass - the mass of 1 mole of atoms (also known as “molar mass”) Molecular Mass – the masses of all of the atoms in a chemical compound. Ex: CH4 Ex: CaCl2

Molecular Mass – Example So, the formula weight of calcium chloride, CaCl2, would be Ca: 1(40.1 amu) + Cl: 2(35.5 amu) 111.1 amu To convert to molar mass, change amus to g/mol. 1 amu = 1 g/mol

Molecular Mass – Example For the molecule methane, CH4, the molecular weight would be C: 1(12.0 amu) + H: 4(1.0 amu) 16.0 amu The molar mass of methane would be 16.0 g/mol

1 mole - different physical states Moles provide a bridge from the molecular scale to the real-world scale.

Examples of Molar Mass List the molar masses of the following: Zn CuSO4 NaCl H2O Al2(SO4)3

Avogadro’s Number Avogadro’s Number - 6.02 x 1023 particles in 1 mole 1 mole of 12C has a mass of 12 g.

Mole Conversions Moles tell you how many atoms you have, AND how much mass in grams you have. Today we will convert from moles to grams.

Mole Conversion Factors Today there are 2 possible conversion factors for mole conversions: Show your work -use a conversion factor every time

Mole Diagram

Mole Examples If you have 8.64g of Mg, how many moles do you have? If you have 1.23 moles of Phosphorous, how many grams do you have?

Mole Diagram

Using your calculator To Enter 6.02 x 1023 into your calculator, use the EE button, so it would appear as 6.02E23. Practice with the two following examples

Examples: If you have 4.25 x 1022 atoms of Al, how many moles do you have? If you have 0.37 moles of Al, how many atoms do you have?

Mole Relationships One mole of: atoms ions molecules contains Avogadro’s number of those particles. molecules or formula units contains Avogadro’s number times the number of atoms or ions of each element in the compound.

Formula mass and % composition Percent Composition = All of the parts should add up to 100% !! Example: What is the mass percent of each element in carvone (C10H14O) ?

C10H14O To find % composition you must 1st find the mass of the whole thing! Then find the mass of each part (you kind of already did that) and divide it by the mass of the whole thing x 100 to find % mass of each part.

Empirical and Molecular Formulas Unit 7 - 2009

Empirical and Molecular Formulas An empirical formula shows the simplest whole number ratio of atoms of each element in a compound A molecular formula shows the actual number of atoms of each element in a compound

Example: Glucose Glucose has a molecular formula of: C6H12O6 It has an empirical formula of: CH2O

Formulas cont’d A molecular formula is always a multiple of empirical formula A compound has ONE molecular formula Many compounds have the same empirical formula

Example 0.18 grams of magnesium react with 0.12 grams of oxygen to form magnesium oxide Convert all grams to moles Divide all numbers of moles by the smallest # present (do a ratio!) Multiply all numbers by the smallest # that will make them WHOLE NUMBERS

Example An oxide of aluminum is formed with 4.151 g of Aluminum and 3.692 g of Oxygen. Calculate the empirical formula of the compound: Convert all grams to moles Divide all numbers of moles by the smallest # present (do a ratio!) Multiply all numbers by the smallest # that will make them WHOLE NUMBERS

Find molecular formulas from empirical formulas A white powder is analyzed and found to have an empirical formula of P2O5. It has a molar mass of 283.88 g/mol. What is the molecular formula for this compound?

Hydrated compounds Sometimes, compounds contain water molecules within their crystal structure If a compound contains water molecules, we write it like this: MgSO4•7H2O

Hydrates MgSO4•7H2O The little dot between the MgSO4 and the H2O is NOT a multiplication symbol – the H2O is just “attached” How many atoms of each element are in the compound above? How about in Na3PO4•6H2O?

Lab 9: Percent Comp of a Hydrate If you know the mass of hydrate (what you start with) and you know the mass after you cook it, what have you lost? That is the mass of the H2O you lost If you know mass H2O and you know mass whole thing….you can calculate % of H2O in the compound!!