4.3 The Mole and Molar Mass

6.3/6.4 The Mole and Molar Mass Qualitative Analysis vs Quantitative Analysis - If I wanted to make 10 water molecules? - Our ratio is the same for each

Problem We live at the macroscopic scale, not the microscopic scale where chemistry occurs. Its extremely difficult to individually sort atoms one at a time. How do we keep track of billions of atoms?

Solution Instead of counting individual atoms, we keep track of it using mass. We can find an atoms mass (called atomic mass) under its symbol on the periodic table. Mass of a hydrogen atom: ~1 units (u) Mass of an oxygen atom: ~16 u

H: (1 u * 2 atoms) = 2 u Mass of 1 water molecule then? O: (16 u * 1 atom) = 16 u Total: 2 u +16 u = 18 u The key to going between our mass at a macroscopic

scale (grams) to the microscopic scale (atomic mass units) is through using something called the mole. The Mole The mole (mol) is the SI base unit for the amount of substance Amount could be referring to atoms, ions or

molecules The mole base unit was determined by the amount of atoms in 12g or carbon-12 It was created to deal with the fact that we cannot easily see an atom Recall all that balancing equations business

2H2 + O2 2H2O What the number out in front now tells us is how many moles of something we have. The ratio remains the same. Thus in the previous equation we have: 2 moles of hydrogen gas

1 moles of oxygen gas 2 moles of water Mole So what does it represent? Avogadros number (NA) = the number of entities (pieces) in one mole - 6.02 1023 to be exact! Big number :)

thus one mole = 6.02 1023 entities (atoms, ions, molecules the mole works for chemists because it is amount that is actually visually observable Think of it like dozen, its another word representing a specific quantity.

one mole of sodium atoms is 6.02 1023 sodium atoms one mole of chlorine molecules is 6.02 1023 chlorine molecules one mole of sodium chloride is 6.02 1023 formula units of NaCl one mole of elephants is 6.02 1023 elephants

Terminology Atomic Mass: the mass of one atom of an element, expressed in atomic mass units (u) Molecular Mass: the mass of one molecule, expressed in atomic mass units (u) Formula Mass: the mass of one formula of an ionic compound, expressed in atomic mass units (u)

Molar Mass: The mass of 1 mol of a substance (g/mol) List the atomic and molar mass of the following chemicals with the appropriate unit Calcium Helium Neon

Gold Iron To obtain the formula mass or molecular mass of a compound we do the following: 1. Know the formula of the molecule i.e. Cu2SO4 # of Cu-2

# of S- 1 # of O-4 2. Look up the atomic mass of all elements involved i.e. Cu= 63.55 *note: depending on the periodic S= 32.06 table, the number may O= 16.00 differ due to decimal places

3. Calculate MCu2SO4= 2(MCu) + 1(MS ) + 4(MO) = 2(63.55) + 1(32.06 ) + 4(16.00) = 223.16 u Ex. 1 Calculate the molar mass of sodium chloride.

Na- 22.99 g/mol Cl -35.45 g/mol MNaCl = 1(mNa ) + 1(mCl ) = 22.99g/mol + 35.45g/mol = 58.44 g/mol Mass to moles

In chemistry we can use molar mass as conversion factor. It allows us to go from a mass (ie. Grams, kilograms) to the mole Or It allows us to find out a required mass of chemical based on an amount (moles)

The term amount is commonly used in chemistry to refer to the mole. Converting Amount to Mass How many grams are in 1.89 moles of palladium?

Converting Amount to Mass How many grams are in 1.89 moles of carbon tetrachloride? Converting Amount to Mass How many moles are in 2.99g of lead (II) sulfate? A lot

Class work! Pg 277 # 4-11 Run it