How to Count Atoms What unit is used to count donuts? Would that unit be appropriate for counting the # of people in Jacksonville? Would it be appropriate for counting # of atoms in a drop of water? We need an appropriate unit for counting things that are too small to see!!

What is mole? Mole Ratio A Ratio of the Amounts of Reactants and Products using the Coefficients of a chemical reaction. Mole is important in Stoichiometry part of chemistry that studies amounts of substances that are involved in reaction. Ex. 1 Cu (s) + 2 AgNO 3 (aq) → 2 Ag (s) + Cu(NO 3 ) 2(aq)

The Mole Concept: a. mole- a counting unit, like a dozen, but MUCH larger, a mole is always equal to Avogadro’s number b. Avogadro’s # = x = 1 mole b/c atoms are so small, their counting unit is HUGE!!, a mole can be used to count anything at the atomic or molecular level **Avogadro’s # is a conversion factor between moles and particles** c. Molar mass- numerically equivalent to amu but in units of #g/mol, also a conversion factor between grams & moles

Molar Mass is a mass of one (1) mole of a substance or any element or compound. Mole is a unit of measurement used in chemistry to express the number of particles of a substance. 1 mole = 6.02 x10 23 particles

Examples: What is the molar mass of Carbon? What is the molar mass of Alum inum? Compounds: H 2 O, H 2 SO 4, CaCl 2. 2H 2 O

*Mole as a Conversion Factor Ex.1 How many particles are in 4.2 moles? 4.2 mol x 6.022x10 23 part.= 1 mole 2.5x10 24 particles EX. 2 How many moles are 4.3 x10 20 atoms? 4.3x10 20 atoms x 1mole = 6.022x10 23 atoms 7.1x10 -4 moles

Mole to Mole Conversion 1. How many moles of H 2 O will produced by 4.8 moles of O 2 ? 2C 4 H 10(g) + 13O 2 (g) → 8CO 2(g) + 10 H 2 O (g)

If there are 5.6 moles of Oxygen, how many moles of CO 2 can be produced? C 2 H 2 (g) + O 2 → CO 2(g) + H 2 O (g)

Molar mass and Moles Problem: You have 16.5 g of oxalic acid, H 2 C 2 O 4 a. What amount(moles) is represented by 16.5 g of oxalic acid? b. How many molecules of oxalic acid are in 16.5 g? c. How many atoms of carbon are in 16.5 g of oxalic acid?

Relating Moles to Mass Molar Mass of a substance… 1. Is the mass in g of exactly 1 mole (6.022x10 23 particles) of that substance 2. Has the units some # g per 1 mole Ex. for C g = 1mole Means that 1 mole of C weighs g Means that 6.022x10 23 atoms of C weigh g 3. Is numerically equal to the average atomic mass but in more useful units, g/mol 4. Is used as a conversion factor

Examples: Molar Mass: (Formula Mass) CuSO 4 H 2 O MgCl 2 Na 3 PO 4

*Molar Mass as a Conversion Factor Ex. 1 How much will 7.51 moles of Al weigh? 7.51 mol Al x g Al = 1 mol Al 203 g Al Ex. 2 How many moles are in a 15.2 kg sample of lithium? 15.2 kg x 1000g x 1mole Li = 1 kg 6.94 g Li 2190 mol Li

How to calculate % Composition? *find molar mass *divide mass of the part you are looking for by molar mass and multiply by 100% *Ex. %O in H 2 O? Molar mass of H 2 O is 18 g/mol Mass of O in H 2 O is 16 g 16 g/18 g * 100% = 88.8%, so water is 88.8% O

More examples… Percent Composition CO 2 C 2 H 5 OH (ethanol) NaHSO 4 C 2 H 6

It is a way to represent a formula including waters of hydration, which are water molecules incorporated into the crystal structure of the salt. *To find the molar mass of a hydrate ADD (not multiply) all the waters of hydration. Ex. CuSO 4 ● 5H 2 O = 5 waters of hydration so ADD 5 x 18 (molar mass of water) to molar mass of CuSO 4

Practice A compound with a mass of g is found to contain g of zinc and g of sulfur. What is the percentage composition of the compound?