Regents Chemistry

What’s a Mole??? One mole of donuts contains x donuts One mole of H 2 O contains x molecules One mole of nails contains x nails One mole of Fe contains x atoms One mole of dogs contains x dogs One mole of electrons contains x electrons One mole of ANY specified entity contains x of that entity. For example:

(Covalently bonded)

These are Formula units!

How can we measure a mole? A mole = x particles Could be a mole of an ionic compound – contains x formula units (made of ions) Could be a mole of a molecular compound – contains x molecules (made of elements) A mole of an element = the average atomic mass listed on the periodic table A mole of a compound = total mass of the moles in the compound

Finding the Mass of a Mole of a Compound

Example #1

Example #2

Summary Formula mass - mass of the smallest unit of an ionic compound; sum of atomic masses in amus Gram Formula Mass - same as formula mass except in grams Molecular Mass – same as FM except for used for molecular substances Mole – x 1023 particles of anything! Just know it is also the GFM of any substance

Regents Chemistry Mass, Mole and Particle conversions

The Conversion Flowchart Mole Number of Particles Mass of compound divide by molar mass multiply by molar mass divide by 6.02 x multiply by 6.02 x Liters of Gas multiply by 22.4 liters divide by 22.4 liters

Practice mole to mass How many grams are in 2 moles of CuCl 2 ? How many grams are in 3.5 moles of H 2 O 2 moles CuCl 2 x 134g per mole = 268 g 3.5 moles H 2 O x 18g per mole = 63 g

Mass to Mole How many moles of NO are in 67.0g of NO? How many moles of KCl are in 125.0g of KCl? 67.0 g NO / 30.0 g per mole = 2.2 moles NO g KCl / 74.5 g per mole = 1.68 moles KCl

Regents Chemistry Finding Percent Composition

What is Percent Composition? Formulas represent the composition of a substance If we use the subscripts and atomic masses of the elements, we can find the percent by mass of each element in a substance Essentially, Percent Composition finds how much of each element is in a substance

How do we do this???? 1. We can add up the total molar mass of all elements involved in the substance 2. We next simply divide the total of the element in question by the total molar mass and multiply by 100%

Example #1 Find the percent composition (in grams) of oxygen in potassium chlorate 1. Find the molar mass KClO 3 K - 1 mole x 39.1 grams = 39.1 g Cl - 1 mole x 35.5 grams = 35.5 g O - 3 moles x 16.0 grams = 48.0 g Molar mass = g 2. Divide and multiply by 100% %O = 48.0 g g x 100% %O = 39.2%

Moles and molecules/formula units Moles - measured in grams molecules / formula units - measured in amu (atomic mass units) So… grams make up moles of a substance and amu (atomic mass units) make up individual molecules/formula units Use the same numbers from the PT!

It’s the same process to find the % of amu in a 1 molecule or formula unit! Find the percent composition (in amu) of oxygen in potassium chlorate 1. Find the mass in amu KClO 3 K - 1 atom x 39.1 amu = 39.1 amu Cl - 1 atom x 35.5 amu = 35.5 amu O - 3 atoms x 16.0 amu = 48.0 amu Formula mass = amu 2. Divide and multiply by 100% %O = 48.0 amu amu x 100% %O = 39.2%

Example #2 Find the percent composition (in amu) of water in sodium carbonate crystals Na 2 CO 3 10H 2 O 1. Formula Mass = amu 2. Total formula mass of H 2 O = amu 3. Divide %H 2 O = amu x 100% amu %H 2 O = 62.9% worksheet

Regents Chemistry Mole Relations in Balanced Equations

RECAP The Law of Conservation of Mass tells us: – Moles (and atoms) in equations must be balanced – Since moles (and atoms) have mass, mass is also balanced (we did this by finding missing mass) – So we have relationship between reactants and products – Thus if we change the moles of reactants (or number of atoms) we change the moles /# of atoms of products..HOW?

Mole Relations Balanced Chemical Equation: 2C 2 H 6 + 7O 2  4CO 2 + 6H 2 O Moles C 2 H 6 Moles O 2 Moles H 2 OMoles CO

Sample Problem How many moles of water will be produced from the complete combustion of 3.0 mol of ethane? 2C 2 H 6 + 7O 2  4CO 2 + 6H 2 O moles ethane:moles water = 2:6 3.0 mole C 2 H 6 = x 2.0 mole C 2 H 6 6 mole H 2 O x = 9.0 mole H 2 O

Finding the Mass Produced Sample Problem Cont.. How many grams of water are produced 9.0 mole H 2 O produced #g H 2 O = 9.0 mole H 2 O 18.0g H 2 O = 162 g H 2 O 1 mole H 2 O ()

Sample Problem #2 How many moles of iron (III) oxide are produced from the combination of 6 moles of Fe ? How many grams? 4Fe + 3O 2  2Fe 2 O 3 6 mole Fe = x mole Fe 2 O 3 4 mole Fe 2 mole Fe 2 O 3 x = 3 mole Fe 2 O 3 equals 480g Fe 2 O 3