IIIIIIIV created by C. Johannesson modified by T. Howard Chemistry Unit 7: Moles C8A- I will define & use the concept of a mole. C8B – I will use the mole concept to calculate the number of atoms, ions, or molecules in a sample of material. C8C – I will calculate percent composition & empirical and molecular formulas.

n A. mole – amount of substance that has particles equal to the number of atoms in 12g of carbon 12 OR the amount of substance that has Avogadro’s # of particles x particles A large amount!!!!

1 mole of hockey pucks would equal the mass of the moon! A. What is the Mole? 1 mole of pennies would cover the Earth 1/4 mile deep! 1 mole of basketballs would fill a bag the size of the earth!

n B. Avogadro’s number – number of particles in 1 mole of a pure substance 6.02 x 10 23

C. atomic mass number – number of protons + neutrons; measured in amu’s ---this is NOT on the p-table D. average atomic mass number – average weighted mass of an atom/element ---this is on the periodic table If you change the units from amu to grams you now have the amount of grams in 1 mole of the element – something you can actually measure on a scale!

avg atomic mass calculation ( % isotope #1) ( mass isotope #1) + ( % iso #2) ( mass iso #2) +… 100 C6D Use isotopic composition to calculate average atomic mass of an element.

The natural abundance for boron isotopes is: 19.9% 10 B (10 amu) and 80.1% 11 B (11amu). Calculate the atomic weight of boron. [(19.9 × 10) + (80.1 × 11)] 100 avg atomic mass is amu

n E. Molar mass – mass of 1 mole of a pure substance----units are grams/mole or g/mol n Turn to p.7 in your packet (Molar Mass Wkst 3)! n Look at right side of page & we will do a couple of examples…the rest is for you to complete

n 1. Molar mass is “equal” to the mass # of an element in amu’s, so if an element has an mass # of amu’s then the molar mass is g/mol you just change the unit of measurement!

n F. formula mass aka formula weight– sum of all the mass numbers of the atoms in a compound n the term formula mass is usually associated with ionic compounds & n the term molecular mass is usually associated with covalent compounds n they’re the same basic thing

n #3 – BeCl 2 Be = 1 x g = g Cl = 2 x g = g g from the periodic table formula mass of BeCl 2 aka molar mass number of atoms in the formula

n #7 – Mg(OH) 2 Mg = 1 x = g O = 2 x = g H = 2 x = g f.m. of Mg(OH) 2 = g You need to do the rest on your own!

n G. percent composition- percent by mass of each element in a compound mass of element x 100 = % element in cmpd mass of total cmpd

n What percent by mass of Mg(OH) 2 is oxygen? n find the formula mass of the Mg(OH) 2 Mg = 1 x = g O = 2 x = g H = 2 x = g f.m. of Mg(OH) 2 = g

mass of element x 100 = % element in cmpd mass of total cmpd g O x 100 = 54.87% oxygen by mass g Mg(OH) 2 That means more than half of the mass of the Mg(OH) 2 (what is the name of the compound?) is due to oxygen!

H. % error= (observed value - actual value) x 100 actual value Observed value refers to the data you got in the lab while actual value is the “correct” or “book” value/answer.