WU: Due: Ch 10 RG or OL Review Quizzes Think back: 1.What is an amu? 2.Why do we use amus for mass instead of grams?

Think about it… How do you measure bananas? – How many? Count – 1 dozen naners or 12 naners – How much? Mass – 1 lb of naners or 400 grams – What volume? 1 bushel of naners 1000 mL

How do you measure matter? – How many? Count - atoms – How much? Mass – grams (ratio still exists) – What volume? Vol – Liters or mL

Composition Stoichiometry Three new conversion factors – Avogadro's constant – Molar mass – Molar volume of a gas

1. The Mole—Counting by weighing The SI unit for the amount of a substance 1 mole = 6.02 x (Avogadro’s number) Definition of the mole will allows us to convert between __________ and ____________ Representative particles: species present in a substance ~atom- ELEMENTS (Fe is composed of Fe atoms) ~molecule- COVALENT CMPDS (water AND DIATOMIC MOLECULES) ~Formula units – IONIC CMPDS (NaCl)

2.The Gram to Mole Link: Molar mass The mass of 1 mole of any compound or element is the molar mass. It is numerically equivalent to the atomic mass on the periodic table. “ Molar mass says that 1 mole of atoms weighs in grams as much as one average atom weighs in amu. So if 1 average atom of carbon has an atomic mass of amu, one mole of carbon atoms has a molar mass of grams.” – So… the mass of 1 mole of sulfur is _____________ – How many atoms are in 55.8 g of Fe_________________? – If I wanted 6.02 x10 23 atoms of carbon, what mass of carbon would I need?___________

Molar mass of compounds: H 2 O NaCl C 2 H 6 Mg(NO 3 ) 2 N 2 O 5

3.Molar Volume 4.1 mole of any gas occupies a volume of 22.4 L at STP (standard temperature and pressure) 1 mole = 22.4 L

Examples: x atoms of silicon to mole mol of potassium to grams mol SO 3 to atoms oxygen

x mol sodium phosphate to grams

x 10 2 liters carbon dioxide to atoms O

X formula units lead(II) iodide to grams

Complete Some Questions in PS 10

Moles of Chalk Lab Mass a piece of ordinary chalk and then write your name or complete a mole problem on lab benches. Weigh the chalk again, and determine the number of moles of calcium carbonate that were used. Weight of chalk before writing: ______________ Weight of chalk after writing: _______________ Grams of chalk required to write: ___________ SHOW YOUR WORK!

Moles in a Sip of Water Lab How many moles of water are in your average sip of water? Compare each person in your group! Then convert to number of atoms in your sip of water.

WU: Study for Molar mass and Mole Calculation Quiz

Percent Composition Without talking; perform the following tasks: Calculate the percent girls in the classroom: If there are 100 students, how many would be girls? If there are 234 students in the class how many would be girls? If there are 80 girls in the class, how big is the class?

To Calculate percent composition Calculate the percent composition of magnesium phosphate. If you have a 54g sample of magnesium phosphate, how many grams of that are oxygen? Calculate the percent composition of water in the following compound in zinc nitrate tetrahydrate

Complete a few PS 10 ?s

Begin Percent Composition Lab Will finish tomorrow after we learn about empirical formulas

WU: Study for % comp quiz

Empirical And Molecular Formula Empirical Formula – the smallest whole number ratio of elements in a compound – Ex. H 2 O 2 has the empirical formula : _____ – The empirical formula for C 6 H 12 O 6 is : ______ – All ionic formulas are empirical Molecular Formulas – – True formula- how the molecule actually exists – It is a whole number multiple of the empirical formula

Label as empirical or molecular. For the empirical formulas suggest possible molecular formulas. For the molecular formulas, write the empirical formula. – C 4 HO 2 – C 22 H 44 O 11 – CH 4 – CaSO 4 – Hg 2 Cl 2

Steps to calculate empirical formula – Convert amounts of all substance to moles – To get the simplest ratio, divide all moles by the smallest moles – If these numbers are round-able, round to the nearest whole number and make them the subscripts in the formula. (if there is a __.5 then multiply by 2 to get a round-able whole number)

Examples: Calculate the empirical formula for the following compounds: 1)94.1%O, 5.9% H 2)A sample of an unknown substance is found to contain 0.321g of fluorine, what is the empirical formula

Molecular formula To calculate: (Empirical Formula) n n =

Calculate the molecular formula for the compounds: 1)The molar mass of the compound from example #1) on the front is 34.0 g/mol 2) The empirical formula is C 2 H 4 S with a molar mass of 179 g/mol. What is the molecular formula.

3.A g sample of white powder contains g potassium g of sulfur, the remainder being oxygen. The experimental molar mass is g/mol what is the molecular formula for the compound?

Finish Percent Composition Lab Must be turned in today! Staple all of your labmates papers together please