BY THE END OF THE CLASS PERIOD TODAY I WILL BE ABLE TO…  Define and Calculate ‘percent composition’ of molecules and compounds.

OUR PROBLEM FOR THE DAY…  What is the percentage composition of ibuprofen??

FIRST THINGS FIRST…  Chex Mix! Your bag of Chex mix contains 15 pretzels and 3 rye crackers and a whole lot of Chex. What is the percent of pretzels in the mixture?

WHAT IS THE PERCENTAGE COMPOSITION OF PRETZELS IN MY MIXTURE?? Mass of Pretzels Total Mass of Chex Mix X 100 = mass % of Pretzels We can use this same idea to calculate the mass % of elements in a compound…consider CaCl 2

IMPORTANT NOTE:  Percent composition: the percentage by mass of each element in a compound.

PERCENT COMPOSITION  The mass percentage of an element in a compound is the same regardless of the sample’s size

PERCENT COMPOSITION Mass of element in 1 mole of compound Molar Mass of Compound X 100 = % element in compound

CLASS EXAMPLE: WHAT I WRITE…YOU WRITE  Calculate the percent composition by mass of each element in a sample of calcium chloride.

 Baking soda is used in cooking to help raise the dough in baked goods. The formula for baking soda is NaHCO 3. Doctors recommend that patients with heart problems avoid baking soda because it contains sodium.  What is the percent composition of sodium in baking soda?

Find the percent composition of ibuprofen, C 13 H 18 O 2. Record answers to the nearest hundredth.

MOLYMPICS COMPETITION #2: SWIM RELAY

WHAT’S GOING TO GO DOWN… 1. Each member/pair of the team will solve their problem (all members of the team are solving their problem at the same time 2. The first leg of the relay will pour the correct amount of water into their graduated cylinder and pass it to the next second leg. 3. Speed and Accuracy…mostly ACCURACY! (I will judge your team on how close you were to the correct number of mL in your graduated cylinder) 1g H 2 O = 1 mL

SWIMMING RELAY COMPETITION EXPECTATIONS 1. $5 footlong voices 2. Stay in your assigned area…movement out of area may result in disqualification

EMPIRICAL AND MOLECULAR FORMULAS

BY THE END OF THE CLASS PERIOD TODAY I WILL BE ABLE TO…  Define empirical and molecular formulas and calculate empirical formulas.

Molecular and empirical formulas A molecular formula tells exactly how many of each atom are in the molecule. molecular formula of sugar = C 6 H 12 O 6 CCCCCCO HHH HHHH H H H H H OO OO O An empirical formula tells the ratio of atoms in a molecule C H H O : : empirical formula of sugar = CH 2 O

EMPIRICAL FORMULA “simplest ratio of elements in a chemical formula”

How do we find a substance’s empirical formula? By dividing all subscripts by the same number. What is the empirical formula of H 4 S 2 O 8 ? SH O SOO O OO OO HH H Divide all subscripts by 2 to get H 2 SO 4

Ethanol is made up of carbon, hydrogen, and oxygen. An g sample of ethanol was found to contain 6.00 g of carbon and 1.51 g of hydrogen. Find the empirical formula of ethanol.

A pure sample was analyzed and was found to contain 6.25 g of lithium, 5.40 g of carbon, & g of oxygen. Calculate the empirical formula.

All the percentages of the elements in a compound add up to 100% Assume a 100g sample, then the weight of each element is the same as the percent EMPIRICAL FORMULAS FROM % COMPOSITION

Cisplatin is a compound that was once used to treat tumors. Use the percent by mass of each element in the compound to calculate the empirical formula… 65.02% Pt 9.34% N 2.02% H 23.63% Cl The ratio of each element in a compound is always the same – no matter the size of your sample!

 “the actual number of elements in a compound” MOLECULAR FORMULA Whole number multiple of the empirical formula

MOLECULAR FORMULA H4S2O8H4S2O8 H 8 S 4 O 16 H 2 SO 4

The empirical formula of a compound of phosphorus and oxygen was found to be P 2 O 5. Experimentation shows that the molar mass of this compound is g/mol. What is the compound’s molecular formula?

A sample of compound containing g of nitrogen and 80.0 g of oxygen has a molar mass of g/mol. Calculate the empirical and molecular formulas.