1. Moles & Stoichiometry By: Skye Smith

2. What is Mass? Mass can be defined as a quantitative measure of an object's resistance to the change of its speed. Scientifically speaking, mass IS different than weight, which is the measure of a planet’s gravitational force on an object Mass is ALWAYS CONSERVED. Scientists use the kilogram (kg) and the gram (g) for units of mass

3. Atomic Mass The actual mass of a single atom is ridiculously tiny (on the order of 10^-23 gram) Using numbers with 10^-23 attached to them all the time would be very inefficient mathmatically Chemists came up with a scale to put this number into more "real" terms This is known as the Atomic Mass Unit, or AMU One AMU=mass of one atom o 1 H atom=1 amu

4. Avogadro's Number We still encounter a major problem in the chemistry world however Chemists don't use "amu's", they use standard units-Kilogram, Liter, Meter...etc. We need a way to relate amu's and grams 6.02*10^23 is the magic number o There are 6.02*10^23 atoms in one mole

5. Molar Mass The mass in grams of 1 mole of a substance is molar mass Same thing as gram formula mass, or gfm With all this information, we can conclude that: o # of moles=grams/gram formula mass For example the gfm of hydrogen is 1. We are given 3 grams of hydrogen and are asked how much that is in moles. Using the above equation, we conclude that: # mol=3grams/1amu=3 moles.

6. What are Moles used for? You will quickly find out in AP chemistry that moles are used in EVERY problem The concept of creating balanced chemical equations is almost entirely based on the mole Without balanced equations, chemists would have a mighty difficult time running reactions because moles determine how much of a substance is needed to properly react in the equation

7. Balancing Equations Some basic rules: o The amount of each element on the reactant HAS to equal the amount on the product side o Coefficients are the chemist's best tool for balancing reactions  Note: The coefficients don't affect the mechanism of the reaction o CAN'T change the subscript of the element, changing it will result in an different substance with different chemical properties Example: H 2 + O 2 yields H 2 O Problem-there are two oxygens on the reactant side and only one on the product side By putting a 2 in front of the hydrogen and the water the equation is balanced 2H 2 + O 2 yields 2H 2 O

8. Dimensional Analysis Simply put, dimensional analysis is a tool for solving many unit-related problems. By using multiplication and division (and correct labeling) chemists can convert moles to coulombs, given the correct information Here's a simple example: o How many feet are in 3.75 miles? (3.75 miles) x (5,280 feet) = 19,800 feet. 11 mile o Since miles is on the top and bottom of the fraction, the unit cancels out, leaving only feet, which is the answer we want.

9. THE END :)