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STOICHIOMETRY

Chemistry 11 Ms. McGrath

STOICHIOMETRY The study of the quantities of reactants and products in a chemical reactions. ex. NaHCO3(s) + CH3COOH(aq)  NaCH3COO(aq) + H2O(l) + CO2(g) According to this reaction, one formula unit of baking soda reacts with one formula unit of acetic acid to form a salt, water and carbon dioxide. If we wanted to carry out this reaction, how would we know the amount of baking soda and vinegar to use? The particles are too small and numerous to be counted.

STOICHIOMETRY LET’S RECALL A FEW IMPORTANT CONCEPTS Isotopes: An element’s atom have different number of neutrons. ex. Carbon can exist with 6, 7, and 8 neutrons, therefore they have varying atomic masses (12, 13 and 14). These carbon atoms are called Carbon-12, Carbon-13 and Carbon-14.

STOICHIOMETRY LET’S RECALL A FEW IMPORTANT CONCEPTS Average Atomic Mass (u): is the average of all the masses of all the element’s isotopes. We have to take into account:  the abundance of each isotope  the mass of each isotope This is the mass that is seen on the periodic table.

STOICHIOMETRY LET’S RECALL A FEW IMPORTANT CONCEPTS Calculating Average Atomic Mass (u) ex. Carbon Carbon-12 Carbon-13 Carbon-14

98.9% abundance 1.1% abundance 1 x 10-10 abundance

We can determine that the average atomic mass is very close to 12.

AVERAGE ATOMIC MASS (U) PRACTICE Page 45 #1, 2, 3, and 4

SECTION REVIEW Page 46 #1, 2, 3 and 4

THE AVOGADRO CONSTANT AND THE MOLE We will learn how chemists group large numbers of atoms into amounts that are easily measured. Certain items, because of their size, are often handled in bulk. Some common quantities: Item Quantity gloves pair soft drinks six-pack eggs dozen pens gross (12 dozen) paper ream

Amount 2 6 12 144 500

THE AVOGADRO CONSTANT AND THE MOLE The Chemist`s Dozen Egg farmers and grocers use the dozen (a unit of 12) to count eggs, chemists use the mole (a much larger number) to represent 6.02 x 1023 atoms, molecules or formula units. When farmers think of two dozen eggs, they are also thinking of 24 eggs. 2 dozen x 12 eggs = 24 eggs 1 dozen

THE AVOGADRO CONSTANT AND THE MOLE 

We can convert between moles and particles in a similar way. For example, 1 mol of aluminum has 6.02 x 1023 atoms of Al. Thus 2 mol of aluminum atoms contain 12.0 x 1023 atoms of Al. 2 mol x (6.02 x 1023 atoms) = 1.20 x 1024 atoms 1 mol

THE AVOGADRO CONSTANT AND THE MOLE Easily measurable amounts of elements contain huge numbers of atoms. Chemists use a quantity that is much larger than a dozen or ream to group atoms or molecules together. This quantity is the mole (symbol mol). A mole = 6.02 x 1023 (Avogadro’s number)

THE AVOGADRO CONSTANT AND THE MOLE 

THE AVOGADRO CONSTANT AND THE MOLE Consider the following balanced chemical reaction: Fe(s) + S(s)  FeS(s)

The above reactants combine in a 1 : 1 ratio. One 56 u atom of Iron reacts with one 32 u atom of Sulfur to yield one 88 u formula unit of Iron Sulfide.

THE AVOGADRO CONSTANT AND THE MOLE How big is a mole? A mole of marbles would spread over the surface of the earth, and produce a layer about 50 miles thick. A mole of sand, spread over the United States, would produce a layer 3 inches deep. A mole of dollars could not be spent at the rate of a billion dollars a day over a trillion years. These examples shows you just how big a mole is. Complete

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questions 2 and 4 of the ThoughtLab on