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Stoichiometry

Stoichiometry. Chemistry 11 Ms. McGrath. Stoichiometry. The study of the quantities of reactants and products in a chemical reactions. ex. NaHCO 3 (s) + CH 3 COOH( aq )  NaCH 3 COO( aq ) + H 2 O(l) + CO 2 (g)

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Stoichiometry

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  1. Stoichiometry Chemistry 11 Ms. McGrath

  2. 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.

  3. StoichiometryLet’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.

  4. StoichiometryLet’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.

  5. StoichiometryLet’s recall a few important concepts Calculating Average Atomic Mass (u) ex. Carbon Carbon-12 98.9% abundance Carbon-13 1.1% abundance Carbon-14 1 x 10-10 abundance We can determine that the average atomic mass is very close to 12.

  6. Average Atomic Mass (u)Practice Page 45 #1, 2, 3, and 4

  7. Section Review Page 46 #1, 2, 3 and 4

  8. 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: ItemQuantityAmount gloves pair 2 soft drinks six-pack 6 eggs dozen 12 pens gross (12 dozen) 144 paper ream 500

  9. 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) It has been determined that there are 6.02 x 1023 carbon atoms in a 12.00 g sample of carbon-12.

  10. The Avogadro Constant and The Mole • It has been determined that there are 6.02 x 1023 carbon atoms in a 12.00 g sample of carbon-12. • One mole of sodium chloride contains 6.02 x 10 formula units (the term referring to the smallest piece of an ionic compound) of NaCl. • One mole of hydrofluoric acid contains 6.02 x 1023 molecules of HF. A mole of any element, therefore, contains 6.02 x 1023 atoms of that element and the MOLAR MASS will be the atomic mass of that element expressed in grams.

  11. 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.

  12. The Avogadro Constant and The Mole How big is a mole?

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