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Stoichiometry

Stoichiometry. Today’s Lesson. The Mole Ar & Mr Experiment Write Up. The Mole. The mole is used to tell us the mass of a particular number of atoms. There are 6.02 X 10^23 atoms in a mole.

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Stoichiometry

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  1. Stoichiometry

  2. Today’s Lesson • The Mole • Ar & Mr • Experiment Write Up

  3. The Mole • The mole is used to tell us the mass of a particular number of atoms. • There are 6.02 X 10^23 atoms in a mole. • When you look at the periodic table, the molecular mass tells you how much 1 mol of that atom weighs. • For example, 1 mol of Hydrogen = 2 grams I was not talking about this mole!! http://crashofcourse.blogspot.com/2010/06/mole-attack.html

  4. The Mole in Liquids • In Chemistry, you might notice that liquids have 1M, 10M, 0.1M on them. • This tells us how many moles of an element or compound are dissolved in 1L of water. • As such, 1M is 10 times stronger than 0.1M etc. http://www.thinkgeek.com/tshirts-apparel/unisex/sciencemath/e635/

  5. Relative Atomic Mass • The relative atomic mass (or Ar), is the average mass of an atom. • Different elements might have different weights due to different isotopes (such as Cl having isotopes with an atomic mass of 35 & 37). • We work it out through percentages (bottom right hand corner of P110)

  6. Relative Formula Mass • The relative formula mass (Mr), is the mass of a compound. It’s just the Ar of the whole compound like below. • C4H4O2 is a compound. It’s worked out the following way. • C = 12, H = 1, O = 16. • So 12 X 4 + 4 X 1 + 16 X 2 = 68

  7. Mass & Moles • Working out the mass from the number of moles is easy. You use the following rules. • Mass of Element = Number of Moles X Ar • Mass of Compound = Number of Moles X Mr • Moles of Element = Mass / Ar • Moles of Compound = Mass / Mr

  8. An Example • I have 20 grams of Magnesium Oxide (MgO). How many moles do I have? • Mr of MgO • Mg = 24 g, O = 16 g • 24 + 16 = 40 g • Moles = 20 g of MgO / 40g (Mr) • We have 0.5 Moles of MgO

  9. Questions & Work • Ar, Mr & Mole Worksheet (download from wiki) • The Masses of Atoms (Page 110-111) Questions 1-5. I suggest you complete this one for homework. • Com

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