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Stoichiometry

Stoichiometry. Today’s Lesson. Some housekeeping Relative Atomic Mass & Percentage Composition in a Compound (Science Maths  ). Answers to Chemistry Test Formula of a Compound. What’s Happening In Science. We have 3 more weeks in this current rotation.

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Stoichiometry

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  1. Stoichiometry

  2. Today’s Lesson • Some housekeeping • Relative Atomic Mass & Percentage Composition in a Compound (Science Maths ). • Answers to Chemistry Test • Formula of a Compound

  3. What’s Happening In Science • We have 3 more weeks in this current rotation. • Our last lesson for this rotation will be Friday the 18th of November. • My understanding is there will be a combined test for this lesson. • Each single lesson have a different test. The next Chemistry test will be much shorter and have less information to cover.

  4. 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)

  5. 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

  6. Percentage Composition • You need to know this very complex formula: • Ar of Element / Mr of Compound • Example is here: CH4. What is the percentage composition of Carbon? • Answer on Next Slide

  7. It’s A Bit Gassy • Mr of Methane =16 • Ar of Carbon = 12 • Ar of Hydrogen = 1 • So 12/16 = 0.75 • 75% of methane weight is Carbon. • 25% is Hydrogen • 4/1 = 4 Hydrogen Atoms

  8. Questions • Complete the following questions: • Q 1, 4 & 5 on Page 110-111. • Q 1, 2, 3 & 4 on P112-113.

  9. Answers For Chem Test • Yay – now to hear me speak more. Fun Fun Fun. • Please write down correct answers as we complete this on the data projector

  10. Formula of a Compound • Some basic ideas we need to know: • Empirical formula shows the simplest ratio in which atoms combine • CO2 and Carbon Dioxide are both the same thing. One is the formula, the other is the worded name. It’s the same for all compounds. • The formula is normally more correct and easier to understand as it can become complex naming and understanding the worded names.

  11. Continued • You normally make a table with the following information: • Elements that combine S O • Masses that combine 32g 32g • Ar (Relative Atomic Mass) 32 16 • Mass / Ar 32/32=1 32/16=2 • Ratio 1:2 • Empirical Formula SO2

  12. Last Questions • Complete Q 1-4 on Page 114/115. • We also need to learn about the following before the test. • Writing Chemical Equations • Learn about The Mole! • Avogadro’s Concept

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