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Moles and Stoichiometry

Moles and Stoichiometry. Chapters 11 & 12. Counting Particles. Particles are counted in moles Types of representative particles Atoms- smallest unit of an element Molecule- smallest unit of a molecular compound Formula Unit- smallest unit of an ionic compound. What is a Mole?.

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Moles and Stoichiometry

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  1. Moles and Stoichiometry Chapters 11 & 12

  2. Counting Particles • Particles are counted in moles • Types of representative particles • Atoms- smallest unit of an element • Molecule- smallest unit of a molecular compound • Formula Unit- smallest unit of an ionic compound

  3. What is a Mole? • 1 dozen = 12 of anything • 1 gross = 144 of anything • 1 ream = 500 of anything • 1 mole = 6.02 x 1023 of anything

  4. Why? • Atoms are inconceivably small • Avogadro’s Number- 6.02 x 1023 is the number of carbon-12 atoms in 12g

  5. Understanding Reactions • N2 + 3H2 2NH3 • 1 molecule of nitrogen and 3 molecules of hydrogen produce 2 molecules of ammonia • 1 mole of nitrogen molecules and 3 moles of hydrogen molecules produce 2 moles of ammonia molecules

  6. Counting Particles • Moles → Particles (multiply by Avogadro’s number) • Example: how many atoms are there in 3 moles of aluminum? • Particles → Moles (divide by AN) • Example: How many moles are there in 5.71x1027 formula units of calcium chloride?

  7. Mass and the Mole • MM (molar mass)- mass of 1 mole of representative particles in a compound or element • Converting Between Moles and Grams • Grams → Moles (divide by molar mass) • Example: How many moles are there in 135.2 g of water? • Moles → Grams (multiply by MM) • Example: How many grams are there in 3.46 moles of calcium carbonate?

  8. Chapter 12- Stoichiometry • Stoichiometry- using chemical formulas to determine molar and mass relationships from balanced chemical equations

  9. The Mole Ratio

  10. All Roads go Through Moles • Calculations between mass and particles are possible by first calculating the number of moles

  11. Percent by Mass (Percent Composition) • Remember? • What is the percent composition of each element in sodium phosphate?

  12. Determining an Empirical Formula • Empirical Formula- lowest whole number ratio of elements in a compound • Use % composition and assume 100g • Divide by MM of each element to get moles • Divide all by lowest number of moles • Multiply to get the lowest whole number ratio • Record empirical formula Example: a compound is determined to be 36.4% nitrogen and 63.16% oxygen, what is the empirical formula?

  13. Determining a Molecular Formula • Molecular Formula- multiple of empirical formula that accurately shows number of each atom • Calculate mass of empirical formula (EFM) • Divide MM of the compound by the EFM • Multiply empirical formula by result • Record molecular formula Example: A compound has a molar mass of 110.0 g/mol. What is the molecular formula if it is 65.45% C, 5.45% H, and 29.09% O?

  14. Practice • Sulfuric acid reacts with sodium hydroxide in a double replacement reaction. If you start with 5.25 moles of NaOH, how many moles of water can you make? • If you start with 11.34 grams of NaOH, how many moles of sodium sulfate can you make? • If you start with 55.1 grams of NaOH, how many grams of sodium sulfate can you produce?

  15. The End of a Long Road... • Limiting Reagents • Percent Yield

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