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Molar Mass & Percent Composition – Unit 2C (p128 – 144)

Molar Mass & Percent Composition – Unit 2C (p128 – 144). Molar Mass – today Moles & practice w/molar mass – tomorrow Percent Composition – Friday Candium in-class lab Flame lab due Retrieving Copper lab – Monday More practice - Wednesday Cracked-up lab – Thursday Quiz Friday.

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Molar Mass & Percent Composition – Unit 2C (p128 – 144)

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  1. Molar Mass & Percent Composition – Unit 2C (p128 – 144) • Molar Mass – today • Moles & practice w/molar mass – tomorrow • Percent Composition – Friday Candium in-class lab Flame lab due • Retrieving Copper lab – Monday • More practice - Wednesday • Cracked-up lab – Thursday • Quiz Friday

  2. The “mole” is coming back… But with a lot more explanation this time. 

  3. Molar Mass – what is it? Basically the same thing as atomic weight. The atomic weight of carbon (C) is ___________ amu. But, we say 1 mole of any element weighs its atomic weight in grams.

  4. Molar Mass of Elements • What is the molar mass of Na? • How much does 1 mole of Na weight? • What is the molar mass or Br? • How much does 1 mole of Br weigh?

  5. Molar Mass of Compounds • Add the molar mass of each element in the compound – assume 1 mole of each element. • What’s the molar mass of NaBr? • What’s the molar mass of H2O?

  6. Molar Mass of Compounds • What’s the molar mass of C6H12O6?

  7. Practice • Work on the problems on the back of the page in class. • For homework, do the “Building Skills 8” green box on page 137. (1-6)

  8. The Mole – Counting a Quantity • Simply an amount of things – • like a pair or a dozen • The mole (mol) is a unit for counting objects (atoms, ions, molecules) • 1 mole = 6.02 * 1023 things (usually molecules or atoms) 1 dozen O2 molecules = 12 O2 molecules 1 billion O2 molecules = 109 O2 molecules 1 mole O2 molecules = 6.02x1023 O2 molecules

  9. Avagadro’s Number • 1 mole = 6.02 * 1023 objects • 60200000000000000000000000

  10. Molar Mass • 1 mole of Carbon weighs ____________ g • So we can create a conversion factor relating mass to mole. molar mass of carbon = ________

  11. Finding the mass of a # of moles • We can determine the mass of a certain number of moles of anything, if we know the molar mass. • Mole to Mass : Multiply by Molar Mass • What is the mass of 4 moles of carbon?

  12. Let’s Practice • What’s the mass of 5 moles of sodium? • What’s the mass of 6 moles of water?

  13. Find # of moles if mass is given. • To do this, we divide by molar mass. • (Or multiply by the reciprocal.) • How many moles are in 48.044 g of carbon?

  14. Let’s try this. • How many moles are in 50 g sodium? • How many moles are in 32 g water? • Careful – You first may have to calculate the molar mass if it is not obvious.

  15. Remember • When given a problem that mentions moles and mass… • Write down what is given. • Write down what you want to find. • Write down the conversion factor so units cancel.

  16. Today • Review % composition • Balancing Equations

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