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lecture 5

# lecture 5 - Lecture 5 Chapter 3 Stoichiometry(continued...

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1 Lecture 5 Chapter 3 Stoichiometry (continued) Reading: section 5-7 Homework 3: 12, 14, 16, 18, 20, 22b, 22d, 24b, 24d, 34, 38, 44, 48, 52, 54, 58, 62, 64, 72, 74. Due: Thursday Oct. 11, 8PM The Mole Problem 1: How many moles of copper are in 2.50g Cu? Problem 2: What’s the mass in grams of one atom of copper? Problem 3: What mass of Ca 3 (PO 4 ) 2 should be weighed out for an experiment that requires 0.836 moles of Ca 2+ ? Problem 4 : How many H atoms are there in 2.50 g of C 2 H 6 O?

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2 Empirical formulas from analyses (procedure): 1: Express composition in grams. If percent composition is given, assume a 100g sample. 2: Determine the number of moles of each element. 3: Divide by the smallest number of moles to obtain the mole ratio which is also the atom ratio. 4: Multiply by a factor to get a whole numbers. 5. Write the formula. Empirical formulas from analyses (examples): Problem1: What is the empirical formula of a compound which contains 69.6% Mn and 30.4% O? Problem2: Analysis of an unknown compound gave 39.72% C, 1.67% H, 58.61% Cl. The molecular weight was found to be 181.4. Determine the molecular formula.
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