Unit 3 Review Sheet - KEY

# Unit 3 Review Sheet - KEY - Name: _ Date: _ WKST #10: Unit...

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Name: ________________________________________ Date: ____________ WKST #10: Unit 3 Review Sheet (20 points) Period: ___________ 1. A sample of ZnCl 2 weighs 14.6g. How many molecules of ZnCl 2 are there? 14.6g x 1 mole x 6.02x10 23 p = 6.51x10 22 moleules 135 g 1 mol 2. If you have 18.5 L of F 2 gas at STP, how much will that sample weigh? 18.5 L x 1 mole x 38 g = 31.4g 22.4 L 1 mol 3. A sample contains 4.75x10 23 atoms of tin. How much does this sample weigh? 4.75x10 23 atoms x 1 mole x 119 g = 93.9g 6.02x10 23 p 1 mole 4. How many water molecules are in a sample that weighs 25.3g? 25.3g x 1 mole x 6.02x10 23 p = 8.46x10 23 molecules 18 g 1 mole 5. What is the percent composition by mass of H 3 PO 4 ? molar mass = 98g/mol H = (3/98)x100 = 3% P = (31/98)x100 = 32% O = (64/98)x100 = 65% 6. What is the difference between an empirical and a molecular formula? Empirical formulas show the ratio of elements in a compound in lowest terms. The molecular formula is the actual formula of the compound. 7.

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## This note was uploaded on 01/01/2012 for the course CHEM 101 taught by Professor Donahue during the Spring '11 term at Long Island U..

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Unit 3 Review Sheet - KEY - Name: _ Date: _ WKST #10: Unit...

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