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Chemistry Fundamentals - Warm-Up and Practice Problems

Refresh your knowledge on formula mass, molecular mass, percent composition, and base units in chemistry. Practice determining mass and percent compositions of various compounds. Get ready for your upcoming quiz!

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Chemistry Fundamentals - Warm-Up and Practice Problems

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  1. Warm-Up: To be turned in • 1km= ________ mm • What is the base unit for temperature?

  2. Formula Mass, Molecular Mass, & Percent Composition

  3. Formula Mass • The total mass of an ionic compound • Sum of the masses of all atoms • Remember- subscripts tell how many of each atom is in the compound! • Ex: NaCl= (1 x 22.990 amu)+ (1 x 35.453 amu)= 58.443 amu

  4. Molecular Mass • Mass of a molecular compound • Process for calculating molecular mass is the same as for ionic compounds • Ex: H2O= (2 x 1.008 amu) + (1 x 15.999 amu) = 18.015 amu

  5. Practice Determine the mass of the following compounds: CO2MgCl2 KI BH3

  6. Percent Composition • Percentage by mass of each element in a compound • Mass of element x 100 = % composition of mass of compound element

  7. Example % composition of O in CO2: • CO2 = (1 x 12.01 amu) + (2 x 16.00 amu)= 44.01 amu • 2 O atoms in CO2, which weigh a total of 32.00 amu (16.00 x 2) • 32.00 amu x 100 = 72.71% 44.01 amu

  8. Practice What is the percent composition of H in H2O? What is the percent composition of Li in Li2O?

  9. Homwwork: due 11/30/2012 • Proof of 3 Trials for Science Fair • Study for quiz (review notes from this week)

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