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Bell Ringer

Engage in a quick quiz on molar conversions and learn how to determine empirical formulas through examples and a fun detective mystery activity. Includes detailed steps and practice problems.

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Bell Ringer

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  1. Bell Ringer • Have HW out on your desk (Moles in Lab and All Molar Conversion) 1. Which of the following has the highest number of grams in one mole? a. PBr3 b. AlBr4 c. PI4 d. PBr4

  2. Questions on HW?

  3. Quiz on Molar Conversions • 15 minutes • Turn in to the box when you are done.

  4. Empirical & Molecular Formulas

  5. CH3 Empirical Formula • Smallest whole number ratio of atoms in a compound • All ionic compound formulas are empirical formulas C2H6 reduce subscripts

  6. Empirical Formula Rhyme: % to g g to mol Divide by smallest Multiply ‘til whole • Change the % to g • Use molar mass to convert grams to moles • Determine the smallest number of moles and divide each by that number • If the ratios are decimals, find a common factor that will make them all whole numbers

  7. 1.85 mol 1.85 mol Empirical Formula Find the empirical formula for a sample of 25.9% N and 74.1% O. 25.9 g N 1 mol 14.007 g N = 1.85 mol N = 1 N 74.1 g O 1 mol 15.999 g O = 4.63 mol O = 2.5 O

  8. N2O5 Empirical Formula N1O2.5 Need to make the subscripts whole numbers  multiply by 2

  9. A “Detective Bob” Mystery Detective Bob’s been giving local crime a rough time lately and there are several people that would like to see him “take a lot of time off.” Bob gets back to his desk one morning and finds a white powder on his usually plain donut. Being a smart detective, Bob takes the donut to the lab. While Bob gets another donut, Police Chemist Francine runs the powder through a machine that breaks the molecules down into their elements, finds the total masses of each type of atom and returns them as a percent (called “% composition”). Bob returns and is told that …

  10. Lab Results(elements listed as % composition) 46.9% Na (Sodium) 24.5% C (Carbon) 28.6% N (Nitrogen) What is the empirical formula? NaCN (sodium cyanide)

  11. A “Detective Bob” Mystery Things are tense after the clear attempt on Detective Bob’s life yesterday. (Tampering with a donut is vicious and low!) Staff at the Department is reviewing security tapes to see if they can get any leads. Meanwhile, Bob is more cautious than usual. He finds a glass of what looks like water on his desk … and (being a coffee drinker) suspects “foul play.” Police Chemist Francine runs the clear liquid through her equipment and returns the following report to Bob …

  12. Lab Results(elements listed as % composition) 2.0% H (Hydrogen) 32.7% S (Sulfur) 65.3% O (Oxygen) What is the empirical formula?

  13. Practice C14H18N2O5 NutraSweet is 57.14% C, 6.16% H, 9.52% N, and 27.18% O.  Calculate the empirical formula of NutraSweet

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