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Warm-up

Warm-up. Determine the molar mass of the following compounds: Magnesium sulfide Potassium fluoride Carbon tetrabromide Dinitrogen hexachloride. Warm-up. How many moles are in… 15 grams of water? 500 molecules of sodium chloride?. Chemistry: More on Moles!!. Unit Five, Day Four Kimrey

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Warm-up

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  1. Warm-up • Determine the molar mass of the following compounds: • Magnesium sulfide • Potassium fluoride • Carbon tetrabromide • Dinitrogenhexachloride

  2. Warm-up • How many moles are in… • 15 grams of water? • 500 molecules of sodium chloride?

  3. Chemistry:More on Moles!! Unit Five, Day Four Kimrey 15 October 2012

  4. The “Mole Hill”

  5. Mole Conversions • Remember the conversions we’ve done!!!! • Start with the given • Write what you want over what you have. • Solve • Ex. How many moles of water are there in 25.0 grams? • 14.2 moles of H2O = ? Molecules

  6. 2 Step Conversions. • Notice on the mole hill there is no way to get to grams from particles directly. • You must go through moles! • Step 1 convert what you have to moles • Step 2 convert moles to what you want.

  7. Example • 5o grams of H2O = ? Molecules • 1.6 x 1040 molecules of MgCl2 = ? Grams

  8. Practice • How many grams of NaCl are in 45.3 moles? • How many atoms of Mg in 35.2 grams? • How many moles are in 50.0 grams of oxygen?

  9. Percent Composition • The percent by mass of each element in a compound is called the percent composition. • Formula: • (Mass of one element/Molar mass of compound) x 100

  10. Steps • Find the formula and formula mass for the compound. • Determine the masses of each element in the compound. • Plug into the formula and solve. • Check yourself!!! The Percentages should add to 100%

  11. Example • Bicarbonate of soda (sodium hydrogen carbonate) is used in many commercial preparations. Its formula is NaHCO3. Find the mass percentages (mass %) of Na, H, C, and O in sodium hydrogen carbonate. • First, look up the atomic masses for the elements. The atomic masses are found to be: Na 22.99H 1.01C 12.01O 16.00

  12. Next, determine how many grams of each element are present in one mole of NaHCO3: 22.99 g (1 mol) of Na1.01 g (1 mol) of H12.01 g (1 mol) of C48.00 g (3 mole x 16.00 gram per mole) of O • The mass of one mole of NaHCO3 is: 22.99 g + 1.01 g + 12.01 g + 48.00 g = 84.01 g

  13. So, the mass percentages of the elements are mass % Na = 22.99 g / 84.01 g x 100 = 27.36 %mass % H = 1.01 g / 84.01 g x 100 = 1.20 %mass % C = 12.01 g / 84.01 g x 100 = 14.30 %mass % O = 48.00 g / 84.01 g x 100 = 57.14 %

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