Formula mass powerpoint


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Formula mass powerpoint

  1. 1. Mg (s) + 2HCl (aq)  H 2 (g) + MgCl 2 (aq) <ul><li>We know Magnesium and Hydrocloric acid react to make hydrogen (remember the experiment that went pop!?) </li></ul><ul><li>As chemists we need to know how much to mix and how much we’ll get. That’s what the next couple of units are about. </li></ul><ul><li>We need to count molecules. </li></ul>
  2. 2. Counting things <ul><li>Shoes come in pairs (2) </li></ul><ul><li>Eggs come in dozens (12) </li></ul><ul><li>Pencils come in a gross (144) </li></ul><ul><li>Molecules come in moles (6.02 x 10 23 ) </li></ul>
  3. 3. Molar mass <ul><li>Molar mass - the molar mass of a substance is equal to the mass in grams of one mole, or 6.02 x 10 23 particles of the substance. </li></ul>
  4. 4. Formula mass <ul><li>Formula mass – the formula mass of any molecule, formula unit, or ion is the sum of the average atomic masses of all the atoms represented in its formula. </li></ul>
  5. 5. Formula Mass & Molar Mass <ul><li>NOTE- These are 2 different terms but both are calculated the same way . Know these terms, but usually we will refer to the molar mass as just that, or we may use “gfm” (the gram formula mass) </li></ul><ul><li>Formula mass Molar mass </li></ul><ul><li>Also called Molecular Weight. </li></ul>
  6. 6. How to Find Formula Mass <ul><li>1. Write a CORRECT formula for the compound </li></ul><ul><li>2. Look up the atomic mass of each element from the periodic table in the compound and round it to two decimal places. </li></ul><ul><li>3. Multiply the rounded atomic mass by the subscripts, if any. </li></ul><ul><li>4. Add all masses of elements together and use the unit, g/mol </li></ul>
  7. 7. Ex: Find the formula mass of calcium phosphate <ul><li>       Formula:  Ca 3 (PO 4 ) 2 </li></ul><ul><li>  </li></ul><ul><li>     </li></ul>Ca = 40.08 (mass) x 3 (how many) = 120.24 P = 30.97 (mass) x 2 (how many) = 61.94 O = 16.00 (mass) x 8 (how many) = 128.00 Total: 310.18 g/mol So, one mole of Calcium Phosphate has a mass of 310.18 grams
  8. 8. I Do: <ul><li>Find the formula mass of barium nitrate </li></ul><ul><li>Formula: </li></ul><ul><li>Calculations: </li></ul>
  9. 9. We Do: <ul><li>Find the formula mass of ammonium sulfate </li></ul><ul><li>Formula: </li></ul><ul><li>Calculations: </li></ul>
  10. 10. You Do: <ul><li>Find the formula mass of dichlorine heptoxide </li></ul><ul><li>Hint: Nonmetal + nonmetal = covalent. Use prefixes! </li></ul><ul><li>Formula: </li></ul><ul><li>Calculations: </li></ul>
  11. 11. Hydrates <ul><li>Some compounds trap water inside their crystal structure and are known as hydrates . You will not be able to predict which compounds will form hydrates. All you have to do is to be able to name them and find their molar masses (including the water) </li></ul>
  12. 12. Hydrates <ul><li>CuSO 4 • 5H 2 0 is an example of a hydrate. This says that one formula unit of copper sulfate will trap 5 molecules of water inside its crystal. </li></ul>
  13. 13. Hydrates <ul><li>Hydrates are named by naming the ionic compound by the regular rules and then adding (as a second word) a prefix indicating the number of water molecules. You will use the word “hydrate” to indicate water. The compound below would be called copper sulfate pentahydrate . </li></ul>CuSO 4 • 5H 2 0
  14. 14. Hydrates <ul><li>To find the formula mass of a hydrate, simply find the mass of the ionic compound by itself and then ADD the mass of water molecule(s) to that mass. </li></ul><ul><li>Mass of ionic + Mass of H 2 O’s = Total </li></ul>
  15. 15. I Do: <ul><li>Find the molar mass of magnesium sulfate pentahydrate </li></ul><ul><li>Formula: </li></ul><ul><li>Calculations: </li></ul>
  16. 16. We Do: <ul><li>What is the formula mass of barium chloride dihydrate? </li></ul><ul><li>Formula: </li></ul><ul><li>Calculations: </li></ul>
  17. 17. You Do: <ul><li>What is the molar mass of aluminum sulfate octahydrate? </li></ul><ul><li>Formula: </li></ul><ul><li>Calculations: </li></ul>