Stoichiometry

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Stoichiometry

  1. 1. What is the pH of the following concentrations? <ul><li>1.0 E -9 </li></ul><ul><li>2.4 E -3 </li></ul><ul><li>6.7 E -7 </li></ul><ul><li>4.4 E -5 </li></ul><ul><ul><li>Classify each as Acid or Base </li></ul></ul>
  2. 2. Stoichiometry I didn’t know there would be math in Chemistry class!
  3. 3. Avogadro’s Number <ul><li>Suppose you have a sample of an element and the mass of the sample is equal to the atomic mass of the element </li></ul><ul><ul><li>AKA: Avogadro’s Number (6.02 x 10 23 ) </li></ul></ul><ul><li>Avogadro’s number of particles is called a mole of particles </li></ul><ul><li>Def: Mole - SI base unit used to measure the amount of a substance and is based off the number if particles in 12g of Carbon-12 </li></ul>
  4. 4. What it is used to convert to
  5. 5. Examples <ul><li>Moles to Number of Particles </li></ul><ul><ul><li>Find the number of molecules that are in 2.25 moles of Bromine (Br 2 )? </li></ul></ul><ul><ul><li>Calculate the number of molecules in 15.7 mol CO 2 </li></ul></ul><ul><ul><li>Calculate the number of molecules in 0.0544 mol of H 2 O </li></ul></ul><ul><ul><li>Calculate the number of moles in 9.22 x 10 23 atom Fe </li></ul></ul>
  6. 6. Mass to moles examples <ul><li>Molar mass= Grams/1 mol </li></ul><ul><ul><ul><li>Calculate the mass of 6.89 mole Sb </li></ul></ul></ul><ul><ul><ul><li>A chemist needs 0.07 mol Se for a reaction. What mass of Se should the chemist use? </li></ul></ul></ul><ul><ul><ul><li>A sample of S has a mass of 223g. How many moles of S are in the sample? </li></ul></ul></ul>
  7. 7. Examples- Mass to No. of Particles <ul><li>Calculate the number of atoms in 2.00g of platinum. </li></ul><ul><ul><li>g  mol  atoms </li></ul></ul><ul><li>How many sulfur atoms are in a metric ton (1 E 6 g) of sulfur </li></ul><ul><ul><li>g  mol  atoms </li></ul></ul><ul><li>How many grams of Hg are in 1.19 E 23 atoms of Hg </li></ul><ul><ul><li>Atoms  mol  grams </li></ul></ul>
  8. 8. Avogadro’s Principle <ul><li>equal volumes of gases at the same temperature and pressure, contain equal numbers of particles </li></ul><ul><li>molar volume – 1 mole of any gas at STP occupies 22.4 L </li></ul>
  9. 9. <ul><li>STP – standard temperature pressure is: </li></ul><ul><li>0.00 ºC </li></ul><ul><li>1.0 atm of pressure </li></ul><ul><li>1 mole 22.4 L </li></ul><ul><li>22.4 L 1 mole </li></ul><ul><li>* Conversion factors for relating moles to volume </li></ul>OR
  10. 10. Molarity (M) <ul><li>the number of moles of solute dissolved per liter of solution </li></ul><ul><li>M = moles of solute </li></ul><ul><li> L of solution </li></ul>
  11. 11. Measure mass of solute (convert it to moles ) Use a volumetric flask to bring it to 1.0 L of solution
  12. 12. Percent Composition <ul><li>percent by mass of any element in a compound </li></ul><ul><li>mass of element x 100 = percent composition </li></ul><ul><li>mass of compound </li></ul>
  13. 13. <ul><li>What is the percent composition of water? </li></ul><ul><li>H 2 O </li></ul><ul><li>% H = 2.016 g H X 100 = 11.2 % H </li></ul><ul><li> 18.016 g H 2 O </li></ul><ul><li>% O = 15.99 g 0 X 100 = 88.8 % O </li></ul><ul><li> 18.016 g H 2 O </li></ul>
  14. 14. What is Stoichiometry <ul><li>Def: the study of quantitative relationships between amount of reactants used and products formed by a chemical reaction </li></ul><ul><li>Based on the Law of Conservation of Mass </li></ul><ul><ul><li>Remember… What goes in to a reaction must come out! </li></ul></ul>
  15. 15. 2Na + Cl 2  2NaCl <ul><li>Use what you know about the LCM to answer the following </li></ul><ul><ul><li>How much sodium is needed to produce a certain amount of table salt? </li></ul></ul><ul><ul><li>How much chlorine is needed to produce a certain amount of table salt? </li></ul></ul><ul><ul><li>Given a certain amount of sodium or chlorine, how much table sale can be produced? </li></ul></ul>
  16. 16. 4NH 3 + 5 O 2  4NO + 6H 2 O <ul><li>Coefficients represent both the numbers of particle and the numbers of moles interacting in the chemical reaction. </li></ul><ul><li>4 molecules NH 3 + 5 molecules O 2  4 molecules NO + 6 molecules H 2 O </li></ul><ul><li>OR </li></ul><ul><li>4 moles NH 3 + 5 molesO 2  4 moles NO + 6 moles H 2 O </li></ul>
  17. 17. 4NH 3 + 5 O 2  4NO + 6H 2 O <ul><li>Use this to find the mass of each reactant and product. </li></ul><ul><ul><li>4 mol NH 3 (17.03g / 1 mol NH 3 ) = 68.12 g NH 3 </li></ul></ul><ul><ul><li>Molar Mass </li></ul></ul><ul><li>Do this for the remaining reactants and products </li></ul><ul><ul><li>Add the masses for the reactants and compare that to the masses of the products </li></ul></ul>
  18. 18. Practice Problems Find the molar mass of each. Remember to balance first! <ul><li>H 2 O 2  O 2 + H 2 O </li></ul><ul><li>H 2 CO 3  H 2 O + CO 2 </li></ul><ul><li>HCl + O 2  H 2 O + Cl 2 </li></ul>
  19. 19. Stoichiometric Calculations <ul><li>Mole-to-mole </li></ul><ul><li>Mole-to-mass </li></ul><ul><li>Mass-to-mass </li></ul>
  20. 20. Mole-to-mole <ul><li>How can you determine the number of moles of table salt (NaCl) produced from 0.02 moles of chlorine (Cl 2 )? </li></ul><ul><ul><li>2Na + Cl 2  2NaCl </li></ul></ul><ul><li>Use the mole ratio to convert the known number of moles of chlorine to the number of moles of table salt. </li></ul><ul><ul><li>0.02 mol Cl 2 (2 mol NaCl / 1 mol Cl 2 ) </li></ul></ul><ul><ul><li>= 0.04 mol NaCl </li></ul></ul>
  21. 21. Try this… <ul><li>A piece of Magnesium burns in the presents of oxygen, forming magnesium oxide (MgO). How many moles of oxygen are needed to produce 12 moles of magnesium oxide. </li></ul>
  22. 22. Mole to mass <ul><li>The following reaction occurs in plant photosynthesis. </li></ul><ul><ul><li>6CO 2 + 6H 2 O  C 6 H 12 O 6 + 6 O 2 </li></ul></ul><ul><li>How many grams of glucose are produced when 24 moles of carbon dioxide react in excess water? </li></ul><ul><li>mol CO 2  mol C 6 H 12 O 2 </li></ul><ul><li>24 mol CO 2 (1 mol C 6 H 12 O 2 / 6 mol CO 2 ) = 4 mol C 6 H 12 O 2 </li></ul><ul><li>mol C 6 H 12 O 2  gram C 6 H 12 O 2 </li></ul><ul><li>4 mol C 6 H 12 O 2 (180.18 g C 6 H 12 O 2 / 1 mol C 6 H 12 O 2 ) = 721 g C 6 H 12 O 2 </li></ul>
  23. 23. Try this… <ul><li>Calculate the mass of NaCl produced when 5.50 mol of Na reacts in excess Cl 2 . </li></ul>
  24. 24. Mass to mass <ul><li>How many grams of NaOH are needed to completely reacts with 50.0 g of Sulfuric acid to form Sodium Sulfate and water </li></ul><ul><li>2NaOH + H 2 SO 4  Na 2 SO 4 + 2H 2 O </li></ul><ul><li>Grams of H 2 SO 4  moles of NaOH </li></ul><ul><li>50g H 2 SO 4 (1 mol H2SO4 / 98.09g H 2 SO 4 ) (2 mol NaOH / 1 mol H 2 SO 4 ) </li></ul><ul><li>= 1.02 mol NaOH </li></ul><ul><li>Moles NaOH  grams of NaOH </li></ul><ul><li>1.02 mol NaOH (40g NaOH / 1 mol NaOH) </li></ul><ul><li>= 40.8 g NaOH </li></ul>
  25. 25. Try this… <ul><li>If 40g of Mg reacts with excess HCl, how many grams of MgCl 2 are produced? </li></ul><ul><li>Mg + 2HCl  MgCl 2 + H 2 </li></ul><ul><li>Grams Mg  moles MgCl 2 </li></ul><ul><li>40g Mg (1 mol Mg / 24.305 g Mg) (1 mol MgCl 2 / 1 mol Mg) </li></ul><ul><li>=1.65 mol MgCl 2 </li></ul><ul><li>Moles MgCl 2  grams MgCl 2 </li></ul><ul><li>1.65 mol MgCl 2 (95.211 g MgCl 2 / 1 mol MgCl 2 ) </li></ul><ul><li>=157.1 g MgCl 2 </li></ul>

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