Announcements

1
Announcements

• To join clicker to class today
• Turn on the Clicker (the red LED comes on).
• Push Join button followed by 20 followed by
  the Send button (switches to flashing green LED
  if successful).

• Exam next Wed.
• Quiz on sections 4.2 4.8 Monday.

• Monday discussion review.
• Monday lecture may have intro to chapter 5if
  want preview look at sections 5.15.2.

2
Review

• Calculating MM of compounds.
• Stoichiometry used to figure out masses or moles
  of reagents used or products produced in a
  chemical reaction.
• Calculating yield.
• Finished with clicker question

3
Final Clicker Question

• Heat 200.00 g CaCO3 (limestone) to get CaO CO2,
  get 80.00 g CO2. What is yield of CO2 (or of
  CaCO3 decomposed)? You were given molar masses
  to save time.
• 85 got the right answer 90.97
• The most common wrong answer was 40.
• Path to correct answer
• Balance equation CaCO3 --gt CaO CO2
• Calculate g of CO2 expected from 200.00 g of
  CaCO3
• Calculate yield
• 100(80.00 g CO2/expected g CO2)

4
Other possible questions with same info.
CaCO3 --gt CaO CO2

• How many g of CaO do I get when 80.00 g of CO2
  are produced?
• MM(CaO) 56.077 g/mol
• MM(CO2) 44.010 g/mol
• MM(CaCO3) 100.087 g/mol
• Concrete is made by slaking CaO with water to
  make Ca(OH)2.How much Ca(OH)2 will I get when the
  CaO is slaked?
• MM(Ca(OH)2) 74.0926 g/mol

5
Example Limiting Reagent Calculation

• RXN 3Na2CO3(aq) 2H3PO4(aq) gt 2Na3PO4(aq)
  3CO2(g) 3H2O(l)
• Have 5.00 g of each reagent. How much CO2 do we
  get?
• M(Na2CO3) 105.988 g/mol Na2CO3
• M(H3PO4)97.994 g/mol H3PO4
• M(CO2)44.010 g/mol CO2

6
Composition useful data for examples

• M(H2O) 18.0153 g H2O/mole H2O.
• Molecules called ethylene and propylene are both
  14.372 by mass H. The rest is carbon (85.628).
• M(ethylene) 28.054 g/mol
• M(propylene) 42.081 g/mol

7
Review

• Stoichiometry used to figure out masses of
  reagents used or products produced in a chemical
  reaction.
• Percent yield
• Reviewed limiting reagents.
• After balancing chemical equations all of these
  calculations require doing the following series
  of conversion given aA gt bB
• g A (MA)gt mol A (b mol B/a mol A)gt mol B
  (xMB)gt g B.
• For limiting reagent we do this process up to the
  moles of B stage for all reagents and only do
  the last step for the smallest moles of B.
• Note that sometimes A and B will be on the same
  side of the balanced chemical equation cC dD
  gt aA bB.