What can chemical equations tell you

1
What can chemical equations tell you?

• 1) Particles (molecules and atoms) coefficients
• 2) Moles (1 mole 6.02 x 1023 particles)
• 3) Mass conserved in equation, coefficients are
  mole ratios, not mass ratios
• 4) Volumes use molar volume (at STP),
  coefficients Liter ratios
• 5) Only mass and number of atoms are conserved
  in every reaction
• Example Interpret a) number of representative
  particles, b) number of moles, c) volumes of
  gases at STP
• I) H2(g) O2(g) ? H2O(g)
• 2) C2H2(g) O2(g) ? CO2(g) H2O(l)

2
Mole-Mole Calculations

• Can determine amount of product, amount of
  reactant with another reactant, amount of product
  from amount of reactant
• For easy calculations (do in head, think)
• Harder use ratios
• Starting quantity, multiply by ratio, think
  what goes on top? bottom?
• Practice
• Al O2 ? Al2O3
• 14.8 mol Al how much O2 reacts?
• 3.7 mol Al2O3 from how much Al?

3
Mass to Mass calculations

• Cannot measure moles in lab, Must convert from
  moles toMASS (grams)
• Setup road map (Grams, Moles, Moles, Grams) Other
  calculations
• Mole to mole
• Mole to mass, mass to mole
• Example
• CaC2 2H2O ? C2H2 Ca(OH) 2
• If you have 49.0 g H2O, how many moles of CaC2
  will combine?
• If you have 5.00 g of CaC2, how many grams of
  C2H2 are produced?

4
Other Calculations

• Mass to mole to particles (atoms, molecules,
  formula units)
• Example
• 2H2O ? 2H2 O2
• 29.2 grams of water produces how many molecules
  of oxygen?
• Volumes using 22.4 L/mol at STP
• Example
• 2C2H2 5O2 yields 4CO2 2H2O
• With 3 moles of C2H2, how many Liters of CO2
  formed at STP?

5
Identifying the Limiting Reactant

• Recipes review limiting reactant
• Chemistry LR
• Reactant that is in short supply
• Determines the amount of product that can be
  formed in a reaction
• Excess reagent
• Not completely used up
• Determine with LR how much gets used and what is
  left over
• Examples
• Must determine how much of reactant goes with
  other reactant
• 2 Na Cl2 ? 2 NaCl
• 6.70 mol Na with 3.20 mol

6
Calculating Theoretical and Percent Yield

• Theoretical yield
• Calculated from reaction (stoichiometry)
• Represents maximum amount formed from reactants
• Actual yield
• Determined from experiment
• Given in a problem, or done in the lab
• Percent Yield
• Ratio of actual to theoretical
• Actual/theoretical x 100
• Should not be gt100 - what are some reasons why
• Usually lt100 - what are some reasons why

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Examples

• CaCO3 ? CaO CO2
• If the theoretical yield of CaO is 13.9 grams,
  and the actual yield is 13.1 grams, what is the
  percent yield?
• 2Al 3CuSO4 ? Al2 (SO4)3 3Cu
• If 1.87 grams of Al reacts with excess CuSO4, how
  much copper is produced?
• Calculate the percent yield if 4.65 of copper is
  actually produced.

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END
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Calculations with Nonchemical Reactions

• Recipes Cooking, Baking
• Grams to Moles Masses of foods to amounts
  (cups, tsp, tbsp)
• Limiting Reactants
• Excess Reactants
• Percent Yield

10
Determining Avogadros Number

• Website

11
Labs

• Finish Hollow Penny (answer all questions)
• Setup Quantitative Analysis A/W 12
• Complete Types of Reactions A/W 11

12
Lab Quantitative Analysis A/W 12

• Objectives
• Measure number of moles of iron consumed and
  copper produced in a reaction
• Determine the coefficients of the balanced
  chemical reaction
• Hypothesis
• Write the balanced equation for the reaction of
  iron metal and copper(II)chloride
• Identify the type of reaction
• Predict observations for the reaction
• Techniques
• Decanting
• Questions (after Day 2) No Going Further

13
Lab Types of Chemical Reactions A/W 11

• Objectives
• Carry out several chemical reactions
• Write balanced chemical equations
• Techniques
• Burning Splint tests
• Burning vs. Glowing
• Safety GG, Acid
• Questions Just 1-5