1 Chapter 4 Recycling and Chemical Mathematics

2 Nature’s Recycling – The carbon cycle

3 Chemical Equations Chemical reaction: the reorganization of the atoms in one or more substances to form a different substance(s). A chemical equation for respiration: C 6 H 12 O 6 (s) + 6O 2 (g) → 6CO 2 (g) + 6H 2 O(l) What does this equation mean?

4 C 6 H 12 O 6 (s) + 6O 2 (g) → 6CO 2 (g) + 6H 2 O(l) “One molecule of glucose solid reacts with six molecules of oxygen gas to give (or produce) six molecules of carbon dioxide gas and six molecules of water.”

5 Accounting for atoms in the process of respiration

6 Example: Example: Recognizing Balanced Equations Is the following equation balanced? CaCl 2 + 2Na 3 PO 4 → Ca 3 (PO 4 ) 2 + 3NaCl

7 Solution: Solution: Recognizing Balanced Equations This is the balanced chemical equation CaCl Na 3 PO 4 → Ca 3 (PO 4 ) NaCl

8 Producing Aluminum via the Hall-Heroult Process 2Al 2 O 3 (l) + 3C(s) → 4Al(l) + 3CO 2 (g)

9 Example: Example: Atomic Masses The mass of an atom is the weighted average of its naturally-occurring isotopes. Gallium has 2 isotopes, 60.10% 69 Ga (= amu) and 39.90% 71 Ga (= amu). average atomic mass What is the average atomic mass of Ga?

10 Solution: Solution: Atomic Masses 60.10% 69 Ga (= amu) and 39.90% 71 Ga (= amu). average atomic mass What is the average atomic mass of Ga? ( x 68.93) + ( x 70.92) = contribution of 69 Ga isotope contribution of 71 Ga isotope amu

11 Formula Masses The sum of the atomic masses of all the atoms in the formula. H 2 O = 2 x x = amu hydrogen oxygen Fe(OH) 3 = 1 x x ( ) = amu iron oxygen hydrogen

12 Avogadro’s Number 1 mol of anything = 6.02 x things 1 mol of C atoms = 6.02 x C atoms 1 mol of Al atoms = 6.02 x Al atoms 1 mol of Al 2 O 3 = 6.02 x Al 2 O 3 formula units 1 mol of frosted flakes = (Yum!) 6.02 x frosted flakes (Yum!)

13 Conversions: Moles to Grams How many grams of Al 2 O 3 are in moles of Al 2 O 3 ? = 3188 g Al 2 O 3 = 3188 g Al 2 O 3

14 Conversions: Grams to Moles How many moles of (NH 4 ) 2 Cr 2 O 7 are in grams of (NH 4 ) 2 Cr 2 O 7 ? = moles of NH 4 Cr 2 O 7 = moles of NH 4 Cr 2 O 7

15 Using Equations for Stoichiometric Calculations How many moles of iron can be formed from 2.8 moles of iron(III) oxide, Fe 2 O 3 ? Fe 2 O 3 + 2Al → 2Fe + Al 2 O 3

16 Solution: Solution: Using Equations for Stoichiometric Calculations How many moles of iron can be formed from 2.8 moles of iron(III) oxide, Fe 2 O 3 ? Fe 2 O 3 + 2Al → 2Fe + Al 2 O 3 = 5.6 moles Fe

17 Using Equations for Stoichiometric Calculations How many grams of Al 2 O 3 can be formed from 1162 grams of Fe 2 O 3 ? Fe 2 O 3 + 2Al → 2Fe + Al 2 O 3

18 Using Equations for Stoichiometric Calculations How many grams of Al 2 O 3 can be formed from 1162 grams of Fe 2 O 3 ? Fe 2 O 3 + 2Al → 2Fe + Al 2 O 3Strategy g Fe 2 O 3 → mol Fe 2 O 3 → mol Al 2 O 3 → g Al 2 O 3

19 Solution: Solution: Using Equations for Stoichiometric Calculations How many grams of Al 2 O 3 can be formed from 1162 grams of Fe 2 O 3 ? g Fe 2 O 3 → mol Fe 2 O 3 → mol Al 2 O 3 → g Al 2 O 3 = g Al 2 O 3

20 Using Equations for Stoichiometric Calculations How many grams of CO 2 can be formed from 80.7 grams of C 6 H 12 O 6 in respiration? Assume excess oxygen. C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 O

21 Using Equations for Stoichiometric Calculations How many grams of CO 2 can be formed from 80.7 grams of C 6 H 12 O 6 in respiration? Assume excess oxygen. C 6 H 12 O 6 + 6O 2 → 6CO 2 + 6H 2 OStrategy g C 6 H 12 O 6 → mol C 6 H 12 O 6 → mol CO 2 → g CO 2

22 Solution: Solution: Using Equations for Stoichiometric Calculations How many grams of Al 2 O 3 can be formed from 1162 grams of Fe 2 O 3 ? g C 6 H 12 O 6 → mol C 6 H 12 O 6 → mol CO 2 → g CO 2 = 118 g CO 2

23 Common Polymers and Their Monomers