Chemical Reactions Chapter 10

For Science Fair Judges Revised instructions! Submit a list of projects that you judged with the associated grade-levels. A brief description of your impression of the projects would be helpful. (Be in SUB Ballroom by 5:00 PM for dinner and instructions.) If you are not a judge, you may attend the Science Expo and write a detailed summary of at least two projects. Either is extra-credit points or a lab make-up.

Types of Chemical Reactions Oxidation-Reduction (Redox) Combination Decomposition Replacement Ion Exchange

Oxidation-Reduction Reactions (electron transfer reactions) Oxidation – an atom loses electrons Reduction – an atom gains electrons 2 Mg (s) + O2 (g) 2 MgO (s) O2 is the oxidizing agent (takes electrons and is reduced) Mg is the reducing agent (supplies electrons and is oxidized) Mg2+O2-

Fig. 10.9 Example of an oxidizing agent (“chlorine”) Others: 1) Bleach 2) Hydrogen peroxide 3) Oxygen 4) Ultraviolet light

Types of Chemical Reactions Oxidation-Reduction (Redox) Combination Decomposition Replacement Ion Exchange

Fig. 10.10 Iron combines with oxygen to form rust (iron oxide) 4 Fe (s) + 3 O2 (g) 2 Fe2O3 (s)

Hydrogen combines with oxygen to form water (dihydrogen monoxide)                 

Types of Chemical Reactions Oxidation-Reduction (Redox) Combination Decomposition Replacement Ion Exchange

Fig. 10.11 Decomposition of Mercury Oxide heat 2 HgO (s) → 2 Hg (l) + O2 (g)

Decomposition of Hydrogen Peroxide 2 H2O2 (l) → 2 H2O (l) + O2 (g) (Demo)

Types of Chemical Reactions Oxidation-Reduction (Redox) Combination Decomposition Replacement Ion Exchange

Fig. 10. 13 Replacement reaction between aluminum Fig. 10.13 Replacement reaction between aluminum metal and the blue copper chloride solution 2 Al (s) 3 CuCl2 (aq) → 2 AlCl3 (aq) + 3 Cu (s) Cu Al AlCl3 CuCl2

Replacement reactions take place when a more active metal gives up electrons to a less active metal. How do we know if a replacement reaction will take place or not occur? Refer to the activity series Fig 10.12, p 264

Fig. 10.12 The activity series for common metals 2 Na + 2H2O 2NaOH + H2 ↑ (Demo) Zn + 2HCl ZnCl2 + H2 ↑ (Demo)

Types of Chemical Reactions Oxidation-Reduction (Redox) Combination Decomposition Replacement Ion Exchange

2 KI + Pb(NO3)2 → PbI2 ↓ + 2 KNO3 Pg 253 PbI2

Ion Exchange Reaction – ions of one compound react with ions of another compound to form: (1) a solid (precipitate) or FeCl3 + 3 NaOH → Fe(OH)3 + 3 NaCl (2) a gas or (3) water CaCO3 + 2 HCl → CaCl2 + CO2 ↑ + H2O CaCO

Atomic mass is the mass of an atom in atomic mass units (u) Micro World atoms & molecules Macro World grams Atomic mass is the mass of an atom in atomic mass units (u) By definition: 1 atom 12C “weighs” 12 u On this scale 1H = 1.008 u 16O = 16.00 u

Average atomic mass of lithium: Natural lithium is: 7.42% 6Li (6.015 u) 92.58% 7Li (7.016 u) Average atomic mass of lithium: (7.42 · 6.015) + (92.58 · 7.016) 100 = 6.941 u

Average atomic mass (6.941)

Dozen = 12 Pair = 2 mole - the amount of a substance that contains as many particles as there are atoms in exactly 12.00 grams of 12C 1 mol = NA = 6.0221367 x 1023 Avogadro’s number (NA)

Molar mass - the mass of 1 mole of in grams marbles atoms eggs shoes Molar mass - the mass of 1 mole of in grams marbles atoms 1 mole 12C atoms = 6.022 x 1023 atoms = 12.00 g 1 12C atom = 12.00 u 1 mole 12C atoms = 12.00 g 12C 1 mole lithium atoms = 6.941 g of Li For any element atomic mass (u) = molar mass (grams)

One Mole of: S C Hg Cu Fe

molecular mass (u) = molar mass (grams) Molecular mass (or molecular weight) - the sum of the atomic masses (in u) in a molecule. SO2 1S 32.07 u 2O + 2 x 16.00 u SO2 64.07 u For any molecule molecular mass (u) = molar mass (grams) 1 molecule SO2 = 64.07 u 1 mole SO2 = 64.07 g SO2