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Chapter 8

Chapter 8. Oxidation and Reduction.

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Chapter 8

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  1. Chapter 8 Oxidation and Reduction Background image source: http://images.google.com/imgres?imgurl=http://www.uni-bayreuth.de/departments/didaktikchemie/umat/lebensmittelfaerben/riboflavin%2520redox.gif&imgrefurl=http://www.uni-.yreuth.de/departments/didaktikchemie/umat/lebensmittelfaerben/lebensmittelfaerben.htm&h=719&w=959&sz=9&tbnid=e4f5fJufHzsJ:&tbnh=110&tbnw=147&hl=en&start=92&prev=/images%3Fq%3Dredox%26start%3D80%26svnum%3D10%26hl%3Den%26lr%3D%26safe%3Dactive%26rls%3DGGLG,GGLG:2005-3,GGLG:en%26sa%3DN

  2. Oxidation and Reduction • TryOIL RIG • Oxidation Is Losing electrons • Reduction Is Gaining electrons • Remember our single-element ions? • Na → Na+ • Cl → Cl- OXIDATION REDUCTION

  3. Assigning Oxidation Numbers • Elemental atoms = net 0 charge • Monoatomic ions = net charge of ion • Polyatomic ions = net charge of ion • Compounds = net 0 charge • Alkali metals = +1 • Alkaline earth metals = +2 • Hydrogen = +1 • Fluorine = -1 • Oxygen = -2 • Halogens = -1, but can be adjusted if necessary • Most electronegative atom has negative oxidation number

  4. Try This! • Assign oxidation numbers to the following: • HClO3 • MnO4- • Cl2O

  5. Oxidation and Reduction • Oxidizing agent = the substance that allows something else to be oxidized • Itself is REDUCED • Reducing agent = the substance that allows something else to be reduced • Itself is OXIDIZED

  6. Oxidation and Reduction • Write the balanced equation: nitrogen and hydrogen gasses combine to form ammonia. • Is this a redox reaction? • If so, what’s being oxidized, and what reduced? • How about the oxidizing and reducing agents?

  7. Let’s try it together… • Consider the reaction between iron (III) oxide and carbon to form iron and carbon dioxide. • Write the equation • Indicate the following: • What is being oxidized • What is being reduced • Oxidizing agent • Reducing agent • Indicate oxidation numbers for all elements and balance the equation.

  8. Redox and You • Batteries • Dry cell • Zinc metal reacts with manganese (IV) oxide and water to form zinc (II) hydroxide and manganese (III) oxide • What is oxidized? What is reduced? • Lead storage • Lead and lead (IV) oxide react with sulfuric acid (H2SO4) to form lead (II) sulfate and water • What is oxidized? What is reduced? Source: http://library.kcc.hawaii.edu/external/chemistry/everyday_battery.html

  9. Redox and You • Corrosion • Rust • Iron is oxidized in reaction with oxygen in the air to form iron (III) oxide (rust) • Tarnish • Silver is oxidized in reaction with H2S in the air • Oxidation • Copper in Statue of Liberty oxidized in reaction with air and water, accelerated by pollution Source: http://statue-of-liberty.visit-new-york-city.com/

  10. Redox and You • Food • Photosynthesis • Oxidizing carbohydrates to form CO2, H2O and energy • Browning of fruit • Enzyme called tyrosinase reacts with oxygen & iron compounds in the fruit (“organic rust”) • Inhibited by acid: deactivates the enzyme • Antioxidants • Acids that slow down harmful redox reactions Source: http://adventurequilts.com/Tips_and_Techniques/Apple_photography.htm

  11. Redox and You • Combustion • Dynamite • Rapid oxidation following detonation • Generation of gas, heat, light • Fertilizer bombs • Ammonium nitrate rapidly decomposes • Barbecue! • Carbon in propane is oxidized Source: http://www.barbecue-store.com/images/kegs.jpg

  12. Redox and You • Photography • Film is coated with silver salt (e.g.)AgBr • Film is exposed to light—light reduces some Ag+ to Ag • Sensitizes surrounding AgBr crystals • Developer: reducing agent • Reacts with sensitized AgBr to form dark Ag deposits • Stopper: stops reduction • Fixer: washes away unreacted AgBr

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