Experiment 8 OXIDATION AND REDUCTION Chemical reactions in which the oxidation numbers of one or more atoms or elements change are known as oxidation-reduction or redox reactions. Oxidation occurs when the atom decreases. Oxidation involves the loss of electrons while reduction. In any redox reaction, oxidation of a substance requires the reduction of another. The oxidizing agent causes the oxidation process; it is the substance that is reduced. The reducing agent brings about the reduction process. It is the substance oxidized.
Redox reactions are frequently encountered in the environment and in industrial processes. Reactions used in energy production are often oxidation-reduction reactions. The metabolism of foods, which supplies living organisms with energy, occurs by a series of redox reactions. The energy supply used by consumers is obtained from the oxidation of fossil fuels. The electricity generated by a battery to operate a pocket calculator is supplied by redox reactions. The production of iron in a blast furnace involves several oxidation-reduction reactions. AIM
To be able to recognize some common oxidation-reduction reactions. MATERIALS 0. 1M silver nitrate, AgNO3, copper wire, 0. 1M potassium dichromate, K2Cr207, 3% hydrogen peroxide, H2O2, 3M sulphuric acid, H2SO4, 0. 02M potassium permanganate, KMnO4, 0. 1M iron(II) ammonium sulphate, Fe(NH4)2(SO4)2, 0. 1M potassium thiocyanate, KSCN, 0. 1M potassium iodide, Kl, 0. 1M iron(III) chloride, FeCl3, 0. 1M potassium ferricyanide, K3Fe(CN)6, carbon tetrachloride, CCl4/hexane, C6H14 APPARATUS Test tube, test tube rack, 10-mL graduated cylinder, medicine dropper
PROCEDURE Observe and note the nature of the products. To indentify some of the products, consult the table below where certain properties of possible products are listed. 1. (a) Place a piece of copper wire in a test tube and add 2 mL of 0. 1 M silver nitrate. AgNO3. Place the tube in the rack. (b) After several minutes, observe and record any changes. It has silver precipitate and the colour changes to gray (copper II nitrate). 2. (a) Put 10 drops of 0. 1M potassium dichromate, K2Cr2O7, in a test tube and add 3 mL of 3M sulphuric acid, H2SO4. b) Add 3% hydrogen peroxide, H2O2, drop by drop, shaking the solution after each addition until a change occurs. Record your observations. From colour orange it change to blue green (chromium III sulphate). 3. (a) place 2 mL of freshly prepared 0. 1M iron II ammonium sulphate, Fe(NH4)2(SO4)2, in a test tube. (b) Add 2 drops of 3M sulphuric acid, H2SO4 and 6 drops of 0. 02M potassium permanganate, KMnO4. Shake the solution and note any change. It become faint pink (MnSO4). (c) Test for the presence of iron III ion by adding a drop of 0. M potassium thiocyanate, KSCN. Iron III ion gives a dark red solution if present. Record your result. It gives dark red solution and presence of iron III. 4. (a) Place 2 mL of 0. 1M iron III chloride, FeCl3, in a test tube and add 2 to 3 drops of potassium iodide, Kl. Shake and observe any change. Nothing change. (b) Divide the solution into two (2) portions. (c) Test one portion for the presence of iron II ion by adding a drop of 0. 1M potassium ferricyanide, K3Fe(CN)6. Iron II ion gives a dark blue precipitate if present. Record your result.
Iron II ion gives a dark blue precipitate (d) Test the other portion for the presence of iodine, I2 by adding 1 mL o f carbon tetrachloride, CCI4/hexane, C6H14 and mixing. Iodine produces a pink carbon tetrachloride/hexane layer if present. Record your result. Iodine produce a pink carbon tetrachloride/hexane layer if present. QUESTIONS 1. Write a balanced equation for each of the four (4) redox reactions observed. Identify in each reaction the oxiding agent, the reducing agent, the product of oxidation, and the product of reduction. 2. How do redox eactions differ from other types of reactions? 3. Why are oxidation and reduction considered as complementary processes? 4. Which of the following changes would be considered as oxidation-reduction reaction? Explain your answer (a) Burning of magnesium ribbon (b) Electrolysis of water (c) thermal decomposition of calcium carbonate into calcium oxide and carbon dioxide (d) Formation of sodium sulphate from sulfuric acid and sodium hydroxide. 5. Enumerate two redox reactions that take place in the environment and in industrial processes.