Chem+19-1

700- #'s 34,36,38,40,41,42,45,47,48

34. What is the main characteristic of oxidation-reduction reactions?  The main characteristic in oxidation-reduction reactions is electron transfer from one atom to another. Oxidation and reduction are complementary processes; oxidation cant occur unless reduction also occurs.  36. An oxidation number is the number of electrons lost or gained by the atom when it forms ions.

40. Copper statues, such as the Statue of Liberty, begin to appear green after they have been exposed to air. In this redox process, copper metal reacts with oxygen to form solid copper oxide, which forms the green coating. Write the reaction for this redox process, and identify what is oxidized and what is reduced. 2Cu + O2 → 2CuO Copper: oxidized Oxygen: reduced

41. Identify the species oxidized and the species reduced in each of these redox equations. a. 3Br2 + 2Ga à  2GaBr3: Bromine is reduced while Gallium is oxidized. b. 2HCl + Zn à    ZnCl2 + H2: Hydrochloric acid is reduced while Zinc is oxidized. c. 3Mg + N2 à  Mg3N2 Magnesium is oxidized while Nitrogen is reduced. 42. Identify the oxidizing agent and the reducing agent in each of the following redox equations. a. N2 + 3H2 à  2NH3 Nitrogen is the oxidizing agent while hydrogen is the reducing agent. b. 2Na + I2  à  2NaI Sodium is the reducing agent while Iodine is the oxidizing agent. 45. Determine the oxidation number of the boldface elements in these substances and ions. a. Ca**Cr**O4 Cr: 6+ b. NaH**S**O4 S: 6+ c.**N**O2- N: 3+ d. **Br**O3- Br: 5+ 47. Which of these equations does not represent a redox reaction? Explain your answer. a. LiOH + HNO3 à  LiNO3 + HOH b. MgI2 + Br2 à  MgBr2 + I2       Equation “B” does not represent a redox equation because there is no change in the oxidation number in the equation.