1 / 24

OXIDATION-REDUCTION REACTIONS

OXIDATION-REDUCTION REACTIONS. Settle in, this is going to take a while…. What is redox?. Reaction where there is a transfer of electrons between reactants O xidation i nvolves the l oss of electrons (OIL) Oxidation number/state of the element increases

renee-acosta
Download Presentation

OXIDATION-REDUCTION REACTIONS

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. OXIDATION-REDUCTION REACTIONS Settle in, this is going to take a while…

  2. What is redox? • Reaction where there is a transfer of electrons between reactants • Oxidation involves the loss of electrons (OIL) • Oxidation number/state of the element increases • Oxidized element is the reducing agent • Reduction involves the gain of electrons (RIG) • Oxidation number/state of the element decreases • Reduced element is the oxidizing agent

  3. Example Complete Reaction: Mg + Zn(NO3)2 Mg(NO3)2 + Zn Net-ionic Reaction: Mg + Zn2+ Mg2+ + Zn The magnesium metal was oxidized by the zinc and the zinc was reduced by the magnesium.

  4. Do what?!?! • The oxidation state of the magnesium changed from 0 to +2 • Oxidation state increased = oxidation • Because magnesium gave its electrons away, it is the reducing agent • The oxidation state of zinc changed from +2 to 0 • Oxidation state decreased = reduction • Because zinc took the electrons, it is the oxidizing agent

  5. How do you know oxidation states? • The oxidation number for any pure element is zero. • Group 1 metals form +1 ions, group 2 metals form +2 ions, group 13 metals form +3 ions. • Transition metals can be all kinds of oxidation numbers (ranging from +1 to +7) • Transition metal oxidation states can be determined based on the nonmetal(s) it’s bonded to…

  6. Nonmetal oxidation states • Fluoride is ALWAYS -1, the other halides are usually -1. • Oxide is usually -2, except when it’s in the peroxide ion (-1) or bonded to fluorine (+2) • Hydrogen is +1, unless it is the hydride ion (-1)

  7. Putting it all together • The total charge on a compound is zero, so all oxidation numbers must cancel out. • The total charge of elements in a polyatomic ion must add to the charge on the ion

  8. Practice What is the oxidation number of each element in the following compounds? • Zn(NO3)2 • H2SO4 • KMnO4 • N2O4 • PCl3

  9. What’s the point? • When an element gains electrons, another element must accept those electrons (Newton’s 3rd law). • If you separate the reaction into half-reactions, you can exploit this electron transfer to generate electricity. • The study of this is electrochemistry, but more on that later…

  10. Half-Reactions? • You can separate a redox reaction into the reduction reaction and the oxidation reaction. • First you have to identify which element is oxidized and which is reduced. • So let’s practice identification first:

  11. Practice Determine the oxidation states of all elements in the following reactions and then identify which element is oxidized and which is reduced. N2 + 3H2 2NH3 2MnO2 + Zn + 2H2O  2MnO(OH) + Zn(OH)2 AgNO3 + Cu  Cu(NO3)2 + Ag

  12. N2 + 3H2 2NH3

  13. 2MnO2 + Zn + 2H2O  2MnO(OH) + Zn(OH)2

  14. AgNO3 + Cu  Cu(NO3)2 + Ag

  15. Separating reactions • Once the oxidized and reduced elements have been identified, separate the reactions. • Use net ionic reactions instead of complete reactions 2AgNO3 + Cu  Cu(NO3)2 + 2Ag 2Ag+1 + Cu  Cu2+ + 2Ag

  16. 2Ag+1 + Cu  Cu2+ + 2Ag • The silver is reduced, so that is the reduction reaction: 2Ag+1 2Ag • The masses are balanced, but the charges are not, so add the electrons being transferred: 2Ag+1 + 2e- 2Ag • Notice that the reduction half reaction has electrons as reactants

  17. 2Ag+1 + Cu  Cu2+ + 2Ag • The copper is oxidized, so that is the oxidation reaction: Cu  Cu2+ • The masses are balanced, but the charges are not, so add the electrons being transferred: Cu  Cu2+ + 2e- • Notice that the oxidation half reaction has electrons as products

  18. 2Ag+1 + Cu  Cu2+ + 2Ag • When you put the 2 half-reactions together they equal the complete reaction: 2Ag+1 + 2e- 2Ag Cu  Cu2+ + 2e- • the electrons cancel out to make the net ionic reaction

  19. More about balancing • Sometimes you need more than electrons to balance a half reaction. • Oxygens and hydrogens can be balanced by the addition of H+, OH-, and H2O depending on if the solution is acidic or basic.

  20. Balancing Acidic Redox • Balance all elements that are not oxygen or hydrogen • Balance O by adding H2O where needed • Balance H by adding H+ where needed • Balance charges by adding e- to the more positive side

  21. Balancing Basic Redox • Follow the steps for acidic balancing first, then… • Count the H+ used to balance the reaction and add the same number of OH- to both sides. • Combine OH- and H+ to make water. • Combine/cancel water molecules as needed.

  22. A LOT of practice Balance the following equation in both an acidic and a basic solution: HOCl + NO(g)  Cl2(g) + NO3-

  23. More practice Balance this reaction in an alkaline environment: MnO2(s) + Zn(s) + H2O  2MnO(OH)(s) + Zn(OH)2(s)

  24. Homework Problems Pick a few homework problems to work through together 

More Related