redux

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redux
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2010-04-06 14:34:14
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redox
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chem redux reactions
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  1. Oxidation Reduction Reaction
    Reactions involving the transfer of electrons

    must have a metal and a non-metal for electrons to transfer

    Cumbustion reactions are also "Oxidization"
  2. Oxidization Number
    Describes how many electrons have been lost or gained by an atom

    we must use oxidation numbers to keep track of the partial gain or loss of electrons by an atom in a molecular compound
  3. Oxidation Number Rule 1-2

    Oxidation numberes are assigned according to seven rules:
    1. a metal or a non metal in the free state has an oxidation number of 0

    2. A monoatomic ion has an oxidation number equal to it's ionic charge
  4. Rule 3-4
    3. A hydrogen atom is usually assigned an oxidation number of 1+

    4.An oxygen atom is ALWAYS assigned an oxidation number of -2
  5. Rules 5
    5. For the molecular compouind (covalent/non-metal), the more electronegative element is assigned a negative oxidation number equal to it's sharge as an anion (tricky
  6. Rules 6-7
    6. For an ionic compound, the sum of the oxidation numbers for each of the stoms in the compounds is equal to 0

    7.
    for a polyatomic ion, the sum of the oxidation number for each of the atoms in the compound is equal to the iconic charge on the polyatomic ion
  7. Rules 8
    For each molecule, the sum of the oxidation numbers for each of the atoms in the compound is equal to 0

    Rules 6,7,8 all the same rule.

    Note: If there is a conflict in these rules, the rule with the lowest number has priority!
  8. Free state of elements - rule 1
    Seven non metals occur naturally as diatomic molecules

    they are: hydrogen (H2), Nitrogen (N2), Oxygen (O2), F2, Cl2, Br2, I2
  9. Redox reactions
    • A chemical reaction that involves the transfer of electrons in an oxidation reducyion reaction.
    • Iron loses electrons Oxidization
    • Fe-> Fe2++ 2e-
    • The sulfur gains electrons and is Reduced


  10. Oxidizing Agents
    Oxidation is the loss of electrons and Reduction is the gain of electrons.

    an Oxidizing agent is a substance that causes oxidation by accepting electrons. The oxidating agent is reduced
  11. Reducing Agent
    Is a substance that causes reduction by donating electrons. The reducing agent is oxidized
  12. Ways to rememebr What oxidation and reduction mean
    • "LEO the lion says GER
    • Loss Electrons Oxidation
    • Gain Eelectrons Rreduction
  13. Redox Reaction
    In a redox reaction, one substance must be oxidized and one substance must be reduced (these always happen simutaneously)

    The total number of electrons lost is equal to the total electrons gain
  14. Ionic Equations
  15. •Redox reactions in aqueous solution are most often shown in the ionic form because ionic equations easily show us the change in oxidation number.
  16. Ionic Equations Continued
  17. •We map out the reaction to show the oxidation and reduction processes and to determine the oxidizing and reducing agents.
    • •We can easily tell that the oxidation number of iron changes from +2 to +3; iron is oxidized.
    • •Manganese is reduced from +7 in MnO4- to +2 in Mn2+; manganese is reduced.
  18. Balancing Redox Reactions
    When we balance redox reactions, the number of electrons lost must always equal the number of electrons gained

    • There are two ways to balance redox reactions:
    • 1. The oxidation Number Method
    • 2. Half-Reaction Method
  19. Balancing Redox Reactions
    Oxidation Number Method three steps
    • 1. Inspect the reaction and the substances undergoing a change in oxidation number
    • a) Write the number above each element
    • b) Diagram the number of electrons lost by the oxidized substance and gained by the reduced substance
  20. Oxidation Number Method
    2. Balanc each element in the equation using a coefficient. Remember , that the electrons lost must equal the electrons gained. If they are not the same, balance the electrons as follows
  21. how to balance electrons
  22. a)In front of the oxidized substance, place a coefficient equal to the total number of electrons gained by the reduced substance.
    b)In front of the reduced substance, place a coefficient equal to the total number of electrons lost by the oxidized substance.Balance the remaining elements by inspection
  23. Oxidation Number Method
    • 3.After balancing the equation, verify that the coefficients are correct.
    • a)Place a check mark above the symbol for each element to verify that the number of atoms is the same on both sides.
    • b)For ionic equations, verify that the total charge on the left side of the equation is the same as the total charge on the right side of the equation.
  24. Half- Reaction Method
    an alternative method for balanching redox reactions is the half-reaction method.

    a half reaction
    shows the oxidation or reduction process of redox reaction separately

    the oxidation half of the reaction is balanced forst then the reducation half of the reaction is balanced second
  25. 5 steps to balance Half redox
    1. write the half reaction for both the oxidation and reduction processes separately

    • a) identify the reaction that is oxidized and its product
    • b) Identify the reactant that is reduced and its product
  26. Half-Reaction step 2
    • Balance the atoms in each half-reaction using coefficients
    • a)balance all elements except O andH
    • b) balance O using H2O
    • c) balance H using H+
    • d) for reactions in a basic solution, add one OH-to each side to neutralize each H+
  27. Step 3 half reaction
    Multiply each half-reaction by whole number so that the total # of e-'s lost by oxidation equal the total# e-'s gained by reduction
  28. Step 4 Half reaction
  29. 4.Add the two half-reactions together and cancel the identical species, including electrons on each side of the equation.
  30. Step 5 half reaction
  31. 5.After balancing, verify that the coefficients are correct by making sure there are the same number of each atom on each side of the reaction and that the overall charge is the same on both sides.
  32. Conclusions
  33. •A redox reaction is a reaction involving the transfer of electrons from one substance to another.
    •The oxidation number describes how many electrons have been lost or gained by an atom.
  34. Con
  35. •Oxidation is the loss of electrons.
    •Reduction is the gain of electrons.
  36. Conclusions Cont
  37. •An oxidizing agent is a substance that causes oxidation by accepting electrons. The oxidizing agent is reduced.
    •A reducing agent is a substance that causes reduction by donating electrons. The reducing agent is oxidized.
  38. In redox reactions, the number of electrons lost must equal the number of electrons gained
  39. •There are two methods to balance redox reactions:
    • –The Oxidation Number Method
    • –The Half-Reaction Method

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