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Worksheet 3A: Balancing Redox Reactions

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    36941
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    Name: ______________________________

    Section: _____________________________

    Student ID#:__________________________

    Work in groups on these problems. You should try to answer the questions without referring to your textbook. If you get stuck, try asking another group for help.

    The half-equation method separates the oxidation and reduction of a redox reaction in half reactions. Overall scheme for the half reaction method:

    • Step 1: Split reaction into half-reactions (reduction and oxidation)
    • Step 2: Balance the charge or oxidation number with electrons
    • Step 3: Balance \(\ce{O}\) by adding \(\ce{H2O}\)
    • Step 4: Balance \(\ce{H}\) by adding \(\ce{H^{+}}\)
    • Step 5: Multiply by some integer to make electrons (lost) = electrons (gained)
    • Step 6: Add half equations and cancel substances on both sides
    • Step 7: (only in basic solution): add \(\ce{OH^{-}}\) and cancel \(\ce{H_2O}\)
    • Step 8: Check atom balance and charge balance on both sides of the equation!

    Complete and balance the following redox reactions using the half-equation method

    Q1

    \[\ce{Zn(s) + H^{+} (aq) -> Zn^{2+} + H2(g)} \tag{in acidic solution}\]

    ______________________________________________________ (reduction half-reaction)

    ______________________________________________________ (oxidation half-reaction)

    ______________________________________________________ (overall)

    Q2

    \[ \ce{ I^{-} (aq) + NO2^{-}(aq) -> I2(s) + NO(g)} \tag{in acidic solution}\]

    ______________________________________________________ (reduction half-reaction)

    ______________________________________________________ (oxidation half-reaction)

    ______________________________________________________ (overall)

    Q3

    \[ \ce{ MnO4^{-}(aq) + Cl^{-}(aq) -> Mn^{2+}(aq) + Cl2(g)} \tag{acidic solution}\]

    ______________________________________________________ (reduction half-reaction)

    ______________________________________________________ (oxidation half-reaction)

    ______________________________________________________ (overall)

    Do the same reaction in basic solution:

    ______________________________________________________ (overall)

    Q4

    \[ \ce{Br2(l) -> BrO3^{-}(aq) + Br^{-}(aq)} \tag{basic solution}\]

    ______________________________________________________ (reduction half-reaction)

    ______________________________________________________ (oxidation half-reaction)

    ______________________________________________________ (overall)

    Q5

    \[\ce{CrO4^{-} + S^{2-} -> Cr^{3+} + SO4^{2-}} \tag{in acidic solution}\]

    ______________________________________________________ (reduction)

    ______________________________________________________ (oxidation)

    ______________________________________________________ (overall)

    Q6

    \[ \ce{H2O2 + NO2^{}- -> H2O + NO3^{-}} \tag{acidic solution}\]

    ______________________________________________________ (reduction half-reaction)

    ______________________________________________________ (oxidation half-reaction)

    ______________________________________________________ (overall)


    Worksheet 3A: Balancing Redox Reactions is shared under a not declared license and was authored, remixed, and/or curated by LibreTexts.

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