Redox Worksheet. Name_________________________________________
“LEO says GER ….. to the RED CAT and AN OX.”.
1. Determine the oxidation state (valence, charge…) of each atom in the following
species.
e.g. Al +32S-23 KMNO4
Na2CrO4 H2Cr2O7 HClO3 Na2S2O3
C6H12O6
BaO2
2. a. Balance the following Redox reactions. Remember that oxidations (increases
in charge) must equal reductions (reductions in charge), and that all atoms and
charges must balance.
b. Label the oxidizing agent (oxidant)… the substance that contains the atom(s)
being reduced.
c. Label the reducing agent (reductant).
i. _____ Ag + _____ NO3- + ____ H+ = _____ Ag+ + _____ NO + _____ H2O
ii. ____I2 + ____ HClO + ____H2O = ____IO3- + ____Cl- + _____H+
iii. ____ MnO4- + ____ SO3-2 + ____ H+ = ____ Mn+2 + ____ SO4-2 + ____ H2O
iv. ____ NO2 + ____ OH- = ____ NO2- + ____ NO3- + ____ H2O
v. ___K2Cr2O7 + ___H2C2O4 + ___HCl = ___ CrCl3 + ___CO2 + __KCl + ___ H2O
vi,vii: Balance in acidic aqueous solutions: i.e. use H+ and H2O wherever needed.
vi. ____ CuS + ____ NO3-
= ____ Cu+2 + ____ SO4-2 + ____ NO
vii. ____ Zn + ____ NO3-
= ____Zn+2 + _____ NH4+
viii, ix: Balance in basic aqueous solution; use OH- and H2O wherever needed.
viii. ____ Al + ____ NO3-
= _____ Al(OH)4- + ____ NH3
ix. ____ ClO2 +
= _____ Cl- + _____ ClO3-
3. To electrolyze 1.0 mole of NaCl in Na and Cl2 , electrons must be moved from
the Cl- to the Na+.
How many moles of electrons? ______ How many electrons? _____________
How many faradays of charge? ________ How many coulombs? ________________
[Conversions: 1 mole of electrons = 1 faraday = 96500 coulombs. An ampere of electrical
current is a flow of one coulomb per second.]
4. To electroplate 15.0 g of Cu from CuSO4 requires how many (a) moles of e-‘s?
(b) electrons? __________ (c) coulombs?_____________ (d) seconds, with a current of
20.amperes? __________
5. The standard half-cell reduction potential, E01/2 , for the half reaction:
Cu+2 + 2e- = Cu. E0 = +0.337 volts. (a) What is the E01/2 for Cu = Cu+2 + 2e- ?
E01/2 = _________
(b) What is the E01/2 for 3Cu+2 + 6e- = 3 Cu? E01/2 = _________
6. Cu+2 + 2e- = Cu. E0 = +0.337 volts. Al+3 + 3 e- = Al. E0 = -1.66 volts.
(a) Combine these half-reactions to produce a balanced whole reaction.
(b) Calculate E0 for this whole reaction; be sure to show sign: E0 = _________ v
(c ) Which way, left or right, under standard conditions, does your reaction in (a) react? ______
(d) As your whole reaction reacts spontaneously, what is oxidized? ____ What is reduced? ____
What is the oxidizing agent? _________What is the reducing agent? ________________
7. A voltaic (galvanic, electrogenic) cell is prepared as shown by the sketch below.
The half-reactions are:
Cr+3 + 3e- = Cr. E01/2 = -0.744 volts
Pb+2 + 2e- = Pb. E01/2 = -0.126 volts
(a) Write a balanced equation for the reaction.
Specify which way it will react spontaneously at
standard conditions.
(b) Calculate E0 for the reaction.
E0 = _________
(c) Label on the diagram the ANODE (oxidation
occurs), the CATHODE (reduction occurs), the –
electrode (excess of e-‘s), the + electrode, and
the direction of flow of electrons through the
external circuit and meter.
(d) If the concentration of Cr+3 was less than the
1.0 M called for by “standard conditions”,
would the actual voltage E, be greater or less
than at standard conditions (E0)?
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