SI Chem 178
Ch 20
Leader: Emily
April 23, 2013
Review:
Reduction means the ______and that the resulting oxidation state is HIGHER / LOWER
Oxidations means the ______and that the resulting oxidation state is HIGHER / LOWER
Which pairs are matched properly?
Oxidizing agent – reduced
Reducing agent – reduced
Oxidizing agent – oxidized
Reducing agent – oxidized
What are the basic steps creating/balancing redox reactions?
Balance the following:
S(s) + HNO3(aq) H2SO3(aq) + N2O(g) (acidic solution)
NO2-(aq) + Al(s) NH4+(aq) + AlO2-(aq) (basic solution)
New Stuff: Voltaic Cells
What is the reading on a voltmeter if there is no salt bridge? Why?
Anodes have a + / - charge and are where oxidation / reduction occurs.
Cathodes have a + / - charge and are where oxidation / reduction occurs.
Salt bridge anions go toward the ______
Salt bridge cations go towards the ______
Electrons go towards the ______
What is potential measured in? What are its units?
A dead battery means the voltaic cell has reached ______, therefore its G=
If a voltmeter has a positive reading, this means G is < / > 0 and that the reducing reaction is…
When calculating Ecell, Oxidation / Reduction equations and values are always used.
When you see a negative E value, the equation is likely an oxidation / reduction in its normal, forward reaction, and in its reduced format, it is spontaneous / non spontaneous.
What is the equation for Ecell? Which reaction were standard state values measured against?
Problems:
20.35 Voltaic cell reaction: Tl3+ + 2Cr2+ Tl+ + 2Cr3+ (all are aqueous)
Measured cell potential: 1.19V
-Write out the two half reactions, complete and label them
-Using appendix E, calculate Ered for Tl3+ Tl+
-Which is the anode/cathode, in which direction are e- going?
Using standard reduction potentials, calculate the following standard state EMFs for the following:
Cl2(g) + 2I-(aq) 2Cl-(aq) + I2(s)
Ni(s) + 2Ce4+(aq) Ni2+(aq) + 2Ce3+(aq)
Fe(s) + 2Fe3+(aq) 3Fe2+(aq)
2NO3-(aq) + 8H+(aq) + 3Cu(s) 2NO(g) 4H2O(l) + 3Cu2+(aq)