3. What is the oxidation number of any element in the free or uncombined state? a. 0 C. -1 b. +1 d. +2 4. What is the sum of the oxidation number of NO2? a. 0 C. -1 b. +1 d. +2 5. What is the oxidation number of Zinc in ZnH₂? a. 0 C. -1 b. +1 d. +2

Consider the following cell running under standard conditions: Fe(s)Fe2+(aq)Al3+(aq)Al(s) a Is this a voltaic cell? b Which species is being reduced during the chemical reaction? c Which species is the oxidizing agent? d What happens to the concentration of Fe3+(aq) as the reaction proceeds? e How does the mass of Al(s) change as the reaction proceeds?

Electrochemical Cells II Consider this cell running under standard conditions: Ni(s)Ni2(aq)Cu+(aq)Cu(s) a Is this cell a voltaic or an electrolytic cell? How do you know? b Does current flow in this cell spontaneously? c What is the maximum cell potential for this cell? d Say the cell is connected to a voltmeter. Describe what you might see for an initial voltage and what voltage changes, if any, you would observe as time went by. e What is the free energy of this cell when it is first constructed? f Does the free energy of the cell change over time as the cell runs? If so, how does it change?

The Nernst equation allows determination of the cell potential for a galvanic cell at nonstandard conditions. Write out the Nernst equation. What are nonstandard conditions? What do , n, and Q stand for in the Nernst equation? What does the Nernst equation reduce to when a redox reaction is at equilibrium? What are the signs of G and when K 1? When K 1? When K = 1? Explain the following statement: determines spontaneity, while determines the equilibrium position. Under what conditions can you use to predict spontaneity?

What is electrochemistry? What are redox reactions? Explain the difference between a galvanic and an electrolytic cell.

Consider the equation G = -nF. What are the four terms in this equation? Why does a minus sign appear in the equation? What does the superscript o indicate?

A 1.0-L sample of 1.0 M HCl solution has a 10.0 A current applied for 45 minutes. What is the pH of the solution after the electricity has been turned off?

In theory, most metals should easily corrode in air. Why? A group of metals called the noble metals are relatively difficult to corrode in air. Some noble metals include gold, platinum, and silver. Reference Table 17-1 to come up with a possible reason why the noble metals are relatively difficult to corrode.

Galvanic cells harness spontaneous oxidationreduction reactions to produce work by producing a current. They do so by controlling the flow of electrons from the species oxidized to the species reduced. How is a galvanic cell designed? What is in the cathode compartment? The anode compartment? What purpose do electrodes serve? Which way do electrons always flow in the wire connecting the two electrodes in a galvanic cell? Why is it necessary to use a salt bridge or a porous disk in a galvanic cell? Which way do cations flow in the salt bridge? Which way do the anions flow? What is a cell potential and what is a volt?

The mass of three different metal electrodes, each from a different galvanic cell, were determined before and after the current generated by the oxidation-reduction reaction in each cell was allowed to flow for a few minutes. The first metal electrode, given the label A, was found to have increased in mass; the second metal electrode, given the label B, did not change in mass; and the third metal electrode, given the label C, was found to have lost mass. Make an educated guess as to which electrodes were active and which were inert electrodes, and which were anode(s) and which were the cathode(s).