Unit 4: Electrochemistry

Question 1

How is the gain or loss of oxygen in a chemical reaction linked to oxidation and reduction?

Answer 1

Oxygen is not required, but it has to do with the loss and gain of electrons, like oxygen does.

Question 2

How is the gain or loss of electrons in a chemical reaction linked to oxidation and reduction?

Answer 2

LEO: oxidation is the loss of electrons
GER: reduction is the gain of electrons

Question 3

What happens to iron when it corrodes?

Answer 3

It becomes Iron (III) oxide (rust) through oxidation.

Question 4

Determine the oxidation number of an atom of any element in a pure substance.

Answer 4

always 0 (zero)

Question 5

Define oxidation and reduction in terms of a change in oxidation number and identify atoms being oxidized or reduced in redox reactions.

Answer 5

oxidation number increase = oxidation

oxidation number decrease = reduction

Question 6

Use oxidation-number changes to balance redox equations

Answer 6

.

Question 7

Use half-reactions to balance redox equations.

Answer 7

.

Question 8

How do we determine what types of redox reactions are best balanced through the half-reaction method?

Answer 8

ionic reactions are best balanced through half-reaction

Question 9

What happens to the voltage of the solution during the KMnO4 and FeCl2 titration?

Answer 9

.

Question 10

What is the balanced net ionic equation for the reaction of KMnO4 and FeCl2?

Answer 10

.

Question 11

What happens to the color of the FeCl2 when the equivalence point is reached?

Answer 11

.

Question 12

For any two metals in an activity series, which metal is more readily oxidized?

Answer 12

the more active metal is oxidized (Li is most)

Question 13

Who created the first electrochemical cell?

Answer 13

Volta

Question 14

How does a voltaic cell produce electrical energy?

Answer 14

by spontaneous redox reactions

Question 15

What occurs in a half-cell?

Answer 15

oxidation or reduction

Question 16

What is the purpose of a salt bridge

Answer 16

allows ions to pass from one half-cell to the other

Question 17

What is the electrolyte in a dry cell?

Answer 17

paste - MnO2, ZnCl2, NH4Cl, H2O, and graphite powder

Question 18

What is the electrolyte in a lead storage battery?

Answer 18

Sulfuric Acid (H2SO4 (aq))

Question 19

How is a lead battery recharged? Why can’t a lead storage battery be recharged indefinitely?

Answer 19

Through the reverse reaction

Due to the loss of lead sulfate to the bottom of the cells

Question 20

How do fuel cells work?

Answer 20

voltaic cells in which a fuel substance undergoes ox & red; from which electrical energy is continuously obtained

Question 21

How does hydrogen-oxygen fuel cell work? What are the products of hydrogen-oxygen fuel cells?

Answer 21

The combination of H and O2 to make water (H2O)

Question 22

What is needed for a redox reaction to be used as a source of electrical energy?

Answer 22

the two half reactions must be physically separated

Question 23

Which electrode (anode or cathode) is positive in an electrolytic cell? In a voltaic cell? What is the direction of electron flow in an electrolytic cell? In a voltaic cell? Where does ox & red occur in these cells?

Answer 23

electrolytic - anode +, cathode -; anode (ox) to cathode (red)

voltaic - anode -, cathode +; anode (ox) to cathode (red)

Question 24

What electrolyte can be used to electrolyze water?

Answer 24

H2SO4, KNO3; any electrolyte (aq) that is more easily ox or red than water

Question 25

What gas is produce at the cathode in the electrolysis of brine?

Answer 25

hydrogen gas (H2 (g)) is produced at the cathode in the electrolysis of brine

Question 26

What is electroplating? In electroplating, where is the object to be electroplating is placed?

Answer 26

the use of an electrolytic cell to deposit a thin layer of metal on an object

the object being electroplated is placed as the cathode