Elechtrochemistry

Question 1

What is the historical term for reduction?

Answer 1

-Reduction historically is the process of producing metals from their compounds.

Question 2

What is the historical definition for oxidation?

Answer 2

-Oxidation is historically the process of a substance reacting with oxygen.

Question 3

What is a half reaction?

Answer 3

-It represents what is happening to one reactant in an overall reaction. It shows either a gain or loss of electrons by a substance.

Question 4

What is a gain of electrons called?

Answer 4

-Reduction.

Question 5

What is a loss of electrons called?

Answer 5

-Oxidation.

Question 6

What does the reducing agent do?

Answer 6

-The reducing agent causes reduction by losing (donating) electrons,
in this process the reducing agent is oxidized.
-The assassin (Ra) doesn’t get murdered itself it causes it.

Question 7

What does the oxidizing agent do?

Answer 7

-The oxidizing agent causes oxidation by gaining (taking) electrons, in this process the oxidizing agent is reduced.

Question 8

What is the difference between reduction+oxidation and the Oa and Ra’s themselves?

Answer 8

-Reduction and Oxidation are processes.
-Oa and Ra’s are chemical entities (species).

Question 9

What are the steps to construction complex half reactions? (HNO2aq–>NOg)

Answer 9

1. Write the chemical formulas for the reactants and products.
2. Balance all atoms, other than O and H .
3. Balance O by adding H2O(l).
4. Balance H by adding H+(aq).
5. Balance the charge on each side by adding e- and cancel anything that is on the same on both sides. (Don’t use whole numbers to equal out the electron amount).

Question 10

How do you know if there’s a spontaneous reaction or not?

Answer 10

-If the Oa is above the Ra in the redox table it’s spontaneous.

Question 11

What is a spontaneous reaction?

Answer 11

-In a spontaneous reaction a reaction occurs once reactions are placed in contact, without the continuous addition of energy.
-Occurs naturally without intervention or external energy.
-Oa above Ra on redox table.

Question 12

What are the steps for predicting simple redox reactions?

Answer 12

1. List all entities present and label possible oxidizing and reducing agent.
2. Identify the SOA using the chart and write the equation for its reduction (follow forward arrow).
3. Identify SRA using the chart and write the equation for its oxidation (follow the reverse arrow).
4. Balance the number of e- lost and gained in the half-reactions equations by multiply one or both by a number, then add the equations together to get the net ionic equation. (Don’t need to balance charges).
5. Predict spontaneity.

Question 13

What are some things to remember about predicting simple redox reactions?

Answer 13

-Aqueous solutions contain H2O(l) molecules.
-Acidic solutions contain H+(aq) ions.
-Basic solutions contain OH-(aq) ions.
-Some elements such as H2O(l) or Cu+(aq) may act as oxidizing OR reducing agents so label both possibilites.
-Some oxidizing and reducing agents are combinations such as MnO4-(aq) and H+(aq).

Question 14

What are diagnostic tests?

Answer 14

-A diagnostic test is a quick lab test with expected evidence, used to identify substances.
-The pop test is a diagnostic test for H2(g).
-A glowing splint reignites is a diagnostic test for O2(g).

Question 15

What is disproportionation?

Answer 15

-Disproportionation is a reaction in which a species is both oxidized and reduced.
-It may occur when a substance acts as both an Oa and a Ra.

Question 16

What are the steps for predicting complex reaction by constructing half-reactions? (TiO2(s) + V2+(aq) —> Ti(s) + V3+(aq))

Answer 16

1. Use info to start 2 half-reaction equations. (Skeleton half-reactions.)
2. Balance each half-reaction equation (use steps for balancing complex half-reactions, balance atoms, Os, Hs, charge, and cancel out similarities.)
3. Multiply each half reaction by whole numbers to balance the electrons.
4. Add the two half reactions equations, canceling the electrons and anything else that is on both sides.

Question 17

When do you have to predict complex reactions by constructing half reactions?

Answer 17

-When half reactions aren’t on the table you create them using similar steps to A2.

Question 18

What are some extra things about oxidation numbers that are important?

Answer 18

-An increase in oxidation number is oxidation
-A decrease in oxidation number is reduction
-If the oxidation numbers don’t change then a redox reaction has not occurred. (No transfer of electrons).

Question 19

What are the steps for balancing redox equations with oxidation numbers?

Answer 19

1. Assign oxidation numbers and identify the atoms/ions whose oxidation change.
2. Using the change in oxidation numbers, write the number of electrons transferred per atom.
3. Using the chemical formulas (subscripts) determine the number of electrons transferred per molecule.
4. Determine the whole number coefficients for the reactants that will balance the total number of electrons transferred. Then balance reactants and products except for O and H.
5. Balance O atoms with H2O(l) and then balance the H atoms with H+(aq).

Question 20

How to get average of titrants to do redox stoichometry?

Answer 20

-Add then up then divide by 3.

Question 21

What are titrants in redox stoichometry?

Answer 21

-The titrants is generally a strong Oa and Ra.

Question 22

What is an electrochemical cell?

Answer 22

An electrochemical cell is a device that continuously converts chemical energy into electric energy (electricity).

Question 23

What are the aspects of a voltaic cell?

Answer 23

-Spontaneous
-Sign of the E cell is (+) positive
-Sign of the cathode is (+) positive
-Sign of the anode is (-) negative
-Direction of electron movement is anode —> cathode
-Direction of ion movement is cations (positive) —> cathode
-Possess a salt bridge which allows ions to be exchanged between 2 electrolytes but prevents them from mixing.
-A voltaic cell consists of 2 half cells separated by a porous boundary. Each half cell consists of an electrode and an electrolyte.
-At the cathode the SOA undergoes reduction.
-At the anode the SRA undergoes oxidation.

Question 24

What are the aspects of an electrolytic cell?

Answer 24

-Non spontaneous (SRA is above SOA on redox table).
-Sign of the E cell is (-) negative
-Sign of the cathode is (-) negative
-Sign of the anode is (+) positive
-SOA undergoes reduction at the cathode
-Direction of electron movement is from anode —> cathode
-Direction of ion movement is cations (positive) —> cathode
-Since the reaction is nonspon it requires electricity to function, (Usually from a power supply to push electrons from anode to cathode).
-Both electrodes are in one electrolyte (no salt bridge).

Question 25

What is the point of a salt bridge?

Answer 25

-When negative ions move from anode to cathode the cathode gets more negative and will cause the cell to break. The salt bridge pulls positive ions towards (+) side and negative towards (-) side.

Question 26

What are inert electrons?

Answer 26

-In some cases a half reactions doesn’t have a Oa or Ra that is a metallic solid. In this case an inert electron is used. -Provides a location to connect a wire on which the half reaction can occur. -Common examples are C(s) (graphite) or Pt(s). -Don’t need an inert electron if the half reactions have a metalloid.

Question 27

What is cell potential?

Answer 27

-The cell potential is the maximum electric potential difference (V) of the cell when operating under standard conditions. -E cell = Er (cathode) - Er (anode)

Question 28

What are fuel cell?

Answer 28

-In a fuel cell fuel and oxygen are continuously supplied to the cell and waste products are removed. -In all other respects it’s voltaic. -Cells in a battery are usually sealed, unlike in a fuel cell.

Question 29

What is the chloride anomaly?

Answer 29

-For electrolysis solutions containing chloride ion, the chloride ion acts as the SRA, even though the table indicates that it shouldn’t be. (Electrolytic cells only).

Question 30

What is corrosion?

Answer 30

-Corrosion is an electrochemical process in which a metal is oxidized by substances in the environment, returning the metal to an ore like state. -In general any metal appearing below the various oxygen half reactions in the redox table will be oxidized in our environment.

Question 31

What is the protective coatings strategy? (Corrosion prevention strategies)

Answer 31

-The metal to be protected can be coated with paint, plastic, or other metals (ex. Zn or Sn). -Iron has been galvanized when it has been coated with a layer of Zn. Zn is a stronger Ra than Fe so it’s oxidized first, which means the Zn will be corroded rather than the iron it’s protecting.

Question 32

What is the sacrificial anode strategy of corrosion prevention?

Answer 32

-A sacrificial anode is a metal that is more easily oxidized than Fe(s). It’s connected to the iron to protect it. The iron will be become the cathode where oxidation can’t happen. -Commonly used for ships, underground tanks, and hot water heaters.

Question 33

What is the cathodic protection strategy (Corrosion prevention strategy).

Answer 33

-In cathodic protection, as in a sacrificial anode, the iron is forced to become the cathode of the cell. In this case it’s accomplished by supplying the iron with electrons. -System is turned into an electrolytic cell with a small electric current applied. Electrons are directed towards the iron making it the cathode. Since reduction takes place at the cathode the iron cannot be oxidized. -Common examples include pipelines, or supercars.