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CHMA11H3 Chapter Notes - Chapter 18: Electrochemistry, Nernst Equation, Electroplating

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viridianworm635
12 Jun 2016
School
UTSC
Department
Chemistry
Course
CHMA11H3
Professor
Heinz- Bernhard Kraatz

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CHMA11H3 Full Course Notes
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Document Summary

Oxidation process that occurs when: oxidation number of an element increases, an element loses electrons, a cmpd adds oxygen, a cmpd loses hydrogen, a half-rxn has e- as products. Reduction process that occurs when: oxidation number of element decreases, an element gains electrons, a cmpd loses oxygen, a cmpd gains hydrogen, a half-rxn has e- as reactants. Agent (in general) facilitates a process. Oxidizing reagents promotes/facilitates oxidation process: undergoes reduction to facilitate oxidation. Reducing reagents promotes/facilitates reduction process: undergoes oxidation to facilitate reduction. Redox rxns involve the transfer of e- (current) from one substance to another. Therefore, redox rxns have the potential to generate an electric current. To use that current, we need to separate the place when oxy is occurring from the place where redu is occurring: if not separated, no efficient flow of e- Not making use of the potential e: separation prevents mixing of 2 sol"ns (cid:0) allows efficient flow of e-

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Related Questions

Answer true or false.

(a) When a substance is oxidized, it loses electrons.

(b) When a substance gains electrons, it is reduced.

(c) In a redox reaction, the oxidizing agent becomes reduced.

(d) In a redox reaction. the reducing agent becomes oxidized.

(e) When Zn is converted to Zn2+ ion, zinc is oxidized.

(f) Oxidation can also be defined as the loss of oxygen atoms and/or gain of hydrogen atoms.

(g) Reduction can also be defined as the gain of oxygen atoms and/or loss of hydrogen atoms.

(h) When oxygen, O2, is converted to hydrogen peroxide, H2O2, we say that O2 is reduced.

(i) Hydrogen peroxide, H2O2, is an oxidizing agent.

(j) All combustion reactions are redox reactions.

(k) The products of complete combustion (oxidation) of hydrocarbon fuels are carbon dioxide, water, and heat.

(l) In the combustion of hydrocarbon fuels, oxygen is the oxidizing agent and the hydrocarbon fuel is the reducing agent.

(m) Incomplete combustion of hydrocarbon fuels can produce significant amounts of carbon monoxide.

(n) Most common bleaches are oxidizing agents.

 

1. (1 point) What are transferred in an oxidation-reduction reaction? *

• atoms

• electrons

• ions

• protons

2. (1 point) In the reaction of beryllium with fluorine, which atom is oxidized? *

• fluorine

• beryllium

• neither of them

• both of them

3. (1 point) Ag - - > Ag ^+ +1 e^- This equation represents the type of reaction called _____. *

• hydrolysis

• oxidation

• redox

• reduction

4. (1 point) What is the reducing agent in the following reaction? 2K + S - - > K2S *

• K

• S

• K2S

• None of the above

5. (1 point) The oxidation number of oxygen when it is in a compound other than a peroxide is ____. *

• -2

• -1

• 0

• +2

6. (1 point) What is the oxidation number for each atom in NH4F? *

• N=+3, H=-4, F=+1

• N=-3, H=+1, F=-1

• N=+3, H+1, F=-1

• N=-3, H=-1, F=+1

7. (1 point) Which atom has a change in oxidation number of +4 in the following redox reaction?K2Cr2O7 + H2O + S - - > KOH + Cr2O3 + SO2 *

• K

• Cr

• O

• S

Metal activity series for question 8

8. (1 point) Of the following metals, which ions are most easily reduced? Use the above table to answer the question. *

• magnesium

• lead

• copper

• sodium

9. (1 point) In a zinc-copper cell, Zn(s) | Zn^+2(1M) || Cu^+2(1M) | Cu(s), which electrode is positive? *

• Cu^+2

• Cu(s)

• Zn(s)

• Zn^+2

10. (1 point) How must a redox reaction that is to be used as a source of electrical energy be set up? *

• One half reaction must involve two metals.

• Two half reactions must use a metal wire electrodes.

• One half reactions must involve more than one electron.

• Two half reactions must be physically separated.

11. (1 point) In a voltaic cell at which electrode does reduction occur? *

• anode only

• cathode only

• both anode and cathode

• Either anode or cathode , depending on the metal

12. (1 point) What assures that there is no charge build up in a voltaic cell as oxidation and reduction occur? *

• one of the half cells

• the electrolyte solutions

• the moving electrons

• the salt bridge

13. (1 point) In the most common dry cell what material is the electrode that is the center rod made of? *

• copper

• graphite

• lead

• zinc

14. (1 point) To charge a lead storage battery you must ________. *

• apply a direct current to it.

• hold a magnet close to it.

• Use alternating current through it.

• increase the oxygen in it.

15. (1 point) In a hydrogen- oxygen fuel cell ______________. *

• hydrogen diffuses through the cathode.

• hydrogen and oxygen are mixed before entering the anode.

• oxygen diffuses through the anode.

• oxygen diffuses through the cathode.

16. (1 point) When electrical energy is used to cause a chemical reaction we call this process _____. *

• electronation

• electrolysis

• hydration

• reduction

17. (1 point) Which of the following is true about an electrolytic cell? *

• It changes chemical energy into electrical energy.

• It is the type of cell used in electrocution

• It uses an electric current to make a nonspontaneous reaction go.

• All of the above

18. (1 point) The products formed in the net reaction of the electrolysis of water are ____. *

• aqueous hydrogen ion and hydroxyl ion

• hydrogen gas and oxygen gas

• hydrogen gas and liquid oxygen

• water vapor

19. (1 point) What occurs in electroplating? *

• decomposition of an ionic compound

• decomposition of a salt layer

• deposition of a metal layer on a material

• deposition of a salt layer on a metal

Open response Questions : Answer questions 20 through 22 in complete sentences

20. ( 5 points) Write the equation for the reaction of calcium and oxygen ( 1 point). Write the oxidation numbers for both the reactants and the products ( 2 points) What is the reducing agent and why? ( 2 points)

21. ( 5 points) Tell how a voltaic cell works. Be sure to mention the various parts of the voltaic cell and what they have to do with how it works.

22. (4 points) What are the signs given to the electrodes in both the voltaic and electrolytic cells? What reaction (oxidation or reduction) is occurring at each?