CHEM-C 243 Lecture Notes - Lecture 18: Line Notation, Strong Electrolyte, Faraday Constant

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plumhorse517

25 Aug 2016

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Department

Chemistry

Course

CHEM-C 243

Professor

Neil Rapp

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Section 1- balancing oxidation-reduction equations: oxidation-reduction (redox) reactions- electron transfer reactions. Results in generation of electric current (electricity) or caused by imposing an electric current. Oxidation- loss of electron(s) by a species; increase in oxidation number; increase in oxygen. Reduction- gain of electron(s) by a species; decrease in oxidation number; increase in hydrogen: electrochemical processes- redox reactions in which: Energy released by a spontaneous reaction is converted to electricity. Electrical energy is used to cause a nonspontaneous reaction to occur: red exponents are oxidation numbers, half-reaction- overall reaction is split into two half-reactions, one involving oxidation and one reduction. Reduction- note: stays: half-reaction method for balancing redox reactions in acidic solution. Some reactions do not balance just using coefficients; electrons do not always balance by running reactions once. Write separate equations for oxidation and reduction half-reactions. For nonbasic aqueous solutions: balance by adding ; if you need 3 oxygens, add 3 waters.

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Having trouble with my Pre-Lab questions I don't understand how to get them.

Introduction An important type of reaction mechanism is the transfer of electrons from one species to another effecting a change in oxidation state. This gain or loss of electrons is referred to as reduction and oxidation, respectively. For example, consider the two balanced, chemical equations (1 & 2) that follow Cu (s) D Cu (aq) 2e (1) Cl2(aq) 2e D 2Cl (aq) (2) The first equation (1) shows elemental copper metal with a oxidation state of zero forming aqueous copper(Il) ions having an oxidation state of +2. This gain in oxidation number, 0 to +2, is called oxidation. The second equation (2) show elemental chlorine having an oxidation state of zero forming chloride ions in aqueous solution with an oxidation state of This decrease in oxidation number, 0 to -1, is called reduction. In any chemical reaction, the electrons gained or lost are conserved, i.e.. there is no net gain or loss of electrons. In fact, the two reactions illustrated above could occur simultaneously with the electrons lost by copper, gained by the chlorine in aqueous solution. Since the copper provides the electrons that subsequently reduce the chlorine copper is referred to as the reducing agent. Likewise, since the chlorine is accepting the electrons from copper, which subsequently oxidizes the copper, chlorine is referred to as he oxidizing agent. The two reactions above (1 & 2) are called half-reactions, as much as they each constitute one-half of the total reaction Equation 1 is the oxidation half reaction showing Cu(s) losing two electrons. In Equation 2, Cla(aq) gains two electrons and is the reduction half-reaction. If these two half-reaction are added together the result is the total oxidation-reduction reaction or "redox" reaction. Adding the two equations yields (3). Cu(s) Cl2(aq) D Cu (aq) 2CI (aq) (3) Whether or not the above reaction is spontaneous proceeds from reactants to products without input of energy into the system, may be determined by observing the reaction mixture if the reactants and products differ greatly in their appearance. Copper metal is a bright copper color and chlorine in aqueous solution will appear yellow. The Cu ion may turn the liquid part of the mixture blue, however, the Cris colorless and cannot be observed directly. Copper, like many of the transition metals, exhibits a variety of oxidation states depending upon the chemical environment in which it is found. In a strong reducing environment copper may exist as the free metal, Cu(s). An example of such a situation is illustrated in the following chemical equation (4). 4Cuo(s) CH4(g) D 4Cu(s) CO2(g) 2H2O(l) (4)

I need help with questions 2-4 I can't figure them out.

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

â¢ atoms

â¢ electrons

â¢ ions

â¢ protons

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

â¢ fluorine

â¢ beryllium

â¢ neither of them

â¢ both of them

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

â¢ hydrolysis

â¢ oxidation

â¢ redox

â¢ reduction

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

â¢ K

â¢ S

â¢ K2S

â¢ None of the above

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

â¢ -2

â¢ -1

â¢ 0

â¢ +2

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

â¢ N=+3, H=-4, F=+1

â¢ N=-3, H=+1, F=-1

â¢ N=+3, H+1, F=-1

â¢ 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 *

â¢ K

â¢ Cr

â¢ O

â¢ 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. *

â¢ magnesium

â¢ lead

â¢ copper

â¢ sodium

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

â¢ Cu^+2

â¢ Cu(s)

â¢ Zn(s)

â¢ Zn^+2

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

â¢ One half reaction must involve two metals.

â¢ Two half reactions must use a metal wire electrodes.

â¢ One half reactions must involve more than one electron.

â¢ Two half reactions must be physically separated.

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

â¢ anode only

â¢ cathode only

â¢ both anode and cathode

â¢ 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? *

â¢ one of the half cells

â¢ the electrolyte solutions

â¢ the moving electrons

â¢ the salt bridge

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

â¢ copper

â¢ graphite

â¢ lead

â¢ zinc

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

â¢ apply a direct current to it.

â¢ hold a magnet close to it.

â¢ Use alternating current through it.

â¢ increase the oxygen in it.

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

â¢ hydrogen diffuses through the cathode.

â¢ hydrogen and oxygen are mixed before entering the anode.

â¢ oxygen diffuses through the anode.

â¢ oxygen diffuses through the cathode.

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

â¢ electronation

â¢ electrolysis

â¢ hydration

â¢ reduction

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

â¢ It changes chemical energy into electrical energy.

â¢ It is the type of cell used in electrocution

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

â¢ All of the above

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

â¢ aqueous hydrogen ion and hydroxyl ion

â¢ hydrogen gas and oxygen gas

â¢ hydrogen gas and liquid oxygen

â¢ water vapor

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

â¢ decomposition of an ionic compound

â¢ decomposition of a salt layer

â¢ deposition of a metal layer on a material

â¢ 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?

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CHEM-C 243 Lecture Notes - Lecture 18: Line Notation, Strong Electrolyte, Faraday Constant

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