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CHEM 0970 Lecture Notes - Lecture 7: Alessandro Volta, Electrochemistry, Equilibrium Constant

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crimsonlizard934
27 Apr 2016
School
Pitt
Department
Chemistry
Course
CHEM 0970
Professor
Maleckar Susan

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Document Summary

Redox: an oxidation reaction and a reduction reaction are both taking place. You need to balance both the atoms and the charges: assign oxidation numbers & identify what"s being oxidized/reduced. H: +1 except when in a hydride (nah, lih, kh, etc. then h = -1) N gained electrons from i, n was reduced, i was the reducing agent. I was oxidized, lost electrons to n, n was the oxidizing agent: split reaction into 2 half reactions. + 2h+ + 1e- no2 + h2o: combine the 2 reactions, multiple each half reaction by _____ so that the electrons cancel, simplify by canceling out species that occur on both sides. + 2h+ + 1e- no2 + h2o] 6h2o + i2 + 10e- + 20h + 10no3 2io3 + 12h + 10e + 10no2 + 10h2o. Cl: goes from +4 to +3, gains electrons, reduced by o, o is reducing agent.

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Related Questions

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?


We used a Cu wire and 0.5 M HC2H3O2 in 0.5 M Na2SO4


In the electrolysis cell we shall study, the reduction reactionof interest will occur in a slightly acidic medium; hydrogen gaswill be produced by the reduction of hydrogen ion: 2H+ (aq) + 2e--> H2 (g)


Known:


Number of moles of hydrogen gas produced in eachtrial: Trial 1: 0.00197 moles; Trial 2: 0.001837moles


Moles of electrons (faradays) used to produce the hydogen gas ineach trial: Trial 1: 0.00394 moles e and Trial 2: 0.003674 molese


Possible reaction for the anode: Cu(s)--> Cu2+ (aq) + 2e Ered= -0.34

and cathode: So42- (aq) + 4H+ (aq) + 2e ---> H2SO3 (aq) + H2o(l) Ered= 0.20


Calculate the following:


1. Knowing the charge of the cations that are produced when themetal anode is oxidized, calculate the moles of metal that wereoxidized in each trial


2. From the loss of mass of the anode and the moles of anodethat were oxidized during the electrolysis, calculate the molarmass of the metal in each trial


3. Compare your molar mass result to the actual value anddiscuss the main sources of error


4. What is being reduced and what is being oxidized? Write thereduction and oxidation half reactions and the overall reaction


5. If 0.5 amps of current flowed for 10 minutes, what volume ofhydrogen gas would be produced at STP (standard temperature andpressure = 0 degrees celcius, 1 atm). Charge= current X time inseconds

HERE IS HOW THIS IS GOING TO WORK! IF YOU ANSWER THE QUESTIONS IWILL GIVE YOU THE 3K POINTS + MORE AFTER I REPOST IT.





2. The amount of heat involved in the synthesis of 1 mole of acompound from its elements, with all substances in their standardstates at 25*C, is called _________.


3. What is a valid unit for specific heat?


4. Use Hess's Law to find the heat of reaction in the examplebelow.

N2O4 (g) ----> 2NO2 (g)


Given that:

N2O4 (g) ----> N2 (g) + 2O2 (g) (Delta H =-9.7kJ)

2NO2 (g) ----> 2O2(g) + N2(g) ( Delta H= -67.7kJ)


5. Use Hess's Law to find the heat of reaction in the examplebelow. (Example doesn't exist btw.)


6. (Delta H) for the formation of rust (Fe2O3) is -826 kJ/mol. Howmuch energy is involved in the formation of 5 grams ofrust?


7. How many kilocalories of heat are required to raise thetemperature of 50g of aluminum from -5*C to 35*C? (Specific heat ofAluminum = 0.21 cal/g*C)


8.Calculate the (Delta H) for this reaction:


Zn(s) + Cu (2+ ion)(aq) ---> Zn(2+) + Cu(s)

(Delta H) for Cu(2+) = +64.4 kJ/Mol; (Delta H) for Zn(2+) = -152.4kJ/mol


9. The following equation shows the reaction that occurs whennitroglycerine explodes.

4C3H5O9N3 ----> 12CO2 + 6N2 + O2 +10H2O + 1725 Kcal


Is this reaction exothermic , endothermic, a combustion reaction ,or a combination reaction?


10. What does it mean for ammonia, (NH3) to have a (Delta H f) =-46 kJ/mol?

(for example: Define heat of formation. What does a negative heatof formation mean? what do the units of kJ/mol mean?)


11. What is the maximum amount of KCl that can dissolve in 500g ofwater?

(solubility of KCl is 34 g/ 100g of water at 20*C)


12.List the ways(operations) that can help make a substancedissolve faster in a solvent?


13. If a crystal added to an aqueous solution causes many particlesto come out of solution, the original solution was (saturate,unsaturated, supersaturated).


14. What is the number of moles of solute in 165 mL of a 0.82 Msolution?


15. What mass of NaCl is needed to make 350 mL of a 1.00 Msolution?


16. Colligative properties depend upon...


17. If one mole of each of these solutes in added to the sameamount of water, which solution has the highest boiling point?(glucose, aluminum sulfate, magnesium acetate, copper (I)chloride)


18. When an acid reacts with a base, what compounds areformed?


19. If the [H+] in a solution is 1x10^(-13) mol/L, what is the[OH-]?


20. If the [OH-] = 1x10^-6 mol/L, what is the pH of thesolution?


21. For a solution to be considered acidic what must be thehydrogen-ion concentration?


22. Which of the following represents a Bronsted-Lowry conjugateacid-base pair?

a) SO3(2-) and SO2 b) CO3(2-) and CO c) H3O and H2 d) NH4(+) and NH3


23. With solutions of "strong" acids and "strong" bases, the word"strong" refers to ...


24. What are the products of Al(OH)3 + H2CO3?


25.What is the concentration of hydrochloric acid if 5.0 mL of acidis neutralized by 30.0 mL of 2.00M sodium hydroxide.


26. At equilibrium, what is the rate of production of reactantscompared with the rate of production of products?


27. What is the equilibrium constant for the following reaction2SO3 ---> 2SO2 + O2


28. How does an increase in pressure affect the following reaction?2SO3 (g) --> 2SO2(g) +O2(g)


29.What stresses would shift the reaction to the right?

2SO3(g) ==> 2SO2(g) + O2(g)







30. The Keq of a reaction 4.9 x 10^(-7). Are products or reactantsfavored at equilibrium?


31. In which of these systems is the entropy decreasing?

a) air escaping from a tire b) snow melting c) a gas condensing d) salt dissolving inwater



32. If an atom is reduced in a redox reaction, what must occur toanother atom in the system?


33. Identify the oxidizing agent in the following reaction: 2Na + S---> Na2S


34. What are transferred in an oxidation -reductionreaction?


35. Give the oxidation number for each atom in KMnO4.


36. Which atom has a change in oxidation number of +4 in thefollowing reaction?

K2Cr2O7 + H2O + S ----> KOH + Cr2O3 +SO2


37. What is the oxidation number of sulfur in each of the following:

a. SO3 c.SO2(2-)

b. Na2SO4 d. S2O4 (2-)


38.Fe(3+) ----> Fe represents oxidation, reduction, orhydrolysis?


39. When the half reactions Br2+ 2e- -----> 2Br- and Na---->e- + Na(+) are combined the balanced redox equation is_____________________ ( WRITE the BALANCED REDOX eq)


40. To balance the oxygen and hydrogen for a redox reaction thattakes place in basic solution, it is necessary to use whichsubstance?


41. What particle completes this nuclear equation? 55/25 Mn + 2/1 H====> _____ +2 1/0 n


42. The half-life of tungsten-182 (182/74 W) is 1.1x10^(17) years.How long would it take for a 376.2 kg sample to decay until only123.0 grams remain?


43. After 3 days, the quantity of certain radioisotope is reducedfrom 13.6 grams to 1.9 grams. Calculate the half-life of theisotope.


44. What is the name of the compound having the formulaC8H18.


45. What is the name of the following compound:

O

//

CH3---CH2----CH---CH2--C

I \

CH3 OH


46. What is an isomer? Give an isomer of hexane (C6H14) and drawit's structure.


47. What is the name of the hydrocarbons with double covalentbonds?


48. Draw the stucture for 3-methylbutanoic acid.


49. Draw the structure for methylbenzene?


50. What is the name of the following compound:


Br

|

CH3----C-----CH3

|

CH3