ChemCom 2013

2 Warm Up: Determine the name and molar mass of the following compounds. NaOH MnO 2 H 2 SO 4

3 How did you do? NaOH g/mol, sodium hydroxide MnO g/mol, Manganese (IV) oxide H 2 SO g/mol, Sulfuric acid Be sure you go back and review the basics…

ELECTROCHEMISTRY

Electron Transfer Reactions Electron transfer reactions are oxidation-reduction or redox reactions.Electron transfer reactions are oxidation-reduction or redox reactions. Result in the generation of an electric current (electricity) or be caused by imposing an electric current.Result in the generation of an electric current (electricity) or be caused by imposing an electric current. This field of chemistry is often called ELECTROCHEMISTRY.This field of chemistry is often called ELECTROCHEMISTRY.

Terminology for Redox Reactions OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen.OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen. REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen.REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen. OXIDIZING AGENT—electron acceptor; species is reduced.OXIDIZING AGENT—electron acceptor; species is reduced. REDUCING AGENT—electron donor; species is oxidized.REDUCING AGENT—electron donor; species is oxidized. OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen.OXIDATION—loss of electron(s) by a species; increase in oxidation number; increase in oxygen. REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen.REDUCTION—gain of electron(s); decrease in oxidation number; decrease in oxygen; increase in hydrogen. OXIDIZING AGENT—electron acceptor; species is reduced.OXIDIZING AGENT—electron acceptor; species is reduced. REDUCING AGENT—electron donor; species is oxidized.REDUCING AGENT—electron donor; species is oxidized.

You can’t have one… without the other! Reduction (gaining electrons) can’t happen without an oxidation to provide the electrons. You can’t have 2 oxidations or 2 reductions in the same equation. Reduction has to occur at the cost of oxidation LEO the lion says GER! GER!

Another way to remember OIL RIG

OXIDATION-REDUCTION REACTIONS Direct Redox Reaction Oxidizing and reducing agents in direct contact. Cu(s) + 2 Ag + (aq) ---> Cu 2+ (aq) + 2 Ag(s)

OXIDATION-REDUCTION REACTIONS Indirect Redox Reaction A battery functions by transferring electrons through an external wire from the reducing agent to the oxidizing agent.

BatteriesBatteries An apparatus that allows a redox reaction to occur by transferring electrons through an external connector.An apparatus that allows a redox reaction to occur by transferring electrons through an external connector. Product favored reactionProduct favored reaction voltaic or galvanic cell results in electric current Reactant favored reactionReactant favored reaction electrolytic cell electric current used to cause chemical change. Batteries are voltaic cells

Warm Up- Write the formulas 1.Calcium hydroxide 2.Carbon monoxide 3.Iron (III) chloride 4.Copper (II) nitrate 5.Sulfur tetroxide 12

AnodeCathode Basic Concepts of Electrochemical Cells

Direct Redox Reaction With time, Cu plates out onto Zn metal strip, and Zn strip “disappears.” Corrodes away With time, Cu plates out onto Zn metal strip, and Zn strip “disappears.” Corrodes away Zn is oxidized and is the reducing agent Zn(s) ---> Zn 2+ (aq) + 2e-Zn is oxidized and is the reducing agent Zn(s) ---> Zn 2+ (aq) + 2e- Cu 2+ is reduced and is the oxidizing agent Cu 2+ (aq) + 2e- ---> Cu(s)Cu 2+ is reduced and is the oxidizing agent Cu 2+ (aq) + 2e- ---> Cu(s)

To obtain a useful current, we separate the oxidizing and reducing agents so that electron transfer occurs thru an external wire.To obtain a useful current, we separate the oxidizing and reducing agents so that electron transfer occurs thru an external wire. CHEMICAL CHANGE ---> ELECTRIC CURRENT This is accomplished in a GALVANIC or VOLTAIC cell. A group of such cells is called a battery.

Electrons travel thru external wire. Electrons travel thru external wire. Salt bridge allows anions and cations to move between electrode compartments.Salt bridge allows anions and cations to move between electrode compartments. Electrons travel thru external wire. Electrons travel thru external wire. Salt bridge allows anions and cations to move between electrode compartments.Salt bridge allows anions and cations to move between electrode compartments. Zn --> Zn e- Cu e- --> Cu <--AnionsCations--> OxidationAnodeNegativeOxidationAnodeNegative Reduction Cathode Positive Reduction Cathode Positive RED CAT

Terms Used for Voltaic Cells

OK… that was a lot… Let’s take a little break and do a cool lab

Do the lab on a separate piece of paper… be sure I get the class set of instructions back! 1.Write the title: Striking it Rich 2.Write the purpose 3.Make a materials list as you do the lab 4.Draw the table that is on the bottom of the page and fill it in as you do the lab. 5.Answer all the questions on the back of the page… you do NOT need to write a conclucing paragraph!

The Procedure 1.Clean 3 pennies using the HCl on the demo desk. 2.Get 4g of granular zinc. 3.Get 25mL of Zinc Chloride solution 4.Put the zinc and ZnCl 2 in the 100ml beaker. 5.Put 2 of the 3 pennies in the beaker and place it on the hotplate. 6.Let the pennies react until they turn a different color. 7.Carefully wave one of your coated pennies over a flame.

Warm Up (10 minutes) Make sure that your lab is complete… Answer all the questions on the back! Debrief the lab… Collect….

Science Choices

Another Lab…Yea!

Warm Up Write and complete the following sentences with these words. Gains, loses, anode, cathode, red, black. 1.Oxidation is when a metal __________ electrons, it takes place at the ________ which is ___________ in color. 2.Reduction is when a metal __________ electrons, it takes place at the ________ which is ___________ in color.

Finish the lab Turn it in!

Have you ever wondered about the voltage on various batteries? 1.7 Volts12.6 Volts

CELL POTENTIAL, E For Zn/Cu cell, potential is V at 25 ˚C and when [Zn 2+ ] and [Cu 2+ ] = 1.0 M.For Zn/Cu cell, potential is V at 25 ˚C and when [Zn 2+ ] and [Cu 2+ ] = 1.0 M. This is the STANDARD CELL POTENTIAL, E oThis is the STANDARD CELL POTENTIAL, E o a quantitative measure of the tendency of reactants to proceed to products when all are in their standard states at 25 ˚C.a quantitative measure of the tendency of reactants to proceed to products when all are in their standard states at 25 ˚C.

Calculating Cell Voltage Balanced half-reactions can be added together to get overall, balanced equation.Balanced half-reactions can be added together to get overall, balanced equation. Zn(s) ---> Zn 2+ (aq) + 2e- Cu 2+ (aq) + 2e- ---> Cu(s) Cu 2+ (aq) + Zn(s) ---> Zn 2+ (aq) + Cu(s) Zn(s) ---> Zn 2+ (aq) + 2e- Cu 2+ (aq) + 2e- ---> Cu(s) Cu 2+ (aq) + Zn(s) ---> Zn 2+ (aq) + Cu(s) If we know E o for each half-reaction, we could get E o for net reaction.

TABLE OF STANDARD REDUCTION POTENTIALS 2 E o (V) Cu e- Cu H + + 2e- H0.00 Zn e- Zn-0.76 oxidizing ability of ion reducing ability of element To determine an oxidation from a reduction table, just take the opposite sign of the reduction!

Zn/Cu Electrochemical Cell Zn(s) ---> Zn 2+ (aq) + 2e-E o = V Cu 2+ (aq) + 2e- ---> Cu(s)E o = V Cu 2+ (aq) + Zn(s) ---> Zn 2+ (aq) + Cu(s) E o = V E o = V Cathode, positive, sink for electrons Anode, negative, source of electrons +

Cd --> Cd e- or Cd e- --> Cd Fe --> Fe e- or Fe e- --> Fe E o for a Voltaic Cell All ingredients are present. Which way does reaction proceed?

From the table, you see Fe is a better reducing agent than Cd. Why?Fe is a better reducing agent than Cd. Why? Cd 2+ is a better oxidizing agent than Fe 2+ Why?Cd 2+ is a better oxidizing agent than Fe 2+ Why? E o for a Voltaic Cell

More About Calculating Cell Voltage Assume I - ion can reduce water. 2 H 2 O + 2e- ---> H OH - Cathode 2 I - ---> I 2 + 2e- Anode I H 2 O --> I OH - + H 2 2 H 2 O + 2e- ---> H OH - Cathode 2 I - ---> I 2 + 2e- Anode I H 2 O --> I OH - + H 2 Assuming reaction occurs as written, E˚ = E˚ cat + E˚ an = ( V) - ( V) = V Minus E˚ means rxn. occurs in opposite direction (the connection is backwards or you are recharging the battery)

Lead Storage Battery Anode (-) E o = V Pb + HSO > PbSO 4 + H + + 2e- Cathode (+) E o = V PbO 2 + HSO H + + 2e- ---> PbSO H 2 O

Charging a Battery When you charge a battery, you are forcing the electrons backwards (from the + to the -). To do this, you will need a higher voltage backwards than forwards. This is why the ammeter in your car often goes slightly higher while your battery is charging, and then returns to normal. In your car, the battery charger is called an alternator. If you have a dead battery, it could be the battery needs to be replaced OR the alternator is not charging the battery properly.

Dry Cell Battery Anode (-) Zn ---> Zn e- Zn ---> Zn e- Cathode (+) 2 NH e- --> 2 NH 3 + H 2 2 NH e- --> 2 NH 3 + H 2

Alkaline Battery Nearly same reactions as in common dry cell, but under basic conditions. Anode (-): Zn + 2 OH - --> ZnO + H 2 O + 2e- Cathode (+): 2 MnO 2 + H 2 O + 2e- --> Mn 2 O OH -

Mercury Battery

Anode: Zn is reducing agent under basic conditions Cathode: HgO + H 2 O + 2e- ---> Hg + 2 OH -

Ni-Cad Battery Anode (-) Cd + 2 OH - ---> Cd(OH) 2 + 2e- Cathode (+) NiO(OH) + H 2 O + e- ---> Ni(OH) 2 + OH -

Ni-Cad Battery

H 2 as a Fuel Cars can use electricity generated by H 2 /O 2 fuel cells. H 2 carried in tanks or generated from hydrocarbons

Warm Up a.Draw a voltaic cell that would have Magnesium and Iron metal and Mg 2+ and Fe 2+ ions. b.Using the table on p.453, determine which metal would be oxidized and which would be reduced. c.Label the anode and the cathode. d.Draw an arrow indicating the flow of electrons. e.Write the half reactions. f.How would we determine the voltage??

Electrolysis describes what happens in an electrolytic cell means to use electricity to make chemicals. Many elements are “made” by electrolysis Pb Al Zn Na K Li H 2 Cl 2 F 2 I 2 O 2

Aluminum Production by Electrolysis Name of the Ore imported from (Guinea and Brazil) Bauxite Al 2 O 3. 3H 2 O Heating drives off the water Al 2 O 3. 3H 2 O + Heat →Al 2 O 3 +3H 2 O Melting point of Bauxite is C This is too hot! Cryolite is added Lowers the melting point to C

Reduction of water You cannot reduce Aluminum in water! It must be molten!

CC DC Power - + DC Power - + Al 3+ O 2- - Reduction Cathode Al e - → Al (s) + Oxidation Anode O 2- → 1 / 2 O 2(g) + 2e - Liquid Al floats to the top and is removed Oxygen gas Al 2 O 3(l) Cation Cathode ReductionAnion Anode Oxidation

Au + CN - Au + CN - Electroplating Au plating a Cu penny Electroplating is the process of reducing a metal on to the surface of another Electrolyte:Must contain the ion of the metal that plates Cathode:The metal to be covered with a new metal Anode:Metal to be plated on top the other metal DC Power - + DC Power - + Au + Oxidation Anode Au (s) → Au + + 1e - e-e- - Reduction Cathode Au + + e - → Au (s) Cu

AuCN -ve +ve stainless steel or Au

Au plated

Copper RingGold Plated

Ready for your Quiz???

Zn +2 NO 3 - Zn +2 NO 3 - Electroplating Zn plating a Penny DC Power - + DC Power - + Zn + Oxidation Anode Zn (s) → Zn e - e-e- Reduction Cathode Zn e - → Zn (s) $1 e-

Electrorefinning Lead Trail, B.C. Teck 16 mines in BC Major World Producer of Zn, Cu, Pb, and Coal

The Electrorefinning of Lead Electrorefining is the process of purifying a metal by electrolysis. The electrolyte must contain Pb Impure metal is oxidized at the anode and pure metal is reduced at the cathode. This is the same as electroplating. DC Power - + DC Power - + Pb 2+ NO Reduction Cathode Pb e - → Pb (s ) Cathode: Pure Pb Anode: Impure Pb

Lead Refinery-Trail

Zn oxidizes Ag does not oxidize Pb oxidizes Au does not oxidize At the Anode The voltage is controlled so that:

Pb 2+ reduces At the Cathode Zn 2+ does not reduce The voltage is controlled so that:

The Electrorefinning of Lead Electrorefining is the process of purifying a metal by electrolysis. The electrolyte must contain Pb Impure metal is oxidized at the anode and pure metal is reduced at the cathode. This is the same as electroplating. DC Power - + DC Power - + Pb 2+ NO Reduction Cathode Pb e - → Pb (s ) Cathode: Pure PbAnode: Impure Pb + Oxidation Anode Zn (s) → Zn e - Pb (s) → Pb e - Zn 2+ AuAg Solid Au and Cu are released from the anode and fall to the bottom