Redox Reactions
description
Transcript of Redox Reactions
![Page 1: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/1.jpg)
Redox Reactions
Or How Batteries Work
![Page 2: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/2.jpg)
REDOX Reactions• The simultaneous transfer of electrons between chemical
species.– Actually 2 different reactions occurring at the same time.
Oxidation: a loss of electronsReduction: a gain of electrons
![Page 3: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/3.jpg)
ReDox
Na +Cl NaCl
Nao +Clo Na+Cl-
Which element was Oxidized?Na
Which element was Reduced?Cl
![Page 4: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/4.jpg)
How do we remember ReDox?
mnemonics
![Page 5: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/5.jpg)
5
LEO growls GER
Losing Electrons Oxidation
Gaining Electrons Reduction
![Page 6: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/6.jpg)
Turn to Page 5
![Page 7: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/7.jpg)
7
OIL RIG
OxidationIsLosing
ReductionIsGaining
![Page 8: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/8.jpg)
How do we know if there is aRedOx Reaction occurring?
We first must find the Oxidation states.
![Page 9: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/9.jpg)
What is the oxidation state of each of the following species?
•Cl in Cl2
• 0•Mg in MgO• +2•Na in NaBr• +1
•F in SrF2
• -1•Sr in SrF2
• +2•O in O2
• 0
![Page 10: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/10.jpg)
10J Deutsch 2003
Regents Question
Which particles are gained and lost during a redox reaction?
(1)Electrons
(2) Protons
(3) Neutrons
(4) Positrons
![Page 11: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/11.jpg)
11J Deutsch 2003
Regents QuestionAs a Ca atom undergoes oxidation to Ca2+, the number
of neutrons in its nucleus
(1)Decreases
(2) Increases
(3) Remains the same
![Page 12: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/12.jpg)
Turn to Page 6
![Page 13: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/13.jpg)
Rules for Determining Oxidation Numbers
1. Free Elements have an oxidation number of zero. Ex: Na, S8, H2
2. All Metals in group 1 have a +1 Oxidation # in compounds. Ex: Na, K, Li
3. All Metals in group 2 have a +2 Oxidation # in compounds. Ex: Mg, Ca, Ba
4. Oxygen has a –2 Oxidation Number1. Unless it is in a Peroxide like H2O2
![Page 14: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/14.jpg)
Continued Rules
5. Hydrogen has a +1 oxidation #.6. Halogens have a -1 oxidation #.7. For any neutral compound, the sum of the
oxidation numbers of the atoms in the compound must equal zero. For ex: H2SO4
8. For a polyatomic ion, the sum of the oxidation #’s must equal the ionic charge of the ion. Ex: SO4 2-
![Page 15: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/15.jpg)
CuF2 PBr3
HNO3 C2O4-2
SO4-2 CO3-2
C12H22O11 H2O
![Page 16: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/16.jpg)
Turn to Page 7
![Page 17: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/17.jpg)
Now we will take a deeper look into Oxidation.
• Can be defined as:– The loss of electrons– The gain of oxygen– The loss of hydrogen
![Page 18: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/18.jpg)
OXIDATION• The loss of electrons
Na(s) Na+ + e-
The sodium ion has been oxidized to the sodium cation.
Na + Cl
Sodium loses electron to chlorine
-ClNa +
+
![Page 19: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/19.jpg)
OXIDATION
• Gain of oxygen– Combustion reactions
are classic examplesC(s) + O2(g) CO2(g)
(burning of coal)
2Fe(s) + 3O2(g) 2Fe2O3(s)
(rusting of iron)
![Page 20: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/20.jpg)
OXIDATION
• Loss of hydrogen– Oxidation can sometimes be best seen as the loss
of hydrogenCH3OH(l) CH2O(l) + H2(g)
Methyl alcohol has been oxidized into formaldehyde
![Page 21: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/21.jpg)
Which one of the following elements were oxidized?
•Cl in Cl2
• 0 → NO•Mg in MgO• +2 → YES•Na in NaBr• +1 → YES
•F in SrF2
• -1 → NO•Sr in SrF2
• +2 → YES•O in O2
• 0 → NO
![Page 22: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/22.jpg)
Turn to Page 8
![Page 23: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/23.jpg)
Now we will take a deeper look into Reduction.
• 3 Definitions
– The gain of electrons– The loss of oxygen– The gain of hydrogen
![Page 24: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/24.jpg)
Gain of electrons– The process of silver
electroplating
Ag+ + e- Ag
Silver cation has gained an electron and has been reduced to silver metal.
REDUCTION
![Page 25: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/25.jpg)
REDUCTION
Loss of oxygen – Reduction can also be seen as the loss
of oxygen in going from reactant to product.
Fe2O2 (s) + 3 CO (g) 2 Fe(s) + 3 CO2(g)
Iron ore is reduced to iron metal in a blast furnace with carbon monoxide
![Page 26: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/26.jpg)
REDUCTION• Gain of hydrogen
A reduction can also be described as the gain of hydrogen atoms going from reactant to product.
CO(g) + 2 H2(g) CH3OH(l)
Carbon monoxide has been reduced to methyl alcohol
![Page 27: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/27.jpg)
One’s loss is another’s gain
• Neither oxidation or reduction can take place without the other.– When those electrons are lost something else has
to gain them.
When trying to remember which is which think of LEO the lion goes GER OIL RIG
Lose Electrons Oxidation Oxidation is LosingGain Electrons Reduction Reduction is Gaining
![Page 28: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/28.jpg)
Turn to Page 9
![Page 29: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/29.jpg)
Use a chart to determineOxidation States.
Elements
Oxidation State
Number of Atoms
Total Charge
![Page 30: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/30.jpg)
First we will do K2PtCl6
Elements K Pt Cl Sum of Oxidation States
Oxidation State
Number of Atoms
Total Charge
![Page 31: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/31.jpg)
Now do the following:
• What is the oxidation state of S in MgSO4?
• What is the oxidation state of N in NaNO3?
• What is the oxidation state of Cl in KClO3?
![Page 32: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/32.jpg)
Now do the following:
• What is the oxidation state of C in CO3-
• What is the oxidation state of Cl in ClO2-
• What is the oxidation state of Cr in CrO42-
• What is the oxidation state of Cr in CrO72-
![Page 33: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/33.jpg)
Packet Page 10-11
![Page 34: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/34.jpg)
Review of Terms
• oxidation-reduction (redox) reaction:–involves a transfer of electrons from the reducing agent to the oxidizing agent.
• oxidation: loss of electrons• reduction: gain of electrons•Reducing Agent get oxidized•Oxidizing agent get reduced
![Page 35: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/35.jpg)
Packet Page 12-13
![Page 36: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/36.jpg)
An oxidation-reduction, (redox), reaction involves the transfer of electrons.
The oxidation numbers of the atoms will change…. one goes up (oxidation) and one goes down (reduction)
Sodium transfers its electrons to chlorine
![Page 37: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/37.jpg)
Reduction is the gain of electrons.
Nonmetals gain electrons to form – ionsThe oxidation number goes down (reduces)
![Page 38: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/38.jpg)
A half-reaction can be written to represent reduction.
Cl0 + 1e- Cl-1
In reduction half reactions, electrons are written on the left because electrons are gained
![Page 39: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/39.jpg)
Oxidation is the loss of electrons.
Metal atoms lose electrons to become + ionsThe oxidation numbers go up (increases)
![Page 40: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/40.jpg)
A half-reaction can be written to represent
oxidation.Na0 Na1+ + 1e-
In oxidation half reactions, electrons are written on the right because electrons are lost
![Page 41: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/41.jpg)
Half-Reactions
• Show either the oxidation or reduction portion of a redox reaction and the electrons gained or lost.
![Page 42: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/42.jpg)
Steps for Writing Half-Reactions
Cu0 + Ag+1N+5O-23 Cu+2 (N+5O-23)2 + Ag0
1. Assign an oxidation number to each element.2. Write a partial half-reaction to show the
change in oxidation state:Oxidation: Cu0 Cu+2
Reduction: Ag+1 Ag0
![Page 43: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/43.jpg)
Steps Continued…
3. Show the number of electrons needed to explain how the oxidation number changed.
Oxidation: Cu0 Cu+2 + 2e-Reduction: Ag+1 +1e- Ag0
4. Last, but not least, achieve conservation of charge: 2Ag+1 +2e- 2Ag0
![Page 44: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/44.jpg)
Practice Problems
1. Mg + Cl2 MgCl2
2. Cu + 2Ag+ Cu2+ + 2Ag3. Al0 + Cr3+ Al3+ + Cr0
![Page 45: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/45.jpg)
Mg + Cl2 MgCl2
![Page 46: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/46.jpg)
Cu + 2Ag+ Cu2+ + 2Ag
![Page 47: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/47.jpg)
Al0 + Cr3+ Al3+ + Cr0
![Page 48: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/48.jpg)
Regents Question:
Given the reaction:Mg(s) + 2H+(aq) + 2Cl–(aq) Mg2+(aq) + 2Cl–(aq)
+ H2(g)
Which species undergoes oxidation?(1) Mg(s)(2) H+(aq) (3) Cl– (aq)(4) H2 (g)
LEO growls GERLEO
![Page 49: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/49.jpg)
Regents Question:
Given the equation:C(s) + H2O(g) CO(g) + H2 (g)
Which species undergoes reduction?(1) C(s)(2) H +
(3) C2+
(4) H2 (g)LEO growls GERGER
![Page 50: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/50.jpg)
Regents Question:In any redox reaction, the substance that
undergoes reduction will
(1) lose electrons and have a decrease in oxidation number
(2) lose electrons and have an increase in oxidation number
(3) gain electrons and have a decrease in oxidation number
(4) gain electrons and have an increase in oxidation number
![Page 51: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/51.jpg)
Regents Question:
Given the equation:2 Al + 3 Cu2+ 2 Al3+ + 3Cu
The reduction half-reaction is(1) Al Al 3+ + 3e – (2) Cu 2+ + 2e – Cu (3) Al + 3e – Al 3+
(4) Cu 2+ Cu + 2e –
![Page 52: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/52.jpg)
Worksheet Page 16-17
![Page 53: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/53.jpg)
Table J tells us if a redox reaction can occur between an atom and an
ion.• A more active metal will replace an ion
below it on Table J.• A more active nonmetal will replace an ion
below it on Table J.• Any metal above H is more active than H
and will react with an acid to produce H2(g)– The higher up the table, the more readily the
replacement will take place.
![Page 54: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/54.jpg)
Regents Question:
According to Reference Table J, which of these metals will react most readily with 1.0 M HCl to produce H2(g)?
(1) Ca(2) K (3) Mg(4) Zn
![Page 55: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/55.jpg)
A more active metal will replace a less active metal from its compound.
• Zn + CuSO4 Cu + ZnSO4
Zinc replaces copper because zinc is more active than copper.
• Cu + ZnSO4 No ReactionCopper cannot replace zinc
Oxidation is on topReduction is on bottom
![Page 56: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/56.jpg)
Review of Terms
• oxidation-reduction (redox) reaction:– involves a transfer of electrons from the reducing agent to the oxidizing agent.
•oxidation: loss of electrons•reduction: gain of electrons
![Page 57: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/57.jpg)
Half-Reactions
•The overall reaction is split into two half-reactions, one involving oxidation and one reduction.
8H+ + Mn+7O4 + 5Fe2+ Mn2+ + 5Fe3+ + 4H2O
Reduction: Mn+7 + 5e Mn2+
Oxidation: 5Fe2+ 5Fe3+ + 5e
![Page 58: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/58.jpg)
AGENTS
• To recap– Oxidizing agent = the species that’s being reduced
– Reducing agent = the species that’s being oxidized
![Page 59: Redox Reactions](https://reader036.fdocuments.us/reader036/viewer/2022062520/56815fcc550346895dcec73d/html5/thumbnails/59.jpg)
Page 18