Upload
andy-rei-kou
View
224
Download
0
Embed Size (px)
Citation preview
8/4/2019 Class12 ChemistryG12 Notes and Homework
1/38
GRADE12CHEMISTRY
OLYMPIADSCHOOL
WEDNESDAY2:304:30
FRIDAY4:456.45
8/4/2019 Class12 ChemistryG12 Notes and Homework
2/38
Oxidation-Reduction Reactions
Oxidation is the loss of electrons. Reduction is the gain ofe ec rons.
In the reaction of zinc atoms with co er II ions the zinc atomslose electrons and undergo oxidation. In other words, the zinc
atoms are oxidized. e copper ons ga n e ectrons an un ergo re uct on. n
other words, the copper(II) ions are reduced.
,
known as an oxidation-reduction reaction or redox reaction.
8/4/2019 Class12 ChemistryG12 Notes and Homework
3/38
Notice that electrons are transferred from zinc atoms to copper(II) ions. The
copper ons are respons e or e ox a on o e z nc a oms. reac anthat oxidizes another reactant is called an oxidizing agent. The oxidizing agentaccepts electrons in a redox reaction. In this reaction, copper(II) is the oxidizing
. .reactant that reduces another reactant is called a reducing agent. The reducing
agent gives or donates electrons in a redox reaction. In this reaction, zinc is the.
A redox reaction can also be defined as a reaction between an oxidizing agentand a reducing agent.
8/4/2019 Class12 ChemistryG12 Notes and Homework
4/38
Half-Reactions ,
represent the oxidation and reduction separately. A half-reaction is a balanced equation that shows the number of
electrons involved in either oxidation or reduction. Because a redox reaction involves both oxidation and reduction, two
half-reactions are needed to represent a redox reaction. One half-reaction shows oxidation, and the other half-reaction shows reduction.
In most redox reactions, one substance is oxidized and a differentsubstance is reduced. In a disproportionation reaction, however, asingle element undergoes both oxidation and reduction in the same
reac on. For example, a copper(I) solution undergoes disproportionation in thefollowing reaction: 2Cu+(aq) Cu(s) + Cu2+(aq)
In this reaction, some copper(I) ions gain electrons, while othercopper(I) ions lose electrons.
The two half-reactions are as follows.Oxidation: Cu+ (aq) Cu2+ (aq) + 1e
Reduction: Cu+(aq) + 1e- Cu(s) a -reac ons a ways come n pa rs: an ox a on a -reac on s
always accompanied by a reduction half-reaction, and vice versa.
8/4/2019 Class12 ChemistryG12 Notes and Homework
5/38
Oxidation Numbers Oxidation numbers are actual or hypothetical charges, assigned
using a set of rules.
ey are use o escr e re ox reac ons w cova en
reactants or products. They are also used to identify redox, .
Consider Lewis Structures. Oxygen (electronegativity 3.44) is
The electronegativity difference is less than 1.7, so the twohydrogen-oxygen bonds are polar covalent, not ionic. In eachbond, the electrons are more strongly attracted to the oxygen
atom than to the hydrogen atom.
8/4/2019 Class12 ChemistryG12 Notes and Homework
6/38
To assign oxidation numbers to the atoms in a water molecule,
more electronegative oxygen atom. Thus, each hydrogen atomin a water molecule is considered to have no electrons, ashydrogen would in a hydrogen ion, H+.
Therefore, the element hydrogen is assigned an oxidation. ,water molecule is considered to have a filled octet of electrons,as oxygen would in an oxide ion, O2. Therefore, the element
oxygen is assigned an oxidation number of 2 in water.
(Note: These are not ionic charges, since water is a covalent
molecule. Also, note that the plus or minus sign in an oxidation, , .
minus sign in an ionic charge, such as 2-, is written after the
8/4/2019 Class12 ChemistryG12 Notes and Homework
7/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
8/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
9/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
10/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
11/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
12/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
13/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
14/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
15/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
16/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
17/38
Balancing Half-Reactions for Acidic
Step 1 Write an unbalanced half-reaction that shows the.
Step 2 Balance any atoms other than oxygen and hydrogen first.
.
Step 4 Balance any hydrogen atoms by adding hydrogen ions.
ep a ance e c arges y a ng e ec rons.
8/4/2019 Class12 ChemistryG12 Notes and Homework
18/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
19/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
20/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
21/38
Balancing Half-Reactions for Basic
Step 1 Write an unbalanced half-reaction that shows the formulas ofthe given reactant(s) and product(s).
Step 2 Balance any atoms other than oxygen and hydrogen first. ep a ance any oxygen an y rogen a oms as e con ons
are acidic.
number of hydroxide ions as the number of hydrogen ions alreadypresent.
Step 5 Simplify the half-reaction by combining the hydrogen ions andhydroxide ions on the same side of the equation into water molecules.
half-reaction.
8/4/2019 Class12 ChemistryG12 Notes and Homework
22/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
23/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
24/38
S f B l i b h
8/4/2019 Class12 ChemistryG12 Notes and Homework
25/38
Steps for Balancing by the
- Step 1 Write an unbalanced net ionic equation, if it is not alreadygiven.
Step 2 Divide the unbalanced net ionic equation into an oxidationhalf-reaction and a reduction half-reaction. To do this, you may need
to assign oxidation numbers to all the elements in the net ionic. Step 3 Balance the oxidation half-reaction and the reduction half-
reaction independently.
electrons in the oxidation half-reaction and the reduction half-reaction. Ste 5 Use coefficients to write each half-reaction so that it includes
the LCM of the numbers of electrons. Step 6 Add the balanced half-reactions that include the equal
numbers of electrons. Step 7 Remove the electrons from both sides of the equation. Step 8 Remove any identical molecules or ions that are present on
both sides of the equation. tep you requ re a a ance c em ca equat on, nc u e any
spectator ions in the chemical formulas. Step 10 If necessary, include the states.
B l i R d R ti i A idi
8/4/2019 Class12 ChemistryG12 Notes and Homework
26/38
Balancing a Redox Reaction in Acidic
Problem Write a balanced net ionic equation to show the, -,
acidic solution to produce chloride ions and nitrate ions.
What Is Re uired? You need to write a balanced net ionicequation for the given reaction.
What Is Given? You know the identities of two reactants andtwo pro ucts, an t at t e react on ta es p ace n ac csolution.
8/4/2019 Class12 ChemistryG12 Notes and Homework
27/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
28/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
29/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
30/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
31/38
The Oxidation Number Method
for Balancing Equations ep r e an un a ance equa on, s no
given.
reaction by assigning an oxidation number to eachelement wherever it appears in the equation.
Step 3 If the reaction is a redox reaction, identify theelement(s) that undergo an increase in oxidation
in oxidation number.
Step 4 Find the numerical values of the increase andthe decrease in oxidation numbers.
8/4/2019 Class12 ChemistryG12 Notes and Homework
32/38
ep e erm ne e sma es w o e-num er ra o othe oxidized and reduced elements so that the total
increase in oxidation numbers e uals the totaldecrease in oxidation numbers.
Step 6 Use the smallest whole-number ratio toa ance t e num ers o atoms o t e e ement s
oxidized and the element(s) reduced
,possible.
Step 8 For reactions that occur in acidic or basicsolutions, include water molecules, hydrogen ions,or hydroxide ions as needed to balance the equation.
8/4/2019 Class12 ChemistryG12 Notes and Homework
33/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
34/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
35/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
36/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
37/38
8/4/2019 Class12 ChemistryG12 Notes and Homework
38/38