MIssing: Blog for March 06, 2007

Sorry it took so long!
But you know what they say, "It's better late than never."

So, just a recap on March 06, 2007:

The "Oxidation-Reduction Compare and Contrast Frame" sheet and the "Redox Reactions" sheet were corrected and handed back.

Here are the corrections:
"Oxidation-Reduction Compare and Contrast Frame"
Oxidation
Historical Definition:
Any reaction that involved a reactant combining with oxygen was an oxidation reaction.
Example:
Burning substances - oxygen present.
Rusting / Corrosion - oxygen reacts with metal.

Present Definition:
A process by which a substance had given up their electrons.
Example:
Al(s) --------> Al³⁺_(aq) + 3e^-

Mnemonic Device:
O - Oxidation
I - Is
L - Losing
or
L - Losing
E - Electrons
O - Oxidation

When Balancing a Redox Reaction:
One substance is oxidized and it is also the reducing agent.
Its oxidation number increases.

Reduction
Historical Definition:
When oxygen is removed by a compound to produce a metal.
Example:
2Fe₂O₃(s) + 3C(s) ------> 4Fe(s) + 3CO₂(g)

Present Definition:
A process in which a substance gains electrons.
Example:
Al³⁺(aq)+ 3e^--------> Al(s)

Mnemonic Device:
R - Reduction
I - Is
G - Gaining
or
G - Gaining
E - Electrons
R - Reduction

When Balancing a Redox Reaction:
One substance is reducedand it is also the oxidizing agent.
It's oxidation number decreases.

"Redox Reactions"
1. Redox reactions are characterized by: d. transfer of electrons.
2. If a calcium atom loses two electron, it becomes: c. oxidized.
3. In a redox reaction, an oxidizing agent is: d. reduced.
4. An oxidation reaction occurs: a. at the same time a reduction reaction occurs.
5. Consider the equation Ca(s) + O₂(g) ------> 2CaO(s). In this reaction, calcium is oxidized because it: c. loses electrons.
6. The number of electron lost by an element when it forms ions is the element's: b. oxidation number.
7. A loss of electrons is: a. oxidation.
8. Redox reactions can involve: d. ions, molecules, or uncharged atoms.

9. - 15. Redox Reactions

Equation:
#16
Oxidized: Cd
Reduced: Ni²⁺
OA: NiO₂
RA: Cd

#17
Oxidized: Fe
Reduced: Cu
OA: SO4
RA: Fe

#18
Oxidized: Sb
Reduced: I
OA: I2
RA: Sb

#19
Oxidized: S
Reduced: O
OA: O2
RA: Cu2S

#20
Oxidized: Pb
Reduced: Pb⁺⁴
OA: PbO₂
RA: Pb

#21
Oxidized: N^-3
Reduced: N⁺⁵
OA: NH4NO3
RA: NH₄NO₃

#22
Oxidized: C
Reduced: Fe
OA: Fe₂O₃
RA: CO

FINALLY!

Ms. Kozoriz had written down steps on "Balancing Redox"

1. Assign oxidation numbers to each element.
2. Identify and write oxidation half reaction and reduction half reaction.
3. Balance in terms of electron numbers and atoms.
4. Add H2O and H to balance acidic reaction.
5. Do a change check for both half reactions.
6. Multiply through so electron number is the same in the reduction and oxidation half reaction.
7. Add both half reactions cancelling electrons and any other substances.
8. Do a final change check!

* Sorry again it took so long but we all know brilliance takes time =P.

By: Jennie

Redox Test Answers

20. Oxidation-Reduction Reactions Worksheet

March 7, 2007

Today we went over the oxidation-reduction worksheet which she handed out yesterday for homework. We did these questions on the white board and Ms.K did some on the smart board.

annnnnd tomorrow is our "brief" test...so study, study, study! thats all no notes just the worksheet.

Wed, March 7 Notes

Missing Scribe For Friday March 2 (sorry)

Well, on Friday, we received worksheets. We had an option to either hand it in on Friday or Monday, but now it would be too late. Well the sheet that was handed in was a review, to check if you know what oxidation and reduction was. The other was about Balancing Equations using a different method, if a redox reaction occured. Here is a guide to interpreting that sheet:

Firstly, find the oxidation numbers, but remembering to use the "Rules for Determining Oxidation Numbers."

Lets use Ag₂S + Al -> Al₂S₃ + Ag

Ag: is reduced because it is gaining one electron. +1 to 0 (more negative number)
S: remains the same, so it isn't oxidized.
Al: is oxidized because it is losing three electrons. 0 to +3 (more positive number)

Multiply the subscripts with the number of electrons lost or gained.

Therefore:

Ag₂S: 2(because you have two Ag atoms) X 1 electron (number of electrons that was gained)

Al: 1(because you only have one Al atom) X 3 electrons (number of electrons that was lost)

Now we have to balance. So that we have the same number of electorns gained and lost. We find their lowest common multiple...Hm...2 and 3, 6 goes into both, so lets multiply both to get 6:

Ag₂S: 2 electrons X 3 = 6
S: 3 electrons X 2 = 6

Use what you multipled there as your coeffcients: so 3 for Ag₂S and 2 for S:

3Ag₂S + 2Al -> Al₂S₃ + Ag

Note: Check both sides are balanced, you may need to balance the rest of the equation. For this case, since you have 6Ag on the reactant side, then you need a 6 in front of the Ag in the end product side. That is all.


Therefore, your answer should be:

3Ag₂S + 2Al -> Al₂S₃ + 6Ag

Tuesday, March 6 Notes

Monday, March 5 Notes

Scribe - feb 28

All we did on wednesday was that we went over the "oxidation and Reduction" hand out that Ms K gave us last week. We went over assigning oxidation numbers and then we had time to work on identifying the reducing agents and oxidizing agents.

here's an example:

FeBr₂ + Br₂ ----> FeBr₃

Fe⁺²Br^-1₂ + Br⁰₂ ----> Fe⁺³Br^-1 ₃ ' identifying the oxidation numbers

Fe loses one electron therefore it is oxidized

Br gains one electron therefore being reduced

FeBr is the reducing agent
Br₂ is the oxidizing agent

Tip:

if one has gained an electron then it's reduced
if one has lossed an electron then it is oxidized
an agent is found on the left side of the arrow ( ----> )

remember that our test tube mystery lab is due on monday

Oxidation Method for Balancing Redox Equations

Scribe Post

Sorry everyone I didn't realize that I was the scribe for Tuesdays class.

Today was the last day to work on the Test Tube Mystery Lab.

I will complete this scribe later on.

The scribe for Wednesday's class is Jefferson :)

Feb.28 Notes

These are today's notes from class

Feb23: Oxidation and Reduction

hello, last friday we learned about oxidation and reduction.
previously we learned that there are 5 type of reactions but on friday we learned that there are only two different families of chemical reactions:
1-those that don't have exchange of electrons-->non-redox reactions
2-those that do have exchange of electrons-->redox reactions

*when a substance lost/gave up its electrons it's an oxidation reaction:
Al(s) --> Al³⁺ + 3 electrons

*when a substance gains electrons it's called a reduction reaction:
Al³⁺ + 3 electrons --> Al(s)

to remember those key points we could use:
Oxidation
Is
Losing

Reduction
Is
Gaining
(OIL RIG)
or:
Losing
Electrons
Oxidation

Gaining
Electrons
Reduction
(Leo Ger)

also an important point is that Oxidation and reduction always occur at the same time, so that the number of electrons gained in a reaction is always equal to the electrons lost.
:. to keep track of the loss and gain of electrons in a reaction we use Oxidation States(imaginary charge an atom would have if both the electrons in an electron pain belonged to the most electronegative element of that pair)
Oxidation numbers are positive and negative numbers that are related to an atom's oxidation state.

the most important part of the lesson was knowing the 9 rules applying to the concept.
DUH RULES:
1-The oxidation number of an atom in an uncombined element is zero.
ex. O₂

2-the SUM of the oxidation numbers of the elements in any neutral molecule is zero.
ex. MgCl₂
+2 + (-1 x 2)= 0

3-the sum of the oxidation numbers of the elements in any ion is equal to the charge on the ion.
ex. NO₃^-1
+5 + (-2 x 3) = -1

4-in compounds the oxidation number of many elements corresponds to their position on the periodic table.
a)elements in Group 1A are always {+1}
ex. H , Li, Na, K, Rb, Cs, Fr

b)the alkaline earth metals are always {+2}
ex. Be , Mg, Ca, Sr, Br, Ra

c)aluminum is always {+3} and zinc is always {+2}

d)halogens are almost always {-1}
ex. F , Cl, Br, I, At

e)Hydrogen always has an oxidation number of {+1} when it's combined with non metals.
ex. HCl

f)oxygen has an oxidation number of {-2} in most compounds (exception:in peroxides where it is -1, ex. H₂O₂ (hydrogen peroxide)
ex. SO₂ S is +4 and O is -2

i guess that's all!
i think we have a scribe for today, so i won't pick.