Redox Reactions

Redox reactions, also known as oxidation-reduction reactions are driven by the transfer of electrons. One of the tricky parts about these reactions is remembering the difference between oxidation and reduction. Contrary to what one would think, reduction is the process of gaining electrons, while oxidation is the process of losing electrons. One way to remember this is:

https://c3.100r.org/media/2013/12/bribery-probe-may-contribute-to-job-cuts-at-texas-oil-explorer/offshore-oil-rig.jpg

OIL RIG. This stands for Oxidation Is Loss of e- and Reduction Is Gain of e-

When solving these reactions , it is important to know how to find the oxidation # of reactants and products. Here are a couple of pictures that really helped me understand the concept.

http://image.slidesharecdn.com/redox-100512065957-phpapp01/95/redox-8-638.jpg

**ADDITIONAL INFORMATION**

Here are 2 great sites that will aid in further learning!

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=6&cad=rja&uact=8&ved=0ahUKEwjpwKSkx7nJAhVSKogKHcPrBRgQtwIINTAF&url=https%3A%2F%2Fwww.khanacademy.org%2Fscience%2Fchemistry%2Foxidation-reduction%2Fredox-oxidation-reduction%2Fv%2Fpractice-determining-oxidation-states&usg=AFQjCNFNS_MtDJeF6BJvpdo5D3cFXTht1w&sig2=VQnpFOHiGF_VtGUho2X2fw

https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=5&cad=rja&uact=8&ved=0ahUKEwjpwKSkx7nJAhVSKogKHcPrBRgQFggvMAQ&url=http%3A%2F%2Fwww.occc.edu%2Fkmbailey%2Fchem1115tutorials%2Foxidation_numbers.htm&usg=AFQjCNFExV7dy5R5XyaeszAqZGYwDX5y9w&sig2=pxL7UEwLLUJYeIQQ1HR-gw

Balancing Chemical Equations

While seemingly simple, it is easy to make simple errors when balancing chemical equations.
Here's a picture explaining how:

When balancing equations with only Carbon, Hydrogen, and Oxygen, it is important to use the CHO method. That means that you need to balance the Carbon atoms first, then Hydrogen, and Oxygen atoms last.

**ADDITIONAL INFORMATION**
Here is a video explaining this concept if you need more practice: https://www.youtube.com/watch?v=eNsVaUCzvLA

Solubility Rules

Solubility rules are crucial to memorize in order to accurately understand and solve chemical reactions; specifically, precipitate reactions or double-replacement reactions. Here are these rules:

 Solubility Rules

1. Salts containing Group I elements are soluble (Li⁺, Na⁺, K⁺, Cs⁺, Rb⁺). Exceptions to this rule are rare.
    Salts containing the ammonium ion (NH₄⁺) are also soluble.

2. Salts containing nitrate ion (NO₃^-) are generally soluble.

3. Salts containing Cl ^-, Br ^-, I ^- are generally soluble. Important exceptions to this rule are halide salts of
    Ag⁺, Pb²⁺, and (Hg₂)²⁺. Thus, AgCl, PbBr₂, and Hg₂Cl₂ are all insoluble.

4. Most silver salts are insoluble. AgNO₃ and Ag(C₂H₃O₂) are common soluble salts of silver; virtually
    anything else is insoluble.

5. Most sulfate salts are soluble. Important exceptions to this rule include BaSO₄, PbSO₄, Ag₂SO₄ and
    SrSO₄ .

6. Most hydroxide salts are only slightly soluble. Hydroxide salts of Group I elements are soluble.
    Hydroxide salts of Group II elements (Ca, Sr, and Ba) are slightly soluble. Hydroxide salts of transition
    metals and Al³⁺ are insoluble. Thus, Fe(OH)₃, Al(OH)₃, Co(OH)₂ are not soluble.

7. Most sulfides of transition metals are highly insoluble. Thus, CdS, FeS, ZnS, Ag₂S are all insoluble.
    Arsenic, antimony, bismuth, and lead sulfides are also insoluble.

8. Carbonates are frequently insoluble. Group II carbonates (Ca, Sr, and Ba) are insoluble. Some other
     insoluble carbonates include FeCO₃ and PbCO₃.

9. Chromates are frequently insoluble. Examples: PbCrO₄, BaCrO₄

10. Phosphates are frequently insoluble. Examples: Ca₃(PO₄)₂, Ag₃PO₄

11. Fluorides are frequently insoluble. Examples: BaF₂, MgF₂ PbF₂.

Here is another source covering the same rules with examples:

Rule 1. All compounds of Group IA elements (the alkali metals) are soluble.

For example, NaNO₃, KCl, and LiOH are all soluble compounds. This means that an aqueous solution of KCl really contains the predominant species K⁺ and Cl^- and, because KCl is soluble, no KCl is present as a solid compound in aqueous solution:
KCl_(s) => K⁺_(aq.) + Cl^-_(aq.)

Rule 2. All ammonium salts (salts of NH₄⁺) are soluble.

For example, NH₄OH is a soluble compound. Molecules of NH₄OH completely dissociate to give ions of NH₄⁺ and OH^- in aqueous solution.

Rule 3. All nitrate (NO₃^-), chlorate (ClO₃^-), perchlorate (ClO₄^-), and acetate (CH₃COO^- or C₂H₃O₂^-, sometimes abbreviated as Oac^-) salts are soluble.

For example, KNO₃ would be classified as completely soluble by rules 1 and 3. Thus, KNO₃ could be expected to dissociate completely in aqueous solution into K⁺ and NO₃^- ions: KNO₃ => K⁺_(aq.) + NO^3-_(aq.)

Rule 4. All chloride (Cl^-), bromide (Br^-), and iodide (I^-) salts are soluble except for those of Ag⁺, Pb²⁺, and Hg₂²⁺.

For example, AgCl is a classic insoluble chloride salt:
AgCl_(s) <=> Ag⁺_(aq.) + Cl^-_(aq.) (K_sp = 1.8 x 10^-10).

Rule 5. All sulfate ( SO₄⁼) compounds are soluble except those of Ba²⁺, Sr²⁺, Ca²⁺, Pb²⁺, Hg₂²⁺, and Hg²⁺, Ca²⁺ and Ag⁺ sulfates are only moderately soluble.

For example, BaSO₄ is insoluble (only soluble to a very small extent):
BaSO_4(s) <=> Ba²⁺_(aq.) + SO₄^2-_(aq.) (K_sp = 1.1 x 10^-10).
Na₂SO₄ is completely soluble:
Na₂SO_4(s) => 2 Na⁺_(aq.) + SO₄^2-_(aq.).

Rule 6. All hydroxide (OH^-) compounds are insoluble except those of Group I-A (alkali metals) and Ba²⁺, Ca²⁺, and Sr²⁺.

For example, Mg(OH)₂ is insoluble (K_sp = 7.1 x 10^-12).
NaOH and Ba(OH)₂ are soluble, completely dissociating in aqueous solution:
NaOH_(s) => Na⁺_(aq.) + OH^-_(aq.), a strong base
Ba(OH)_2(s) => Ba²⁺_(aq.) + 2OH^-_(aq.) (K_sp = 3 x 10^-4)

Rule 7. All sulfide (S^2-) compounds are insoluble except those of Groups I-A and II-A (alkali metals and alkali earths).

For example, Na₂S_(s) <=> 2Na⁺_(aq.) + S^2-_(aq.)
MnS is insoluble (K_sp = 3 x 10^-11).

Rule 8. All sulfites (SO₃⁼), carbonates (CO₃⁼), chromates (CrO₄⁼), and phosphates (PO₄^3-) areinsoluble except for those of NH₄⁺ and Group I-A (alkali metals)(see rules 1 and 2).

For example, calcite, CaCO_3(s) <=> Ca²⁺_(aq.) + CO₃⁼_(aq.) (K_sp = 4.5 x 10^-9).

**ADDITIONAL SOURCES**

Website explaining the rules: http://www.chem.sc.edu/faculty/morgan/resources/solubility/

Here are some flashcards: https://quizlet.com/232395/solubility-rules-practice-flash-cards/

Here's a helpful song: https://www.youtube.com/watch?v=VJoKQ3ULCVs

Comments/Reflection

Part of the grade we receive for running this blog comes from completing 6 comments on other people's blogs. Here are my 6 comments!

P.S- In a mini reflection of the unit test, I thought it went terribly. I was completely confident in this unit and knew how to complete all problems accurately, but with the time given, I could only complete just about half of the questions. If I receive a low grade, it won't be because of my knowledge, it will be because of the time allocated. 

Hydrate Lab

Yesterday we did another lab in class. This time, it was about hydrates!

In this lab we determined the formula of the hydrate CuSO4 · nH2O.

We took 2 cm of the hydrate, weighed it, heated it to remove the water, and measured the mass of the dried salt.

With these numbers we were able to figure out the 'n' in the hydrate.



Here is a picture of us heating the hydrate to remove excess H2O,




*** If you're having trouble with the math equations for this unit, here are some helpful links that I studied from:
1. http://www.chemteam.info/Solutions/Molarity.html

2. http://www.chemteam.info/Mole/Avogadro-Number-CalcsII.html

3. http://www.chemteam.info/Mole/Empirical-MolecFormulas.html

Aspirin Lab

The other day we weighed our dried Aspirin after letting it sit out all fall break plus a few days. Once we obtained that measurement, we converted it into moles.


I used the data Lauren and I collected:

Starting mass of salicylic acid in grams: 5.0451 g
Mass of watch glass in grams: 36.8387 g
Ending mass of acetylsalicylic acid in grams: 5.1795 g
Mass of filter paper: 0.4114 g

Starting mass of salicylic acid (C7H6O3): .03652 mol C7H6O3

Ending mass of acetylsalicylic acid (C9H8O4): .02875 mol C9H8O4

Chemical Composition Equations

These equations intimidated me when I first saw them. But, once I broke them down and wrote why numbers were what they were, they seem OK. Here's how I keep things organized:

1. Find mass of hydrate (everything in the test tube/crucible)
2. Find mass of anhydrous salt (I write down 'salt' to simplify things)
3. Find mass of H2O (hydrate -  salt)
4. Convert amount of H2O and amount of salt into moles
5. Divide water from salt ( H2O/Salt)
6. Round to whole number.

Hope this helps! If you're still confused, here are some good ~*LINKS*~ to check out:

1. Hydrate Help from Chem.com

2 Help from Study. com (pictures)

3. Here's a video if you're a visual learner: http://study.com/academy/lesson/hydrates-determining-the-chemical-formula-from-empirical-data.html

Pretest

Last pretest I got a 55%. This time, I got a 33%. If that doesn't say anything, then I don't know what will. I am going into this unit with absolutely no prior knowledge, so I will definitely have to buckle down and study hard. I know that moles are sorta cute little fuzzy creatures, but once they're thrown into chemistry- I no longer like them. We will see how this unit turns out; with the topic being so foreign and the grading scale being much different.

This...

https://universityofnebras599-public.sharepoint.com/SiteAssets/species-information/moles/Fig%202%20Ventral%20view%20of%20eastern%20mole.jpg


Goes to this....


https://www.chem.tamu.edu/class/majors/tutorialnotefiles/stoich9.gif