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Net Ionic equations and Oxidation Numbers

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Joined: Feb 2007
Net Ionic equations and Oxidation Numbers

Okay, so my class is getting ready for finals, and in doing so, we're working on chapter tests that we never did earlier in the year. The big problem is that we've never learned some of the stuff the tests are over. So, can anyone please explain to me net ionic equations and oxidation numbers? Please? My book doesn't really explain this at all, and the little bit it does makes no sense. I've included a few example questions with with I think are the correct answers. If you see that they are wrong, could you please tell me and explain why they are wrong and how to find the correct ones? Thank you so much!

1) When aqueous solutions of AgNO3 and KI are mixed, AgI precipitates. What is the balanced net ionic equation?
A: I think it's Ag+ (aq) + I- (aq) -> AgI (s).
If I understand this a little bit, to find the ionic equation you have to find the spectator ions and get rid of them. However, I'm not always sure how to get the spectator ions.

2) In which reaction does the oxidation number of oxygen increase?
a. Ba(NO3)2 (aq) + K2SO4 (aq) -> BaSO4 (s) + 2 KNO3 (aq)
b. HCl (aq) + NaOH (aq) -> NaCl (aq) + H2O
c. *I think this is the answer* MgO (s) + H2O (l) -> Mg(OH)2 (s)
d. 2 SO2 (g) + O2 -> 2SO3 (g)
e. 2H2O (l) -> 2H2 (g) + O2.

3) Which of the following is an oxidation-reduction reaction?
a. Cu (s) + 2AgNO3 (aq) -> 2Ag (s) + Cu(NO3)2 (aq)
b. *I think this is the answer* HCl (aq) + NaOH (aq) -> H2O (l) + NaCl (aq)
c. AgNO3 (aq) + HCl (aq) -> AgCl (s) + HNO3 (aq)
d. Ba(C2H3O2)2 (aq) + Na2SO4 (aq) -> BaSO4 + 2NaC2H3O2 (aq)
e. H2CO3 (aq) + Ca(NO3)2 (aq) -> 2HNO3 (aq) + CaCO3 (s)

If you can help me at all, I would greatly appreciate it!

LUC:D

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Joined: Sep 2005

1) I'm pretty sure that you're correct on this one. About finding spectator ions, all you have to do is figure out which compounds used dissociate in solution. Really, all you have to know is your solubility rules. For example, you have AgNO3 as a reactant in your equation. While Ag is normally insoluble, you know that all nitrates are, so you can break that compound down to its ions.

2) I think that you're wrong here, and that the answer is e. When finding oxidation numbers, remember that some elements are assigned a certain number. Oxygen is one of those numbers--it is permanently -2, unless it is found as a element because all elements have a number of 0.

3) Let me get back to you tomorrow. Jet lag is catching up with me--I gotta go.

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Thank you so much! I forgot about the elements being 0. Gah. So many rules at once!
Jet lag is horrible, isn't it? But the good news is that it gives you an excuse to sleep. :-)

LUC:D

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Joined: Sep 2005

Lol, that's true!

Let's see...number three's answer is a. A is the only one that has a change in oxidation numbers (a quick little shortcut to see this is because it has elements that aren't in compounds on both sides of the equation, in this case Cu as a reactant and AG as a product. Since elements have a charge of 0, they both have to change their oxidation numbers). I think that you're getting acid-base reactions mixed up with oxidation-reactions. The equation that you picked out was an acid-base reaction. I think that an equation can be both (I haven't heard that they CAN'T be), but they are two different types of reactions.

Do you want any more help, or a more in-depth description of anything? I don't mind giving one if you'd like me to.

The hardest thing about riding horses is the ground
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Joined: Feb 2007

Ah. I did mix them up. Now when I look back at my work, I have no clue how I got b to be the answer. That is a nice little shortcut! You have no idea how much you've helped! I'll probably be asking more questions later on as we learn new stuff. And your explanations make more sense than my book and study guide. Thanks again!

LUC:D

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Joined: Sep 2005

Sweet! Well, I'm glad that I was a help. These sort of things are some of my favorite stuff to do, so feel free to ask me any questions that you want to. Good luck on your final ;)

The hardest thing about riding horses is the ground
[CENTER][IMG]http://i29.photobucket.com/albums/c295/xenahorse/Photoshop%20Fun/Ed_Ein_...

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