AP Chemistry 2010 Study thread! Come on people!

<p>I’m pretty sure they’d still give you credit for H2CO3 though…</p>

<p>H2CO3 is unstable, so it breaks down to CO2 and H2O.</p>

<p>The reaction is double replacement, right?</p>

<p>So, 2HNO3 + CaCO3 –> Ca(NO3)2 + H2CO3
NO3- is a spectator ion.</p>

<p>2H+ + CaCO3 –> Ca2+ + H2CO3</p>

<p>H2CO3 is unstable. It breaks down into H2O and CO2, always. The final reaction:</p>

<p>2H+ + CaCO3 –> Ca2+ + H2O + CO2</p>

<p>That’s from the 2007 exam, guys, so it’s probably good to know.</p>

<p>i didnt say carbonic acid though i said bicarbonate.
edit: okay thanks man</p>

<p>@aryus It doesn’t say it gives credit for H2CO3 in the scoring rubric.</p>

<p>nonexistant can you explain why it doesnt make bicarbonate?</p>

<p>My mistake I was confusing myself with the H2SO4/ H+ + HSO4, which they whould give you credit for either one. Wow thats a good one, thanks.</p>

<p>Can anyone answer my resonance, bond strength one a few posts earlier?</p>

<p>Well, it’s double replacement…so they switch ions to make 2 new ionic compounds. HCO3- isn’t an ionic compound, so it doesn’t work. You have to balance the charges in the ion to make it netural, so it’s H2CO3…which becomes H2O and CO2.</p>

<p>resonance is when an electron can switch postions in a intramolecular interaction like any ion molecule. when CO2 are drawn , they usually look like this O=C=O this double bonds mean the bond has a value of 2 because they are two bond, as for one bond =1 and triple bond= 3. When one resonates, depending on the number of bonds in a molecule the bond would be a fraction of a bond.</p>

<p>alright next one!</p>

<p>I see, but what is the answer to the question with NO2 and NO3?</p>

<p>aryus–If you draw it out, you have three resonance structures, where the double bond can be with any of the 3 oxygens. The bond length is between that of a single bond and a double bond, though since the bond is spread through 3 bonds, I think it would be closer to a weaker, single bond. I’m not entirely sure, but that sounds right…anyone wanna double check?</p>

<p>For NO2-, you have 2 resonance structures, with the double bond being with either oxygen. Again, the bond length is between that of a single bond and a double bond. Since it’s spread out only over 2 bonds, though, I think the bond might be closer to a double bond, making it shorter/stronger. Again, not certain, but it sounds right.</p>

<p>I believe your explanation is right(and greatly appreciated), but my prep book (08-09 5 steps to a 5) says the NO3 is shorter and stronger, but doesn’t give an adequate explanation</p>

<p>nonexistant im pretty sure youre right but idk its kinda late
nitrite would have two bonds so that one electron resonating will take half and half because its two thus its value is 1.5
nitrate on the other hand has three bonds for just one electron to move around. thus the bond when 1 electron/ 3 bonds = .33 of a bond. thus it would be 1.33 for nitrate. this same bond stuff then goes into formal charge etc</p>

<p>aryus its true because it just has more bonds than nitrite so nitrogen can recieve more electrons to fullfill its octet</p>

<p>anyone else confused about acids/bases and titration?! btw…can someone help me with the whole voltaic and electolytic cells?</p>

<p>Yeah, I’m not sure why it’s NO3.</p>

<p>Monicat, this may help with voltaic cells: [Khan</a> Academy: Galvanic Cells](<a href=“http://khanexercises.appspot.com/video?v=N4L3dDIixSU]Khan”>http://khanexercises.appspot.com/video?v=N4L3dDIixSU)</p>

<p>As for acid/base titrations, I did a bunch of questions from my textbook and it helped a lot.</p>

<p>@rawk: thats the exact explanation my prep book gave, but I still don’t get it… can you explain how u calculated 1.33 and 1.5?</p>

<p>@moni: those are actually my two weakest points… titrations and electrochem. Indeed, any explanations or main points would be greatly appreciated</p>

<p>Thanks so much nonexistent!
Aryus…how are you studying these areas?</p>

<p>@existent: Yeah thanks, Ill check that out.</p>

<p>@Monicat: I was planning on finding FRQs that delt with those two subjects specifically – usually i find reading FRQ explanations are the best way to study.</p>

<p>Okay the Chem Gods might kill me for saying this but when one electron resonances it basically divides over the number of bonds in any molecule. so nitrate has three bonds right? and each is one since its a single bond. so that one electron shares with all three bonds at once, sharing just a fraction of itself. thus each bond of the three would have one third of that electron</p>