<p>@orangefroot: Not sure why molar mass doesn’t count . . . it just doesn’t.
That’s a terrible explanation.
Just associate it with more electrons, I guess. xD</p>
<p>There was a question on that that I saw somewhere. It was about Ni2+ being dissolved in NH3 and it said that at first it precipitated, but when more NH3 was added the precipitate disappeared, then asked why. I guessed (correctly) that Ni2+ and NH3 formed a complex ion. I’m guessing it’s a situation where a metal is in a solution such that it is surrounded by ligands at least twice the number of it’s charge (the most common have 2,4,and 6 ligands, so I hear)</p>
<p>@godzilla-
if dG is negative, it is spontaneous and if positive it is not. The equation is at equilibrium if it equals 0.
for dH and dS make a chart
dH dS
-
+ always spontaneous
-
+ spontaneous at high temps
-
- spontaneous at low temps
-
- never spontaneous</p>
<p>I would just memorize these relationships</p>
<p>Knowing that the electrons lost and gained must be the same, would you rather the Honors chem stoic problem 10Br- => 5Br2 + 10e-
or the time consuming
2MnO4- + 16H+ +10e- => 2Mn2+ 8H20
It’s a matter of preference</p>
<p>@TheMysteriousOne:
That was #60 on the 2008 MC.
I guessed it right, too, haha.</p>
<h1>67, I got wrong. Could someone please explain?</h1>
<h1>71. Why is it C and not D?</h1>
<p>How do you do #74?</p>
<p><a href=“http://griffithchem.com/AP/AP%20Tests/2008%20AP%20MC%20Test.pdf[/url]”>http://griffithchem.com/AP/AP%20Tests/2008%20AP%20MC%20Test.pdf</a></p>
<p>Wow I found that if you do pretty well on the MC - 64/75 and bomb the FRQ 32/60 you can scrape a 5. According to the AP pass calculator…o.0</p>
<h1>67- you need to balance the equation not just so you have equal elements on both sides but also equal charges. It took me awhile but it comes out to be 8H+ plus 2NO2 plus Cr2O7-2 goes to 2Cr+3 plus 3NO3- plus 4HOH. The overall charge is then +3. I use plug and chug for these. Takes awhile but I get it.</h1>
<h1>71 O-F is the least polar because they are closest to each other on the periodic table meaning their electronegativity is closest to being the same. Hydrogen is off in the corner so it normally forms polar bonds and I-F are not as close as O-F which are in the same row.</h1>
<ol>
<li>not D because the I and F are in the same group. I is lower down the group so beacsue of shielding it has a lower electronegativity compared to F. BUT O and F are next to each other on the periodic table. So it has similar electronegativities. The electron cloud should be not pulled closer to either atoms. SOOO its least polar :D</li>
</ol>
<p>IM FREAKIN. its 8 30pm. And I seriously bombed my FRQ. I heard 2008 MC is easy so my pretty high score doenst mean much. GAHHHH</p>
<p>@orangefoot- just breath. Go over what you missed and try a new frq. I took the 2001 mc and got about the same score as the 2008 test. Let’s just hope for an easy test like last year.</p>
<p>11:30!!! I should sleep… both chem and psych tomorrow</p>
<p>for # 74 on the 2008 test, I know you use the equation
Mols of X = It/nF </p>
<p>How do you know that n= 2 electrons?</p>
<p>…(Cr2O7)2- + 14H+ +6e- => 2Cr3+ +7H2O Reduced</p>
<p>NO2- + H2O => NO3- + 2H + 2e- Oxidized
Make sure #electrons cancel</p>
<p>…(Cr2O7)2- + 14H+ +6e- => 2Cr3+ +7H2O </p>
<h1>+3[NO2- + H2O => NO3- + 2H + 2e-]</h1>
<p>=>2Cr3+ +3NO3- +8H+ + 4H2O
Only showed the products because that’s all we care about.</p>
<p>For electrochem reactions like these, I suggest breaking the reaction down in terms of separating the oxidized from the reduced. Then do the one that’s easiest and then use that to solve for the harder one if you haven’t already answered the question.</p>
<p>nvm I think that it’s two because Ni 2+ forms when the two nitrates come off of it, right?</p>
<p>The 2008 was easier?!
Ahh that is not a good sign.
I barely got a 5. ):</p>
<p>11:30 for me as well . . . woohoo.
What time are you guys waking up?</p>
<p>@Abrayo - #74
Multiply the # of mol by the # of e needing to transfer to form Ni metal. Convert to Faraday (1 mol e = 1 F). Convert F to Coulombs (1 F = 96500 C). Since C is A/t, solve the equation to get the time.</p>
<p>1 mol * 2 e = 2 mol e
2 mol e = 2 F
2 F * 96500 C = 193,000 C
193,000 C = 1 A * t
t = 193,000 s</p>
<h1>67) This is a REDOX reaction. Balance it however you’ve been taught (I use the half-reaction method) and see what the coefficient of H2O is after everything’s been cancelled out.</h1>
<h1>71) Non-metals in order of decreasing electronegativity: FONClBrISCH. To be LEAST polar, the difference in electroneg. has to be the smallest. Since F and O are right next to each other, F-O is least polar, even though F and O are 2 of the most electronegative nonmetals.</h1>
<h1>74) It’s a conversion. 1.00 ampere is 1 coulomb/second. You’ll need the following conversion factors:</h1>
<p>1 mole electrons/96500 coulombs
2 moles electrons/1 mole Ni2+ (because of the 2+ charge)</p>
<p>Multiply it out, and you should end up with seconds/mol Ni2+. That’s going to be your answer.</p>
<p>Ni in Ni(NO3)2 has a charge of +2 based on NO3 has a charge of -1 and there are two NO3’s. Then it says it is going to nickel metal (Ni with no charge) so you know its 2 electrons</p>
<p>@abrayo I’m on track to be sleeping at 12am. Gna plan to wake at 5 30. But I’ll probably wake at 6 00am.</p>
<p>Did you find that the 2008 FRQs were a bit tricky. esp Q5 and 6?? Why is pyridine polar???</p>
<p>Any major colors of elements or compounds we have to memorize? I’ve got K (violet), Cr2072- (orange), Cu (blue/green), Li and Sr (red), and Na (yellow). That’s about it, right? Do we need to know colors of some major gases too?</p>
<p>Can someone explain 13 and 14 on the 2008 MC?</p>