2010 AP Chemistry Free Response Discussion

Test Preparation AP Test Preparation
41

<p>The answer should be Zn+2. While Zn+2 has the same number of electrons has Ni, Zn+2 has two more protons. So, Zn+2 has a much higher nuclear charge (electron trends about ionization energy only work if the NUCLEAR CHARGE increases if you go along a period).</p>

<p>If you compare Zn+2 and Zn, Zn has two more electrons but the same nuclear charge. Taking the 1st electron from Zn would be the regular first ionization energy. However taking the 1st electron from Zn+2 would be the third ionization energy for regular uncharged Zn.</p>

<p>[url=<a href=“http://www.chemicool.com/elements/zinc.html]Zinc[/url”>Zinc]Zinc[/url</a>]

</p>

<p>hope that made sense</p>

42

<p>dillonjay sorry about that :wink:
yes but Ni is electronegatively same with Zn+2 but the fact is that Zn+2 has already ahd 2 electrons removed from its shell from Zn. so Z* increases sheilding decreases and the electrons move closer to nucleus that electrons of Zn. And also the ionization energy of Zn+2 equals the 3rd ionizaton energy of Zn</p>

43

<p>anyone know if they will take points off for putting a positive dT for 2a?</p>

44

<p>I still disagree lol
As you proceed from left to right you obviously gain more protons…and electrons as well
since Zn has an even number of protons and electrons…it’s force between the two will be stronger!!!</p>

45

<p>exactly brownman</p>

46

<p>if you said it decreased by the amount then I dont think they will care, but if you just left it positive then it will be wrong because in this case the the sign is very important in the understanding of what is happening in the problem.</p>

47

<p>Can anybody do a score prediction for me?</p>

<p>around 50 multiple choice correct; -15~</p>

<p>1/3 of number 1 correct; 3/4 of number 2 correct; 3/4 of number 3 correct; 1/2 of number 4 correct; 3/4 of number 5 correct; 1/2 of number 6 correct. Is this good enough for a four?</p>

48

<p>question 3</p>

<p>1)
a)
i) .250=x/.025
x=.00625 moles</p>

<p>ii) pv=nrt
(.950)(x)=(.00625/2)(.0821)(295)
x=.08 Liters</p>

<p>b) i) reaction order of 2
ii) reaction order of 1</p>

<p>c)
i) rate = k(MnO4)(Cl-)^2 (H+)^3</p>

<p>ii) 2.25e-8=k(.0040)(.0104)^2 (3)^3</p>

<p>k= 1.92e-3 l^5/M^5 sec</p>

<p>d) no because there are many species and it’s gonna take a lot of steps to get the products</p>

49

<p>grrr that makes sense LOL
I guess I just didn’t learn that as well as I thought</p>

50

<p>@DillonJay: effective nuclear charge in Zn^2+ on the valence electrons > effective nuclear charge on the Zn because there are less electrons – the entire original outer orbital in Zn does not exist in Zn^2+</p>

51

<p>thrack, that looks like it will be a 4 for sure</p>

52

<p>well wait…I do know that you remember now that you remove 4s electrons before you do 3d ones…what does that mean exactly in terms of the question? lol</p>

53

<p>part d number 3 = how the hell are we supposed to know that? I just guessed no</p>

<p>I got the same stuff as you omgpie on that question at least.</p>

54

<p>@aGGieENGiNeeR: rate law is determined by the slowest substep of a reaction, if the whole reaction was only one step, then the experimental rate law would have to match the rate law they gave u at the top.</p>

<p>They dont match, so that means that some other step was the slow one therefore it has to be more than one step</p>

55

<p>aGGieENGiNeeR
H+ does not exist naturally you would have to put it in solution</p>

56

<p>i know wut u mean. however this is an oxidaton redox reaction and they will occur in two different steps</p>

57

<p>okk, that makes sense. Probably got half credit then for saying no at least</p>

58

<p>Anyone wanna create a score point chart thing for the questions? As in how many points each will be worth – percentage values are 20% 20% 20% 10% 15% 15%</p>

59

<p>Is zinc one of those crazy exceptions? lol
It’s 4s0 3d10 or something like that isn’t it?
so you’re saying zn2+ is 4s2 3d10
that makes sense lol because my reasoning could support that if that’s the case…hahahaha if I had known the rules about silly transition metals hahaha</p>

60

<p>for the Zn electron config, i put …4s2, 3d8. i figured taht the 3d orbital is higher energ taht the 4s and would be removed first</p>