Chemistry Help Forum

Test Preparation SAT Subject Test Preparation
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<p>I felt like it would be nice to have a consolidated thread for chemistry questions.</p>

<p>This thread is:
- for asking Questions on Chem topics
- for helping each other out
- hopefully a useful study tool</p>

<p>I'm taking the chem test in November (again), but this is really just a good place to get some things clarified for not only me but really any future test taker. I'm sure a lot of people have the same questions, so we might as well archive them in an orderly fashion here.</p>

<p>Ask away, and CC shall giveth.</p>

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<p>I’ll be glad to answer all doubts too :)</p>

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<p>Electrode potentials are :
Zn –> Zn2+ + 2e E=+0.76
Au –> Au3+ + 3e E=-1.42
If a gold foil were placed in a solution containing zinc ions, what would be the reaction potential.</p>

<p>I got +2.18 but the book says the answer is -2.18</p>

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<p>It is probably electrolytic.</p>

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<p>Alright, I just have a general question.
What should I emphasize on in my studying?
What should I memorize?
Should I memorize Polyatomic Ions or there’s no need?
Should I even focus on memorizing everything organic chemistry and the functional groups, or are you not expected to know em on the test?</p>

<p>Thanks!</p>

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<p>O-chem and polyatomics come in handy. At least a general or functional knowledge of things like that is advised, though the test might not ask so much implicitly.</p>

7

<p>Electrode potentials are :
Zn –> Zn2+ + 2e E=+0.76
Au –> Au3+ + 3e E=-1.42
If a gold foil were placed in a solution containing zinc ions, what would be the reaction potential.</p>

<p>I got +2.18 but the book says the answer is -2.18</p>

8

<p>What books do you guys reccommend using to supplement an Honors Chem course as prep for the subject test?</p>

9

<p>I recommend Princeton Review, Barron’s, and Sparknotes. I only did those three and crammed for three weeks, doing a couple practice tests every week. I had taken chemistry before but had forgotten most of the material, but these books were really good for refreshing. I did an average of low 700s for Barron’s, mid 700s for Princeton Reviews, and mid 600s for Sparknotes, but got a 790 for the October test.</p>

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<p>Ok, cool! I have PR and Barrons and SN is online! 800 here I come :smiley: Thanks</p>

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<p>OK, can somebody please tell me how you can tell if a compound/molecule is a base? I thought I knew (I always thought bases were proton acceptors) until I found this
[Which</a> of the following does not react with a dilute H2SO4 solution: Why? - Yahoo!7 Answers](<a href=“Yahoo | Mail, Weather, Search, Politics, News, Finance, Sports & Videos”>Yahoo | Mail, Weather, Search, Politics, News, Finance, Sports & Videos)</p>

<p>Na2S, Na3PO4, Na2CO3</p>

<p>Accordingly, those three compounds are all bases. How are these bases? I’m really confused, please help, thanks!</p>

12

<p>Sodium almost always dissociates leaving a negatively charge ion in all three cases.</p>

<p>S -2, PO4 -3, CO3 -2
These can pick up a positive hydrogen</p>

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<p>Thanks!</p>

<p>I have another question, and the problem can be found here:
<a href=“http://talk.collegeconfidential.com/sat-subject-tests-preparation/141922-hard-chemistry-question-someone-good-chemistry-please-help.html[/url]”>http://talk.collegeconfidential.com/sat-subject-tests-preparation/141922-hard-chemistry-question-someone-good-chemistry-please-help.html&lt;/a&gt;&lt;/p&gt;

<p>Please elaborate it here, thanks!</p>

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<p>@Richardaddo:</p>

<p>The two half-reactions are (in the right directions):
Au -> Au3+ + 3e- E(ox)=-1.42
Zn2+ + 2e- -> Zn E(red)=-.76</p>

<p>E(cell) = Ecathode(reduction) - Eanode(reduction).</p>

<p>The anode in this cell is the solid gold, since that’s the site of oxidation. Its E(ox) value is
-1.42, so its E(red) value is 1.42.</p>

<p>The E(red) of the cathode is -.76.</p>

<p>Thus, E(cell) = -.76 - 1.42 = -2.18</p>

15

<p>Thus it is electrolytic</p>

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<p>…AlCl3(aq) + …NH3(aq) + …H2O -></p>

<p>Which of the following is one of the products obtained from the reaction above?
A) AlN
B) AlH3
C) Al
D) Al(NO3)3
E) Al(OH)3</p>

<p>Answer is E. Anyone know why?</p>

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<p>… And another one.</p>

<p>A 0.1 molar solutiuon of hich of the following compounds has the lowest hydrogen ion concentration?</p>

<p>A) HCl
B) AlCl3
C) NaHCO3
D) NaOH
E) HC2H3O2</p>

<p>Now, I coulda sworn the answer is B, even though I know NaOH is a strong acid. There’s no H in AlCl3! Anybody care to explain?</p>

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<p>@simo14
How do you know that the Au should undergo oxidation. Does it mean that every time, the metal placed in the solutions acts as the anode. I know that Zn is more active and electropositive than Au and that it stands a higher chance of undergoing oxidation.</p>

<p>I would be glad if you could explain this to me.</p>

<p>Thanks in advance.</p>

19

<p>^ The question says that a gold foil is placed in zinc ions. So the reactants are Au and Zn2+, so Au has to get oxidized and Zn2+ is reduced.</p>

20

<p>Thanks so much, I get it now.</p>