Official January Chemistry SAT II Thread

Test Preparation SAT Subject Test Preparation
1

<p>Here's a thread where we can discuss questions and worry together! =)</p>

<p>I actually have a few questions about the test:</p>

<p>1) In the T/T/CE Section, there was a chromotography question. Which of three components travel the fastest? (The bottom, middle, or top component?) Does the bottom component have the greatest binding to the stationary?</p>

<p>2) In the T/T/CE Section, the second part of a question asked if a catalyst changes the reaction mechanism. </p>

<p>3) In the T/T/CE part, Na3PO4 is mixed with water. 1) The solution is basic 2) Does PO4 -3 accept an H+ and form HPO4 -2 and OH-? I put T/F</p>

<p>4) There are two unknown substances.</p>

<p>Substance A ~ -2 melt point and 81 boil pt 0.8 density
Substance B ~ -3 mp, and 150 bp 1.3 density</p>

<p>If the substances are at room temp, how would you separate them?</p>

<p>Distillation
Filtration
Precipitation
Crystallization
And a wrong fifth answer that I forgot</p>

<p>Is it distillation?</p>

<p>5) In the T/T/CE part, there was a question about phosphorus compounds and nitrogen compounds. Would the nitrogen compound have stronger bonds because it is more electronegative?</p>

<p>6) In the T/T/CE part, 1) The reaction 2H2 +O2 -> 2H2O is endothermic because 2) The products have stronger bonds than the reactants.</p>

<p>I put F/T...</p>

<p>7) What was the deal with atomic speed? I remember it asked which of the atoms were the fastest, but I only remember the Ar, Ne and F2 options.</p>

2

<p>1.) For Chromotography, I said the fastest was the top one (which equated to a False I think?) and I said that the bottom one was stationary. Weird question.</p>

<p>2.) I said Catalyst didn't affect reaction mechanism, but not so sure about that anymore. It depends on whether they meant if the catalyst affected the rate of the reaction in terms of slow, rate-determining step etc or just actually participate in the mechanism. </p>

<p>3.) I put T/T/CE on that one. Not sure either :(</p>

<p>4.) Mos. def. distillation on that one. The Big boiling pts just scream out distill me.</p>

<p>5.) Errr, not sure. I remember nitrogen having triple bonds. </p>

<p>6.) I think I agree with you, F/T</p>

<p>7.) I think the fastest one was CH4 due to comparatively lower mass (see effusion rate equation).</p>

3

<p>Some other things I remembered:</p>

<p>Iodine, when heated, gives off purple vapors (pretty sure about this).</p>

<p>What did you guys put for the conducts electricity question where answer choices were (Si, K, and other stuff at beginning) I put Si, but not sure since its only a semiconductor.</p>

<p>Bunsen burner question I put blue flame is hottest.</p>

<p>Flame test question was Sodium (pretty sure).</p>

4

<p>A few things I have questions on:</p>

<p>1.) The CxHy question which asks for moles of Hydrogen in one molecule of compound, did anyone get 4?</p>

<p>2.) In the Roman Numeral question involving ammonium, hydroxide, barium, and some other element. I put that it formed a precipitate only and not the other 2 choices (H20 is present and Nh3 is present in aqueous form). Doesnt Nh4OH simply disociate into Nh4+ and OH-?</p>

<p>3.) Another roman numeral question: "Wut kinds of bonds in (Na)2CO3?" I put ionic AND covalent. Aren't there covalent bonds in carbonate ion? hope so.</p>

<p>And thats.... all i remember.</p>

5

<p>1) For the roman numeral question involving ammonium, hydroxide, barium, I put all three - precipitate forms with barium, and ammonium (acid) and OH- neutralize to form H2O and NH3
2) On the T/T/CE question about the catalyst, I put T/F, because a catalyst does indeed speed up the rate of reaction. It also changes the reaction mechanism, since the activation energy is lower, or in terms of reaction diagram, the bump is lowered, therefore forming a different mechanism.
3) On the CxHy question, I got H to be 8 moles. I think I got .8 for moles of hydrogen in water, and since there was .1 mol of the unknown, and water was the only product containing H, then y would be 8
4) Yeah, I put T/T/CE for Na3PO4 too
5) And yeah Liberal, Na2(CO3) had both ionic and covalent bonds, between sodium and carbonate and between carbon and oxygen, respectively.
6) What did you guys put for the multiple choice question where it had the graph of the reaction of X and Y? Y stayed the same while X was gradually added. I think I put I, II, and III.
7) And there was one question asking about a white precipitate with H2SO4 or something. The only choice that formed a precipitate with the acid was, I think, the compound with Ba, but doesn't Ba form a yellow precipitate?
8) Also, on the T/T/CE question about the bonds between NH3 and PH3, did you guys put T/T/CE? The second part was definetely true, since N is more electronegative than P, but is N-H weaker than P-H? I put yes, since N pulls electrons closer to itself and makes H easy to break.
9) And on the surface tension T/T/CE? I put T/T/CE</p>

6

<p>btw, I think we should move this thread to SAT Subject Tests forum</p>

7

<p>Agreed on moving this to Subject Test forum (admin anywhere?)</p>

<p>1.) The reason why I didn't put all three on the ammonium question was that I know that ammonia is supposed to act as a mild base in water, and if it is one, then it should remain in its NH4+ state in water. After the precipitate is formed, you have NH4OH, but how do you know that these split? If NH3 is basic (which it is according to barron's), I thought it would remain NH4+ and not give its H+ away to the OH- (cuz this would make it acidic). Also, check this page out:
<a href="http://www.elmhurst.edu/%7Echm/vchembook/182bases.html%5B/url%5D"&gt;http://www.elmhurst.edu/~chm/vchembook/182bases.html&lt;/a&gt;&lt;/p>

<p>If you check out google, there are a lot of entries for ammoniumhydroxide as a base. If it gave up its H+ to combine with the OH-, it would be acting like an acid (contradictory). Soooo, in the end, Im still unsure either way, hah.</p>

<p>3.) I am sure it was .4 mol H to the .1 mol (not .8) compound deacon. I can ALMOST guarantee it. </p>

<p>5.) TIGHT!</p>

<p>6.) I got the same as you deacon (like 70% sure). Numeral I was saying that X reacted all the way at 2 or something. Numeral 2 was something about excess? I don't really remember.</p>

<p>7.) lol, i googled barium sulfate in Google pics and u can find lots of pics of white crystals. So, I think its cool if you put white (I did). </p>

<p>8+9.) Ahh, can't remember anymore. I was conflicted about these two as well.</p>

8

<p>are you sure itz .4 mol of H? Don't you multiply by 2 since itz H2O, and there are two hydrogens?</p>

9

<p>What about the one with 12g of O2 in a 10L container and the molar mass of 12g of gas X in a 20L container? I don't remember what I put, but I think I did it right... although I have my doubts. But for the CxHy problem, I think I also got 8 moles of H.</p>

10

<p>gahhh, maybe im thinking about another question then :( ..or i just got it wrong which is more probable.</p>

11

<p>how many can you get wrong on average and still get an 800?</p>

12

<p>If you left 8 blank... and miss like 10 questions... is there any possiblity that you can score above 700+</p>

13

<p>K is a conductor since it's a metal!!!</p>

14

<p>4 wrong for 800.</p>

15

<p>the Na3PO4 when mixe with water -> it will only dissociate. PO4 cannot take a proton (H+) off because OH- is a VERY STRONG conjugate base -> stronger than (PO4 )3- and reactions go strong to weak. Therefore it cannot be basic solution.
I put F/F</p>

16

<p>the O2 H2 and H20 one -
the product H2O does not have stronger bonds. Water is constantly loses proton (H+) and gives it to another water molecule. H2 and O2 have really really stable bonds!!!</p>

17

<p>anyone about the idea about 8 blank and 8-10 mistake to get 700+?</p>

18

<p>nitrogen compound will have weaker bonds because of the electronegativity!
the more EN the atom is the more ionic character the bond will have -> the easier to break. as we know:
ionic<<covalent
by analogy:
polar covalent < less polar covalent < non-polar covalent.</p>

19

<p>you should expect 700-720. I don't know if the test was easier or harder than usual though.</p>

20

<p>also making water from H2 and O2 is highly EXOTHERMIC. EXPLOSION> BIG EXPLOSION. The electricity needed is to surmount the activation energy barrier.</p>