<p>@athena I used to do that a LOT, but not so much anymore. I guess it’s through years of practice (I’ve been doing SAT since I was in 8th grade and spent all of my summer last year and weekends during the school year till January doing practice tests) because after a while you start to get to recognize when you’re about to make a silly mistake and are able to avoid it. Or you look at a question and know exactly what you’re supposed to do. I move pretty quickly through tests, but not so fast that I make mistakes. If I read a question and don’t get what it says, I’ll read it at least two more times before moving on.</p>
<p>@thelemonisinplay: A took a lot of those practice tests and the answer key especially on part B tends to be incorrect. I didn’t really look at those questions but more than likely, you’re correct. [EDIT] And yeah, I get what you’re saying. For me, I make these mental associations that occasionally mess me up. (Ex: When I see “Ag” and “NO3” and “precipitate” I always assume it’s the answer with “Ag” in it.) </p>
<p>@twogirls: It’s <em>said</em> that the Barron’s is harder than the real thing. The last SAT2 I took, I thought it was way easier but I could’ve just been lucky. </p>
<p>@Intelligentsia: will do. </p>
<p>Questions…How do you guys time yourself? For me, I either go too slow and can’t finish the multiple choice questions at the end, or I go too fast (about 14 minutes left over) and make stupid mistakes on the way.</p>
<p>I do it at a pace I’m comfortable with. I take enough time to do it carefully but not too much. I normally finish in 30-40 minutes.</p>
<p>I go at a fairly quick pace; while I’m taking the questions, I’m always aware of the time passing, and I frequently look up to check the clock. But my main focus is, obviously, on the questions. I usually finish with about 15 mins to go back to questions I skipped and quickly check over all the rest.</p>
<p>I just go through the test in rounds. I answer the "duh"s first, go back and then answer the "okay yeah this makes sense; I probably just didn’t read it/look at all of the answer options/whatever the first time"s, followed by the “I’m not sure, but I think this makes a least a bit of sense” to the "I surrender"s. By that point, ~45 minutes have passed. Wavering between two options is also included in there somewhere.</p>
<p>Speaking of surrendering, I think I’m done with chemistry for the day. Time for history.</p>
<p>I’m really confused here.</p>
<p>How much heat energy is released when 8 grams of hydrogen are burned? The thermal equation is 2H2+O2->2H20+483.6 KJ.</p>
<p>I answered 483.6 kJ but the right answer on the Barron’s test says it’s double that. Someone help explain?</p>
<p>I think that in this equation, only 4 grams, (2 moles of h2) are used.
So since you are using 8g you need 4 moles of h2. I hope this helps.</p>
<p>Oh my. This is exactly what they were just talking about.
I misread this problem D:
Thank you!</p>
<p>@nsojori</p>
<p>We know that the molecular mass of hydrogen is 2 grams/mol (diatomic, 2 atoms of 1g each) If we have 8 grams of hydrogen that means that we have 4 mols of H2 gas. By applying the mole ratio we see that 4 mols of hydrogen gas will react with 2 mols of oxygen gas to create 4 mols of H2O. This entire reaction has been doubled in size and therefore the amount of heat has to be doubled as well because it’s 483.6kJ of heat for every 2 moles of reacted hydrogen gas.</p>
<p>Thanks everyone lol.
Next thing,</p>
<p>What is the Ksp for silver acetate if a saturated solution contains 2x10^-3 moles of silver ion/liter of solution?</p>
<p>I chose A) 2X10^-3 because when I saw acetate, what immediately came into mind was it was related to a weak acid, acetic acid. So I thought it would just partially dissociate and barely change at all.
The right answer was 4x10^-6.
Does the “weak acid” thing not apply to the Ksp at all?
Sorry for the word vomit. I’m not really good in explaining things :O</p>
<p>The Ksp is asking you how soluble stuff is in water…Anything with acetate will dissolve in water…which means, it will split to Ag+ and acetate (forgot the formuala…sorry).
Therefore, it will split into two particles…silver acetate is solid (i think) so you don’t count it in the Ksp formula. So you have [Ag+][acetate]. They disassociate evenly, so the answer is the concentration of Ag+ times the concentration of acetate. Therefore:
(2<em>10^-3)(2</em>10^-3) = 4* 10^-6.
Remember, multiply the mantissas, add the exponents.</p>
<p>Well silver acetate is AgCH2COOH which dissociates like this:</p>
<p>AgCH2COOH(s) → Ag+ (aq) + CH2COOH- (aq). </p>
<p>We know this dissociates with a one to one ratio. So, if there is 2x10^-3 moles of Ag+ then there also will be 2x10^-3 moles of Acetate. </p>
<p>Apply the Ksp equation of ksp= [Ag][CH2COOH-] which is (2x10^-3)(2x10^-3) which equals 4x10^-3.</p>
<p>Hey guys can anyone send me a picture of the chemistry test from the Collegeboard Blue Book? I simply cannot go to the bookstore right now to get it. I would really, really appreciate it! Thanks! My email is rahulm442@**********</p>
<p>Anybody have last minute websites or resources for memorizing rules?</p>
<p>How many grams of H2SO4 are in 1,000 grams of a 10.% solution?(1 mole of H2SO4 = 98 g)
The right answer was 100. grams.
What happened with the molar mass of h2so4? Why isn’t it 98 grams?</p>
<p>That question doesn’t need molar mass. If H2SO4 comprises 10% of something that weights 1000 grams then H2SO4 would weight 100g</p>
<p>@Matthew5: check out sparknotes. In general, it’s pretty over if you don’t know crap by now unless you have an eidetic memory.</p>
<p>Whew, finally raised my practice score to 740. Still made some stupid mistakes though.</p>
<p>I keep on getting caught on the relationship analysis questions again, especially for the True-True and True-True-Correct Explanation answer choices. I just can’t seem to tell when the second statement directly explains the first statement. Here are four of these questions I got wrong:</p>
<p>Water boils below 100C at high altitudes BECAUSE atmospheric pressure varies inversely with altitude. (T,T,CE)
Gases are more easily compressed than liquids BECAUSE gases expand to fill their container. (T,T,CE)
The freezing of water is an exothermic process BECAUSE energy is lost when covalent bonds are formed. (T,T)
The electronic geometry of the ammonia molecule is tetrahedral BECAUSE ammonia obeys the octet rule. (T,T,CE)</p>
<p>Can somebody please explain why these answers are the way they are? I don’t exactly think like ETS wants me to, apparently.</p>
<p>The freezing of water is an exothermic process BECAUSE energy is lost when covalent bonds are formed. (T,T)</p>
<p>It’s not TTCE because phase changes of water don’t involve forming and breaking of covalent bonds. During water’s phase changes, the intermolecular forces either become stronger or weaker. Chemical bonds aren’t broken or made</p>
<p>I know the electron geometry of NH3 (Ammonia) is technically in a tetrahedral shape, shouldn’t the actual shape be trigonal pyramidal because it has a lone electron pair?</p>