SAT Chemistry Questions

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<p>I'm trying this again...would really appreciate your help for my test next week. And page references that I give for questions in the Barron's book aren't that important (I think you can get the gist of my question from just reading what I write). Thanks.</p>

<p>Questions</p>

<p>1) Which is the more reactive – fluorine or francium? (I know that F is the most reactive nonmetal, and Fr is the most reactive metal).</p>

<p>2) Are electrostatic bonds considered intermolecular forces of attraction?</p>

<p>3) “Minimum repulsion between two electron pairs in a molecular compound will result in a linear structure”  This statement is TRUE. I thought it was false though because I thought repulsion would be maximum since the electron pairs would be 180* apart, the furthest possible.</p>

<p>This statement is also TRUE. “The VSEPR model says that like charges will orient themselves so as to diminish the repulsion between them.” But again, I thought the repulsion would be maximized. Why am I wrong for both these statements? (Btw, the answer is TTCE just incase you’re wondering)</p>

<p>4) 2K + 2H2O  2KOH + H2(g) Can O2 be a product instead of H2?</p>

<p>5) What is the 2n^2 rule for the valence electrons? (Like the first shell has 2 electrons, then 8, then 18, etc…is the “rule” that turned out to be not right?) I remember seeing it somewhere in Barron’s book and then lost it and haven't been able to find it since.</p>

<p>6) What is the difference between subshells and sublevels?</p>

<p>7) Reference – page 72, Barron’s: Where does the + charge on the NH4+ ammonium ion come from?? Also on this page, I do not understand the potential energy graphs at all. Would you be able to please simply explain them to me?</p>

<p>8) page 72 - London forces cause nonpolar substances like noble gases to condense into liquids, then freeze into solids because the London forces cause the particles to generally be closer together? Is that a correct explanation?</p>

<p>9) also on page 74 - what is electron density?</p>

<p>10) page 75 - resonance structures. What are they? The diagrams just seem to be rotated, and this could be done for any molecule. Nothing seems to distinguish the three sulfur trioxide structures, or the two benzene ones.</p>

<p>11) page 155 – can someone please explain gram-equivalent mass and normality please?</p>

<p>12) Specific gravity essentially is just density?</p>

<p>13) Is gram-atomic mass essentially the molar mass without the moles? And same with gram-formula weight? (Also, difference between the mass in gram-atomic mass and weight in gram-formula weight?)</p>

<p>14) Definition of monoatomic on page 69 – “elements that show no tendency to combine with iether like atoms or other kinds of elements” – so I figured noble gases. BUT, on page 88, rule number 1 says “The oxidation number of a monoatomic ion is the same as the charge on the ion. Therefore, in NaCl, the oxidation number assigned to sodium is +1, and the oxidation number of chlorine is -1” WHAT?! This doesn’t seem to have anything to do with the original monoatomic???</p>

<p>15) Any easy way to remember solubility rules? Any mnemonic methods?</p>

<p>16) Page 159 - What is the difference between orthorhomic, triclinic, and tetragonal crystal structures? The three structures just seem to have different bases (perhaps the internal axis?)</p>

<p>17) Page 160 #11 – The question asks “When another crystal was added to a water solution of the same substance, the crystal seemed to remain unchanged. Its particles were:</p>

<p>A) going into an unsaturated solution
B) exchanging places with others in the solution
C) causing the solution to become supersaturated
D) not going into solution in this static condition</p>

<p>The answer was B. But my question is, how do you tell the difference between the situation in B (equilibrium) vs. the situation in C (supersaturation)? Don’t the two situations look the same physically?</p>

<p>18) Do I need to memorize the activity series?</p>

<p>19) Why does the universe prefer exothermic reactions if the universe likes low energy, high entropy? Don’t exothermic reactions release energy, so the energy is therefore high? Or do I have this reversed?</p>

<p>20) I am sooo bad at mental math – any tips/tricks for doing square roots of numbers in scientific notation? Or dividing/multiplying/decimal places? I know for multiplying, add the exponents on the 10; for dividing, subtract the exponents but I’m pretty bad with the rest. How hard does the math on the test get?</p>

<p>21) Degrees kelvin can never go negative, right? (Because then an endothermic reaction, a negative entropy level could make a negative delta G, but according to Barron’s on pg. 197, that is impossible)</p>

<p>22) Is Ca(OH)2 a strong base? In PR, it is not. But it seems like Barron’s is implying that it is on page 202 because it is completely or near completely ionized in water.</p>

<p>23) I think I am mixing up aqueous solutions with something else, but on page 203, under Broader Acid-Base theories, it talks about reacting HCl with NH3 to make a white solid, NH4Cl. But, according to the solubility rules all Cl compounds are soluble. However, NH4Cl isn’t soluble, because it isn’t in an aqueous solution, right? The questions will make sure to state that we are dealing with aqueous solutions?</p>

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<p>3) The repulsion is minimized when they are further away. Think of them like magnets; if you hold two magnets with the same pole toward each other, the closer they are the stronger you feel the repulsion. Further away = less repulsion.</p>

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<p>thanks bigmrpig!</p>

<p>Anyone else..?</p>

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<p>1.) F is the reactive element period.</p>

<p>4.) It has to be hydrogen based, so O2 isn't allowed.</p>

<p>5.) first orbital subshell (s) has 2(1)^2 = 2 electrons, 1st + 2nd subshell (s + p) has 2(2)^2 = 8 electrons, 1st + 2nd + 3rd (s + p + d) has 2(3)^2 = 18 electrons, 1st + 2nd + 3rd + 4th (s + p + d + f) has 2(4)^2 = 32 electrons, and so on.</p>

<p>6.) to what i know, electron subshells are s,p,d,f and sublevels are 1s,2s,2p,3s,3p,3d, etc.</p>

<p>7.) NH4+ means that it is a cation and its extra electron has been torn off in an aqueous solution</p>

<p>10.) Resonance deals with the superposition of all stable lewis structures of a certain compound- it shows that bonds will not necessarily will be single or double or triple, but in the middle between two. It is done to better model the observations on these compounds.</p>

<p>14.) Monatomic simply means it is found in nature as one atom (Mg, Ca, etc., not F2, O2, H2). Monatomic entities will have ox #s that replicate its ion when in a compound (ex. MgCl2--> Mg naturally makes Mg2+ ion, and Cl naturally makes Cl- ion, so Mg has +2 and Cl has -1. Note that (+2) x 2(-1) = 0 --> the sum of the ox #'s should reflect the charge of the total compound.)</p>

<p>21.) Kelvin is an absolute scale, so it can never be a negative number</p>

<p>22.) Ca(OH)2 is not exactly a weak base, but it doesn't completely ionize in water, so for purposes of the exam, we consider it a weak base.</p>

<p>23.) They will have to tell you it is in an aqueous solution. It cannot split into ions otherwise.</p>

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<p>Ahh, sweet, thank you stupak! :)</p>

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<p>Buummmppppp!</p>

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<p>17) Choice B. When more solute is added and no changes occurred, this indicates that the solution is saturated. In a saturated solution, there is equilibrium; and whenever solute is added, they will go in but dissolved solute will be precipitate back out from the solution in order to maintain equilibrium. That's why it is the same as exchanging places with others in the solution.</p>

<p>18) If you know those three metals that would not react, and the one that is the most reactive, that would be enough.</p>

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<h1>19</h1>

<p>First, nothing wants to work.</p>

<p>Entropy can be defined as disorder.
Universe prefer high entropy (disorder) since it does not require work nor energy.
For example: Solid > Liquid > Gas
In reverse, when going back from gas to solid, work is required. And, nothing wants to work, therefore this is not preferred. </p>

<p>Enthalpy is energy.
Exothermic is preferred because they release heat or energy.
Endothermic is not preferred because they need heat or energy.</p>

<p>High entropy and Low enthalpy is kind of impossible to exist together as you said. That's why every reaction is kind of in the middle, and even if being extreme, there will be reverse reaction to balance the extreme off.</p>