AP Chemistry 2010 Study thread! Come on people!

<p>@sporty04:</p>

<p>For the NH4Cl and HCl, there wouldn’t be much of a reaction because both compounds are acids, one weak, one strong. So therefore there’s no color changes, no gases released, no light emitted, and hardly any change in temperature, which are often the four most common signs of a reaction. </p>

<p>Covalent bonds are bonds in which two atoms share their electrons to complete their shells so there are an octet of electrons in each atom’s outer shell, giving the atom stability. For example, fluorine has 7 electrons in it’s shell. In order to become stable, it often bonds with another fluorine atom, sharing a pair of electrons between the two, allowing the shared electrons to go back and forth between the two, essentially giving an electron to each one to make it 8.</p>

<p>London dispersion forces are instantaneous attractive forces that are formed by the random motion of electrons around atoms. By chance, electrons will sometimes end up on the same side of an atom at the same time, giving that section of the atom a negative charge and the opposite side a positive charge for that one moment.</p>

<p>The reason why the London dispersion forces are the attraction forces between methane molecules is that London dispersion forces are intermolecular forces, meaning between molecules, whereas covalent bonds are intramolecular forces, meaning that they are forces within the molecule holding it together.</p>

<p>@manbean: Covalent bonding is LESS than 1.7 difference in negativity because there isn’t enough difference in charge to make ions, which is when the difference is greater than 1.7.</p>

<p>Also, London dispersion can happen in any molecule, it would just be the greatest influencing in nonpolar molecules.</p>

<p>And Ionic and Covalent bonds are stronger than all those 3.</p>

<p>Are ionic bonds inter or intra forces? Intra right?</p>

<p>Can anyone figure out the question i posted on page 24?
Any help would be appreciated.Thanks guys</p>

<p>@iamsocool - I think ionic bonds are intramolecular forces, because they are bonds that occur within molecules to hold atoms together. Intermolecular forces are attractions between molecules (like dipole-dipole or London dispersion)</p>

<p>@Adelk001: I think I posted the answer two posts below, but I’ll repost it here.</p>

<p>Ok, so we can use PV=nRT to help us.</p>

<p>Experimental: PV=nRT
(750)(0.843) = (x)(63.2)(296)
x = 0.034 mol CO2</p>

<p>Theoretical: PV=nRT
(750)(0.843) = (x)(63.2)(296)
x = 0.034 mol CO2</p>

<p>So up to this point it’s the same thing.</p>

<p>Now you can use the molar masses you have to see how many grams there should be.</p>

<p>Theoretical: (x g CO2)/(0.034 mol CO2) = (40.1 g CO2)/(1 mol CO2)
x = 1.355 g CO2</p>

<p>Experimental: (x g CO2)/(0.034 mol CO2) = (44 g CO2)/(1 mol CO2)
x = 1.487 g CO2</p>

<p>This means that you had less grams of CO2 in the actual experiment, which means that air, which has a smaller molar mass, weighed less when the mass of the gas inside was calculated, causing the molar mass to be smaller.</p>

<p>Does anyone have a useful online resource for tips on the MC non-calculator math? I can do most of it fairly quickly, but I have trouble with the more advanced stuff like calculating pH from a concentration. -log(.01) just doesn’t click for me without a calculator. Any tips for stuff like this and others?</p>

<p>i’ve got questions from the 1994 AP test:
39. samples of F2 and Xe gas are mixed in a container of fixed volume. the initial partial pressure of the F2 gas is 8.0 atm and that of the Xe gas is 1.7 atm. when all he Xe gas has reacted, forming a solid compound, the pressure of the unreacted F2 gas was 4.6 atm. the temperature remained constant. what is the formula of the compound?
a) XeF
b) XeF3
c) XeF4
d) XeF6
e) XeF8</p>

<ol>
<li>in which of the following compounds is the mass ratio of chromium to oxygen closest to 1.62 to 1.00?
a) CrO3
b) CrO2
c) Cro
d) Cr2O
e) Cr2O3</li>
</ol>

<p>@manbean,
most log conversions aren’t too hard…
basically, -log(0.01) = -log(10^-2)
so the answer is 2. </p>

<p>makes sense? and you don’t even have to get confused with the signs…because pH is always positive!</p>

<p>thanks for all your help everyone!
manbean, unfortunately i’m kind of struggling with that like you so I can’t really help you there. sorry.</p>

<p>I have a few more questions to ask from thne 2008 exam if thats ok.
Did you guys understand numbers 5 and 6? (the titration graph)
and number 26 (rate laws experiment question)
Number 30—why would you include 25.00 in sig figs?
40. On the basis of stregth of intermolecular forces, which of the following elements would be expected to have the highest melting point? (I don’t get why the answer is Br2)</p>

<p>Hope this helps everybody with their studying too! :)</p>

<p>Can anyone tell me what scores will roughly constitute as a 5? I heard 66% in MC and similar scores in the FRQ will usually get you a 5.</p>

<ol>
<li><p>B</p></li>
<li><p>B</p></li>
</ol>

<p>@Freelance: That is correct.</p>

<p>@newaccount:
19’s right
but unfortunately, 39 isn’t…</p>

<p>how did you do 19?</p>

<p>ANYONE get an answer to this yet? theres a strong possibility ksp will be on the test tmr!!!</p>

<p>There is a 500.00 mL solution that is
.0100 M in silver nitrate
.0200 M in lead II nitrate</p>

<p>Ksp AgCl = 1.8 x 10^-10
Ksp PbCl2 = 1.6 x 10^-5</p>

<p>a. What salt can be added in order to precipitate the lead II and/or silver ions?</p>

<p>b. If the salt is added speck by speck, which ion will precipitate first?</p>

<p>c. At the point which the other ion is just about to precipitate, what is the concentration of the first ion remaining in solution?</p>

<p>*ASSUME NO VOLUME CHANGE IN SOLUTION </p>

<p>*hint: adding a soluble chloride lol</p>

<p>Anyone an international on here?</p>

<p>haha i like that first statement – ;D
KSP WILL BE ON THE TEST TOMORROW! </p>

<p>i’m not sure what it’s asking to be honest…
was this on an AP exam?</p>

<p>39 is C. Silly mistake on my part.</p>

<p>Keep the questions coming. I can explain my (correct) answers if you wish.</p>

<p>NewAccount can you explain 39 please? I got 2FXe with atm=3.4 and im stuck…</p>

<p>Sure.
The reaction is:
Xe + F2 -> XeF2</p>

<p>All of the Xe reacted, and it is the limiting reactant. This gives 1.7 atm of Xe in the product. 8.0-4.6 = 3.7 atm of F2 reacted. This means that Xe and F2 are in a ratio of 1 Xe : 2 Fe2. This gives the formula Xe2(F2) or XeF4.</p>