<p>This is a great review for me too. Keep the questions coming.</p>
<p>@miheonigirisan: I’m not exactly sure on this one, but I’ll give it a shot.</p>
<p>So you have 14.020 g of CO2 released. This means you have around 0.32 mol CO2 released.</p>
<p>Since the combustions release the same amount of CO2, that means that you can divide the moles of CO2 released between the two to get 0.16 mol CO2 released by each combustion.</p>
<p>This means that you have 0.16 mol methanol and 0.08 mol ethanol. Convert these to grams and you get 5.13 g methanol and 3.69 g ethanol. </p>
<p>This gives you a mass percentage for methanol of about 58.2%.</p>
<p>Hope this is right, haha</p>
<p>@tmanneopen: Thanks! i was thinking the same thing but i was having some doubts, its good to know someone agrees :P</p>
<p>thanks again for the quick response! :O</p>
<p>if anyone disagrees please respond!</p>
<p>how are you supposed to know that N2O5 + H2O yields HNO3?</p>
<p>^All nonmetal oxides in water yield an acid.</p>
<p>Well N2O5 is known as an acid anhydride. </p>
<p>An acid anhydride is any nonmetal combination, usually between two nonmetals, such as C,N, and S, combined with oxygen. These always form acids when put into water.</p>
<p>So N2O5 + H2O -> 2HNO3</p>
<p>There’s also something called a base anhydride, which is usually a metal, such as Li, K, and Ca, that when combined with oxygen and put in water, form bases, like:</p>
<p>Li2O + H2O -> 2LiOH</p>
<p>EDIT: Haha, I got sniped. Nice job HBrown</p>
<p>lol im basically gonna stalking this thread until tuesday morning</p>
<p>^thanks for ur contributions tmanneopen =D</p>
<p>^I agree I love everybody on this thread…soooooooooo… much</p>
<p>anyways, yeah i’m back with another question (no surprise haha…)</p>
<p>Mixtures that would be considered buffers include which of the following? </p>
<p>I. .10M HCl + .10M NaCl
II. .10M HF + .10 M NaF
III. .10 M HBr + .10M NaBr</p>
<p>can anybody explain why only II is considered a buffer? and can anybody explain the concept of buffers to me because I don’t really get them</p>
<p>Is anyone familiar with the scoring of the exam???</p>
<p>^ because HF is the only weak acid
buffers must be made froma weak acid + base</p>
<p>not sure about explaining though Dx</p>
<p>I is not a buffer because I is a strong acid + salt of conjugate base
III is not a buffer for the same reason</p>
<p>In general there are 4 ways buffers can be formed</p>
<ol>
<li><p>weak acid and the salt of its conjugate base
HF with LiF
H+ + CH3COO- => CH3COOH
CH3COOH + OH- => H2O + CH3COO</p></li>
<li><p>weak base and the salt of the conjugate acid
C6H5NH2 + H+ => C6H5NH3+
C6H5NH3+ + OH- => C6H5NH2 + H2O</p></li>
<li><p>weak acid and half as many moles of strong base
HA+ OH- => H2O + A-
add 1 acid, .5 base form .5,.5,.5</p></li>
<li><p>weak base and half as many moles of strong acid
B + H+ => BH+</p></li>
</ol>
<p>How come NaCl isn’t considered a solid in my earlier question? Isn’t NaCl just common table salt?</p>
<p>AP Chem makes me feel like an idiot.</p>
<p>ahh thank you guys!
ok now buffers make sense to me as well… i swear i’m studying by posting questions on this thread i haven’t opened my ap book at all</p>
<p>AP Calculus BC this week made me like I have the intelligence to qualify as a human</p>
<p>By the way, you guys are all amazing. Like honestly. I owe you all tremendously. :)</p>
<p>zzxjoanw3, NaCl is in aqueous solution which means that it will dissociate into Na+ and Cl- ions so it’s not a solid</p>
<p>I hope that makes sense</p>
<p>let me rephrase: why does N2O5 + H2O yield HNO3 and not HNO2?</p>
<p>@zzxjoanw3: I have really laggy internet right now so sorry i didnt bother to find ur question ■■■■■ sorry again</p>
<p>NaCl is a soluble salt, all group Is are soluble because of high charge density and whatnot, when in water NaCl(s) does not exist, only NaCl(aq) as a rule of thumb, u always write NaCl(aq) unless they specifically say solid sodium chloride (NaCl)</p>
<p>jacmoo, generally when you do those reactions the trick is to add up the number of Oxygens on the reactants side </p>
<p>because it is N2O5 + H2O
there are 6 oxygens in total, and the ratio is N2O6 so it would yield NO3 because 6/2 is 3. I don’t know why conceptually but the reactions usually work that way</p>
<p>Can any of you guys please explain the answer for this question from the 02 AP? </p>
<ol>
<li>A pure, white crystaline solid dissolves in water to yield a basic solution that liberates a gas when excess acid is added to it. On the basis of this information, the solid could be</li>
</ol>
<p>a. KNO3
b/ K2CO3
c. KOH
d. KHSO4
e KCL</p>
<p>Correct answer is B.</p>