AP Chemistry 2010 Study thread! Come on people!

Test Preparation AP Test Preparation
381

<p>Can you explain these please? </p>

<p>On the basis of stregth of intermolecular forces, which of the following elements would be expected to have the highest melting point? Br2, Cl2, F2, Kr, N2 </p>

<p>Equal masses of He and Ne are placed in a sealed container. What is the partial pressure of He if the total pressure in the container is 6 atm? 1, 2, 3, 4, 5 atm</p>

<p>When diluting concentrated H2SO4, one should slowly add acid to a beaker of water rather than add water to a beaker of acid. The reason for this precaution is to ensure that
A. there is complete ionization of the H2SO4
b. there is a sufficient volume of water to absorb the heat released
c. the water does not sink beneath the acid and remain unmixed
d. the acid doesn’t react with impurities in the dry beaker
e. any SO2 released quickly redissolves in the water</p>

<p>(I thought the answer would be something along the lines of…the reason for this precaution is to avoid violent splattering…)</p>

382

<p>newaccount, yes! C is correct.
can you please explain #19?</p>

383

<ol>
<li><p>A - Highest melting point = greatest molar mass = Br2</p></li>
<li><p>E - 5 atm. Assume 20 g of each. 20 g He = 5 mol, 20g Ne = 1 mol. Ratio = 5:1. So, 5 atm of He and 1 atm of Ne. </p></li>
<li><p>B - adding an acid or base to H2O generates a great amount of heat</p></li>
</ol>

384

<p>@sporty04</p>

<ol>
<li><p>Br2…it has the most electrons and more shells so all the crap is moving more than the others.</p></li>
<li><p>Equal masses, so 20/4=5 mol He 20/20= 1 mol Ne. Mol is proportional to pressure, so 5atm He.</p></li>
<li><p>B heat is generated when adding an acid to water.</p></li>
</ol>

385

<p>Explanation for 19:</p>

<p>Molar mass of chromium is about 50 (ok to approximate), and the molar mass of oxygen is about 16. You basically want a ratio of 1.5:1, so I said that if there’s 50 grams of Cr present, there need to be about 32 grams of O (O2). 50/32 is about 1.57. This is close enough to 1.62.</p>

386

<p>@sporty04 Yes, an intense amount of heat is generated. My teacher by accident added H20 to concentrated HCL and it got so hot it burned the label off the bottle. Pretty cool but not something to mess around with.</p>

387

<p>couple more…thanks! </p>

<ol>
<li>Gaseous cyclobutene undergoes a first-order reaction to form gaseous butadiene. At a particular temperature, the partialpressure of cyclobutene in the reaction vessel drops to one-eighth its original value in 124 second. What is the half-life for this reaction at this temperature?
A. 15.5 sec
b. 31
c. 41.3
d.62
e. 124</li>
</ol>

<p>i thought you had to do 124/8…</p>

<ol>
<li><p>The nonvolatile compound ethylene glycol, C2H6O2, forms nearly ideal solutions with water. What ist he vapor pressure of a solution made from 1.00 mole of C2H6O2 and 9.00 moles of H2O if the vapor pressure of pure water at the same temperature is 25.0 mm Hg?
a. 2.5 mm Hg
b. 7.5 mm Hg
c. 12.5
d. 22.5
e. 27.5 </p></li>
<li><p>A 360. mg sample of aspirion, C9H8O4, (molar mass 180. g), is dissolved in enough water to produce 200. mL of solution. What is the molarity of aspirin in a 50. mL sample of this solution?
a. 0.08M b. 0.04M c. 0.02M d. 0.01M e. 0.0025M</p></li>
</ol>

388

<p>@classicgirll: haha yep but no one is answering : ( xD</p>

<p>nah its from a practice my teacher gave, except he didnt supply the answer to c so i have no idea how to do it : /</p>

<p>anyone? hahaha</p>

389

<p>questions!

  1. what volume of 0.15 molar HCl is required to neutralize 25 mL of 0.120-molar Ba(OH)2?
    a) 20 mL
    b) 30 mL
    c) 40 mL
    d) 60 mL
    e) 80 mL </p>

<ol>
<li><p>when dilute nitric acid was added to a solution of one of the following chemicals, a gas was evolved. this gas turned a drop of limewater, Ca(OH)2, cloudy, due to the formation of a white precipitate. the chemical was…
a) NH3 ammonia
b) baking soda, NaHCO3
c) table salt, NaCl
d) epsom salts MgSO4*H2O
e) bleach, 5% NaOCl</p></li>
<li><p>which of the following has the lowest conductivity?
a) 0.1 M CuSO4
b) 0.1 M KOH
C) 0.1 M BaCl2
d) 0.1 M HF
e) 0.1 M HNO3</p></li>
</ol>

390

<ol>
<li>C - 1/8 its original value is the same is 1/2 * 1/2 * 1/2 or 3 half lives. 124/3 = approximately 41.3</li>
</ol>

391

<p>Whats the likelyhood calorimetery will be on the test tmr? itd be a shot to the head, anyone wanna quickly summarize it? =D</p>

392

<p>

</p>

<p>C.) 41.3 is the answer</p>

<p>Explanation. ln(Nt/No)=-kt<br>
ln(1/8)=-k(124)
k=.0168</p>

<p>next, t1/2= .693/k = .693/.0168 = 41.3</p>

<p>But I need help, i needed to use a calculator for the LN multiplication. How do you do this without a calculator?</p>

<p>edit: thanks newaccount, that works</p>

<p>

-(mc(delta T))of substance 1 = +(mc(delta T)) of substance 2</p>

393

<p>@sporty04:

  1. C
  2. no idea…A?
  3. D?</p>
394

<p>classic:</p>

<ol>
<li>C</li>
<li>B</li>
<li>D</li>
</ol>

395

<p>I have the answers but I just don’t get the explanations. lol…im so screwed for tomorow… sigh</p>

396

<ol>
<li><p>what volume of 0.15 molar HCl is required to neutralize 25 mL of 0.120-molar Ba(OH)2?
a) 20 mL
b) 30 mL
c) 40 mL <– ANSWER
d) 60 mL
e) 80 mL </p></li>
<li><p>when dilute nitric acid was added to a solution of one of the following chemicals, a gas was evolved. this gas turned a drop of limewater, Ca(OH)2, cloudy, due to the formation of a white precipitate. the chemical was…
a) NH3 ammonia
b) baking soda, NaHCO3 <– ANSWER? (please verify)
c) table salt, NaCl
d) epsom salts MgSO4*H2O
e) bleach, 5% NaOCl</p></li>
<li><p>which of the following has the lowest conductivity?
a) 0.1 M CuSO4
b) 0.1 M KOH
C) 0.1 M BaCl2
d) 0.1 M HF <– ANSWER!
e) 0.1 M HNO3</p></li>
</ol>

397

<p>@classicgirll</p>

<p>Answer to 2 is B i think because of the following reaction:</p>

<p>NaHCO3 + HNO3 –> NaNO3 + H2O + CO2</p>

<p>Gas forming reaction?</p>

398

<p>This is correct. ^</p>

399

<p>What is the logic behind number 3?</p>

400

<ol>
<li>what volume of 0.15 molar HCl is required to neutralize 25 mL of 0.120-molar Ba(OH)2?
a) 20 mL
b) 30 mL
c) 40 mL <– ANSWER
d) 60 mL
e) 80 mL </li>
</ol>

<p>is there a typo? it HAS to take less than 25 mL doesn’t it?</p>

<p>OH WAIT NVM Ba(OH)2 breaks into TWO moles of OH so then 20mL(which i originally calculated) x2 = 40XD thanks now maybe I’ll catch that on the test tomorrow</p>

<ol>
<li><p>when dilute nitric acid was added to a solution of one of the following chemicals, a gas was evolved. this gas turned a drop of limewater, Ca(OH)2, cloudy, due to the formation of a white precipitate. the chemical was…
a) NH3 ammonia
b) baking soda, NaHCO3 <– ANSWER? (please verify)
c) table salt, NaCl
d) epsom salts MgSO4*H2O
e) bleach, 5% NaOCl
because CaCO3=white precipitate i believe although i have yet to study that packet</p></li>
<li><p>which of the following has the lowest conductivity?
a) 0.1 M CuSO4
b) 0.1 M KOH
C) 0.1 M BaCl2
d) 0.1 M HF <– ANSWER!
e) 0.1 M HNO3
just to verify, although i’m sure everyone knows, HF is a weak acid so it splits into… i guess between… .1 and .2 mols of ions</p></li>
</ol>

<p>YAY CHEM IS THE ONLY TEST I’M READY FOR OUT OF ALL THE ONES I’M TAKING/HAVE TAKEN</p>