<p>About how much math is required on the chem SAT II? I am looking thru my Kaplan review book and I <em>know</em> that I could not do some of these in a reasonable amount of time because I am not good at long division. </p>
<p>Ex. 27.0 g silver was reacted with excess sulfur according to this equation:
2Ag + S –> Ag2S</p>
<p>25.0 g of silver sulfide was collected. What are the theoretical yield, actual yield, and percent yield? </p>
<p>The equation comes out to (27g Ag * 248g Ag2S)/(108g Ag * 2 mol Ag) = theoretical yield = 31g</p>
<p>Simple math, yes, but I mess up numbers really easily. I even have trouble dividing 25 by 31 to get percent yield. 
yesIsuck.</p>
<p>In addition to that, how precise are the answers? This book is rounding the decimal places off these molar masses…</p>
<p>yeah, i think for the prac problems, you can use a calculator b/c it really is impossible w/o one. but for the prac tests, don’t use one. i have the same book… i just gave up doing the review problems.</p>
<p>Urg…I’m still struggling thru them. Calculatorless I got ~70.5g. w/ calc ended up with 8.8g.(Correct freakin’ answer!) See? Seeseesee! I can’t do maaaath!</p>
<p>I gave up doing the review questions dealing with math in Kaplan. The conceptual questions are all easy, but as soon as I see numbers, I blank out and just move on…</p>
<p>Your equation is not hard. There is always a trick to these</p>
<p>27/108 = 1/4 and 248/2 = 144 now 1/4 * 144 = 31. They could have a problem like that on the test. Don’t be surprised but yes even I admit some of those Kaplan problems should require calculators.</p>
<p>Yeah, little tricks like that are good.</p>
<p>27g of Ag is .25 mols. Half as much Ag2S should be produced, or .125 moles. Break it into steps. 248<em>1/4</em>1/2 (since .125=1/8).</p>
<p>Actual yield: 25 grams was produced (MM of Ag2S is 248), and 25 is approximately 1/10 of 248. So about .1 mol Ag2S was produced.</p>
<p>.1/.125 is the percent yield. You should know that .125 is equal to 1/8. Then you can rewrite this division problem as 1/10*8/1, which equals 8/10 or .8 or 80%.</p>