Help with AP Chemistry

Test Preparation AP Test Preparation
1

<p>I've been having trouble with a few problems in my AP Chemistry summer homework. I was wondering if someone might be able to help me out.
(By the way this is from Chemistry Seventh Edition written by Zumdahl in case you were wondering)</p>

<p>Chapter 2
Question 6. You take three compounds consisting of two elements and decompose them. To determine the relative masses of X,Y, and Z, you collect and weigh the elements, obtaining the following data:
Elements in Compound Masses of Elements
X and Y X=.04g Y=4.2g
Y and Z Y=1.4g Z=1.0g
X and Y X=2.0g Y=7.0g</p>

<p>a) What are the assumptions in solving this problem?
b)What are the relative masses of X,Y, and Z?
c) What are the chemical formulas of the three compounds?
d) If you decompose 21g of compound XY how much of each element is present?</p>

<p>Question 90. You have two distinct gaseous compounds made from element X and element Y. The mass percents are as follows:
Compound I: 30.43%X, 69.57%Y
Compound II: 63.64%X, 36.36%Y</p>

<p>In their natural standard states, element X and element Y exist as gases. (Monatomic? Diatomic? Triatomic? that is for you to determine.) When you react "gas X" wiht "gas Y" to make the products you get the following data (All STP)</p>

<p>1 volume of "gas X"+2 volumes "gas Y"----> 2 volumes of Compound I
2 volumes of "gas X"+ 1 volume "gas Y" ----> 2 volumes of Compound II</p>

<p>Assume the simplest possible formulas for reactants and products in the chemical equations above. then, determine the relative atomic masses of element X and element Y.</p>

<p>(( seems like those relative atomic mass questions get me pretty good all the time D: ))
Thanks for the help, since I haven't even taken the class yet and this book is really bad at teaching (in my opinion of course) and our teacher isn't around for help. </p>

<p>:3 Ambi-chan</p>

2

<p>The first one makes no sense. What do you mean by masses?.. If you weighed the elements.. then don't you have the masses?....................</p>

<p>Question 90 is a tricky one... that requires thinking. It's very mean for a teacher to give that difficult of a question to a first-time student. That is something a book cannot teach you well. However, because of the fact the two ratios are nearly reciprocals of each other, it's a big hint to the answer of the problem when you compare that to the balanced equations. I'll give a hint. The two gases have very similar molar masses and bond in a very interesting way.</p>

3

<p>On the first one all the masses are different and they are asking you to find the relative mass of each one. I'm guess this is able to be solved by the first assumption you must make. I'm sorry if the question was not clear enough. Of course to solve the problem you need to know what this assumption is and unfortunately I don't ;_;</p>

<p>Thanks for the hint but unfortunately >.< I am not very good with textbooks or the hint that you gave me. I'm sorry but I am not quite understanding what you are saying there. If you could restate it maybe that might help.</p>

<p>D: Yeah I don't know why my teacher decided to give us a lot of difficult problems >> I mean I'm only in 12th grade and we haven't even had a class yet all we have are the books and luckily I got a 5 steps to a 5 review book which helps some (but not a lot) T_T Thanks once more for trying. It means a lot.</p>

4

<p>I really think number one is not right. There is no way that a two-element compound can have the mass percent of x be .9434%, and suddenly the mass percent of x jumps up to 22.22%. Those two compounds are made of the exact same elements.
The only element that possibly could have x be .94% of it's total mass is Palladium Hydride. </p>

<p>As for the 2nd one, they have very similar molar masses, and one of the elements is nitrogen.</p>