Hard SAT chem question.

Test Preparation
1

<ol>
<li>Three balloons are filled with the same number of atoms of He, Ar, and Xe, respectively. Which statement is true under the same conditions of temperature and pressure?</li>
</ol>

<p>(A) The balloons contain the same mass of gas. </p>

<p>(B) All balloons have the same volume.</p>

<p>(C) The densities of the three gases are the same. </p>

<p>(D) The average speed of the different types of atoms is
the same.</p>

<hr>

<p>I put <a href="D">b</a>** because I thought if the temperature was the same, therefore the average speed of the molecules is the same too. Because V(rms) is proportional to temperature.</p>

2

<p>B. Volume constant under same conditions like STP. 22.4molgas/liter. If you have teh same number of atoms, then you have the same number of moles per gas, hence the same number of liters.</p>

3

<p>When the species NH4+, H3O+, and H2F + are arranged in order of increasing H–X–H bond angles, what is the correct order?</p>

4

<p>NH4+, H3O+, and H2F + </p>

<ol>
<li>H2F+ (Bent or linear)</li>
<li>3. NH4+ (Tetrahedral)</li>
<li>H30+ (Trigonal Pyramidal)</li>
</ol>

<p>I think.</p>

5

<p>My guess:</p>

<ol>
<li>H3O+: Trigonal pyramidal, 107 degrees</li>
<li>NH4+: Tetrahedral: 109.5 degrees
3: H2F+: Linear: 180 degrees</li>
</ol>

6

<p>No, for the first one it is D. Temperature is defined as average speed of the particles, so since temperature is the same, average speed is the same. Those aren’t ideal gases, so they don’t follow PV=nRT exactly.</p>

7

<p>^Is it reasonable to believe that a Xe atom and an He atom would move at the same speed, even though the Xe atom is more than 30 times as massive as the He atom?</p>

8

<p>(A) H3O+ < NH4+ < H2F+
(B) H2F+ < H3O+ < NH4+
(C) NH4+ < H2F+ < H3O+
(D) NH4+ < H3O+ < H2F+</p>

<p>H2F+ = sp3 (4 bonds, 2 lone pair, 2 with hydrogen) = bent structure
H3O+ = sp3 (4 bonds, 1 lone pair, 3 with hydrogen) = pyramidal
NH4 += sp3 (4 bonds, 0 lone pair, 4 with hydrogen) = tetrahydral</p>

<p>lone pairs repel more than regular bonds so H2F will be pushed the most (least bond angle)</p>

<p>It follows: H2F < H30 < NH4</p>

<p>(B)</p>