AP CHEMISTRY. What is wrong with this solution?

Test Preparation AP Test Preparation
1

<li>A gas has a density, at STP, of 3.48 g/L. The most reasonable formula for this compound is</li>
</ol>

<p>(A) C2H6
(B) HF
(C) CCl4
(D) C6H6 (TEACHER/BOOK ANSWER)
(E) CaF2 (MY ANSWER)</p>

<p>My Solution:</p>

<p>Molar Mass = dRT/P = (3.48)(0.08206)(273)/1 = 77.96 g/mol.</p>

<p>(A) C2H6 (Molar Mass = 30.08 g/mol)
(B) HF (Molar Mass = 20.01 g/mol)
(C) CCl4 (Molar Mass = 153.81 g/mol)
(D) C6H6 (Molar Mass = 78.12 g/mol)
(E) CaF2 (Molar Mass = 78.02 g/mol)</p>

<p>Clearly, according to my solution, the answer should be E. Why is the “correct” answer actually D? This was a test question.</p>

2

<p>If you take it to 3 sig figs, C6H6 is 78.0 g/mol while CaF2 os 78.1 g/mol.</p>

3

<p>perhaps because CaF2 wouldn’t be a gas unless its temperature is 90000000 K</p>

4

<p>

If you take it to 3 sig figs, C6H6 is 78.0 g/mol while CaF2 is 78.0 g/mol. You have it switched around. Clearly, E is the right answer!</p>

5

<p>

How do you know that CaF2 is NOT a gas and C6H6 IS a gas?</p>

6

<p>ionic compounds are solids @ room temperatures… they’re lattice structure is very rigid so it takes a lot to get them to be gases</p>

<p>C6H6 is covalent and many covalent compounds are gases @ room temp</p>

7

<p>it says STP, the temperature that Caf2 would be a gas is not at STP</p>