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Answer: A certain anesthetic contains 64.9 percent C, 13.5
Chapter 5, Problem 49P(choose chapter or problem)
A certain anesthetic contains 64.9 percent \(\mathrm{C}, 13.5\) percent \(\mathrm{H}\), and 21.6 percent \(\mathrm{O}\) by mass. At \(120^{\circ} \mathrm{C}\) and \(750 \mathrm{mmHg}, 1.00 \mathrm{~L}\) of the gaseous compound weighs \(2.30 \mathrm{~g}\). What is the molecular formula of the compound?
Questions & Answers
QUESTION:
A certain anesthetic contains 64.9 percent \(\mathrm{C}, 13.5\) percent \(\mathrm{H}\), and 21.6 percent \(\mathrm{O}\) by mass. At \(120^{\circ} \mathrm{C}\) and \(750 \mathrm{mmHg}, 1.00 \mathrm{~L}\) of the gaseous compound weighs \(2.30 \mathrm{~g}\). What is the molecular formula of the compound?
ANSWER:Step 1 of 2
The goal of the problem is to find the molecular formula of the anesthetic compound.
Given:
T = 120°C = 120 + 273 = 393 K
P = 750 mmHg
V = 1.00 L
Mass of compound \(=2.30 \mathrm{~g}\)
Mass percent of \(\mathrm{C}=64.9 \%\)
Mass percent of \(\mathrm{H}=13.5 \%\)
Mass percent of \(\mathrm{O}=21.6 \%\)
First, let's convert pressure in mmHg to atm:
\(1 \mathrm{~atm}=760 \mathrm{mmHg}\)
Therefore, \(750 \mathrm{mmHg}\) in atm is:
\(=750 \mathrm{mmHg} \times 760 \mathrm{mmHg}\)
\(=0.986 \mathrm{~atm}.\)
We know, the ideal gas equation:
\(\mathrm{PV}=\mathrm{nRT}\)
First, let's find the number of moles:
\(\begin{aligned}\mathrm{n}=& \frac{P V}{R T} \\=& \quad\left[\mathrm{R}=\text { gas constant }=0.0821 \mathrm{~L} \cdot \mathrm{atm} \mathrm{K}^{-1} \mathrm{~mol}^{-1}\right] \\&=0.986 \mathrm{~atm} \times 1.0 \mathrm{~L} \\&=0.0305 \text { moles }\end{aligned}\)
Now, let's calculate the molar mass:
We know the formula to calculate the number of moles:
\(\text { Number of moles }(\mathrm{n})=\frac{\operatorname{mass}(\text { in } g)}{\operatorname{Molarmass}(M)}\)
This can be rewritten as:
\(\begin{aligned}\mathrm{M} &=\frac{\operatorname{mass}(\operatorname{in} g)}{n \text { mberof moles }} \\&=\frac{2.30 \mathrm{~g}}{0.0305 \mathrm{~mol}} \\&=75.40 \mathrm{~g} / \mathrm{mol}\end{aligned}\)