A 2.85 -g sample of an unknown chlorofluorocarbon decomposes...

A 2.85 -g sample of an unknown chlorofluorocarbon decomposes and produces 564 mL of chlorine gas at a pressure of 752 $\mathrm{mm} \mathrm{Hg}$ and a temperature of 298 $\mathrm{K}$ . What is the percent chlorine (by mass) in the unknown chlorofluorocarbon?

Key Concepts

Ideal Gas Law

This concept relates pressure, volume, temperature, and the number of moles in a gas sample using the equation PV = nRT. It provides a fundamental relationship in chemistry to determine the amount of substance (in moles) given conditions of pressure, volume, and temperature.

Unit Conversions in Gas Calculations

Accurate calculations require converting measurements into consistent units, such as converting pressure from mmHg to atm and volume from mL to L. This ensures that the values used in the Ideal Gas Law are compatible with the constant R and yield correct results.

Stoichiometry and Molar Mass

This concept involves relating the mass of a substance to the number of moles through its molar mass. It allows for determining the chemical makeup by connecting the measured amounts (mass and moles) to individual components like chlorine in a compound.

Percent Composition by Mass

This concept is the calculation of the fraction of a compound's total mass that is due to a specific element. It is performed by dividing the mass of the element of interest (obtained through stoichiometric analysis) by the total mass of the compound, and then multiplying by 100 to obtain a percentage.

Transcript

00:01 Question number 96, mass of this compound of chloro -chloro -floral carbon is 2 .85 gram.

00:25 So this compound, cf, cl, i can you just write a, b, c, because i'm not sure of, i don't know, we don't know the actual molecular formula when it's decompose.

00:42 It gives chlorine plus other products so we are told that this gives 564 milliter of chlorine at pressure of 752 and at temperature of 298 so my approach to know this to this question we want to calculate the percentage of chlorine in this you know it's going to be a mass of chlorine defined by the total mass of the compound which is 2 .85, that's 100.

01:37 But to know the mass of chlorine is the main thing we have to focus on now.

01:46 So if i can get the volume at stp, i can get the mass, the volume of chlorine, and then the mass of chlorine.

02:00 Okay, let me call this one v1.

02:03 Volume p1 and t1 but this is not hcp let me confine the volume v2 at stp as the volume at stp then my pressure p2 at stp is one atmosphere and my temperature at stp is also 25 reprocessive which is 298 kelvin so it means i am only needing this i can comfort my pressure p1 to atmosphere 752 millimeter mercury defined by 760 so that gives me that will give me let me do that 752 752 752 252 5 5 760 that is 0 .9 8 my 0 .9 atmosphere so i want to use v1 p1 equal v2 p2 that is charge law or from the general gas law just cancel our temperature because the temperature is the same so my v2 will be 3 1 p1 divided by p2 so i have to calculate my v2 is this is this my b2 will be v1 which is 564 millimeter by p1 to 0 .9 atmosphere divided by p2 which is 1 and i get v2 to be 5 .5 8 .0 6mm...

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