Answer to Question #279233 in General Chemistry for Emre

Question

A) A 3.2 g of unknown fluorocarbon compound is decomposed at 298K and produced

310 mL of fluorine gas (F2) is collected over water at 25 °C. What is the percent Fluorine

by mass in this unknown fluorocarbon compound [The vapor pressure of water at 25 °C

is 23.76 mmHg]

B) When 1 mole of this fluorocarbon compound was completely combusted in a bomb

calorimeter, it liberates 3870 kJ of heat which causes the temperature to increase from

25 °C to 26.5 °C. Compute the heat capacity of the bomb calorimeter?

Answer 1

PV$=nRT,$ let 1atm$=760mmHg$

$P_{TOTAL}=P_{F_2}+P_{H_2O}$

Let Barometric pressure$=745.4mmHg$

Pressure of Fluorine $=745.4-23.76\\=721.64mmHg$

$P_{F_2}=721.64×\frac{1\>atm}{760\>mmHg}$

$=0.9495atm$

$n=\frac{PV}{RT}=\frac{0.9495×0.310}{0.08210×298}$

$=0.012031$

Mass of $F_2=38×0.012031$

$=0.4572$

$\%$ by Mass $=\frac{0.4592}{3.2}×100\%=14.29\%$

Part B

$\Delta\>H=C\Delta\>\theta$

$3870=C×(26.5-25)$

$C=2580kJ/K$