In a chemical reaction, A(s) --> B(s) + C(g) occurs when substance A is strongly
ID: 926691 • Letter: I
Question
In a chemical reaction, A(s) --> B(s) + C(g) occurs when substance A is strongly heated. The molecular mass of the gaseous product was to be determined from the following experimental data. Mass of A: 4.962 g ; Mass of residue (B) after cooling and weighing when no more gas was evolved: 3.684 g. When collected and stored in a 658.5 mL glass vessel at 30.4 °C, the gas exerted a pressure of 748.5 torr. Determine the apparent molecular mass of C, assuming it behaves as an ideal gas.
a. 6.54 g mol -1
b. 47.5 g mol -1
c. 49.1 g mol -1
d. 71.6 g mol -1
e. 141. g mol -1
Explanation / Answer
answer : c. 49.1 g mol -1
solution :
T = 30.4 + 273 = 303.4 K
P = 748.5 /760 = 0.980 atm
V = 658.5 mL = 0.6585 L
P V = n R T
0.980 x 0.6585 = n x 0.0821 x 303.4
n = 0.026 = moles
mass of gas = A - B = 4.962- 3.684 = 1.278
moles = mass / molar mass
0.026 = 1.278 / molar mass
molar mass = 49.1 g/mol