In: Chemistry
A 1.10 −g sample of dry ice is added to a 765 −mL flask containing nitrogen gas at a temperature of 25.0 ∘C and a pressure of 715 mmHg . The dry ice is allowed to sublime (convert from solid to gas) and the mixture is allowed to return to 25.0 ∘C.
What is the total pressure in the flask?
Express your answer using three significant figures.
Step 1: Explanation
The ideal gas law is the equation of state of a hypothetical ideal gas. It is a good approximation of the behavior of many gases under many conditions.
We know the ideal gas equation, PV = nRT
where, R=universal gas constant ( it may vary in unit like 0.08206 L-atm mol-1 K-1)
T=Temperature ( Unit = Kelvin )
P=Pressure ( Unit= atm )
V=Volume ( Unit=Litre )
n=moles ( Unit = mol )
Step 2: calculate the moles of dry ice (CO2)
Molar mass of dry ice (CO2) = 44.01 g/mol
mass given = 1.10 g
Moles of dry ice = mass / molar mass = 1.10 g /44.01 g/mol = 0.02499432 mol
Step 3: Calculate the pressure of dry ice
moles(n) = 0.02499432 mol
volume(V) = 765 mL= 0.765 L
[ Note : => 765 mL × (1 L / 1000 mL ) = 0.765 L ]
Temperature = (25 +273.15)K = 298.15 K
By using the ideal gas equation
P = nRT / V
P = (0.02499432 molx 0.08206 L -atm /K -mol) x 298.15 K) / ( 0.765 L) = 0.799367 atm = 607.519 mmHg
[ Note: 1 atm = 760 mmHg => 0.799367 atm × (760 mmHg / 1 atm ) = 607.519 mmHg
Step 4: Calculation of total pressure
Given,
pressure of nitrogen gas = 715 mmHg
we got pressure of dry ice = 607 mmHg
Total pressure of flask = pressure of dry ice + pressure of nitrogen gas
=> Total pressure of flask = 607 mmHg + 715 mmHg = 1322 mmHg
hence, the total pressure of the flask = 1.32 × 103 mmHg