How many moles of helium are present in a 6.3 L cylinder stored at 25 degree C a

Question

How many moles of helium are present in a 6.3 L cylinder stored at 25 degree C and 1.0 atm? In a typical automobile, the fuel/air mixture in the cylinder is compressed from 10 atm to 9.5 atm. If the volume of the cylinder is 750 mL, what is the volume when fully compressed? Given the following percent compositions by mass, determine the simplest formula for the compound: a) 54.53%Carbon, 9.15% Hydrogen, 36 32 oxygen b) 66.67% Carbon, 11.11% Hydrogen, 22.22% Oxygen c) 85.63% Carbon, 14.37%Hydrogen

Explanation / Answer

PV= nRT

P = Pressure in atm

V= Volume in Liter

n = number of moles

R = Gas constant = 0.0821 L atm K-1 Mol-1

T = Temperature in Kelvin

Question 1

P = 1 V = 6.3 L T = 298 K

Number of Moles = PV / RT

Number of Moles = 1 x 6.5 / 0.0821 x 298 = 0.2656 Moles

0.2656 Moles of He is present

Question 2

P1V1 = P2 V2

P1 = 1 atm P2 = 9.5 atm

V1 = 0.75 L V2 = ?

The substitute these values into the equation P1V1 = P2V2 and solve for V2

1 x 9.5 = 0.75 x V2

V2 = 9.5 / 0.75 = 12.66 Liter

Volume of gas is 12.66 Liter

Question 3 a

Moles of carbon = 54.53 /12 = 4.5

Moles of hydrogen = 9.15 /1.0058 = 9

Moles of oxygen = 36.32 /16 = 2.27

Simplest formula = C4H8O2

Question 3b

The same calculation can be used

Simplest formula = C4H8O

Question 3c

The same calculation can be used

Simplest formula = C7H14

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