Chlorine pentafluoride gas is collected at -17.0 °C in an evacuated flask with measured volume of 35.0 L. When all the gas has been collected, the pressure in the flask is measured to be 0.180 atm. Calculate the mass and number of moles of chlorine pentafluoride gas that were collected. Be sure your answer has the correct number of significant digits.

1. The mass of Chlorine pentafluoride, ClF5, is 39.16g

2. The number of mole of Chlorine pentafluoride, ClF5, is 0.3mole

Explanation:

1. To solve the mass of Chlorine pentafluoride, ClF5, first, let us calculate the molar mass of ClF5. This is illustrated below:

Molar Mass of ClF5 = 35.5 + (5 x 19) = 35.5 + 95 = 130.5g/mol

From the ideal gas equation:

PV = nRT (1)

Recall:

Number of mole(n) = mass (m) /Molar Mass(M)

n = m/M

Now substituting the value of n in equation 1, we have:

PV = nRT

PV = mRT/M

Now we can obtain the mass of Chlorine pentafluoride ClF5 as follow:

Data obtained from the question include:

T (temperature) = -17.0 °C = - 17 + 273 = 256K

V (volume) = 35L

P (pressure) = 0.180 atm

R (gas constant) = 0.082atm.L/Kmol

m (mass of Chlorine pentafluoride) =?

M (molar mass of Chlorine pentafluoride) = 130.5g/mol

PV = mRT/M

0.180 x 35 = m x 0.082 x 256/ 130.5

Cross multiply to express in linear form as shown below:

m x 0.082 x 256 = 0.180x35x130.5

Divide both side by 0.082 x 256

m = (0.180x35x130.5) /(0.082x256)

m = 39.16g

Therefore, the mass of Chlorine pentafluoride, ClF5, is 39.16g

2. The number of mole of ClF5 can be obtained as follow:

Mass of ClF5 = 39.16g

Molar Mass of ClF5 = 130.5g/mol

Mole of ClF5 =?

Number of mole = Mass /Molar Mass

Mole of ClF5 = 39.16/130.5g

Mole of ClF5 = 0.3mole

The number of moles ClF5 is 0.300 moles, this is 39.1 grams ClF5

Explanation:

Step 1: Data given

The initial temperature of the Chlorine pentafluoride gas = -17.0 °C = 256 K

The initial volume of the gas = 35.0 L

The pressure measured = 0.180 atm

Molar mass chlorine pentafluoride = Molar mass: 130.445 g/mol

Step 2: Calculate moles of Chlorine pentafluoride

p*V= n*R*T

n = (p*V) / (R*T)

⇒with n = the number of moles Chlorine pentafluoride = TO BE DETERMINED

⇒with p = the pressure of the gas = 0.180 atm

⇒with V = the volume of the gas = 35.0 L

⇒with R = the gas constant = 0.08206 L* atm/mol*K

⇒with T = the temperature = -17 °C = 256 K

n = (0.180 * 35.0)/ (0.08206*256)

n = 0.300 moles

Step 3: Calculate mass of ClF5

Mass ClF5 = moles ClF5 * molar mass ClF5

Mass ClF5 = 0.300 moles *  130.445 g/mol

Mass ClF5 = 39.1 grams

The number of moles ClF5 is 0.300 moles, this is 39.1 grams ClF5