An Erlenmeyer flask that weighs 93.667g has a quantity of liquid vaporized in it

Question

An Erlenmeyer flask that weighs 93.667g has a quantity of liquid vaporized in it at 96.4oC and a pressure of 1583.8 torr. The mass of the cooled flask is 94.345g. When the flask is filled with water, the mass of the flask and water is 268.92g.

(a). Determine the molecular weight of the unknown liquid.   g/mol    ** Write answer in decimal form to one decimal place, NO units in answer**

(b). Given the following compounds:

Liquid             Molecular Weight (g/mole)

Pentane                     72.2

Acetone                     58.1

Methanol                   32.0

Hexane                      86.2

Ethanol                      46.1

Propanol                    60.1

What is the identity of the unknown liquid?

Explanation / Answer

Solution :-

Mass of the flask = 93.667 g

Mass of cooled flask = 94.345 g

Mass of flask filled with water = 268.92 g

Mass of water = 268.92 g – 93.667 g = 175.25 g

So the volume of flask = 175.25 ml = 0.17525 L

Because density of water is 1 g/ml

Mass of liquid = 94.345 g – 93.667 g = 0.657 g

Now lets convert pressure to atm

1583.8 torr * 1 atm / 760 torr = 2.084 atm

Temperature = 96.4 C +273 = 369.4 K

Now lets calculate the moles of the vapor in the flask

PV= nRT

n= PV/RT

n= 2.084 atm * 0.17525 L / 0.08206 L atm per mol K * 369.4 K

n= 0.012048 mol

now lets calculate the molar mass of the liquid using the moles and mass

molar mass = mass / moles

                     = 0.657 g/0.012048 mol

                     = 54.5 g per mol

So the closest molar mass is the acetone = 58.1 g per mol

So the identity of the compound is acetone

Related Questions

Navigate

• Browse (All)
• Browse A
• Subjects

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.