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A student observes that a 126 mL dry flask with a foil capweighs 50.162g. The student then adds 5 mL of an unknown volatileliquid and heats the flask in a boiling water bath at 99.2C(degrees) until all liquid disappears. The flask, foil, andunknown after heating that is dry and cool weigh 50.610 g. Thebarometric pressure in the laboratory is 743.3 mm Hg; thelaboratory temperature averages 22.3 C(degrees); the vapor pressureof the unknown liquid is 160 mmHg at 20 C(degrees), and the densityof dry air at STP is 1.2929 g/L.

a) What are the experimental conditions of T and P thatwill be used to calculated the mass of air in the flask?

the answer for this is pressure: 743.3mmHg and Temperature is 22.3 degree C

b) Calculate the density of air at the experimentalconditiosn identified in part a.

Answer: 1.17g/L

c) Calculate the mass of air in the flask before the liquid was added.

0.147g

d) Calculate the partial pressure of air in the flaskafter the liquid was heated and then cooled.

583.3 mmHg

e) Calculate the mass of air in the flask after the liquidwas heated and then cooled.

0.120g

f) Calculate the mass of air lost.

0.027g


HELP


g) Calculate the mass of liquid, vapor and air in theflask before you correct for air lost.

h) Calculated the mass of liquid, vapor and air in theflask after you correct for air lost.

i) Calculated the molecular weight of the unknownliquid.


HELP

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Related questions

A student observes that a 126 mL dry flask with a foil capweighs 50.162g. The student then adds 5 mL of an unknown volatileliquid and heats the flask in a boiling water bath at 99.2C(degrees) until all liquid disappears. The flask, foil, andunknown after heating that is dry and cool weigh 50.610 g. Thebarometric pressure in the laboratory is 743.3 mm Hg; thelaboratory temperature averages 22.3 C(degrees); the vapor pressureof the unknown liquid is 160 mmHg at 20 C(degrees), and the densityof dry air at STP is 1.2929 g/L. a) What are the experimental conditions of T and P thatwill be used to calculated the mass of air in the flask? the answer for this is pressure: 743.3mmHg and Temperature is 22.3 degree C b) Calculate the density of air at the experimentalconditiosn identified in part a. Answer: 1.17g/L c) Calculate the mass of air in the flask before the liquid was added. 0.147g d) Calculate the partial pressure of air in the flaskafter the liquid was heated and then cooled. 583.3 mmHg e) Calculate the mass of air in the flask after the liquidwas heated and then cooled. 0.120g f) Calculate the mass of air lost. 0.027g HELP g) Calculate the mass of liquid, vapor and air in theflask before you correct for air lost. h) Calculated the mass of liquid, vapor and air in theflask after you correct for air lost. i) Calculated the molecular weight of the unknown liquid

Please give me Post lab questions 2 and 3 at the bottom.

Experiment 7 - Molar Mass of a Volatile Liquid

Introduction. Given the mass of vapor at conditions of known pressure, volume, and temperature, one can determine the molar mass of the vapor. The Ideal Gas Law mathematically relates the quantities of pressure (P in atm), volume (V in liters), and temperature (T in Kelvin) and the quantity of gas (n in moles). Using the expression PV=nRT where R equals the Ideal Gas Constant 0.0821 L*atm/K*mol, one can determine the quantity of gas under given conditions of pressure, volume and temperature. The number of moles of gas is found by

PV

RT

n =

Because the molar mass (MM) is defined as the mass of one mole of substance in units of g/mol, the molar mass of the vapor can be determined by

MM= mass of vapor in grams/moles of vapor

In this experiment, an unknown volatile liquid is heated in a boiling water bath and is vaporized. The vapor forces air from the flask until the pressure within the flask equals the barometric pressure of the lab. As with all gases, the vapor occupies the entire volume of its container. The temperature of the vapor equals the temperature of the boiling water bath. After 8-10 minutes, the vapor is cooled. The mass of the condensed liquid is determined and the molar mass is calculated as described above.

Notes:

Check out unknown from stockroom

Record unknown number

Before weighing your condensed vapor, thoroughly dry the outside of the flask and make sure that no water is trapped under the foil cover

Do not rinse your flask with water between trials

Dispose of waste in appropriate container

Procedure. You will record your data and calculations in your lab notebook.

Obtain an unknown liquid and a 3 inch aluminum foil square. You will need two 600 or 800 mL beakers, and 3 or 4 boiling chips.

Add 3 or 4 boiling chips to the water in an 800 mL beaker and heat the water to the boiling point. Continue heating for 8 to 10 minutes after the water comes to a rolling boil. The temperature of the boiling water is 100.0oC. This will be the temperature of the vapor. Convert the temperature to Kelvin and record in your lab notebook.

800 mL Beaker

250 mL Flask


11.

Chemical Molar Mass

1-chlorobutane 92.6 g/mol

t-butyl chloride 92.5 g/mol

trichloroethylene 131 g/mol

2-propanol 60.1 g/mol

Ethyl acetate 88.1 g/mol

n-hexane 86.2 g/mol

cyclohexane 84.2 g/mol

2-butanone 72.1 g/mol

Post Lab Questions: Answer the following questions using complete sentences. Include them after your conclusion.

1. If a lab group did not keep the flask submerged in boiling water for a full ten minutes, and some unknown never vaporized, how would that affect the calculated molar mass? In other words, would it make the calculated value too high or too low? Explain why.

2. While performing this experiment, ten lab groups have ten different unknown volatile liquids with a range of molar masses. If all lab groups have exactly the same size of flask (255 mL), and all groups took their unknown vapor to the same temperature (100.0oC) and pressure (760.0 mmHg), how would the number of molecules within the different flasks compare? Would it vary with molar mass? How? Explain.

3. A student has determined that an unknown liquid is either 1-chlorobutane or t-butyl chloride. What other physical property(s) could be used to determine the identity of the unknown?

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