I have a lab today, need answers for these questions based on the procedure?

[bamdavis]

1. After the vapour has condensed to a liquid why is it important to obtain the weight of the liquid "without delay" in number 8?

 

2. What assumptions are made about the vapour of the substance in this labratory?

 

 

 

Lab Info

 

1. Weigh a clean , dry 100ml volumetric flask together with a square of aluminum foil to 4 decimal places. Record this mass in the data table.

2. Pour 3 to 5 ml of an unknown liquid into the volumetric flask. Record the unknown letter in the data table.

3. Cover the flask with the foil and make a tight seal. Make a small hole in the top of the foil using a pin.

4.Place a 600ml beaker on a hot plate and lower the volumetric flask into the beaker to within 1 cm of the bottom. Use a clamp to hold the volumetric flask in place. Pour water into the beaker to cover at least the round portion.

5. Gently boil the water in the beaker until all of the unknown liquid vapouraizes in the flask and then for about additional minutes. The total time for vapourization will be about 15 minutes.Record the temperature of the water in the data table.

6. Quickly remove the flask from the beaker and cool to room temperature by running cold water over the surface of the flask. All the vapour will condense to a liquid.

7. Dry the flask with paper towel and by blowing air over the surface.

8. Weigh the cooled and dry flask and liquid without delay. Record this value in the data table.

9. To determine the volume of the volumetric flask, fill to the top with water and pour this water into a graduated cylinder.

10. Record the the barometric pressure in the data table.

[Mr Skeptic]

I won't give you answers, just big hints.

 

1. Might the amount of liquid in the flask change over time? Why?

 

2. Are you boiling the water out of the liquid, or the other way around?

[bamdavis]

Ill say what i think, then you give more hints, or the answer.

 

1. I think you have to weigh it fast or some of the liquid will turn to vapour again?

 

2. i have no idea.

 

2. your boiling the water out of the liquid?

[Mr Skeptic]

1. the weight of the unknown substance over time will increase because liquid is heavier than vapour?

 

2. I think you are boiling the water out of the liquid. But i dont understand if the vapour of unknown liquid is condensed to a liquid' date=' does the water vapour stay as vapour or condense to liquid?[/quote']

 

No need to send me a private message. Leave everything in the thread unless there is a good reason to.

 

Ill say what i think, then you give more hints, or the answer.

 

1. I think you have to weigh it fast or some of the liquid will turn to vapour again?

 

2. i have no idea.

 

2. your boiling the water out of the liquid?

 

Both your answers for #1 are contradictory. However, if either one is true is a valid reason why you would want to weigh it immediately. Look again at your procedure, it will tell you which of your suggestions is correct.

 

For #2, why do you think you had to make a hole in the foil? What would have happened otherwise?

 

As for me giving you the answers, I won't as that is against homework help policy.