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23 Nov 2019

This Thermodynamics Lab is somewhat different from the norm. I have attached the Thermo lab that normally would be performed by the student for this Thermo class. Each student would be one of several in a small group of students taking their turn at performing an experiment on a single, small steam boiler. As may be read in the Lab Protocol, the experiment consists of measuring the temperature and pressure of the water as it is electrically heated from liquid water to vapor steam as a function of time. It is an interesting experiment BUT I think a more interesting experiment (even if it is only a Gedanken Experiment[1]) would be to transform this lab theme into a practical example. I’ve chosen a simple experiment that involves a 2 or 4-cup espresso coffee pot as a practical example of the heating and thus the pressurization of water in a closed vessel. The espresso coffee pot is used in homes and not in cafes where a more sophisticated steam generator is used to produce the rich espresso coffee (see Attachment No. 1 for “human interest” story related to this coffee pot

[1] A Gedanken Experiment was often used in the early years of the 1900’s in physics by the Leaders of theoretical physics such as Bohr, Einstein, Madame Curie, Schrodinger, Heisenberg, et al. It consists of a simple sketch and a very basic thought experiment of “…what would happen if”. It was often used when experimental apparatus was not yet available to actually do the experiment to test a hypothesis.

The coffee pot will be available for your inspection in class and the attached photo of an “exploded view” of the pot is offered for your review. If you have access of one of these pots, then your reward for actually doing the experiment will be to enjoy the coffee that is produced. However, this lab

can be completed as a simple “thought experiment” with some calculations required.

By inspecting the attached sketch you will note that the pot is actually a closed vessel once the pot is filled with water, the coffee basket/strainer is filled with coffee, and the top is tightly screwed together with the bottom that is filled water. There is a pressure relief valve shown and a gasket on the top chamber that keeps a tight seal between the top and bottom halves. The heated fluid will be forced through the coffee strainer via the inverted spout that is submerged in the water. If the experiment is successful, the espresso coffee is found in the top chamber.

The “experiment” is essentially to answer the following questions. BUT, the Lab Report should present a professional summary of the experiment using a sketch and/or photo (from any source with appropriate credit given) and any necessary calculations that was performed in order to answer the question.

Question 1. Clearly and carefully describe the heating process with a concise written description of the process. It is suggested that the description will be easier to explain if it is accompanied by a sketch of the process on a P (or T) vs. v (specific volume). Try to sketch what you believe to be the shape of the temperature change of the pot and water vs. time for the entire process. Also indicate what could happen if the source of heat is not turned-off after the coffee is produced. What is the motive force that moves the cold water to the top chamber?

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Related questions

Experiment 1: Grind Size

For each treatment (coarse, medium fine):

1. Weigh 35g of coffee for each treatment (coarse, medium, fine) and add it to each French press.

2. On the stove, heat 5 cups of water to 85°C.

3. Quickly pour 1 ½ cups water into each French press. Be careful! The glass will be HOT.

4. Stir each mixture twice with a spoon and brew for 4 minutes, using a timer.

5. After 4 minutes, slowly press the plunger and pour coffee into cups.

6. Evaluate all treatments at the same time, when they are cool enough to taste. Each student should take 3 Styrofoam cups and rinse them after each experiment.

7. Pour any remaining coffee down the sink, and scrape the grounds out into the trash with a spoon.

Experiment 2: Temperature

For each treatment (70°C, 85°C and 100°C):

1. Weigh 35g of medium grind coffee for each treatment and add it to each French press.

2. On the stove, heat 3 batches of 2 cups of water to 70°C, 85°C and 100°C.

3. Quickly pour 1 ½ cups water into each French press. Be careful! The glass will be HOT.

4. Stir each mixture twice with a spoon and brew for 4 minutes, using a timer.

5. After 4 minutes, slowly press the plunger and pour coffee into cups.

6. Evaluate all treatments at the same time, when they are cool enough to taste. Each student should take 3 Styrofoam cups and rinse them after each experiment.

7. Pour any remaining coffee down the sink, and scrape the grounds out into the trash with a spoon.

Experiment 3: Contact Time

For each treatment (2 minutes, 5 minutes, 8 minutes):

1. Weigh 35g of coffee of medium grind coffee for each treatment and add it to each French press.

2. On the stove, heat 5 cups of water to 85°C.

3. Quickly pour 1 ½ cups water into each French press. Be careful! The glass will be HOT.

4. Stir twice with spoon and brew for each treatment time, using a timer.

5. After each treatment time, slowly press the plunger and pour coffee into cups.

6. Evaluate all treatments at the same time, when they are cool enough to taste. Each student should take 3 Styrofoam cups and rinse them after each experiment.

7. Pour any remaining coffee down the sink, and scrape the grounds out into the trash with a spoon.

1. In this lab we explored a number of ways to alter coffee extraction efficiency. If you brewed a weak cup of coffee, describe how you would increase the flavor strength of the next batch using insight you gained from the three experiments in today’s lab. Explain why each method would increase your coffee flavor strength. (6 pts)

2. What flavor profile can you expect from coffee that was brewed using an excessively long contact time between the coffee and water? Why? (4 pts)

3. What flavor profile can you expect from coffee that was brewed using beans that were ground too coarsely? Why? (4 pts)

4. We used a burr grinder to grind the beans for today’s lab. Describe how a burr grinder works (what are the parts, how does this control particle size?), and how it is different from a common propeller grinder? Aside from the particle size, what other detrimental effect can a propeller grinder have on the ground coffee? What affect do these factors have on extraction during brewing? (6pts)

1-How many grams of NaCl would be needed to prepare 150.00 L of a 1.402 M NaCl solution?

............................................................................................................................................................................

2- first a standardized solution of sodium hydroxide (NaOH) will be quantitatively diluted to about 0.1 M but not exactly 0.1M. The molarity of the dilute NaOH will be calculated! A similar quantitative dilution was done in experiment 3 when you diluted 5.0 M HCl to 0.50M HCl using a volumetric flask and pipet.

The second part of the experiment is very similar to the last part of experiment 6 where samples of the unknown were weighed out, dissolved in water, and titrated with the dilute NaOH using phenolphthalein as the indicator to determine the percent by mass of a compound in the unknown. The compound will be different than the compound used in experiment 6. The molecular formula of the compound will be provided during the final. You must know how to weigh by difference (Preweigh, tare sample and small container to zero, transfer sample to flask, and place the small container back on balance to get mass) and titrate the sample using the buret in order to do well.

Be sure to read the instructions for the practical toward the end the CHM151L lab manual and do the practice problem on the next page.

You will have 1.5 hours to do the practical. You may only use a calculator and a pencil on the practical. There is no talking during the practical such that students cannot help each other and the TA may only help you with equipment problems.

It would be a good idea to wash any glassware you might use the lab period before the lab practical. There will also be a help session before the lab practical.

At the end of the lab final you will wash all glassware used or any dirty glassware in your locker, wash your unknown vials and remove the labels, checkin your locker and return your key, and evaluate the lab.

Please put the following statements in the correct order relating to the day of the lab practical:
1 2 3 4 5 6 Wash all your glassware and unknown vials, checkin your locker, evaluate the lab, and check your grades.
1 2 3 4 5 6 Do at least 3 good trials (weigh and titrate sample) as time allows.
1 2 3 4 5 6 Start the lab practical by diluting the NaOH solution.
1 2 3 4 5 6 Before the day of the practical clean glassware, read the practical instructions and do the practice problem in the lab manual and complete the loncapa problems for the final.
1 2 3 4 5 6 Calculate the molarity of the dilute NaOH, the percent by mass of the compound in you unknown for each trial and then the median.
1 2 3 4 5 6 Come to the help session before the lab final.

............................................................................................................................................................................

3-

A NaOH solution was prepared by diluting 5.00 mL of 2.205 M NaOH to a final total volume of 100.00 mL. What is the exact molarity of the dilute NaOH (use 4-5 significant figures)?


............................................................................................................................................................................

4-For the problem above, select glassware and size from the list below to conduct the dilution.

A Amber Bottle
B Mohr pipet
C Buret
D Volumetric Flask
E Volumetric Pipet or Pipettor
F Graduated cylinder
G Erlenmeyer flask
H Beaker


A B C D E F G H <= Glassware used to transfer the 2.205 M NaOH to be diluted
A B C D E F G H <= Glassware used to measure the final volume of the diluted M NaOH.

5 10 15 20 25 50 100 250 500 1000 <= Volume of the glassware chosen to transfer the concentrated NaOH above
5 10 15 20 25 50 100 250 500 1000 <= Volume of the glassware chosen to contain the final dilute NaOH above.

Freezing Point Depression Lab

Objective: To use freezing point to determine the molecular weight of an unknown substance.

In this lab, we used benzophene as the solvent, which has a freezing point of 48.1 degrees celsius and Kf value of 9.80 degrees C/m. The procedure consisted of measuring out 10 g benzophenone in a test tube and melting the substance in a warm water bath. When melted, we removed the test tube from the bath and allowed it to cool. We observed the freezing point. Next, we added half a gram of an unknown substance to the test tube and melted the soultion once more. We observed the freezing point.

My question is the following: How would the experiment be different if we had used water as the solvent? Explain what you would have to change to account for this difference and how you would do it.

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