ME 360 Midterm: ME 360 Alabama Test3 Spring07
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Below, is a completed lab. After completing this lab, I was asked the following question:
What changes would you make, if any, if you did this lab again?
I'm having a hard time thinking of what I would do different. Please help!
Observations & Questions for Part 1
Record your observations and your time and temperature data in tables. Use one table for the pure water and one table for the salt solution.
Data Table 1: Pure Water and Salt Solution | ||||
Seconds | Distilled H20 Room temp | Distilled H20 Ice bath | Saltwater Room temp | Saltwater Ice bath |
0 | 23 | 23 | 17 | 23 |
30 | 23 | 10 | 20 | 7 |
60 | 23 | 4 | 22 | 1 |
90 | 22.5 | 1 | 22 | 0 |
120 | 22.5 | 0 | 22 | 0 |
150 | 0 | 22 | -1 | |
180 | -1 | 22 | -1 | |
210 | -1 | 22 | -2 | |
240 | -2 | -2 | ||
270 | -1 | -2 | ||
300 | -1 | -2 | ||
330 | -1 | -2 | ||
360 | -1 | |||
390 | 0 | |||
420 | 0 | |||
450 | 0 | |||
480 | 0 | |||
510 | 0 | |||
540 | ||||
570 | ||||
600 | ||||
630 | ||||
660 |
Make two graphs of your data. On one graph plot the data from the pure water. On the other graph plot the data from the salt solution. On both plot temperature on the y-axis and time on the x-axis.
A. Record the freezing point of the pure water and the freezing point of the salt solution.
Freezing point of salt Sol: -2 degree Celsius
Freezing point of pure H2O: 0 degree Celsius
B. How do these two freezing points compare?
The freezing point of salt water is lower than the freezing
point of fresh water. Salt in the water lowers the freezing point
of water.
C. What are some practical applications of freezing point depression, boiling point elevation, and vapor pressure lowering?
Some practical applications of freezing point depression
are antifreeze in a radiator and salt on the road used to melt
ice in the winter. Some practical applications of boiling point
elevation are a sealed container and possibly a pressure cooker.
Some practical applications of vapor pressure lowering are freeze
drying and steam engines.
Questions - Part 2
To what biological structure is the dialysis bag comparable? How is it similar? How is it different?
The plasma membrane is comparable to the dialysis bag.
The similarity between them is that they are both semipermeable.
The difference is the dialysis bag acts as a permeable membrane,
however, purely based on its pore size, the small molecules are
able to get through but the bigger molecules are unable to. The
plasma membrane is a more complex system that uses both active
and passive transport to allow the molecule to move through.
In biological systems if a cell is placed into a salt solution in which the salt concentration in the solution is lower than in the cell, the solution is said to be hypotonic. Water will move from the solution into the cell, causing lysis of the cell. In other words, the cell will expand to the point where it bursts. On the other hand, if a cell is placed into a salt solution in which the salt concentration in the solution is higher than in the cell, the solution is said to be hypertonic. In this case, water will move from the cell into the solution, causing cellular death through crenation or cellular shrinkage. In your experiment is the Karo
I need help writing a decent conclusion. Every time I submit a lab report the professor slams my conclusion saying it needs work. She wants us to state what the results mean and if they are as expected and explain the possible reasons for variation in your results. The lab is below with data/results. Please, please help.
The Ideal Gas Equation: The Determination of Gas Constant, R
Introduction:
The purpose of this experiment is to determine the gas constant R and the percentage of KClO3 in the KClO3 â KCl â MnO2 mixture using the moles of O2, the original weight of the mixture, and the stoichiometry of the reaction. Consider a plot PV vs. nT for a gas sample where P is the pressure of the gas, V is the volume occupied by the gas, n is the number of moles of gas, and T is the temperature of the gas in Kelvin. If the temperatures and pressures fall in normal ranges, the plot will yield a straight line. Thus, PV = nRT where R is the constant of proportionality between the PV product and the nT product. The object of this experiment is to determine P, V, n, and T for a gas sample and determine the gas constant R, using the equation PV = nRT. The gas sample used will be a sample of oxygen gas generated by the MnO2 catalyzed decomposition of KClO3. Following is the equation of the reaction:
For decomposition of the KClO3 in a KClO3 â KCl â MnO2 mixture, the mass of O2can be determined by taking the difference between the mass of the original mixture and the mass of the residue after the decomposition. This mass is then converted to moles of O2 using the molecular weight of oxygen. The volume of the sample will be determined by water displacement in such a way that the pressure of the sample can be determined from the barometric pressure and the vapor pressure of water. The temperature of the sample will be directly measured.
Procedure:
Assemble the equipment for the apparatus shown in figure 1. With the Florence flask filled to the neck with water, the beaker one-third filled with water, and the pinch clamp open, blow into the tube which connects to the test to create a siphon between the flask and the beaker. Reverse the siphon a few times by raising and lowering the beaker. This will fill the tube connecting the flask and the beaker with water and will also remove air bubbles from the system. Adjust the siphon such that the flask is filled to the neck with water, and close the pinch clamp.
Weigh the eight inch test tube. Add approx. 1.5 grams of the KClO3 â KCl â MnO2mixture to the test tube and weigh the test tube containing the mixture. Record each weight to three decimal places. (Also, be sure and record the sample number for the KClO3 â KCl â MnO2.)
Clamp the test tube to the ring stand, and insert the stopper as shown in figure 1. With the pinch clamp open, raise the level of the beaker such that the water level in the beaker is several inches above the water level in the flask. If a significant amount of water runs into the flask, there is an air leak in the system. If you have an air leak, it must be closed before proceeding. Equalize the pressure in the flask with atmospheric pressure by bringing the water level in the beaker to the same height as the water level in the flask. After closing the pinch clamp, empty and dry the beaker. Open the pinch clamp. A small amount of water will run into the beaker: this will not affect your results since later in this experiment, you will again equalize the pressure in the flask with atmospheric pressure. Ask your instructor to check your apparatus before proceeding.
Heat the mixture with a blue flame until the mixture first begins to melt and then solidifies again; and then heat for an additional 2 mins. (Donât heat more than 7 mins.) Allow the system to cool for 15 mins. Equalize the pressure with atmospheric pressure, as before; then close the pinch clamp and open the system. Quickly measure the temperature of the gas in the flask; also measure the volume of water in the beaker. Record the barometric pressure reading from professor. Weigh the test tube with the residue and record the mass to three decimal places.
Data/Results:
Trial 1 | |
Weight of test tube | 41.912 g |
Weight of test tube + mixture | 43.343 g |
Weight of mixture | 1.431 g |
Weight of test tube + residue | 43.211 g |
Weight of oxygen | 0.132 g |
Moles of oxygen | 0.00413 mol |
Temperature of water (under oxygen) | 21.0 0C |
Temperature of oxygen | 20.5 0C |
Barometric pressure | 761.5 torr |
Vapor pressure of water | 18.7 torr |
Pressure of oxygen | 742.8 torr |
Volume of water displaced | 0.101 L |
Gas constant, R | 61.9 |
Mass of KClO3 in mixture (use balanced equation) | 0.338 g |
% of KCLO3 in mixture | 23.6 % |