labs

Formal Lab Grading Criteria

Formal Lab Requirements

Sample Formal Lab


EXTRA QUESTIONS FOR MOLAR VOLUME OF A GAS LAB (due 12-16)

1.  Suppose that the volume of the gas was read in the eudiometer without placing it in the tall graduated cylinder.  If the water level in the eudiometer was above the level of the water in the beaker, the gas pressure inside the eudiometer would NOT be the same as the external gas pressure.  Would it be lower, higher, or the same?  Why?  Carefully explain your response.

2.  According to the data collected in the lab, what would have been the maximum length of magnesium ribbon that could’ve been used where the volume of the hydrogen gas generated could still be accurately read using the eudiometer tube?

3.  The magnesium ribbon was measured with a ruler.  Explain how the significant digits in the computations would have been affected if the digital scale had been used instead.


PRECIPITATE LAB EXTRA QUESTIONS:  (due 12-9)

** Do not try to insert the answers to "correlating your facts" into your report.  It would be awkward for the "flow" of the report.  Instead, pick one of the four boxes that you wrote "PPT" for, and apply the correlating concepts to that box - giving the aqueous species present before mixing the solutions, the full ionic equation (not just the net), and the spectator ions involved.   **

1.  The two precipitates formed in this lab were "insoluble" in water.  Look up actual solubilities of these compounds at room temperature in mol/L.

For questions 2-3, consider the solution sodium chromate that you worked with in this lab.
2. Name one aqueous solutions (not used during the lab) that would mix with sodium chromate to form a precipitate. (Hint: answers can vary and it may be helpful to the handout given during class)

3. Write the net ionic equation for the formation of the precipitates that would form in #2.



EXTRA QUESTIONS FOR MAGNESIUM OXIDE LAB:  (Due 11-23 by paper:  11-25 electronically))
1.  Suppose that some magnesium oxide already existed on the surface of the magnesium strip before performing this lab. 
-  How would this have effected your determination of the percent of magnesium after performing the lab?  (Be specific – tell if it would be higher or lower and exactly why.)
-  What precaution could have been taken to prevent this?  (hint:  research other procedures for this lab on the internet)
2.  Some magnesium nitride may have formed during the reaction. What is the formula of this compound?  Where did the nitrogen come from?
3.  Suppose you tried to combine 42.0 g of magnesium with 45.0 g of oxygen.  Using the “actual” ratio that you calculated from the periodic table, how much magnesium oxide would you predict to be formed? (Show work and remember your actual ratio involved moles!)
Would there be any magnesium or oxygen left over?  If so, which element and how much?  (Explain your reasoning!)


EXTRA QUESTIONS FOR DEFINITE PROPORTIONS LAB:  (Due 10-24 at 4:00 PM)
1.  Find three alternative hydrates that could have been used in this lab under the full flame.  (Hint:  you  must research the temperature of a Bunsen Burner flame and be sure that the hydrate's melting temperature is not too low)
2.  This experiment is sometimes done to verify/illustrate a law known as the Law of Definite Composition.  State this chemical law and apply it to the first part of the lab.
3.  Use the terms endothermic and exothermic as they would apply to the dehydration and rehydration of the copper (II) sulfate.

EXTRA QUESTIONS FOR ZINC COATING LAB: (give your sources)  (Due 9-23 at 2:30 PM)
1. The zinc coating protects steel underneath from corrosion. What elements make up the alloy steel?
2. Compare the cost of some building/shop material that is galvanized with an identical object that is not galvanized. What percent does the price increase for this extra protection?
3.  What is pressure treated lumber and why does it required heavily galvanized nails and fasteners?


EXTRA QUESTIONS FOR SPECIFIC HEAT OF METAL LAB:  (Due 1-15 by noon)
1. One of the biggest challenges in this lab was the small temperature change that needed to be measured.  Identify two different modifications to the lab that could have resulted in bigger changes of temperature for the water in the foam cup, and what would make those modifications difficult to implement (why are they maybe impractical?).
2.  Describe at least three different changes to the equipment/procedures that would result in lower percentage errors for this lab.
3.  How many grams of zinc, at the boiling point of water (assume 100 degrees) would be needed to raise the temperature of 100 grams of water from room temperature to human body temperature?  (you will need to research the specific heat of zinc and body temperature in Celsius before attempting this question)







EXTRA QUESTIONS FOR BAKING SODA TO SALT LAB:  (due 11/25)
1. Look up the melting point of sodium chloride and explain how this property of the compound allows you to easily separate it from water through evaporation.

2. Why weren't large volumes of hydrochloric acid added (instead of adding it drop by drop after the initial 10 mL)?
(Hint: where would the excess acid eventually end up?)

3. Suppose that 12.5 g of baking soda is reacted with 9.5 g of hydrochloric acid. Which reactant is totally used up? How much of the other reactant remains after the reaction?


EXTRA QUESTIONS FOR "Percent of Water in a Hydrate" Lab (due Friday, Nov 6)
1.  How did both parts of this lab exemplify the Law of Definite Composition?

2.  If the anhydrous compound that resulted from our lab procedures was very “hygroscopic”, why would it be especially important to immediately weigh the product or to use a dessicator?

3. The barium found in the chemical is highly toxic by ingestion to the human body. The Flinn chemical manual lists its toxicity as LD50 118 mg/kg. Explain what this number means, and calculate how much of the chemical would be lethal for a person exactly your mass.


EXTRA QUESTIONS FOR THE “Size of a Fatty Acid Molecule” LAB:  (due Friday, Oct 30)
(Be sure to explain or show the work for each numerical answer)

1. Use the following reasonable assumptions to calculate the approximate volume of an oleic acid molecule in nm3:
- assume its shape is approximated by a square column
- assume that it the height of the square column (the thickness that you determined in the lab) is 4 times more than the dimensions of its base

2. Determine the total number of atoms in one molecule of this compound. Using the answer to the question above, what would be the volume of an “average atom” in this compound? Assuming the atom to be spherical, what would be the radius of the “average atom”?

3. Citing your sources, find the accepted values for the radius of a carbon, hydrogen, and oxygen atom.   Use the information to discuss the accuracy of your experimental determination radius in problem 2 above.


EXTRA QUESTIONS FOR DETERMINATION OF RELATIVE MASS LAB - lab due by 4:00 PM, Monday October 19th
Questions to be addressed in analyzing the data:
1. This same lab is sometimes performed by putting an iron nail in a solution of copper (II) sulfate.  In what way would the procedures have to be changed to accommodate the nail in place of the steel wool?

2. How many grams of copper would you expect to ultimately precipitate out if a 32.0 g nail is used? (assume enough copper (II) sulfate is present)
Be sure to explain how you mathematically predicted your result.

3.  Explain how electron transfer was related to the results of this lab.  (It will be helpful to consider the chemical equation and then to research the concept of "redox" reactions in chemistry.)


EXTRA QUESTIONS FOR DENSITY OF PENNIES LAB - lab due 10/9/15 by 3:00 PM


  1. Research the actual percentages of copper and zinc in pre-1982 and post-1982 pennies.  Cite your source.
  1. Determine your absolute and relative error for the answer that you found in question number 4 on the lab worksheet.
  1. It seems that many groups did not get very accurate results.  How could the procedures of this lab be modified to get better results?


 




EXTRA QUESTIONS FOR RATE OF SOLUBILITY LAB - lab due 1/5/15 by 4:00 PM
1. Create a solubility curve for potassium nitrate using the four values obtained by the class.  The y-axis should be measured in g/100 g water and the x-axis should be temperature in degrees Celsius.

2. Which of the following, if any, would increase the solubility value for sodium thiosulfate pentahydrate? Stirring, crushing, heating
(Please note, this question is NOT referring to how fast it would dissolve.)

3. After timing how long it took 4 different 1-gram samples of sodium thiosulfate pentahydrate (in steps 5-8) to dissolve in 100 mL of water, to what extent was the solution that resulted saturated? Specifically, what percent of sodium thiosulfate pentahydrate was dissolved compared to a saturated solution?  (the answer to this question will require some research - cite your source)


EXTRA QUESTIONS FOR EMPIRICAL FORMULA OF A HYDRATE LAB
1. Using average atomic masses from the periodic table, what the theoretical percent of hydration for the copper sulfate pentahydrate ( CuSO4 x 5 H20 ) that was heated in the test tube. How do the lab results compare?

2. If the anhydrous compound that resulted from our lab procedures was very “hygroscopic”, why would it be especially important to immediately weigh the product or to use a dessicator?

3. The barium found in the chemical is highly toxic by ingestion to the human body. The Flinn chemical manual lists its toxicity as LD50 118 mg/kg. Explain what this number means, and calculate how much of the chemical would be lethal for a person exactly your mass.


EXTRA QUESTIONS FOR HEAT OF CRYSTALLIZATION LAB:
1.  What is the freezing temperature of sodium thiosulfate pentahydrate?

2.  Why would the lab be less effective if the test tube were placed into a bath of room temperature water?

3.  Draw what a temperature (y-axis) versus time (x-axis) graph would look like if:
      - the seed crystal is added at exactly the moment that the solution in the test tube is at the freezing temperature
     - the seed crystal is added late, after the temperature has fallen too much and the solution is allowed to supersaturate



EXTRA QUESTIONS FOR SINGLE REPLACEMENT/ACTIVITY SERIES LAB:
1.  If a potassium nitrate solution were added as column 6, what would you predict the results to be with each of the four metals?  Explain your reasoning.

2.  According to the activity series in your text, what metal would be the worst oxidizing agent?  Explain your conclusions.




EXTRA QUESTIONS FOR MAGNESIUM OXIDE LAB:  (finally!)
1.  Suppose that some magnesium oxide already existed on the surface of the magnesium strip before performing this lab. 
-  How would this have effected your determination of the percent of magnesium after performing the lab?  (Be specific – tell if it would be higher or lower and exactly why.)
-  What precautions did you take in your procedures to keep this magnesium from initially being present?


2.  Some magnesium nitride may have formed during the reaction. What is the formula of this compound?  Where did the nitrogen come from?


3.  Suppose you tried to combine 42.0 g of magnesium with 45.0 g of oxygen.  Using the “actual” ratio that you calculated from the periodic table, how much magnesium oxide would you predict to be formed? (Show work!)

Would there be any magnesium or oxygen left over?  If so, which element and how much?  (Explain your reasoning!)





EXTRA QUESTIONS FOR CHROMOTOGRAPHY LAB:
(First be sure to answer all the questions on the 2nd day's worksheet in your lab report)
extra questions:
1.  Polarity, which is related to solubility (how well something dissolves), is one factor that determines a pigment's Rf value.  Research another variable that affects this value, and explain..  (cite your source)

2.  Compare and contrast the results to the one shown at the link below:
spinach leaf chromograph
(print this in color and include in your report as well)

3.  Explain how the black light contributed to any of the findings in this lab.  Did it make any of the pigments easier to detect, and if so, which ones?


EXTRA REQUIREMENTS/QUESTIONS FOR ENZYME LAB:
Extra requirement for data:
Enter the data for both graphs into the program Graphical Analysis.  Be sure to have appropriate labels for axes, scaling that displays the data well, and turn off the feature that connects the dots.   Hand-draw your curve or line-of-best-fit.

Questions:
1.  What is the balanced chemical equation for the decomposition of hydrogen peroxide?  Why is the enzyme catalase not included as a reactant or product?
2.  What enzyme is present in blood to catalyze the breakdown of hydrogen peroxide?
3.  Explain the famous "elephant toothpaste" demonstration, including how it is performed, what is observed, and the catalyst used for the reaction.
















EXTRA QUESTIONS FOR CHROMATOGRAPHY LAB:
1.  Find two other practical applications of chromatography in biology/chemistry that are different than what was experienced in this lab.  (cite your sources)

2.  Find the wavelengths (in nm) for the colors of the rainbow (no citation needed).  Then use the chart in the lab handout to determine what color bands you would expect from green algae.  Explain how you arrived at your answers.








LAW OF DEFINITE COMPOSITION LAB: (extension given until Monday you whiners!!!)
1. Using average atomic masses from the periodic table, find the theoretical decimal fraction of copper sulfate that should have remained after the copper sulfate pentahydrate ( CuSO4 x 5 H20 ) was heated. How do the lab results compare?

2. An undesirable product of the heating of magnesium that wasn't tested for was magnesium nitride. What is its chemical formula, where does the nitrogen come from, and how could have its presence been tested for?

3. Answer the summary question at the end of the 1st part of the lab.

** In your conclusion, be sure to point out how both parts of this lab illustrated the law of definite composition, even though the mass went up in one part of the lab and down in the other. **


FLAME TEST LAB EXTRA QUESTIONS (cite yours sources)
1. In some labs, the flames are viewed through cobalt blue glass. What is the purpose of this?

2. The colors that were "seen" in the lab were usually a combination of spectral colors. Research the wavelengths of each of the spectral lines given off by strontium in its excited state.

3. Find the colors associated with at least three other metals that were not tested during this lab.

HESS'S LAW EXTRA QUESTIONS
1. Look up the accepted molar heat of solution for sodium hydroxide and compare to your results in reaction #1. Cite your source, and determine your percentage error.

2. Foam cups are not the best calorimeters. Why is this fact not a significant source of error in this lab that attempts to verify Hess's Law?

3. Sodium hydroxide is also sometimes referred to as "lye." Research the uses and dangers of this fairly common chemical. Cite your sources.



SOLUBILITY AND TEMPERATURE EXTRA QUESTIONS

1. On the internet, find an accepted solubility curve for potassium nitrate, copy and paste it into your report, and cite your source.

2. Use the curve from #1 to determine the “accepted” solubilities for each of the six temperature values that you found in your lab. Find the absolute and percent errors for each. (information can be organized into a table - only need to show a “sample” calculation for one data point)

3. Explain how adding significantly more or less water to the chemical than the specified 20 drops would possibly affect the subsequent lab procedures. Be very specific, addressing both more and less.



PRECIPITATE LAB EXTRA QUESTIONS:
Consider the solution barium nitrate that you worked with in this lab.
1. Name two aqueous solutions (not used during the lab) that would mix with barium nitrate to form a precipitate. (Hint: answers can vary and it may be helpful to refer to table B.9 in the appendix of your text on page R54)

2. Write the net ionic equation for the formation of each of the precipitates that would form in #1.

3. What are the spectator ions in the formation of these precipitates?



EXTRA QUESTIONS FOR VOLUME-TEMPERATURE OF A GAS LAB:
Your extra requirement for this lab is to create one high quality graph and to examine its characteristics and how well it verifies Charles’s Law (probably would also be wise to state Charle’s Law somewhere in your report before this analysis!):

Using your volume-temperature data, input the data into the program Graphical Analysis which can be found on the network at S:\Teacher Data\Voeller\graphical analysis. Temperature should be the x-variable. For this graph, input the temperatures in Kelvin. Volume should be the y-variable.

To make a quality graph, be sure to:
- Double-click column headings and be sure to have proper labels/units
- Go to the analyze menu and autoscale the graph
- Under the menu options, choose graph options: uncheck the box for “connect points” and check the box for point protectors
- Use the 2nd-to-last button on the tool bar to have the computer complete a line of best fit.

Print this graph and include your report.
Then answer the following questions about the graph:

1. According to Charles’ Law, what shape should the graph have? Does your graph support this?

2. What is the value of correlation for the linear fit? Research what this value is telling you.

3. What is the value of the y-intercept of your graph? What should it be?

4. What is the value of the slope on your graph? What does the value mean? (hint: consider its units)