"Work, finish, publish."
Michael Faraday
Remember this advice:
- Find the Variables! Once you have the variables identified, work out which one is the INDEPENDANT, which is the DEPENDANT, and the remainder will be controls.
- Write down, not up! your not trying to impress me, your trying to make a clear experiment that anyone taking Accelerated Chemistry can follow.
The Pre-Lab
A "pre-lab," is a demonstration of student preparation for the up-coming experiment. It typically consists of the following sections:
Objective
Take a moment to think about the general objective of the lab. Work out what the independent and Dependant variables are, then string the whole thing together in an objective statement.
Take a moment to think about the general objective of the lab. Work out what the independent and Dependant variables are, then string the whole thing together in an objective statement.
Hypothesis
Ultimately, this is the most difficult section of a lab to complete. The hypothesis is prediction statement, and requires the experimenter to have a vision of how the experiment will proceed, and what the results will be. I find that the best way to write a hypothesis is to write it and revise it, as I review the laboratory hand-out. Take your time with it, and understand that you may have to re-write it many times. Here are the basics:
Ultimately, this is the most difficult section of a lab to complete. The hypothesis is prediction statement, and requires the experimenter to have a vision of how the experiment will proceed, and what the results will be. I find that the best way to write a hypothesis is to write it and revise it, as I review the laboratory hand-out. Take your time with it, and understand that you may have to re-write it many times. Here are the basics:
| If... | What will you alter in a controlled manner? | Abscissa (or "x" axis) |
Independent variable |
| ...then... | What will you measure as a result of this alteration? | Ordinate (or y axis) |
Dependant variable |
| ...because... | What will you expect the results to be? | The Proportionality | shape of the expected curve |
I believe that it helps to try to envision what I believe my data will look like in the final graphical form.
The following writing tips are also useful:
The following writing tips are also useful:
- There is a difference between "measured..." & "determined..." Measured refers to a physical act of reading a scale, while determining a value is to calculate/infer the value by mathematical operation.
- Never mention Natural Laws in hypotheses. The idea is that if a hypothesis is proved incorrect/rejected, you have to have a reason, don't let that reason be the natural law itself! Imagine mentioning the first law of thermodynamics in your hypothesis, then later on (in your conclusion) you have to reject the hypothesis. Is this because the first law of thermodynamics is wrong, or doesn't apply in this situation? I doubt it!
- Don't use equations or symbols in hypotheses. If it is important, it would have a name!
- Use directional statements where you can. Don't use phrases such as "alter," use phrases such as "increase," or "decrease."
Discussion
The important part of the discussion is to identify the variables (the parts that you are going to alter and monitor) and the parts that you expect to have no effect on your results even if they do alter (those are the control variables). Ideally every lab should have two monitored variables (Dependant and independent) and I ask for at least two high quality control variables. The difficulty is determining the control variables of quality, I have reviewed many lab notebooks that state items like: Accuracy of a Balance, or Time to Reach Thermal Equilibrium, both of which are very poor control variables! The trick is to find a way in which the variables are linked (this is typically an equation of one form or another) and see if the link contains any constants. Equation constants are a link to the experimental controls.
Remember to clearly show any link between the variables (such as an equation) and display it with an explanation of what the terms mean and their units.
Materials and Procedure
Start this section with a list of materials that you are going to use. However, there is no need to mention the obvious ones such as "wash bottle," it is implied in every chemistry lab that you have the very basic equipment. Once you have the equipment list, follow it with a clear, well labeled diagram, that shows how the equipment will be organized.
For the procedure, use a series of well spaced numbered instructions (this helps in following them), that are a "digest," version of the laboratory hand-out. Make-sure that the instructions make sense to you., and that they would be very clear for your lab partner to follow.
The important part of the discussion is to identify the variables (the parts that you are going to alter and monitor) and the parts that you expect to have no effect on your results even if they do alter (those are the control variables). Ideally every lab should have two monitored variables (Dependant and independent) and I ask for at least two high quality control variables. The difficulty is determining the control variables of quality, I have reviewed many lab notebooks that state items like: Accuracy of a Balance, or Time to Reach Thermal Equilibrium, both of which are very poor control variables! The trick is to find a way in which the variables are linked (this is typically an equation of one form or another) and see if the link contains any constants. Equation constants are a link to the experimental controls.
Remember to clearly show any link between the variables (such as an equation) and display it with an explanation of what the terms mean and their units.
Materials and Procedure
Start this section with a list of materials that you are going to use. However, there is no need to mention the obvious ones such as "wash bottle," it is implied in every chemistry lab that you have the very basic equipment. Once you have the equipment list, follow it with a clear, well labeled diagram, that shows how the equipment will be organized.
For the procedure, use a series of well spaced numbered instructions (this helps in following them), that are a "digest," version of the laboratory hand-out. Make-sure that the instructions make sense to you., and that they would be very clear for your lab partner to follow.
The Post-Lab
After the data has been gathered, the calculations and interpretation of the findings completes the experiment. It typically consists of the following sections:
After the data has been gathered, the calculations and interpretation of the findings completes the experiment. It typically consists of the following sections:
Results
The three main parts of the results table are a meaningful title, units in the measurement descriptions only, and the key to the values of the measurements is that each type has the same number of decimal places. The decimals reflect the accuracy of the device, and as such should be consistent.
Calculations
Clearly display one sample of every type of calculation. Start by showing how you convert units, or how you determine the mass of a substance added to the reaction vessel, then move on with trial data and show step-by-step how you arrive at your final answer. Make this crystal clear! Then, simply display the results for the other trials, and show how you determine your mean value. Watch those significant figures!
Graphs
This should be straight forward if you follow the lab evaluation sheet. Make sure that the lab notebook remains in the normal reading position (you shouldn't have to turn the notebook) and it should take up the majority of the page. Lastly, remember that it is the data that is important not the graphical "origin," We don't need to see the zero-zero point and have our beautiful data crammed away in a corner! Display that part of the graph that is relevant to the data itself.
Remember to use your calculators (they are not just for Uncle Worm!) I typically input all my data into my STAT PLOT and have the calculator graph the data for me. If you zoom in on the data (ZOOM DATA) if will show you where to start and finish your axes. Then you can also have the calculator run a regression analysis (typically linear regression or LINREG on the calculator) and it will show you the equation of the "best fit line," and show you where it lies on the graph with respect to your data. Also, if your DIAGNOSTICS are on (see your calculators catalog commands for DiagnosticOn) it will also give you some significant statistics (like the r2 or correlation co-efficient squared). Again, learn to drive your calculators!
Error Analysis
A typical measure of uncertainty is the percentage error calculation:
The three main parts of the results table are a meaningful title, units in the measurement descriptions only, and the key to the values of the measurements is that each type has the same number of decimal places. The decimals reflect the accuracy of the device, and as such should be consistent.
Calculations
Clearly display one sample of every type of calculation. Start by showing how you convert units, or how you determine the mass of a substance added to the reaction vessel, then move on with trial data and show step-by-step how you arrive at your final answer. Make this crystal clear! Then, simply display the results for the other trials, and show how you determine your mean value. Watch those significant figures!
Graphs
This should be straight forward if you follow the lab evaluation sheet. Make sure that the lab notebook remains in the normal reading position (you shouldn't have to turn the notebook) and it should take up the majority of the page. Lastly, remember that it is the data that is important not the graphical "origin," We don't need to see the zero-zero point and have our beautiful data crammed away in a corner! Display that part of the graph that is relevant to the data itself.
Remember to use your calculators (they are not just for Uncle Worm!) I typically input all my data into my STAT PLOT and have the calculator graph the data for me. If you zoom in on the data (ZOOM DATA) if will show you where to start and finish your axes. Then you can also have the calculator run a regression analysis (typically linear regression or LINREG on the calculator) and it will show you the equation of the "best fit line," and show you where it lies on the graph with respect to your data. Also, if your DIAGNOSTICS are on (see your calculators catalog commands for DiagnosticOn) it will also give you some significant statistics (like the r2 or correlation co-efficient squared). Again, learn to drive your calculators!
Error Analysis
A typical measure of uncertainty is the percentage error calculation:
Remember that the result is a plus/minus value, not a plus or minus!
This is a statement of your laboratory accuracy, and can be a
reflection of your laboratory technique.
Two other common error analyses are the percentage difference and the squared correlation co-efficient. To calculate the percentage difference use the percentage error formula, except this time the answer will be either a positive value or a negative value, depending upon your data. The square of the correlation coefficient is found when your data has been graphed and you have run a regression (typically linear) analysis. If you have turned your calculators DIAGNOSTICS on, the squared correlation coefficient (R2) will simply be displayed. This number is very important, as it can indicate if there are any outlying data.
Two other common error analyses are the percentage difference and the squared correlation co-efficient. To calculate the percentage difference use the percentage error formula, except this time the answer will be either a positive value or a negative value, depending upon your data. The square of the correlation coefficient is found when your data has been graphed and you have run a regression (typically linear) analysis. If you have turned your calculators DIAGNOSTICS on, the squared correlation coefficient (R2) will simply be displayed. This number is very important, as it can indicate if there are any outlying data.
Data Analysis
Conclusion
The
hallmark of data analysis is pattern recognition. Looking for
data trends is the essence of experimental procedure. Use bullet
points and always reference which data/trials you are talking about.
Start by analyzing which data runs were best and which were worst. What was the difference between them? Does this pattern run across all your data runs? If you were to re conduct the lab, what conditions would you change to decrease your percentage error (that is not an Independent or Dependant variable)? What is the range of your data? How precise was your data? How accurate was your data?
Ask your self these questions and write your data analysis as firm statements. This will make the conclusion so much easier to write!
Start by analyzing which data runs were best and which were worst. What was the difference between them? Does this pattern run across all your data runs? If you were to re conduct the lab, what conditions would you change to decrease your percentage error (that is not an Independent or Dependant variable)? What is the range of your data? How precise was your data? How accurate was your data?
Ask your self these questions and write your data analysis as firm statements. This will make the conclusion so much easier to write!
Conclusion
From a good data analysis flows an excellent conclusion! The
patterns that the data revealed form the bulk of the conclusion.
However, initially we need to validate our hypothesis.
Start by restating it, and then decide (based upon your data,
empiricism is so very important!) whether you will accept or reject the
hypothesis. Be specific. Use terms such as "the first
trials indicated..." or "the second data set shows..."
Never use the phrase "...and my data shows this." or "...this can
be seen in my data." This type of weak language smacks of weak
understanding! Again be very specific!
Items to aviod:
Items to aviod:
- "Better Equipment" is not a valid improvement. This could be the answer to all science i it were!
- Where do your significant figures come from? If you could change that, would it change your accuracy? Precision?
- Use bullet points and don't waffle! Please re-read your conclusions before you turn in your notebook. If you don't understand a particular item in the laboratory don't discuss it, or simply state that you had difficulty understanding that piece of the experiement.
Notes
Homework
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