Available Lab Equipment
- Bunsen Burner
- Hot plates
- Hot water baths
- Measuring volume
- Graduated cylinders, beakers, flasks
- Pipets (disposable, micropipets, glass pipets of various sizes)
- Gas collection glass tube
- Measuring mass
- electronic balances (0.01 g)
- triple beam balances
- Vacuum filtration set-ups with traps
- 6V variable DC power supplies (along with ammeters and voltmeters) (physics)
- blender, microwave, refrigerator,
Lab Grading Policy
I will break down each lab into skills so that each lab will get 1 to 7 grades depending on what you are
required to do. Not all skills will be assessed in a quarter, although I make an attempt to do so. Each skill will be given a score on the 4 to 0 scale. Each skill is about 5% of your grade (some are less, please see syllabus).
The point of this is that you recognize the skills that are being assessed in a particular lab rather than
just seeing a lab as independent from all other labs. My hope is that you will start to view each lab as an
opportunity to improve your skills in collecting data, designing experiments, drawing conclusions, etc and
internalize the knowledge of what makes a good lab. The lab skills you will be assessed on are:
- Formatting/Data Notebook
- Design (defining a question, identification and definition of variables, procedures, controls
- Data Collection and Organization
- Data Processing (showing logical argument with math, graphs, presentation of data, answering questions)
- Analysis and Conclusion
- Error Analysis and Improvements
- Error Propagation (IB ONLY)
Data notebooks will be graded up to two times per semeseter as a whole. This grade is to ensure that you are maintaining a lab notebook as expected. This grade is in addition to the formatting grade you get with each specific lab. Lab notebook checks will be assessed based on the following:
- All labs accounted for and completed
- Pages numbered, dated, and signed
- Table of contents filled in
- Clean-up stickers received (part of safety grade)
|Always used lab notebook for data collection. Up-to-date TOC.
||Most labs are in lab notebook (80%) or Table of contents only 75% up-to-date. Page headings and page #'s on each page.
||Has at least 75% the labs in notebook, but has not filled in TOC, evidence of ripped out pages, mostly does not include page headings.
||Contains at least 25% of labs done and has attempted to fill in TOC. Page headings are done correctly sometimes.
||Student used Data notebook less than 25% of the time.
Lab write-ups will generally be collected the class after a lab write-up is assigned. They will be graded according to the Lab Report Guidelines document. You will be told before turning it in what sections will be graded. Generally, every lab will have a data notebook grade, a data collection grade and a data processing grade. When I collect lab write-ups, you will place the typed portion into the lab notebook where the data is located.
See above for links to lab guidelines documents and checklist.
Percent Error Help
- Calculated density (measured by you in lab): 5.0 g/L
- Actual density (according to a book): 5.2 g/L
- Find difference = 5.0 - 5.2 = 0.2
- Calculate % error = 0.2/5.2 = 4%
Example Lab Write-ups
Defining the problem and selecting variables
The student clearly stated the problem and identified variables. The wavelength of light used could have been mentioned in the list of variables but has been mentioned in the method.
The method allowed for effective control of the relevant variables.
Developing a method for the collection of data
The method allowed for the collection of appropriate data and was sufficient (the minimum of five data points) to plot a graph. The spread of points was uneven and ideally another data point or two should have been planned for in the concentration range 0.250 to 0.500 M. It did, however, cover the full range from the maximum available concentration of copper sulfate to zero concentration. This is a case where “complete” does not mean perfect.
Data collection and processing
Recording raw data
The student recorded all raw data, qualitative observations and uncertainties (although there was no need to convert all the absolute uncertainties into percentage uncertainties unless they were to be propagated later). The uncertainty associated with the concentration of the solution would have been better presented with the raw data but it is present and so the aspect is fulfilled.
Processing raw data
This is quite a simple processing task since the raw data is ready to be directly plotted and there is no need to calculate a gradient. Since the student in her conclusion stressed the linearity of the graph to support the Beer-Lambert Law, this is acceptable to assess data processing, that is, the shape of the graph was the crucial result. If, however, the purpose of the task was to simply show that increasing concentration increases absorbance, then the graph would not have fulfilled any purpose and the processing would have been deemed incomplete, that is, partial.
Presenting processed data
The student has plotted and annotated the graph appropriately. Uncertainties have been considered but the y‑axis error bars have been calculated wrongly (the uncertainty in concentration should have been shown as an x‑axis error bar). However, error bars are not required in chemistry internal assessment and therefore the suitable best-fit line is sufficient to secure complete. Students who try to go beyond the aspect descriptors should not be penalized for doing so if there is a slight mistake as a result.
Conclusion and evaluation
A valid conclusion was reached based on the data gathered and processed. The student correctly noted that the graph is linear within the limits of random error. The conclusion is correctly justified through reference to accepted theory.
The results are evaluated and few weaknesses were identified. The uneven spread of data points or limited range of concentrations (copper (II) sulfate can be made up to nearly 2 M at room temperature) should have been commented on. The student has seen the linear relationship confirmed and has then ceased to look critically.
Improving the investigation
The student suggested further research away from the focused research question under consideration rather than modifications to reduce random error (only suggesting repeats) or to increase the range over which conclusions could be drawn.