Labs are an integral part of the chemistry experience.
There are several important safety rules that should be followed at all times:
- Wear splash-proof goggles
- No eating or drinking
- Do not touch, tast or directly smell chemicals
- Tie back all loose clothing, hair and jewelry
- Always read the procedure ahead of time and follow it closely
- Never return unused chemicals to the original container
- Dispose of all chemicals as instructured
- Always report all incidents (spills, breakage, mistakes in performing a procedure) to our instructor!
Common Lab Procedures
Some common lab techniques:
- Always point the end of the test tube away from people when heating
- Waft smells towards you to smell
- Add acid to water to prevent concentrated acid splashes
- Use a fume hood when working with toxic fumes
- Never mouth pipette
Tips for finding mass: Use a balance, don’t put hot things on the balance, don’t put chemicals directly on the balance, record exact mass. When finding volumes, use a graduated cylinder, read with level at eye level (you go to its level), record exact amount.
Some common techniques for separating mixtures: filtration (solid & liquid), chromatography (liquids based on attractions or size) and distillation (liquids based on boiling points). Some other common lab techniques are calorimetry—indirectly measuring energy changes, density—measure mass and volume of several samples, and titration—Find concentration of unknown solution.
Types of labs
Inquiry labs have student written procedures while traditional labs have teacher given procedures. Discovery labs are done before teaching the content while confirmatory labs are done after. It’s good to combine both inquiry and traditional with discovery and confirmatory throughout the year to give a variety of experiences.
Teaching Inquiry Labs
Teach inquiry labs “backwards” by having students write the lab in the order that we do:
- Background information
- Results/calculations (identify needed equations)
- Data table
Remind students that there’s often more than one correct way and that they can change their procedure during the lab if they find a better way (or if they’ve made a mistake) as long as they change the written procedure in their final turned-in report as well.
Setting up a lab
Take steps to insure a smooth-running lab and fewer last minute panics on your part!
- Make a list of all need materials
- Check availability and if not, do you have work-able substitutions?
- Calculate the amount needed for all of your classes
- Gather equipment and distribute as you choose
- Inform students of any substitutions (in writing, preferably)
- Make sure you know how to dispose of chemicals
Tips during a lab
- Always include written safety information and go over it verbally
- Go over any new techniques or equipment ahead of time
- Walk around and keep an eye on everything!
- Refill chemical supply when needed—but not too much to keep waste down
- Ask students questions to engage them with the procedure
- Anticipate questions—if you see one group having a question or problem, others will as well!
After the lab
- Students can form misconceptions and erroneous results in any format of lab.
- Always have a de-briefing session to clarify any misconceptions or false conclusions.
- Use worksheet format labs and grade as you would any assignment or test (assigning points for different areas)
- Use a rubric to grade formal lab write-ups