Lab Quiz
Questions: 16 · 10 minutes
1. Sterile cultures repeatedly become contaminated soon after transfers. Which change most directly addresses contamination during handling?
Increase the incubation temperature so the intended culture grows faster
Minimize how long containers are open and avoid touching sterile surfaces while using the designated clean technique
Add more growth medium to dilute any contaminating organisms
Inspect the cultures more often by opening their containers
2. Several similar sample tubes will be stored overnight. Which labeling approach best reduces the chance of a mix-up?
Use only the researcher’s initials because the notebook contains the details
Label only the storage rack rather than the individual tubes
Use cap color alone so the tube remains easy to read
Include sample identity, relevant concentration, date, hazards, and owner as applicable
3. A scientist proposes that a new treatment improves cell growth under all laboratory conditions. Which finding would most directly challenge that claim?
A controlled, repeatable test finds no improvement under a defined condition
The treated cells look different under one microscope setting
Another laboratory uses a different brand of growth medium
The treatment costs more than the standard treatment
4. Before measuring samples with a spectrophotometer, a researcher measures a blank containing the solvent and other non-analyte components. What is the blank mainly used for?
To increase the analyte concentration to a detectable level
To confirm that every sample has the same chemical identity
To sterilize the cuvette before samples are added
To account for background absorbance from the solvent, cuvette, and reagents
5. How should the volume of a clear aqueous liquid with a concave meniscus usually be read?
From the upper edge of the meniscus while looking down
From the bottom of the meniscus at eye level
From either edge, provided the same edge is used each time
From the center of the liquid column above eye level
6. In an experiment testing whether fertilizer affects plant growth, one group receives fertilizer while both groups otherwise receive the same treatment. What is the role of the group without fertilizer?
It is a replicate of the treatment group
It is the dependent variable
It is the control group used for comparison
It is the source of experimental bias
7. When using a standard air-displacement micropipette to aspirate liquid, which sequence is appropriate?
Immerse the tip without pressing, then pump the plunger several times
Immerse the tip, press to the second stop, and withdraw it while pressed
Press to the second stop, release in air, and then immerse the tip
Press to the first stop, immerse the tip, and release the plunger slowly
8. A balance produces measurements of 12.4 g, 0.56 g, and 3.221 g. Using the addition rule for decimal places, how should their sum be reported?
16.2 g
16 g
16.18 g
16.181 g
9. You need 100 mL of a 0.50 M solution from a 2.0 M stock. Using C₁V₁ = C₂V₂, how much stock is required?
10 mL
20 mL
25 mL
50 mL
10. Which piece of glassware is designed to prepare a solution at one precise final volume?
Volumetric flask
Erlenmeyer flask
Beaker
Test tube
11. Compared with a solution at pH 5, a solution at pH 3 has approximately how many times the hydrogen ion concentration?
Two times
Three-fifths as much
One hundred times
One thousand times
12. An unknown liquid has spilled on a laboratory bench, and no one nearby knows what it is. What is the most appropriate immediate response?
Warn others, move away from exposure, notify the designated supervisor, and follow the spill protocol
Absorb it with paper towels before it spreads
Smell it carefully to help identify it
Pour water over it because dilution makes every chemical safer
13. A chemical splashes into a researcher’s eye. What should the researcher do first?
Wipe the eye with a dry tissue before seeking help
Keep the eye closed until a supervisor arrives
Check the chemical’s pH before deciding whether to rinse
Immediately use the eyewash, begin flushing as directed, and alert others
14. Before running two sample tubes in a centrifuge, how should they normally be arranged?
Next to each other with equal liquid height
Opposite each other with equal total mass
In any two positions if the rotor lid closes
Opposite each other even if their masses differ substantially
15. What is the main sterilizing agent used by a standard laboratory autoclave?
Dry air at room pressure
Pressurized steam
Ultraviolet light in a vacuum
Concentrated alcohol vapor
16. Repeated measurements are tightly clustered together but far from an accepted reference value. How are the measurements best described?
Accurate and precise
Accurate but not precise
Precise but not accurate
Neither accurate nor precise because they differ from the reference