Scientific Inquiry, Measurement, and Laboratory Safety
What to know
This domain tests experimental design, measurement quality, and safe lab practice. Understand independent and dependent variables, controls, hypotheses, and sources of error. Know significant figures, precision versus accuracy, unit conversions, and proper use of glassware and instruments.
Be able to identify systematic versus random error, choose appropriate equipment (graduated cylinder vs. volumetric flask vs. burette), and record data with correct uncertainty. Safety content includes PPE, fume hood use, chemical storage and compatibility, waste disposal, and emergency procedures such as eyewash and spill response. Know that you never return unused chemicals to stock bottles and that acids are added to water, not the reverse.
Traps
- Confusing accuracy (closeness to true value) with precision (reproducibility).
- Miscounting significant figures, especially with zeros and in multiplication versus addition.
- Treating a systematic error as random; a miscalibrated balance shifts all readings the same way.
- Ignoring safety: heating a closed system, smelling chemicals directly, or improper dilution of concentrated acid.
- Selecting a beaker for precise volume measurement; beakers are approximate.
Worked example
Significant figures: 12.11 + 0.3 = 12.4 (addition limits to the least decimal place), while 2.0 × 3.00 = 6.0 (multiplication limits to the fewest significant figures).
Rule of thumb: always add acid to water slowly with stirring; never water to concentrated acid.