Scientific Inquiry, Measurement, and Laboratory Safety
This domain tests how you design investigations, record and analyze data, and keep a secondary chemistry laboratory safe. Expect items on significant figures, uncertainty, graphical analysis, and OSHA-aligned safety practice rather than memorized vocabulary.
Measurement rules
- Significant figures: addition and subtraction keep the least precise decimal place; multiplication and division keep the fewest significant figures.
- Report uncertainty to one significant figure and match the measurement's decimal place.
- Distinguish accuracy (closeness to an accepted value) from precision (repeatability). Systematic error shifts all results in one direction; random error scatters them.
- Match glassware to purpose: burette for titration volumes, analytical balance for precise mass, graduated cylinder for approximate volume.
Safety essentials
- Locate the SDS, eyewash, safety shower, fire extinguisher, and spill kit before any lab.
- Goggles and aprons are required for corrosive or flammable work; volatile toxins go in a fume hood.
- Never return unused reagents to stock; label waste by hazard class.
- Neutralize acid spills with sodium bicarbonate and report all exposures.
Worked example
A student finds the mass of a 10.00 mL sample to be 10.24 g. Density = 10.24 g / 10.00 mL = 1.024 g/mL. Both values have four significant figures, so report 1.024 g/mL. If the accepted density is 1.000 g/mL, percent error = |1.024 - 1.000| / 1.000 x 100 = 2.4%. Repeated trials that are consistently high indicate systematic error, not random error.
Traps that cost marks
- Applying multiplication rules to an addition calculation.
- Reading 0.00450 as two significant figures when it has three.
- Confusing precision with accuracy in error analysis.
- Treating a fume hood as a substitute for PPE.