Laboratory Equipment, Instruments and Their Operation
Candidates should be able to match an instrument to its purpose and describe correct operation and limitations. Key equipment includes analytical balances (read to 0.1 mg, enclosed draft shield, levelling bubble, calibration with certified weights), top-pan balances (0.01 g or 0.001 g), micropipettes (variable volume, tip fit affects accuracy), burettes (for titration, read at the meniscus), volumetric flasks and pipettes (single fixed volume, not for heating), graduated cylinders (estimate only), pH meters (two- or three-point calibration with buffers), centrifuges (balance tubes by mass opposite each other), autoclaves (moist heat sterilisation, 121 degrees Celsius at 15 psi for 15-20 minutes), incubators, spectrophotometers (blank first, cuvette orientation), microscopes (start on low power, coarse then fine focus) and fume hoods (sash at correct height, airflow indicator).
Traps: a top-pan balance cannot weigh 5 mg accurately; a volumetric flask must not be used to store solutions long-term; a pipette must never be pipetted by mouth; a centrifuge must never be run with unbalanced tubes or with the lid open; glassware that is chipped must be discarded, not used. Know the difference between sterilisation (killing all microorganisms) and disinfection (reducing pathogens).
Worked example: To prepare 250.0 mL of a standard solution, weigh on an analytical balance, dissolve in a beaker, transfer with rinsings into a 250 mL volumetric flask, then make to the mark with the meniscus on the line at eye level, and invert to mix. Reading a balance or flask at the wrong angle introduces parallax error.
Rule of thumb: choose the instrument whose smallest graduation is at least ten times finer than the tolerance you need.