Laboratory Safety and Experimental Technique
Laboratory Safety and Experimental Technique
This domain tests whether you can plan bench work at the scale you propose, identify the controlling hazard, and choose containment and emergency controls. Questions often combine a practical scenario with a calculation.
Core rules
- Complete a written risk assessment before weighing: identify hazard, exposure route, and the hierarchy of control (elimination, engineering, administrative, PPE). In a UK context this is the COSHH assessment; PPE is the last line, never the only line.
- Work with volatile or toxic material at least 15 cm inside a functioning fume hood, with the sash low. A hood is not storage; bulky items on the baffle disrupt airflow.
- Date and test peroxide-forming solvents (diethyl ether, THF, dioxane, isopropyl ether). Test with acidified KI/starch or commercial strips; never distill to dryness.
- Cryogens: liquid nitrogen can condense oxygen in a cold trap, producing an explosive oxidiser. Vent Dewars, never seal them, and use cryogenic gloves and face protection.
- Schlenk lines: use a cold trap, check the manifold for leaks, and never apply vacuum to a closed system. Inspect glassware for star cracks before evacuation.
Worked example
You plan to quench 5.0 g of 60% NaH dispersion (3.0 g NaH, 0.125 mol) with propan-2-ol. The quench produces one mole of H2 per mole of NaH, so 0.125 mol × 24.0 L mol⁻¹ ≈ 3.0 L of hydrogen at room temperature. That is a flammable atmosphere if released into a 1 L flask, so the reaction must be vented through the hood, cooled in ice, and the alcohol added dropwise with stirring. The calculation, not the appearance of the mixture, sets the control.
Traps
Using a fume hood as a solvent store; trusting an undated ether bottle; quenching reactive metal hydrides quickly or in a sealed vessel; putting chemical waste into the wrong halogenated stream; assuming small scale removes the need for a risk assessment.