Practical and Laboratory Skills
What the domain covers
Practical and laboratory skills tests safe and accurate bench work: calculations, solution preparation, pH, sterilisation, micropipetting, centrifugation, microscopy, chromatography, electrophoresis, aseptic transfer, and record keeping. Expect questions that require unit conversion and identification of procedural errors.
Core rules and concepts
- Molarity = moles of solute per litre of solution. Mass needed = molarity × volume in litres × molar mass.
- Always add concentrated acid to water, not water to acid, and wear eye protection.
- Autoclave heat-stable media and glassware; filter-sterilise heat-labile solutions. Do not autoclave volatile or heat-sensitive reagents.
- Micropipettes are chosen for the volume range; use smooth pipetting and change tips between samples.
- Centrifugation separates by density and size; balance tubes before spinning.
- Agarose gel electrophoresis uses a buffer, appropriate agarose concentration, and a voltage that resolves fragments without overheating.
- Good records include date, reagent, concentration, instrument settings, observations, and deviations.
Worked example
Prepare 100 mL of 0.1 M NaCl. Molar mass of NaCl is 58.44 g/mol. Mass = 0.1 mol/L × 0.100 L × 58.44 g/mol = 0.5844 g. Weigh 0.584 g, dissolve in less than 100 mL distilled water, transfer to a volumetric flask, and make up to the mark. Reasoning: molarity is per litre of final solution, not per litre of water added.
Traps
Do not confuse molarity with normality or percentage concentration. Do not make up volume before the solute dissolves. Do not use a serological pipette for precise small volumes when a micropipette is appropriate. Do not ignore label instructions or waste segregation.