Chemical Safety — Video Notes (Laboratory Practices and Safety)

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Objectives: identify chemical hazards with SDS and GHS pictograms; follow SOP and use lab equipment (pipettes, weighing scale, pH meter, fume hood) for safe solution prep; apply good lab practices and PPE; explain fume hood function.
Pre-lab: read L04 Pre-reading; familiarise with equipment; note that navigation may differ but steps are the same.
NaOH SDS questions (NaOH pellets):
- PPE in lab when handling NaOH: gloves (and general lab PPE).
- GHS pictogram: corrosive.
- Actions on contact: rinse body part with water.
- NaOH solution prep: add NaOH pellets to water (not water to NaOH); explains why.
- Disposal: discard NaOH solution in a bottle labeled NaOH in the fume hood.
Key concept: NaOH is caustic; dissolution can be exothermic.

Why add NaOH to water: to control the exotherm; pouring water into NaOH pellets can cause a more vigorous reaction and splashing.
Disposal: follow lab rules; use labeled NaOH waste container in the fume hood.

PPE for lab work: lab coat, closed shoes, safety glasses/goggles, latex or nitrile gloves.
General safety: read safety slides and complete online quiz; no eating/drinking; know exits; ask if unsure; stay focused; keep PPE on; follow procedure safety precautions.
Specific safety for NaOH: NaOH is caustic; dissolution is exothermic; add NaOH to water.
Materials provided (summary): per pair and per class items for NaOH prep and use (spatula, weighing boats, RO water, glass rod, serological pipettes, pipette bulb, beaker, tubes, rack; NaOH pellets; weighing balance; 1000 mL bottle; pH meter; wipes).

Goal: prepare 100 mL of 0.6 M NaOH.
Calculations:
- M = n/V, so M = \frac{n}{V}; for 0.6 M in 0.100 L, n = M\cdot V = 0.6 \times 0.100 = 0.060\text{ mol}.
- NaOH molar mass Mw = 40.0\ \,\text{g/mol}; mass required m = n\cdot Mw = 0.060\times 40.0 = 2.40\text{ g} (do not exceed 2.45 g).
Steps:
1) Attach pipette bulb filler to 5 mL serological pipette.
2) Dispense 10 mL RO water into a 50 mL beaker.
3) Tare the weighing boat on the balance.
4) Weigh ~2.40 g NaOH on the boat.
5) Slowly add 2.40 g NaOH to the beaker of water; stir until dissolved (exothermic).
6) Transfer dissolved NaOH to a 100 mL volumetric flask; rinse beaker to collect all NaOH.
7) Add RO water to reach the 100 mL mark; mix.
8) Attach bulb filler to a 25 mL pipette; pipette 25 mL into a 50 mL tube; label as NaOH.
9) Pour remaining NaOH into the class 1000 mL bottle.
Safety notes: avoid skin contact; NaOH is hygroscopic; reaction can heat up quickly.

pH measurement: use a pH meter that has been calibrated (calibration not required for this session).
Procedure:
1) Measure 25 mL of each solution P, Q, R, S into beakers.
2) Uncap pH probe; rinse with RO water into a waste beaker.
3) Blot dry with KimWipes; do not rub on the glass bulb.
4) Follow benchtop guide to operate the pH meter; place probe into each centrifugal tube.
5) Wait for reading to stabilise; record in Table 1.
6) Repeat rinsing and measurement for all samples.
7) After measurements, rinse the pH meter with RO water; dry; replace cap on the probe.
8) Pour the measured solutions P, Q, R, S into designated waste beakers in the fume hood.
Table 1 (example values): NaOH ~ 13.27; P ~ 2.68; Q ~ 6.29; R ~ 2.06; S ~ 8.51.
Waste disposal: follow designated chemical waste containers in the fume hood.

Fume hood function: a ventilated enclosure that keeps gases, vapours and fumes away from the user and prevents them from escaping into the lab.
Activity: Take a photo of the fume hood, label its parts, and state its function.

Types of experiments requiring a fume hood: use when hazardous chemicals are involved or when toxic gases may be produced (eg, making NaOH solution, displacement reactions).

Ventilation best practices (3):
1) Check that the fume hood is functioning properly.
2) Check the airflow indicator/tag on the sash.
3) Work at a practical sash height to maintain adequate ventilation.
image-based question: best practice is Image C.
Good Laboratory Practices recap (weighing balance):
- Close the two glass doors when weighing to prevent airflow from affecting the reading.
Lab safety reminder: taring removes the weight of the boat; keep work area clean and dust off residual pellets after weighing.

pH meter usage recap:
- Before use, there is an emphasis on calibration; in this session the instrument is pre-calibrated.
- Rinse probe with RO water before use to avoid cross-contamination and ensure accuracy.
- When using the pH meter, avoid contaminating other solutions; ensure accurate readings.

Cap and electrode care: placing the cap on the pH meter preserves the electrode’s glass bulb, prevents drying out, and protects from contamination.
Additional note: maintain the pH electrode in good condition for reliable measurements.