酸和碱浓度

Weigh 25 g of NaOH pellets and add them to a 125-mL Erlenmeyer flask. Measure 25 mL of deionized water and add it to the flask. Mix on a stir plate with a magnetic stir bar until homogeneous. The solution generates heat, so allow it to cool before transferring to a labeled polyethylene bottle for storage in a corrosive storage cabinet.

Use a 1-mL volumetric pipette to measure 0.85 mL of stock 14.8 M phosphoric acid and add it to a 25-mL volumetric flask. Fill the flask with deionized water to the volume marking. Mix with a magnetic stir bar until homogeneous, then transfer to a labeled polyethylene bottle and store in a corrosive storage cabinet.

Transfer 2.5 mL of ethanol into an Erlenmeyer flask and add 0.05 g of phenolphthalein. Stir until dissolved, then rinse the weigh boat with ethanol to transfer residual phenolphthalein. Add 2.5 mL of deionized water and mix until homogeneous. Transfer the solution to a labeled dropper bottle for use.

Potassium hydrogen phthalate (KHP) is dried overnight in an oven at 125 °F to remove moisture that could affect the accuracy of titration calculations. Dry KHP serves as a reliable primary standard for standardizing base solutions. Once dried, the container is sealed and cooled at room temperature before use.

Each station requires a 50-mL glass burette, 60-mL plastic burette, three 250-mL Erlenmeyer flasks, graduated cylinders, beakers of various sizes, a glass stirring rod, ring stand with clamps, pipettes, a pH sensor probe, stir plate with magnetic stir bar, and a data acquisition system to record measurements.

Both NaOH and phosphoric acid solutions must be transferred to labeled polyethylene bottles and stored in a corrosive storage cabinet. Polyethylene containers resist chemical degradation from strong acids and bases, preventing leaks and contamination. Proper labeling ensures safe identification and prevents accidental misuse.

When dissolving NaOH pellets in water, the reaction is highly exothermic and produces significant heat. Cover the flask with paraffin film during mixing and allow the solution to cool completely before handling or transferring. This prevents burns and ensures safe handling of the caustic reagent.