Jove Lab Chem
Acid and Base Concentrations — Lab Prep
Source: Smaa Koraym at Johns Hopkins University, MD, USA
- Preparation of Reagents
Here, we show the laboratory preparation for 10 students working in pairs, with some excess. Please adjust quantities as needed.
-
Prepare 25 mL of 50% w/w NaOH solution. 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.
-
Add a magnetic stir bar and mix the solution on a stir plate until the solution appears homogeneous. After mixing, cover the opening of the flask with paraffin film. Note: The solution produces heat, so allow it to cool before handling.
-
Once cooled, use a powder funnel to pour the solution into a polyethylene bottle labeled ‘50% w/w NaOH’. Store the solution in a corrosive storage cabinet until it is needed.
-
Prepare 25 mL of 0.5 M phosphoric acid. 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. Add a magnetic stir bar and mix the solution until it is homogeneous.
-
Use a powder funnel to transfer the solution to a polyethylene bottle labeled ‘0.5 M H3PO4’. Store the solution in a corrosive storage cabinet until it is needed.
-
Prepare 5 mL of 1% phenolphthalein. Use a volumetric pipette to transfer 2.5 mL of ethanol into an Erlenmeyer flask.
-
Weigh 0.05 g of phenolphthalein and add it to the ethanol. Rinse the weigh boat with ethanol to transfer residual phenolphthalein.
-
Add a stir bar and mix the solution until the phenolphthalein dissolves and the solution appears homogeneous.
-
Add another 2.5 mL of deionized water to the flask and stir. Once the solution is well-mixed, transfer it to a labeled dropper bottle.
-
Prepare dry potassium hydrogen phthalate (KHP). Weigh approximately 20 g of stock KHP into a glass container with a lid.
-
Place the uncovered glass container in an oven at 125 °F to dry the KHP overnight.
-
When the KHP is dry, secure the lid and set it by the balance to cool.
-
Make sure there is a clean and dry spatula, several weigh boats, and a 150-mL beaker labeled, ‘Excess’.
-
- Preparation of Laboratory
-
Set out the following glassware and equipment at each lab station (we suggest that students work in pairs):
1 50-mL glass burette 1 60-mL plastic burette with 2-valve system 3 250-mL Erlenmeyer flasks 1 10-mL graduated cylinder 1 50-mL graduated cylinder 1 100-mL beaker 1 250-mL beaker 1 400-mL beaker 1 Glass stirring rod 1 Ring stand 1 Medium 2-prong clamp 1 Burette clamp 1 1-mL pipette 15 1-mL pipette tips 1 500-mL polyethylene bottle with cap 1 Drop counter 1 pH sensor probe 1 Stirplate 1 Stir bar 1 Data acquisition system 1 Flash drive
-