To make a phosphorus standard solution, you typically start with a stock solution of a higher concentration and then dilute it to the desired concentration. Here's how:
1. Prepare a 1000 ppm Phosphorus Stock Solution:
- Weigh the Potassium Dihydrogen Phosphate (KH2PO4): Accurately weigh 4.3937 g of dried KH2PO4. Drying the KH2PO4 beforehand ensures its purity and accurate mass.
- Dissolve in Deionized Water: Dissolve the weighed KH2PO4 in deionized water (dH20) in a 1-liter volumetric flask.
- Dilute to 1 Liter: Add deionized water to the flask until the solution reaches the 1-liter mark. Ensure the bottom of the meniscus aligns with the calibration mark. Mix thoroughly. This yields a 1000 ppm (parts per million) phosphorus stock solution.
2. Prepare Working Standard Solutions (e.g., 10 ppm and 80 ppm):
Now, dilute the 1000 ppm stock solution to create the desired working standard solutions. Here are examples for 10 ppm and 80 ppm:
- 10 ppm Phosphorus Standard:
- Pipette 1 mL of the 1000 ppm stock solution into a 100 mL volumetric flask.
- Add deionized water to the flask until the solution reaches the 100 mL mark. Mix thoroughly.
- 80 ppm Phosphorus Standard:
- Pipette 8 mL of the 1000 ppm stock solution into a 100 mL volumetric flask.
- Add deionized water to the flask until the solution reaches the 100 mL mark. Mix thoroughly.
Summary
In essence, making a phosphorus standard solution involves dissolving a specific amount of KH2PO4 in deionized water to create a stock solution, followed by appropriate dilutions to reach the desired standard concentrations. Accurate weighing and volumetric measurements are crucial for accurate results.
