Final answer:
To prepare a 300.0 mL 0.250 M KH2PO4 solution, calculate the moles needed (0.075 moles) and multiply by the molar mass (136.09 g/mol) to find the mass required (10.207 g). Dissolve this in enough water to make up the volume to 300.0 mL.
Step-by-step explanation:
To prepare 300.0 mL of a 0.250 M KH2PO4 solution, one must first calculate the amount of substance needed. Molarity (M) is defined as the number of moles of solute per liter of solution. Therefore, the number of moles of KH2PO4 needed is given by the equation:
M = moles of solute / liters of solution
0.250 M = moles of KH2PO4 / 0.300 L
moles of KH2PO4 = 0.250 M × 0.300 L = 0.075 moles
The molar mass of KH2PO4 is approximately 136.09 g/mol. To find the mass required:
mass = moles × molar mass
mass = 0.075 moles × 136.09 g/mol = 10.207 g of KH2PO4
To create the solution, weigh out 10.207 g of KH2PO4 and dissolve it in a volumetric flask. Add water to reach the 300.0 mL mark and ensure the solute is fully dissolved by stirring or swirling. This process results in a 0.250 M KH2PO4 solution.