WHAT METHOD CAN BE USED TO PREPARE 0.2M POTASSIUM PHOSPHATE BUFFER USING KH2PO4 AND KOH?
H2PO4^- + OH^- ==> H2O + HPO4^-2
Weigh an appropriate amount of KH2PO4, add an appropriate amount of KOH. You find appropriate amounts by using the Henderson-Hasselbalch equation.
To prepare a 0.2M potassium phosphate buffer using KH2PO4 and KOH, you need to follow a two-step process.
Step 1: Calculation of Amounts
First, you need to calculate the amount of KH2PO4 and KOH required to prepare the desired concentration of the buffer solution (0.2M). This calculation involves considering the molecular weights of the chemicals.
1. Calculate the molar mass of KH2PO4:
K (potassium) = 39.10 g/mol
H (hydrogen) = 1.01 g/mol
P (phosphorus) = 30.97 g/mol
O (oxygen) = 16.00 g/mol
Molar mass of KH2PO4 = (39.10 + 2 * 1.01 + 30.97 + 4 * 16.00) g/mol
2. Calculate the molar mass of KOH:
K (potassium) = 39.10 g/mol
O (oxygen) = 16.00 g/mol
H (hydrogen) = 1.01 g/mol
Molar mass of KOH = 39.10 + 16.00 + 1.01 g/mol
3. Convert the desired concentration (0.2M) to moles:
Moles required = concentration (M) * volume (L)
Considering you want to prepare a specific volume of buffer solution, substitute the above value into the equation to find the required amounts of KH2PO4 and KOH.
Step 2: Preparation of the Buffer Solution
1. Dissolve the calculated amount of KH2PO4 in distilled water.
Add approximately half of the final desired volume of water to a clean container, then slowly add the calculated mass of KH2PO4 while stirring to ensure complete dissolution.
2. Adjust the pH of the solution using the calculated amount of KOH.
In a separate container, dissolve the calculated mass of KOH in a small volume of distilled water to prepare a concentrated KOH solution. Gradually add the KOH solution dropwise to the phosphate solution while continuously monitoring the pH using a pH meter or pH paper. Slowly adjust the pH to the desired value, which is typically around 7.4 for a phosphate buffer.
3. Once the pH is adjusted, make up the final volume with distilled water.
Add the remaining volume of distilled water to reach the final desired volume of the buffer solution. Mix well to ensure uniformity.
Note: It is always recommended to double-check your calculations and use accurate weighing techniques to ensure the preparation of a precise 0.2M potassium phosphate buffer.