how to calculate a primary standard buffer using Kh2po4 and Na2Hpo4..
This question is far to general; I suggest you post a specific problem. When you do that please explain what you don't understand.
To calculate a primary standard buffer using K₂HPO₄ (potassium phosphate monobasic) and Na₂HPO₄ (sodium phosphate dibasic), follow these steps:
1. Determine the desired pH of the buffer solution. This will guide the selection of the acid and base components.
2. Identify the pKa values of the acid and base that correspond to the desired pH. K₂HPO₄ is the acid and Na₂HPO₄ is the base in this case.
3. Calculate the ratio of concentration between the acid and base using the Henderson-Hasselbalch equation:
Ratio = (base/acid) = ([HPO₄²¯] / [H₂PO₄⁻]) = 10^(pH - pKa)
4. Determine the desired total buffer concentration. This value will depend on your application; a concentration between 0.1 to 1 M is common.
5. Calculate the individual concentrations of K₂HPO₄ and Na₂HPO₄ using the ratio obtained in step 3 and the desired total buffer concentration. For example, if the desired total buffer concentration is 0.1 M and the ratio is 10, then K₂HPO₄ would be 0.01 M and Na₂HPO₄ would be 0.1 M.
6. Dissolve the calculated amounts of K₂HPO₄ and Na₂HPO₄ in the required volume of solvent (such as water) to make the desired buffer solution. Stir gently to ensure complete mixing.
7. Adjust the pH of the buffer solution, if necessary, using small amounts of a strong acid (e.g., HCl) or a strong base (e.g., NaOH), followed by pH measurement until the desired pH is achieved.
Remember to always use proper laboratory equipment and observe safety precautions when working with chemicals.