Question

Calculate how much acid and base you need to make 100 ml of each buffer at an overall molarity of 0.1M.

1. Acid- NaH2PO4 molecular weight - 156.01.
a. PH 5.8 - 95.1 mM
b. PH 6.6 - 59.87 mM
c. PH 7.4 - 24.6 mM

2. Base Na2HPO4- molecular weight - 177.99.
a. PH 5.8- 4.9 mM
b. PH 6.6 - 40.28 mM
c. PH 7.4 - 75.4 mM

Answer 1

The student is required to calculate the amounts of acid and base needed to prepare 100 mL of a 0.1M buffer solution at pH levels 5.8, 6.6, and 7.4 using NaH2PO4 and Na2HPO4. By using molarity, volume, and molecular weight, one can determine the exact mass of each component required.

Step-by-step explanation:

Preparing different buffer solutions at specific pH levels requires careful calculation of the amounts of acid and base components to be mixed. Taking sodium dihydrogen phosphate (NaH2PO4) and disodium hydrogen phosphate (Na2HPO4) as the acid and base components, respectively, the student is asked to calculate the amounts required for making 100 mL of a 0.1M buffer at pH 5.8, 6.6, and 7.4.

For example, to prepare a buffer solution at pH 5.8, one would need 95.1 mM of NaH2PO4 and 4.9 mM of Na2HPO4. As the molecular weight of NaH2PO4 is 156.01, and Na2HPO4 is 177.99, the mass of each compound needed can be calculated by using the formula: Mass = Molarity × Volume × Molecular Weight. It's essential to also consider buffer capacity and buffer range when preparing these solutions, to ensure they effectively resist changes in pH upon addition of acids or bases.