You are instructed to create 600. mL of a 0.56 M phosphate buffer with a pH of 7.6. You have phosphoric acid and the sodium salts NaH2PO4, Na2HPO4, and Na3PO4 available. (Enter all numerical answers to three significant figures.)

H3PO4(s) + H2O(l) equilibrium reaction arrow H3O+(aq) + H2PO4−(aq)
Ka1 = 6.9 ✕ 10−3
H2PO4−(aq) + H2O(l) equilibrium reaction arrow H3O+(aq) + HPO42−(aq)
Ka2 = 6.2 ✕ 10−8
HPO42−(aq) + H2O(l) equilibrium reaction arrow H3O+(aq) + PO43−(aq)
Ka3 = 4.8 ✕ 10−13

What is the molarity needed for the acid component of the buffer?

What is the molarity needed for the base component of the buffer?

How many moles of acid are needed for the buffer?

How many moles of base are needed for the buffer?

How many grams of acid are needed for the buffer?

How many grams of base are needed for the buffer?

First, you decide which of the ionizations you need. That's Ka2 because pH of 7.6 requires pKa close to that value and that is Ka2 having a pKa of 7.21.

You have two equations. Eqn 1 is
pH = pKa2 + log [(B)/(A)]
7.6 = 7.21 + log [(B)/(A)]
(B/A) = 2.45 and
(B) - 2.45(A)

equn 2 is
(B) + (A)= 0.56 M

Solve these two equations simultaneously for (A) and (B). That gives you answers for 1 and 2.

For 3 and 4.
mols = M x L. You know M and L (that's 600 mL), solve for mols.

For 5 and 6.
grams = mols x molar mass = ?

To determine the molarity needed for the acid and base components of the buffer, we need to consider the Henderson-Hasselbalch equation:

pH = pKa + log([base]/[acid])

Given that the buffer has a pH of 7.6, we can rearrange the equation as follows:

pKa = pH - log([base]/[acid])

Now, let's calculate the molarity needed for the acid component of the buffer.

Step 1: Calculate the pKa needed for the acid component.
pKa = 7.6 - log([base]/[acid])

Step 2: Determine the molarity of the acid component using the pKa value and the equilibrium reactions given.

For the acid component, we have the following equilibrium reactions:
H3PO4(s) + H2O(l) ⇌ H3O+(aq) + H2PO4−(aq), Ka1 = 6.9 × 10−3

From the equilibrium equation, we can see that the acid component is H2PO4−. Therefore, we need to find the molarity of H2PO4−.

[H2PO4−] = [acid]

Now, we can calculate the molarity needed for the acid component.