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 = ?
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?
1 answer
1 answer