A solution is made by the addition of 0.34 mole of Na₂HPO₄ and 0.65 mole of NaH₂PO₄ and sufficient water to give a total volume of 1.2 L. How many grams of NaOH would need to be added to increase the pH by 0.2 pH units?If needed, use the following equation: pH = pK_a + log(A^-/HA)

Question

Quizplus · Accepted Answer

The correct answer is C because the addition of NaOH will increase the concentration of OH- ions, which will in turn increase the pH of the solution. The amount of NaOH needed to increase the pH by 0.2 units can be calculated using the Henderson-Hasselbalch equation:pH = pKa + log([A-]/[HA])where pKa is the dissociation constant of the acid, [A-] is the concentration of the conjugate base, and [HA] is the concentration of the acid.In this case, the pKa of NaH2PO4 is 7.21. The concentration of NaH2PO4 is 0.65 mole/1.2 L = 0.54 M. The concentration of Na2HPO4 is 0.34 mole/1.2 L = 0.28 M.Substituting these values into the Henderson-Hasselbalch equation, we get:7.21 = 7.21 + log([A-]/[HA])log([A-]/[HA]) = 0[A-]/[HA] = 1This means that the concentration of NaH2PO4 is equal to the concentration of Na2HPO4.To increase the pH by 0.2 units, we need to increase the concentration of OH- ions by a factor of 10^0.2 = 1.58. This means that we need to add enough NaOH to increase the concentration of OH- ions by 1.58 * 0.28 M = 0.44 M.The molar mass of NaOH is 40 g/mol. Therefore, we need to add 0.44 M * 40 g/mol * 1.2 L = 21.1 g of NaOH to increase the pH by 0.2 units.

A Solution Is Made by the Addition of 0