Question

A compound has two carboxyls and one aminium group. The pK_as of the groups are 2.0, 4.4, and 9.5, respectively. A biochemist has 100.0 mL of a 0.10 M solution of this compound at a pH of 5.3. She adds 40.0 mL of 0.10 M NaOH. To the nearest hundredth of a unit, what will be the pH of the solution after addition of the NaOH (assume full stirring to reach a new equilibrium)?

The answer is 9.11 but I have no idea how to do this problem.

Answer 1

A compound has two carboxyls and one amine group

The pKa values of the groups are 2.0, 4.4, and 9.5, respectively.

pH

a figure expressing the acidity or alkalinity of a solution on a logarithmic scale on which 7 is neutral, lower values are more acid and higher values more alkaline. The pH is equal to −log₁₀c, where c is the hydrogen ion concentration in moles per litre.

pH is defined as the decimal logarithm of the reciprocal of the hydrogen ion activity, a_H+, in a solution.

the two carboxyls are acids and one amine grop is a base the added NaOH is a one of strong base . the range of pH for acids (here carboxyls) 0.7 in the case of bases the pH is 7- 14

NaOH is a strong base so we should work in terms of pOH NaOH(aq) → Na+(aq) + OH- (aq). Therefore the concentration of OH- in the final solution is 0.10 M. pOH = -log[OH-] = -log(0.10) = 1.00 pKW = pH + pOH = 14.00 pH = 14.00 – 1.00 = 13.00 (3)** A solution has a pH of 6.88.

here the chemist added the solution 0.10M NaOH (40ml) pH is 6.88

so the total solution fully stirred so the solution contains two carboxyls one amine and NaOH the total volume of solution pHG is equal to 9.11