The ocean has a natural carbonate buffer system, which helps to regulate the pH

Question

The ocean has a natural carbonate buffer system, which helps to regulate the pH of seawater. a. Write the two successive dissociation reactions for carbonic acid (H_2CO_3), and their associated acid dissociation constants (K_a expressions). What is the pH of a buffer that is created by combining 65.0 mL of 1.00 M H_2CO_3 and 35.0 mL of 0.800 M NaHCO_3? Assume the second dissociation is negligible and don't forget to account for dilution. What would the pH of the solution be after 1.5 mL of 2.5 M HC1 is added?

Explanation / Answer

a )

H2CO3 <--------------------> H+ + HCO3-

Ka1 = [HCO3-][H+]/[H2CO3]

HCO3- <---------------------> CO3-2 + H+

Ka2 = [CO3-2][H+]/[HCO3-]

b)

Ka1 = 4.5x 10^-7

pKa1 = -log Ka1

pKa1 = 6.35

pH = pKa1 + log [NaHCO3 / H2CO3

pH = 6.35 + log (35 x 0.8 / 65 x 1)

pH = 5.98

c)

millimoles of HCl = 1.5 x 2.5 = 3.75 = C

millimoles of H2CO3 = 65 x1 = 65

millimoles of NaHCO3 = 35 x 0.800 = 28

pH = pKa1 + log [NaHCO3 -C / H2CO3 + C]

pH = 6.35 + log (28 - 3.74 / 65 + 3.75)

pH = 5.90

Related Questions

Navigate

• Browse (All)
• Browse T
• Subjects

---

---

Integrity-first tutoring: explanations and feedback only — we do not complete graded work. Learn more.