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How many mL of a 5.0-M solution of sodium borate must be added to a 200-mL solution of 50 mM boric acid in order for the pH to be 9.6?

a. 19 mL
b. 0.087mL
c. 2.3mL
d. 4.6mL

User Tony
by
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1 Answer

3 votes

Final answer:

To find the volume of 5.0-M sodium borate needed to achieve a pH of 9.6 in a 200-mL solution of 50 mM boric acid, use the Henderson-Hasselbalch equation to determine the ratio of conjugate base to acid. Then calculate the volume using molarity and volume relationships.

Step-by-step explanation:

To determi0-M solution of sodium borate must be added to a 200-mL solution of 50 mM boric acid to achieve a pH one how many mL of a 5.f 9.6, we must understand the concept of buffer solutions and Henderson-Hasselbalch equation. The sodium borate and boric acid system create a buffer solution. The Henderson-Hasselbalch equation is pH = pKa + log([A-]/[HA]), where [A-] is the concentration of the conjugate base, and [HA] is the concentration of the acid.

in this case, we're targeting a pH of 9.6, and the pKa of boric acid is typically around 9.24. We can rearrange the equation to solve for the ratio of [A-] to [HA]:

[base]/[acid] = 10^(pH - pKa)

After calculating the ratio, we can find the volume of the 5.0 M sodium borate solution needed by using molarity and volume relationships. The answer would be one of the given choices after performing the correct calculations.

User Sergey Pleshakov
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8.2k points
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