A biochemist has 100 mL of a 0.10 M solution of a weak acid with pKa of 6.3. She adds 6.0 mL of 1.0 M HCL which changes the pH to 5.7. What was the pH of the original solution?

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A biochemist has 100 mL of a 0.10 M solution of a weak acid with pKa of 6.3. She adds 6.0 mL of 1.0 M HCL which changes the pH to 5.7. What was the pH of the original solution?

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Md Ariful Islam · Answer 1 · Apr 23, 2024 17:02:59

Find hydrogen ion concentration of the original solution using the law of mass conservation after some further algebraic manipulation: [H+]2+Ka[H+]-KaCa=0 (Ka - weak acid dissociation constant, Ca – weak acid concentration) Ka=10-6.3=5.01*10-7 Set up the quadratic equation: [H+]2+5.01*10-7*[H+]-5.01*10-7 *0,10=0 Solve the quadratic equation: [H+]=2*10-4 pH=3.7

A biochemist has 100 mL of a 0.10 M solution of a weak acid with pKa of 6.3. She adds 6.0 mL of 1.0 M HCL which changes the pH to 5.7. What was the pH of the original solution?

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