Multiple Choice
Determine the pH of a 0.036 M solution of formic acid (HCO2H), given that the acid dissociation constant (Ka) is 1.8 x 10^-4. The dissociation reaction is: HCO2H (aq) ⇌ H+ (aq) + HCO2- (aq).
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17. Acid and Base Equilibrium
pH of Weak Acids
Multiple Choice
What is the pH of the solution when 20.00 mL of 0.1563 M aniline hydrochloride (C6H5NH3+Cl-) is titrated with 15.00 mL of 0.1249 M NaOH? (Ka for aniline = 2.40 x 10^-5)
A
pH = 4.85
B
pH = 6.25
C
pH = 7.00
D
pH = 5.35
Verified step by step guidance1
Calculate the initial moles of aniline hydrochloride (C6H5NH3+Cl-) using the formula: moles = concentration (M) × volume (L). Convert the volume from mL to L before calculation.
Calculate the moles of NaOH added using the same formula: moles = concentration (M) × volume (L). Again, ensure the volume is in liters.
Determine the moles of aniline (C6H5NH2) formed after the reaction by subtracting the moles of NaOH from the initial moles of aniline hydrochloride, as NaOH will react with C6H5NH3+ to form C6H5NH2 and water.
Calculate the concentration of the aniline (C6H5NH2) and the remaining aniline hydrochloride (C6H5NH3+Cl-) in the solution by dividing their respective moles by the total volume of the solution in liters (sum of the volumes of both solutions).
Use the Henderson-Hasselbalch equation to find the pH: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{C}_6\text{H}_5\text{NH}_2]}{[\text{C}_6\text{H}_5\text{NH}_3^+]} \right) \), where \( \text{pK}_a = -\log(\text{K}_a) \). Calculate \( \text{pK}_a \) using the given \( \text{K}_a \) value and substitute the concentrations into the equation to find the pH.
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