Multiple Choice
20.0 mL of 0.500 M HC2H3O2 is titrated with 0.350 M KOH. Determine the pH after 15.0 mL of the base has been added. Ka for HC2H3O2 = 1.8 × 10−5.
18. Aqueous Equilibrium
Titrations: Weak Acid-Strong Base
Multiple Choice
In order to create a buffer 7.510 g of sodium cyanide is mixed with 100.0 mL of 0.250 M hydrocyanic acid, HCN. What is the pH of the buffer solution after the addition of 12.0 mL of 0.300 M NaH? Ka = 4.9 × 10−10.
A
6.82
B
10.01
C
8.52
D
10.17
Verified step by step guidance1
Calculate the moles of sodium cyanide (NaCN) using its mass and molar mass. The molar mass of NaCN is approximately 49.01 g/mol. Use the formula: \( \text{moles of NaCN} = \frac{\text{mass of NaCN}}{\text{molar mass of NaCN}} \).
Determine the initial moles of hydrocyanic acid (HCN) using its concentration and volume. Use the formula: \( \text{moles of HCN} = \text{concentration} \times \text{volume} \).
Calculate the moles of NaOH added using its concentration and volume. Use the formula: \( \text{moles of NaOH} = \text{concentration} \times \text{volume} \).
Use the Henderson-Hasselbalch equation to find the pH of the buffer solution. The equation is: \( \text{pH} = \text{pK}_a + \log \left( \frac{[\text{A}^-]}{[\text{HA}]} \right) \), where \( \text{pK}_a = -\log(\text{K}_a) \), \([\text{A}^-]\) is the concentration of the conjugate base (CN\(^-\)), and \([\text{HA}]\) is the concentration of the acid (HCN).
Adjust the concentrations of the acid and base in the buffer solution after the addition of NaOH, considering the reaction between NaOH and HCN. Recalculate the concentrations and substitute them back into the Henderson-Hasselbalch equation to find the new pH.
Related Videos
Related Practice
