Final answer:
To find the pH after adding 6.0 mL of 0.155 M HBr beyond the equivalence point in a titration of CH₃NH₂ with HBr, one needs to calculate the moles of excess HBr, which then determines the concentration of H+ ions in the solution, and use this to compute the pH level.
Step-by-step explanation:
The student is asking about determining the pH of a weak base CH₃NH₂ after titrating it with a strong acid HBr and adding an excess of acid beyond the equivalence point.
To calculate the pH after adding 6.0 mL of 0.155 M HBr beyond the equivalence point, first, calculate the moles of excess HBr added.
Then, determine the concentration of HBr in the total volume of the solution, and subsequently find the concentration of H+ ions.
From the concentration of H+ ions, the pH of the solution can be calculated using the pH formula:
pH = -log[H+]
In this situation, the initial moles of CH₃NH₂ are 0.023 L × 0.175 M. After neutralization at the equivalence point, any further addition of HBr will remain in the solution as excess H+ ions.
For 6.0 mL of 0.155 M HBr, the moles of H+ are 0.006 L × 0.155 M. These excess moles of H+ determine the new pH.