Question

You are asked to bring the pH of 0.500L of 0.550 M NH4Cl to 7.00. Which of the following solutions would you use: 12.0 M HCl or 12.0 M NH3? How many drops (1 drop 0.05 mL ) of this solution would you use?

The answer to part one is 12.0 M NH3 but how do you answer the second part?

Thank you

Answer 1

1 drop is approximately 0.05mL. Since 0.500L of 0.550M NH4Cl contains 0.275mol of substance (calculated by using c=n/V formula), equal amount of substance of NH3 is needed to neutralize this solution (since pH of 7 is neutral solution). Thus, we need 0.0275L of NH3, i.e. around 550 drops.