Question

You are asked to bring the pH of 0.500 L of 0.450 M NH4Cl to 7.00.
12.0 M NH3

How many drops (1 drop 0.05 mL) of this solution would you use?

What I did, but its incorrect

Using HH equation
I found out NH4 pKa = 9.24 from table
pH = pKa + log [A-] / [HA]

7.00 = 9.24 + log [NH3] / [NH4+]
[NH3] / [NH4+] = 0.00575

n= CV
n NH4+ = (0.450M)(0.500L)
= 0.225 mol

n NH3 = 0.00575 = NH3 / 0.225 mol NH4
= 0.00129375

n=CV
mol NH3 = (12.0M)(V)
0.00129375 mol = (12M)(V)
1.078125x10^-4 L = V

convert to mL
(0.1078mL) (1 drop / 0.05 mL)
= 2.156
= 2.2

Express your answer as an integer.
539 / 250

Answer 1

I worked the problem and came up with 2.16 mL which tells me your 2.156 mL is correct. I think your problem is that if you are to express your answer as an integer, then 2.156 converts to 2