[SOS]

before i attempt the question, ammonia (NH3) is a weak base correct?

Question:A 10 mL solution is 0.67 mol/L of Ammonia is titrated with 20 mL of 0.14 mol/L of hydrochloric acid. What’s the pH of that solution?

NH3 + HCl -->
0.01L x 0.67M=6.7x10^-3mol NH3
0.02 x 0.14M=2.8x10^-3mol HCl
Limiting is HCl, Excess is NH3
Leftover NH3 is 6.7x10^-3 - 2.8x10^-3=3.9x10^-3mol
Total Volume: 30mL--> 0.03L
3.9x10^-3mol/0.03L=0.13M NH3
2.8x10^-3mol/0.03L=0.093M
The problem didn't give me a Kb, so I got it off of somewhere else.
Kb for NH3 is 1.8x10^-5
Use the Henderson-Hasselbalch Equation: pOH=pKb + log([acid]/[base])
pOH=-log(1.8x10^-5)+log(0.093M/0.13M)
pOH=4.59
pH=14-4.59=9.41

so am I correct?

[Borek]

OK.

One thing that is not clear o me is whether you used rounded down values in your calculations, or not - it is OK to report intermediate values rounded won, but it is incorrect to use them in the calculations, use either all digits you have or at least several guard digits to not lose accuracy.

[SOS]

Alright thanks. So everything else here is correct?

[Borek]

Yes.