Posted by Sharon on .
What would a titration curve look like for 25 mL of 0.400 M NH3 (aq) with 0.200 M HCl (aq)
find initial pH
find 1/2 equivalence point pH and volume of HCl required to reach this point
find equivalence point pH and volume required to reach this point
find pH at some volume just past equivalence point.

Chem 
DrBob222,
http://www.chemguide.co.uk/physical/acidbaseeqia/phcurves.html
Here are some titration curves. Scroll down to the weak base versus strong acid (there is a curve there where the acid is run INTO the base). Divide the curve up into 4 regions.
A. beginning point.
C. equivalence point.
B. all points between A and B.
D. All points after C.
A. You have a pure weak base. Make an ICE chart, substitute into Kb expression and solve for OH^ and convert to pH.
C. The equivalence point is determined by the salt produced. The equation is
NH3 + HCl ==> NH4Cl
The NH4^+ acts as a BronstedLowry acid and hydrolyzes. Write the hydrolysis equation and make an ICE chart for that, substitute into Kb expression, and solve for H^+, then convert to pH. Many students forget to take into account the dilution of the salt but you need to do that, too.
B. All points between A and B use the HendersonHasselbalch equation.
D. All points AFTER the equivalence point are determined by the amount of excess HCl which is a strong acid (it ionizes 100%).
The first think you should do is determine how many mL it takes to reach the equivalence point so you can properly divide the curve into the proper regions.