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Chem

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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 -

    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 Bronsted-Lowry 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 Henderson-Hasselbalch 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.

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