Name: Date: Period: #: TITRATION NOTES

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1 TITRATION NOTES I. Titration and Curves - Titration: lab technique in which one solution is used to analyze another (analyte/titrant) - point: point in a titration where just enough standard solution has been added to react completely with all the unknown solution (commonly acids and bases) o moles of acid = moles of base (neither is in excess) - point: defined by the change in color of the indicator; the end point should be as close to the equivalence point as possible - All acid-base reactions are neutralization reactions and go to - The titration equation works for any acid-base combo (strong, weak) when provided with and asking for concentrations and volumes (not ) #H + M a V a formula = M #OH - bv b formula II. Molarity and Units Reminder - ml M = mmol - mmol ml = Molarity III. Strong Acid Strong Base Titrations 1) NI Equation: 2) Produces a: 3) at equivalence point: Controlled by: Volume of NaOH added 4) Particulate views A (Initial) B (Before eq. pt.) C (At eq. pt.) D (After eq. pt.) Practice #1: Calculate the after ml of M HCl have been added to ml of M NaOH.

2 IV. Weak Acid Strong Base Titration 1) NI Equation: 2) Produces a: 3) at equivalence point: Controlled by: Volume of NaOH added 4) Particulate views A (Initial) B (Before eq. pt.) C (At eq. pt.) D (After eq. pt.) Note: The weaker the acid, the greater the at the equivalence point (due to the production of a stronger conjugate base). Practice #2: A 25.0 ml sample of M HC2H3O2 is titrated with 25.0 ml of M NaOH. Find the at this point in the titration. (acetic acid Ka = 1.8 x 10-5 ) Practice #3: A 25.0 ml sample of M HC2H3O2 is titrated with 50.0 ml of M NaOH. Find the at this point in the titration. (acetic acid Ka = 1.8 x 10-5 )

3 V. Weak Base Strong Acid Titration 1) NI Equation: 2) Produces a: 3) at equivalence point: Controlled by: Volume of HCl added 4) Particulate views A (Initial) B (Before eq. pt.) C (At eq. pt.) D (After eq. pt.) Practice #4: A 30.0 ml sample of M NH3 is titrated with 5.0 ml of M HBr. Find the of the solution at this point in the titration. (ammonia Kb = 1.8 x 10-5 ) Practice #5: A 30.0 ml sample of M NH3 is titrated with M HBr. Find the of the solution at the equivalence point. (ammonia Kb = 1.8 x 10-5 ) (5.22)

4 Practice #6: A 30.0 ml sample of M NH3 is titrated with 20.0 ml of M HBr. Find the of the solution at this point in the titration. (ammonia Kb = 1.8 x 10-5 ) VI. Weak Acid Weak Base Titration at equivalence point: Depends on: Volume of HCl added VII. Titrations of Polyprotic Acids - Diprotic Acid - Triprotic Acid Volume of base added Volume of base added

5 VIII. Acid-Base Indicators - These mark the end point of a titration by changing color. - Although the equivalence point, defined by the stoichiometry, is not necessarily the same as the endpoint, careful selection of an indicator will ensure the error is negligible. - The most common indicators are complex (HIn). (In = indicator) - They are one color when the proton is attached and a different color when the proton is removed. - Example: phenolphthalein HIn H + + In - K a = [H+ ][In - ] [HIn] - Adding an acid will increase the [H + ] and cause the indicator equilibrium to shift - Adding a base will remove H + via a reaction with OH and cause the indicator equilibrium to shirt - The color change range for an indicator is ±pka - Example: Phenolphthalein s Ka is 1.0 x 10-9, so the pale pink color is seen over the range of. We would choose this indicator for an expected equivalence point of 8-9 when titrating an acid with a base (approaching the equivalence point from the side of the curve) - Example: Methyl orange s Ka is 1.0 x 10-4, so the pale pink color is seen over the range of 3-5. We would choose this indicator for an expected equivalence point of when titrating a base with an acid (approaching the equivalence point from the side of the curve) - More general selection: o Strong acid strong base: choose an indicator near 7 o Weak acid strong base: choose an indicator whose color change should be in the basic region o Strong acid weak base: choose an indicator whose color change should be in the acidic region Indicator Acid Transition Base Litmus Red Purple, violet Blue Phenolphthalein WA/SB pka = 9 Methyl Orange WB/SA pka = 4 Bromothymol Blue SA/SB pka = 7 Colorless Red < 3 Yellow < 6 Pale pink 8-10 Orange 3-5 Green 6-8 Bright pink Yellow > 5 Blue > 8 Practice #5: An indicator HIn (Ka = 1.0 x 10-6 ) where HIn is red and In - is blue, is placed in a solution of strong acid. The solution is then titrated with NaOH. At what will a color change occur? Practice #6: Two drops of an indicator, HIn (Ka = 1.0 x 10-8 ) where HIn is yellow and In - is blue, are placed in 100. ml of 0.30 M HCl. a) What color is the original solution? b) This solution is titrated with 0.20 M NaOH. At what will the color change be visible? c) What color will the solution be after 300. ml of NaOH has been added?

6 TITRATION CALCULATION FLOWCHART STOICHIOMETRY Write neutralization reaction BCA table using mmol Must determine limiting reactant Chose one of the three options below to calculate Only HA/A - or B/BH + remains Only A - or BH + remains Only H + /BH + or OH - /A - remains BUFFER: Henderson-Hasselbach STRONG C.A. or C.B.: Write equilibrium equation with RICE table MIXTURE: Use [H + ] or [OH - ] only Recalculate concentrations using total volume Use K a or K b expression for A - or BH + to find [H + ] or [OH - ]