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Acid-Base Titration to Determine Molecular Weight

Math & Results

Sources of Error

Second Derivative Graphs

-4

Let's Take a Closer Look

-Calibration

-Incorrect Mass in Beaker #1

Calculated Molecular Weight

-Actual Volume vs. Volume Read

Calculated Molecular Weight

-Estimating Equivalence Point

Calculated Molecular Weight or

-Stability of pH

Calculated Molecular Weight

Beaker 1: 8.28 mL

Beaker 2: 8.02mL

  • HX(s) + NaOH(aq)<->NaX(aq) + H2O(l)
  • Beaker 1 Calculations:

-Mol Unknown Acid = 0.08903M NaOH x 0.00828L x 1acid/1base = 7.371684*10 mol Unknown Acid

-Molecular Weight= 0.159g/(7.371684*10 ) mol = 215.6902005g/mol Unknown Acid

  • Beaker 2:

-Mol Unknown Acid: 7.140206*10 mol

-Molecular Weight: 218.4810914g/mol Unknown Acid

  • Beaker 3:

-Mol Unknown Acid: 6.988855*10 mol

-Molecular Weight: 223.2125291g/mol Unknown Acid

-4

Beaker 3: 7.85mL

Real-World Applications

-4

  • Quality Control/Analysis in Modern Medicine

  • Pregnancy Tests

Pertinent Chemical

Principles

Quality Control/Analysis in Modern Medicine

Pregnancy Testing

Learning Objectives

  • pH Probe: Friend or Foe?
  • Titration: Master of the Meniscus!

-n

n

  • Spreadsheet Analysis

  • Calculate Molecular Weight of Unknown
  • Acids vs. Bases
  • Neutralization Reaction

  • H X + nOH <-> X + nH2O
  • Equivalence Point

  • Moles Titrant = V x M

  • Moles Acid = moles base x acid/base ratio

  • Molecular Weight = mass acid sample/moles acid

titrant

Data Observations

____

___________

More Math

…but no Derivatives

  • pH 4 = pink, 0.86V 2.44V

  • pH 10 = purple, 0.86V

  • Describe Unknown

-White crystals, like salt

First Derivative Graphs

  • Molarity NaOH: 0.08903M
  • Unknown Solid #2 = HX

  • Masses Unknown:

-Beaker 1: 0.159 grams

-Beaker 2: 0.156 grams

-Beaker 3: 0.156 grams

  • Equivalence Point Volumes:

-Beaker 1: 8.28mL

-Beaker 2: 8.02mL

-Beaker 3: 7.85mL

  • Observed Sources of Error

-Beaker 1 Mass

-Droplets on Buret Tip

-Stabilization of pH

in Beaker 1

Average Molecular Weight of Unknown Acid:

(215.6902005g/mol+218.4810914g/mo+223.2125291) =

3

= 219.1279403g/mol ≈ 219g/mol

Conclusion

Questions?

pH Probe = New Best Friend

Buret, conquered! pH, probed!

Deciphered Excel

Beaker 1 - Titration Family's

Black Sheep

  • Beaker 1: 216g/mole
  • Beaker 2: 218g/mole
  • Beaker 3: 223g/mole
  • Average: 219g/mole

pH vs. Volume Graphs

By: Angela Boney &

Robert Lewellen

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