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Experiment 6: Standardization of a Solution for AP Chemistry

By — McGraw-Hill Professional
Updated on Feb 2, 2011

For a quick review on stoichiometry, refer to the following concepts:

Synopsis

The concentration of a solution is determined by titration with a sample of known composition.

Equipment

      analytical balance
      buret
      desiccator
      drying oven
      Erlenmeyer flask
      pH meter
      pipet
      support stand
      volumetric flask
      wash bottle
      clamp

Refer to figure 19.3 for general titration set-up.

Measurements

  1. the mass of an empty flask
  2. the mass of the flask plus the sample
  3. the initial reading of the buret
  4. intermediate readings from the buret
  5. the final reading of the buret
  6. the pH of the solution at various times during the reaction

Calculations

The mass of the sample is calculated from the differences between masses 1 and 2. The volume added is calculated by taking the difference between measurement 3 and either measurement 4 or 5.

A plot of pH versus the volume added is made. This graph or the difference between measurements 3 and 5 gives the volume of titrant.

The volume of titrant is converted to liters.

The mass of the sample is converted to moles by using the molar mass. The moles of titrant may be calculated from a consideration of the moles of sample and the balanced chemical equation. The moles of titrant divided by the liters of solution gives the molarity of the solution.

Comments

A solution could be prepared by dissolving a known amount of solute in a volumetric flask and diluting to volume.

The course of the titration could be followed with an acid–base indicator instead of a pH meter.

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