Experiment 6: Standardization of a Solution for AP Chemistry
For a quick review on stoichiometry, refer to the following concepts:
- Moles, Molar Mass, and Molarity for AP Chemistry
- Percent Composition and Empirical Formulas for AP Chemistry
- Reaction Stoichiometry for AP Chemistry
- Limiting Reactants for AP Chemistry
- Percent Yield for AP Chemistry
The concentration of a solution is determined by titration with a sample of known composition.
- analytical balance
- drying oven
- Erlenmeyer flask
- pH meter
- support stand
- volumetric flask
- wash bottle
Refer to figure 19.3 for general titration set-up.
- the mass of an empty flask
- the mass of the flask plus the sample
- the initial reading of the buret
- intermediate readings from the buret
- the final reading of the buret
- the pH of the solution at various times during the reaction
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.
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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