Titrations: Techniques and Calculations
A titration is one of the most common quantitative lab techniques for determining the concentration of an unknown chemical. The power of the process is its simplicity, as there is a visual indication, a color change, that allows the reaction process to be monitored and the amounts of reactants measured.
Titrations are often associated with acid/base reactions but can be used for any reaction that can be monitored visually, through a color change like enzyme catalysis. Specific vocabulary identifies the known and unknown concentrations of reactants and when the reaction process has reached the ideal stoichiometric proportions. Review the vocabulary below.
- Titration: a process for determining the unknown concentration of a reactant by reacting it with a reactant of known concentration
- Acid-base titration: determines the concentration of an unknown acid or base by neutralizing it with an acid or base of known concentration
- Titrant: the standardized (known) solution that is added during titration
- Analyte (or titrand): the unknown solution whose concentration is being determined in the titration
- Equivalence point: the point at which an added titrant’s moles are stoichiometrically equal to the moles of the sample; the smallest amount of titrant needed to fully neutralize or react with the analyte
For an explanation of solution preparation, Carolina offers a preparation guide for common educational solutions. The guide includes a video, instructions for preparing molar solutions and dilutions, and recipes for common acid and base solutions.
Below is a list of the essential materials for completing a titration. (Notice alternative spellings for buret and pipet.)
- Buret (burette), clamp, and stand
- White paper (used to see a color change in the solution)
- Volumetric pipet (pipette) and pipet bulb
- pH indicator (the type depends on the reactants)
- Erlenmeyer or conical flask
- Titrant (the standard solution of known concentration)
- Analyte, or titrand (the solution of unknown concentration)
- Wash bottle
- Waste container or beaker
Equivalence Point Indicators
Choosing a suitable indicator for the titration process is critical. An equivalence point indicator will produce a color change at the end point, which is close to the reaction’s equivalence point. This is the point at which equivalent amounts of the reactants and products have reacted. For a review of indicators, their equivalence point ranges, and suggested solution strengths, see the article “Acid-Base Indicators.”
Below are some common acid/base equivalence point indicators:
- Strong acid-strong base titration: phenolphthalein indicator
- Weak acid-weak base titration: bromthymol blue indicator
- Strong acid-weak base titration: methyl orange indicator
Review the titration steps below and watch the titration demonstration video for detailed steps.
- Inspect the buret. Markings must be visible and readable, the stopcock should rotate freely and no chips of glass missing from the tip.
- Clean the titration equipment.
- Rinse the buret with deionized water; if water beads on the inside of the buret, clean the buret or get another.
- Rinse the buret with the standard solution, allowing it to run through the stopcock and out the tip.
- Rinse the pipet with the unknown solution.
- Rinse the Erlenmeyer flask with distilled water.
- Place an accurately measured volume of the analyte in the Erlenmeyer flask using the pipet. Add a few drops of indicator.
- With the stopcock in the closed position, place the standard solution, or titrant, in the buret. Let a small amount of standard run out into a waste container.
- Check the column and stopcock for air bubbles. No titrant should be leaking from the stopcock.
- Indicate the initial starting point of the titrant in a lab notebook. The initial reading should be between 0.0 mL and about 1.0 mL. The meniscus should not be above 0.0 mL.
- Rough estimate titration is a procedure to estimate the amount of known solution necessary to neutralize the unknown solution.
- Let the solution out of the buret until the indicator changes color and the color remains constant.
- Record the final value on the buret. Subtract the final value from the initial value to determine the volume of titrant used. This is the first titration, and it is not very precise. It should be excluded from any calculations.
- Perform 2 or 3 more titrations for accuracy, considering where the end point will roughly occur. Read from the bottom of the meniscus and record the initial and final readings on the buret.
- Subtract the initial volume from the final volume to determine the amount of titrant used to reach the end point. The end point is reached when the indicator permanently changes color.
Calculations and Graphing
Calculations to determine the concentration of the analyte are generally the next step in the titration process. A simplified calculation is represented by the following formula:
Molarity 1 × Volume 1 = Molarity 2 × Volume 2
This simplified version does not consider the stoichiometric ratios for the balanced chemical equation, but that ratio must be considered before a final answer is rendered.
For a more complete discussion of titration calculations, watch the second video in the titration series.
During an acid/base titration, pH changes can also be recorded in the Erlenmeyer flask with a pH meter and graphed against the volume of analyte used. Looking at the shape of the titration curve and identifying the number of inflection points indicates the number of protons (hydrogen ions) the acid can contribute during the neutralization reaction. For practice graphing titration curves, click here.
Once your students have mastered titration techniques and calculations, have some fun. Set up a titration race between classes for bragging rights, or let students race against you or a local forensic technician.
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