Titration

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A titration is a laboratory procedure for quantitative analysis. In a titration two reagents are mixed, one with a known concentration and one with an unknown concentration. There is some way to indicate when the two reagents have reacted essentially completely, and at the end of the titration the unknown solution's concentration can be calculated.

Buret and flask setup

Typically, one reagent is a solution and is added from a buret. This solution is called the titrant. The solution from the buret is added to a flask that contains either a measured volume of a solution or a weighed quantity of solid that has been dissolved. The buret has graduations that are used to read the volume of titrant added to the flask.

What is the solution in the buret called? Answer

Rinse a clean buret several times with 5 mL portions of the titrant (the solution that will be added to the flask).

Rinsing buret by rotating between fingers

Allow the titrant to drain through the buret stopcock so that the tip gets rinsed with titrant as well.

Video: Draining the buret ( 764K )

Discard the rinse solution in a waste beaker. Clamp the buret into place, and fill it with the titrant.

Video: Filling the buret ( 3.07 M )

Remove air bubbles from the tip of the buret and the stopcock by draining several milliliters of titrant. Dispose of the drained titrant in a waste beaker.

Close-up of the buret tip.
Note the large air bubble that must be removed.

Video: How to remove air bubbles ( 3.00 M )

Make sure the volume reading in the buret is at the 0.00 mL mark or below (the meniscus does not need to be on the 0.00 mL mark to begin the titration). Record the volume reading on the buret. Determine the volume by reading from the bottom of the meniscus at eye level. All certain digits and one uncertain digit should be recorded.

Buret reading of 52.7 mL (temp.)

Video ( 1.61 M ) Suggest a better way to fill the buret. Answer

If the sample to be titrated is a solution, pipet the desired volume into an Erlenmeyer flask. Record the exact volume transferred. Dilute the sample with a small portion of distilled water (about 10 to 20 mL). If the sample is a solid, weigh the desired mass, add the solid to an Erlenmeyer flask, and dissolve it in distilled water. Be sure to record the exact mass of sample used.

Change in color of a chemical indicator is usually used to signal the endpoint of the titration. If necessary, add a few drops of an appropriate indicator to the solution.

The rate of addition of titrant is determined by the rate at which the indicator changes color. At the beginning of the titration, titrant may be added quickly since the indicator color disappears rapidly. When the color persists for longer periods of time, add titrant more slowly (a drop or less at a time).

Video: Addition of titrant ( 3.24 M )

Be sure to mix the two reactant solutions thoroughly by swirling the flask as the titrant is added.

If solution splashes up to the side of the flask, you can use distilled water to wash it back into the solution. Placing the flask on a piece of white paper will often help you observe the first appearance of color change.

You accidentally allowed all of the titrant to drain out of the buret and into the reaction flask. What should you do next? A. Discard the solution and begin the titration again. B. Add more titrant to the buret and continue the titration. Answer

Overshooting the endpoint of the titration by adding too much titrant is a common error. The endpoint for this titration is reached when you reach a pale color that persists throughout the solution for several seconds.

Flask before endpoint...	...approximately at endpoint... (very faint pink tinge)	...after endpoint (overshot)

Video: Reaching an endpoint ( 2.83 M )

Remember to record the volume reading of the buret when you have reached the endpoint. The volume added to the flask is equal to the final volume reading minus the initial volume reading.

Video ( 2.43 M ) Explain why the student has not seen the endpoint even though she has added a large volume of titrant to the flask. Answer

Miscellaneous Exercises

Video ( 980K ) In the video, the student who titrated the solution recorded a volume of 22.61 mL of titrant needed to reach the endpoint. Is this volume reliable? Answer

Related modules: Pipet, Balance, Hotplate/Magnetic Stirrer