Titration

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Titration

• Description
• Preparing the Burette
• Preparing the Sample
• Adding the Titrant

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Titration

• In a titration two reagents are mixed, one with a
  known concentration and one with an unknown
  concentration.
• This is some way to indicate when the two
  reagents have reacted essentially completely, and
  at the end of the titration the unknown
  solutions concentration can be calculated.

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Titration

• Typically, one reagent is a solution and is
  added from a burette.
• This solution from the burette 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 burette has graduations that are used to
  read the volume of titrant added to that flask.

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Preparing the Burette

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

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Preparing the burette

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

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Video Draining the burette
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Preparing the Burette

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

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Video Filling the burette
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Preparing the Burette

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

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Preparing the Burette

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

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Video How to remove air bubbles
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Preparing the Burette

• Make sure the volume reading in the burette 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 more reproducible
  results usually occur when the initial reading is
  not 0.00 mL.

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Preparing the Burette

• Record the volume reading on the burette.
  Determine the volume by reading from the bottom
  of the meniscus at eye level.
• All certain digits (markings on the glassware...)
  and one uncertain digit (an estimate of the
  fraction between the markings...) should be
  recorded.

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Preparing the Sample

• The sample to be titrated is a solution
• pipette 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).

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Preparing the Sample

• The sample to be titrated 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.

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Preparing the Sample

• 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.

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Indicator

• An indicator changes colour according to the pH.
• Phenolphthalein and methyl orange are two common
  indicators.

colourless red
red yellow
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Adding the Titrant

• 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).

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Video Addition of Titrant
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Adding the Titrant

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

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Adding the titrant

• 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.

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Determining the Endpoint
approximately at endpoint (very faint pink tinge)

• Flask before endpoint

after endpoint (overshot)
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Determining the Endpoint

• Remember to record the volume reading of the
  burette when you have reached the endpoint.

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-End-