Lesson 6: Volumetric Analysis

Volumetric Analysis

Measurement of the volume of a solution whose concentration is known and applied to determine the concentration of the analyte.

Titration or Titrimetric method

delivery of a solution of known concentration into a solution of unknown concentration

Acid–base titrations

in which an acidic or basic titrant reacts with an analyte that is a base or an acid

Complexometric titrations

involving a metal–ligand complexation reaction

Redox titrations

where the titrant is an oxidizing or reducing agent

Precipitation titrations

in which the analyte and titrant react to form a precipitate

Equivalence point.

• For a titration to be accurate we must add a stoichiometrically equivalent amount of titrant to a solution containing the analyte. We call this stoichiometric mixture the

• a theoretical point reached when the amount of added titrant is chemically equivalent to the amount of analyte in the sample

Titrant/standard solution

solution of known concentration used in titration (added from burette)

Titrate/Analyte

unknown solution which we determine its concentration

End point

physical change associated with the condition of chemical equivalence.

Indicators

• are often added to the analyte solution to produce an observable physical change (signaling the end point) at or near the equivalence point.

• Complex organic compound which shows clear visual change after the reaction between titrant and titrate is just complete.

• Phenolphthalein

• Methyl orange, blue

• Thymol blue

Titration error

• The difference between the end point volume and the equivalence point volume is a determinate method error, often called the ____.

• If the end point and equivalence point volumes coincide closely, then the ____ is insignificant and can be safely ignored. Clearly, selecting an appropriate end point is critical

Buret

Typical setup for carrying out a titration. The apparatus consists of a ___, a ____ stand and clamp with a white porcelain base to provide an appropriate background for viewing indicator changes, and a wide-mouth Erlenmeyer flask containing a precisely known volume of the solution to be titrated. The solution is normally delivered into the flask using a pipet.

Erlenmeyer flask

Typical setup for carrying out a titration. The apparatus consists of a buret, a buret stand and clamp with a white porcelain base to provide an appropriate background for viewing indicator changes, and a wide-mouth ____ containing a precisely known volume of the solution to be titrated. The solution is normally delivered into the flask using a pipet.

0.01 mL

Detail of the buret graduations. Normally, the puret is filled with titrant solution to within 1 or 2 ml. of the zero position at the top. The initial volume of the buret is read to the nearest ____.

Pink

Before the titration begins. The solution to be titrated an acid in this example, is placed in the flask, and the indicator is added as shown in the photo. The indicator in this case is phenolphthalein, which tums ____ in basic solution.

Over titrate 

If you overshoot the endpoint, it will cause an error in the calculation of the solution being titrated. If the volume of titrant is in error because it is higher than it should be, the moles of titrant will be incorrect and the resulting calculation for the solution titrated will not be accurate.