3. Preparation of Standard Solution with Volumetric Flask

General Remarks

As the example of how to use a volumetric flask or a measuring flask, the movie explains the preparation of the standard solution of potassium iodate (KIO3) in "Idometry of Volumetric Analysis Experiment".
A volumetric flask is employed when a solution of a definite concentration is prepared.
The volume of a volumetric flask is the volume of a liquid in the flask which is filled up to the marked line.
When a standard solution is prepared from a solid sample, it is not dissolved in a volumetric flask but in another container. Then, the solution is transferred into the volumetric flask.
Because the volume may change at mixing of a sample and a solvent, the sample should not be diluted directly to the marked line without stopping.
After the final dilution, the solution is mixed thoroughly, by inverting the flask and shaking. The mixing is not enough when it is shaken without inverting.
Volumetric flasks just like volumetric pipettes and burette should not be dried by heating. When an aqueous solution is prepared, a wet flask washed with distilled water can be employed without drying.
Volumetric flasks should not be washed with brushes because the inside might be flawed and the volume might be changed. They are washed by repeated rinsing with solvents.
The washing method is also explained in "6. Rinsing of Volumetric Glassware with Standard Solution".

To make up a standard solution, add first a less amount of distilled water than required to the solid sample weighted precisely.
Next, stir it to be dissolved completely using a stirring stick.
Transfer the solution into the volumetric flask with a stirring stick or a funnel.
In order to transfer the remaining solution in the container and on the stirring stick, rinse them some times with distilled water.
Shake the flask gently to make the solution homogeneous.
Repeat the operation of adding a small amount of distilled water and shaking until the height of the solution reaches just below the marked line.
Move your eye to the level of the marked line of the flask at the final addition of distilled water. Adjust the meniscus of the solution to the line by adding distilled water dropwise with a transfer pipette.

After the final dilution, mix the solution thoroughly by inverting the flask and shaking with holding tightly the stopper.