Chemistry 121/123 Laboratory Techniques Tutorial

Weigh the sample on an analytical balance <b style='color: black'>by differences</b> into a beaker.

Dissolve the sample in a small volume of water. KHP is best dissolved in warm water.

You may use the hotplate set to "2" to speed the dissolution. Make sure the solid has completely dissolved before proceeding further.

The glassware used to prepare the standard solution must be clean. Rinse the volumetric flask and funnel with de-ionized water.

Quantitatively transfer the solution into the volumetric flask: Rinse the beaker, funnel, and stirring rod with de-ionized water into the flask to ensure that all the dissolved sample is transferred to the flask.

Rinse the beaker several times with de-ionized water. Why do you need to rinse the beaker?

Fill the volumetric flask with water to a few cm below the calibration line. At that point use a Pasteur pipet to carefully add water dropwise until the bottom of the meniscus rests on the calibration line. Take care not to go over the line! If you do, you will need to repeat the entire procedure again (why?).

Hold the stopper firmly and invert the flask several times to ensure good mixing. Make sure the solution is completely homogeneous. The concentration of the solution must be the same throughout. If when you hold the flask up to a light you can still see shimmering waves inside the flask, mix it some more.