Thursday, 19 February 2015

8.1.1 - Laboratory Activity : Preparation of soluble salt potassium and sodium salts

Laboratory Activity 8.1.1:
Preparation of soluble salt potassium and sodium salts
Aim: To prepare potassium chloride through acid-alkali neutralisation

» Dilute hydrochloric acid (2M)
» Potassium hydroxide

» Burette
» Retort stand
» Pipette (25cm3)
» Conical flask
» White tile
» Beaker
» Glass rod
» Bunsen burner
» Filter funnel
» Filter paper

1. 25cm3 of potassium hydroxide is transferred into the conical flask. Add 2-3 drops of phenolphthalein.
2. The burette is filled with hydrochloric acid. The initial reading is recorded.
3. Acid is added from the burette to the alkali a little at a time with constant shaking until the alkali changes colour at a drop of acid from pink to colourless. The reading is recorded and the volume of acid used to neutralise the alkali is calculated.
4. The steps are repeated with 25cm3 of KOH with Vcm3 of HCl but without adding phenolphthalein.
5. The filtrate is evaporated until a saturated solution(⅓ of original volume) of potassium chloride is obtained.
6. The saturated solution is allowed to cool down until white crystal are formed.
7. The salt crystals are filtered, washed with a little distilled water and dried with filter paper.

Phenolphthalein is used to determine the end point. Once the end point is obtained, it is not used again, in order to prepare a salt without foreign matter.

Potassium chloride is prepared by neutralising hydrochloric acid with potassium hydroxide.

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