preparation of salts

method 1 - soluble salt from an acid and an insoluble base

the method for preparing a soluble salt from an acid and an insoluble base

• dilute acid is placed in a beaker, and excess base is added

• the base begins to react and gas bubbles are given off. the bubbles stop when all the acid has been used up

• as it was added in excess some base was left in the beaker. it is removed by filtering. the resulting solution (the filtrate) is an aqueous salt solution

• the filtrate is gently evaporated to concentrate the salt solution until crystals start to form

• the concentrated solution is cooled to let the crystals form

• the crystals are filtered off and are washed with a little distilled water

• the crystals are carefully dried between filter papers

method 2 - soluble salt from an acid and a soluble base (alkali)

• using a 25cm³ pipette, 25cm³ of the alkali is added to a conical flask

• a few drops of indicator (eg. phenolphthalein, litmus or methyl orange) are added. if phenolphthalein is being used the solution would turn pink

• the acid is added from a burette, a little at a time

• the flask is swirled to let the acid and alkali mix

• near the end point (when all the alkali is fully reacted the indicator suddenly changes colour, ie. turning colourless if phenolphthalein is used), the acid is added dropwise. at the end point the solution is neutral

• the volume of acid added is recorded by reading the burette scale

• repeat step 1 without using an indicator

• the filtrate is gently evaporated to concentrate the salt solution until crystals start to form

• the concentrated solution is cooled to let the crystals form

• the crystals are filtered off and are washed with a little distilled water

• the crystals are carefully dried between filter papers

method 3 - preparation of INSOLUBLE SALTS: precipitation reaction

• add two solutions together

• the solid precipitate is removed by filtering and washed with a little distilled water

• the precipitate is carefully dried between filter papers

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