8.3 Preparation of salts

8.3 Preparation of salts

Preparing salts in the lab (all on pages 124 and 125) Starting with a metal:

1. Add excess metal to an acid
2. When bubbling (hydrogen) stops the reaction is done
3. Filter off excess metal (because a metal is a solid, except mercury)

Starting with an insoluble base:

1. Add insoluble base to acid and heat gently, it will dissolve
2. Keep adding until no more dissolves (reaction is done)
3. Filter out the insoluble (excess) base

(Titration): Starting with an alkali (soluble base):

1. Put a certain amount (e.g. 25cm3) alkali in a flask
2. Add phenolphthalein (pink in alkaline, colourless in acid or neutral) you could use a different indicator but this is quite simple
3. Add acid from a burette, slowly while stirring, until it goes colourless
4. Find out how much acid you used (using the scale on the burette).
5. Repeat, this time add the same amount of base, but you know exactly how much acid to add to get a neutral solution, don’t add indicator though (you don’t need it anymore, and it would make it impure)
6. Evaporate the water from the neutral solution using a Bunsen flame and an evaporating dish

If they don’t tell you if the salt is soluble or not then you need to know this: