Making salts

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  • Created by: Elca
  • Created on: 01-04-15 19:00

Making soluble salts using a metal or an insoluble

1) You need to pick the right acid, plus a metal or an insoluble base (a metal oxide or metal hydroxide). E.g. if you want to make copper chloride, mix hydrochloric acid and copper oxide. 

2) You add the metal, metal oxide or hydroxide to the acid - the solid will dissolve in the acid as it reacts. You will know when all the acid has been neutralised because the excess solid will just sink to the bottom of the flask. 

3) Then filter out the excess metal, metal oxide or metal hydroxide to get the salt solution. To get pure, solid crystals of the salt, evaporate some of the water (to make the solution more concentrated) and then leave the rest to evaporate very slowly. This is called crystallisation. 

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Making soluble salts using an alkali

1) You can't use the method above with alkalis (soluble bases) like sodium, potassium or ammonium hydroxides, because you can't tell whether the reaction has finished - you can't just add an excess to the acid and filter out what's left. 

2) You have to add exactly the right amount of alkali to just neutralise the acid - you need to use an indicator to show when the reaction's finished. Then repeat using exactly the same volumes of alkali and acid so the salt isn't contaminated with indicator. 

3) Then just evaporate off the water to crystallise the salt as normal. 

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