Making Salts

  • Created by: jaaaz_v
  • Created on: 01-04-15 15:47

Making Salts Using a Metal or Insoluble Base

Soluble salts can be made by reacting an acid with a metal or an insoluble base (an oxide or hydroxide). The right acids and metal/insoluble base need to be selected to make the salt that you want.

Eg. If you wanted to make copper chloride, you'd mix hydrochloric acid (acid) with copper oxide (insoluble base)

To make the salt, you need to add the metal/insoluble base to the acid. The solid should dissolve in the acid as it reacts, and when excess solid startes to appear at the bottom, the acid has been neutralised.

The excess can then be filtered out, leaving you with a salt solution.

To get pure crystals of the salt, you need to evaporate the solution. This part is called crystallisation.

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Making Salts Using an Alkali

When making soluble salts with alkalis (soluble bases), you cannot use the same method that you would do for making salt with metals and insoluble bases. This is because you have no way of knowing if the reaction has finished.

You need to add exactly the right amount of alkali to the acid to neutralise it, which means that you need to use an indicator. You'd then need to repeat the reaction, using the same volumes of acid and alkali minus the indicator, so that the salt isn't contaminated with indicator. 

The solution formed from this can then be crystallised to leave the pure crystals of the salt.

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Making Insoluble Salts

Precipitation reactions can be used if the salt that you want to make is insoluble

You need to pick out two solutions that contain the ions that you need.

Eg. to make lead chloride you need a solution that contains lead ions and one that has chloride ions.

The two solutions can be mixed together, and once the salts have precipitated (are lying at the bottom) you filter them out. They can them be washed and dried.

Precipitaion reactions can also be used to get rid of poisonous ions from drinking water.

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