gcsescience.com                                          37                                          gcsescience.com

Acids and Alkalis

Precipitation Reactions.

The process of making a solid come from a solution is
called precipitation. The solid itself is called a precipitate.

An insoluble salt (one that doesn't dissolve)
can be made by reacting the appropriate soluble salt
with an acid or alkali or another salt.

For examples of precipitation, see tests for ions including
precipitation using the alkali sodium hydroxide
the barium chloride test for sulfate ions
and the silver nitrate test for bromide, chloride and iodide ions.

Precipitation reactions
can be used to remove ions from water.
carbonate can be used to precipitate calcium carbonate.
This is a way of making hard water into soft water.

calcium chloride + sodium carbonate  arrow  calcium carbonate + sodium chloride.
CaCl2(aq)      +       Na2CO3(aq)     arrow             CaCO3(s)    +      2NaCl(aq)

The ionic equation is    Ca2+(aq)  +  CO32-(aq)  arrow  CaCO3(s)

A precipitate can be separated from the solution by filtration.
The precipitate can then be left somewhere warm to dry.

       Links        Acids and Alkalis         Revision Questions        next

gcsescience.com    The Periodic Table    Index    Neutralisation Quiz    gcsescience.com

Home      GCSE Chemistry      GCSE Physics

Copyright © 2015 gcsescience.com. All Rights Reserved.