Types of Reaction – Precipitation Reactions

Types of Reaction – Precipitation Reactions

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We have an aqueous solution of cobalt
chloride which is pink and a clear solution of sodium hydroxide. The word
equation and the balanced equation for the reactants are shown. The full ionic
equation is shown here and it shows all of the ions present in the solution
followed by the net ionic equation for the reactants here on mixing when the
cobalt and hydroxide ions meet they will form a precipitate this precipitate will
be a blue color. The cobalt hydroxide blue precipitate
will be shown in the ionic equation and the spectator ions sodium and chloride
ions will be removed. The solubility table here shows what
ions will precipitate out of the solution when they come in contact with
each other, for example in a solution of sodium chloride, the sodium and the alkali metal ions will never precipitate out and always
exists as aqueous solutions whereas hydroxide and most compounds of
hydroxide will precipitate out. Using solubility rules we can explain what is
going on at a molecular level in these equations. Looking at aqueous cobalt chloride solution we can see that the cobalt and the chloride exist
as separate ions in the ratio of one cobalt ion to two chloride ions. Looking
at the aqueous sodium hydroxide solution at a molecular level. It shows that there’s a
one-to-one ratio of sodium ions to hydroxide ions and the solution is
colorless. However, on mixing both solutions come into contact with each
other and the ions that were in separate solutions are now mixed together and in
this scenario we have the cobalt, the sodium, chloride and hydroxide ions
moving around freely. Now when the cobalt and hydroxide ions
will meet they will form an insoluble precipitate and consulting the
solubility table shown before we will see that the cobalt and hydroxide will
form cobalt hydroxide solid, as you can see here and then they will move
to the bottom because solids are denser and they all congregate to the bottom of
the solution. Now the complete ionic equation is shown here, including the aqueous dissolved ions and the ions which
precipitated out. The unreacted ions, this spectator ions can be
omitted, leaving the precipitate and this can be shown in a net ionic equation where
we’ve canceled the spectator ions and is shown here. Cobalt plus Hydroxide goes
to Cobalt Hydroxide solid

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