E2 Dissolution And Precipitation Solubility Rules Worksheets Page 2
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1
2
3The next step is to consider what happens when the solution of one salt is mixed with the solution of another. For
example silver nitrate dissolves in water, as does sodium chloride:
+
-
AgNO
(s)
Ag
(aq) + NO
(aq)
3
3
+
-
NaCl(s)
Na
(aq) + Cl
(aq)
If the two solutions are mixed there will be a combination of silver ions, sodium ions, nitrate ions and chloride ions
present. Silver chloride is insoluble so as silver cations and chloride anions meet, they will combine to precipitate silver
chloride. The other combination of ions leads to sodium nitrate, which is soluble, and so these ions remain in solution
and are termed spectator ions. In chemistry, all reactions are represented by an ionic equation that indicates the change
that has occurred. Consequently, no spectator ions are included in the equation, as they have not undergone any change.
+
-
Ag
(aq) + Cl
(aq)
AgCl(s)
In this experiment, the solubility of a number of compounds is investigated and the application of these solubilities
studied. It is important to maintain clean equipment in order to prevent contamination and to use the recommended
quantities in order to get consistent results.
Hydroxides, oxides and carbonates
Although most hydroxides, oxides and carbonates are insoluble in water, they all react with acids as shown by the
following general equations. In these examples, M represents any metal ion, which for illustrative purposes has been
taken as divalent. The same type of reaction applies to the compounds of all metals.
+
2+
M(OH)
(s) + 2H
(aq)
M
(aq) + 2H
O(l)
2
2
+
2+
MO(s) + 2H
(aq)
M
(aq) + H
O(l)
2
+
2+
MCO
(s) + 2H
(aq)
M
(aq) + H
O(l) + CO
(g)
3
2
2
Let us look at these processes in a little more detail. Hydrochloric acid is a strong acid which means it is completely
+
-
dissociated in water into its constituent ions. It thus forms a solution that contains H
(aq) and Cl
(aq), and no HCl(aq).
+
It is the H
that reacts with the carbonate to give water, carbon dioxide and release the metal ion into solution. The
chloride ion is merely a spectator ion; although it is present in the solution it takes no part in the reaction. If the water is
then evaporated the metal ion and the chloride ion combine to form a chloride salt. In this way one salt may be
converted into another by a series of chemical processes.
For example, to convert strontium carbonate to strontium iodide you might dissolve solid strontium carbonate in
hydroiodic acid and then evaporate the water from the resulting solution.
+
2+
SrCO
(s) + 2H
(aq)
Sr
(aq) + H
O(l) + CO
(g)
3
2
2
2+
-
Sr
(aq) + 2I
(aq)
SrI
(s)
2
Remember that the acids you use are aqueous solutions so if a salt dissolves in water, it would be expected to dissolve
in the water of a dilute acid solution. In your observations, look for changes which occur - there are the obvious ones
such as a solid dissolving or bubbles of a gas being produced but also less obvious ones such as evolution of heat. These
observations can be used to infer that a chemical reaction has taken place.
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