Experiment 27 Barium chloride method for determining the
composition of a carbonate/hydroxide mixture
.
Theory
Barium, an alkaline earth element, forms a soluble hydroxide but
the carbonate has a very low solubility product. Hence if a
barium chloride solution is added to a mixture containing the two
ions, the carbonate ions will be effectively removed as
precipitate. If this mixture is then titrated against acid under
conditions of high pH (greater than 7), only the hydroxide ions
will be neutralised.
Method
Pipette 25.00 cm3 of the solution `E', into a conical
flask and add about 10 cm3 of 10% barium chloride. Titrate the
mixture with the standard acid using phenolphthalein as the
indicator. Into a clean flask place a further 25.00 cm3 aliquot
of the mixture and titrate directly with the acid using screened
methyl orange as the indicator. Carry out the entire operation in
duplicate to obtain consistent results and calculate the
composition of the mixture (g/dm3 of NaOH + Na2CO3).
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