Experiment 27 Barium chloride method for determining the composition of a carbonate/hydroxide mixture



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.


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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