Large deposits of 'Trona' ( N a 2 C O 3 ⋅ NaHC O 3 ) are found in the deserts of Egypt. A sample of Trona (containing some inert impurities) is dissolved in water and titrated against

Question

Large deposits of 'Trona' ( N a 2 ​ C O 3 ​ ⋅ NaHC O 3 ​ ) are found in the deserts of Egypt. A sample of Trona (containing some inert impurities) is dissolved in water and titrated against 0.1 M HCl . Which of the following readings are possible when x and y ml of HCl are required for equal volumes of this solution, using phenolphthalein and methyl orange respectively as indicators?

TestHub · Accepted Answer

Trona gives C O 3 2 − ​ : HC O 3 − ​ = 1:1. Phenolphthalein: x \propto n ( C O 3 2 − ​ ) ; methyl orange: y \propto 3n ( C O 3 2 − ​ ) , so y = 3x regardless of inert impurity. Only x = 15, y = 45 fits, option (a).

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