In the mysterious deserts of Egypt, large deposits of 'Trona' (Na₂CO₃·NaHCO₃) are found. If a sample of 'Trona' (containing same inert impurities) is dissolved in water and titrati

Question

In the mysterious deserts of Egypt, large deposits of 'Trona' (Na₂CO₃·NaHCO₃) are found. If a sample of 'Trona' (containing same inert impurities) is dissolved in water and titration against 0.1 M HCl, which of the following readings are possible when x and y ml of HCl are required for titration against equal volumes of this solution, one using phenolphthalein and the other using methyl orange respectively as indicators?

TestHub · Accepted Answer

Trona supplies CO₃²⁻ and HCO₃⁻ in a 1:1 molar ratio. Phenolphthalein: x \propto n(CO₃²⁻); methyl orange: y \propto 2n(CO₃²⁻) + n(HCO₃⁻) = 3n(CO₃²⁻). Hence y = 3x (inert impurities only scale both readings equally). Only x = 10, y = 30 fits, option (b).

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