A 100 ml mixture of Na₂CO₃ and NaHCO₃ is titrated against 1 M HCl. If V₁ L and V₂ L are consumed when phenolphthalein and methyl orange are used as indicators, respectively, in two separate titrations

Question

A 100 ml mixture of Na₂CO₃ and NaHCO₃ is titrated against 1 M HCl. If V₁ L and V₂ L are consumed when phenolphthalein and methyl orange are used as indicators, respectively, in two separate titrations, which of the following is true for molarities in the original solution?

TestHub · Accepted Answer

With phenolphthalein, Na₂CO₃ is neutralized only to NaHCO₃, so V₁ L of 1 M HCl = V₁ mol = mol of Na₂CO₃ in 0.1 L → M(Na₂CO₃) = 10V₁. With methyl orange, both are fully neutralized: mol Na₂CO₃ + mol NaHCO₃ = V₂ - V₁, so M(NaHCO₃) = 10(V₂ - 2V₁). Only (b) is true; (a) overcounts by a factor of 2, and (c), (d) use wrong combinations.

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