A 2.50-g sample containing As2O5, Na2HAsO3 and inert material is dissolved and the pH is

adjusted to neutral with excess NaHCO3. The As(III) is titrated with 0.150 M I2 solution, requiring

11.3 mL to just reach the end point. Then, the solution (all the arsenic in the +5 state

now) is acidified with HCl, excess KI is added, and the liberated I2 is titrated with 0.120 M

Na2S2O3, requiring 41.2mL. Calculate the percent As2O5 and Na2HAsO3 in the sample.

Question

A 2.50-g sample containing As2O5, Na2HAsO3 and inert material is dissolved and the pH is

adjusted to neutral with excess NaHCO3. The As(III) is titrated with 0.150 M I2 solution, requiring

11.3 mL to just reach the end point. Then, the solution (all the arsenic in the +5 state

now) is acidified with HCl, excess KI is added, and the liberated I2 is titrated with 0.120 M

Na2S2O3, requiring 41.2mL. Calculate the percent As2O5 and Na2HAsO3 in the sample.

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