A 1.150 g sample containing an unknown amount of arsenic trichloride, with the rest being inerts, was dissolved into a NaHCO3 and HCl aqueous solution. To this solution was added 1.920 g of KI and 50.00 mL of a 0.00885 M KIO3 solution. The excess 13− was titrated with 50.00 mL of a 0.02000 M Na2S2O3 solution. What was the mass percent of arsenic trichloride in the original sample?

13.04%

Explanation:

KIO₃, IO₃⁻, reacts with KI, I⁻, thus:

IO₃⁻ + 8I⁻ + 6H⁺ → 3I₃⁻ + 3H₂O

Producing triiodide ion.

KIO₃ is limiting reactant, moles are:

0.05000L ₓ (0.00885mol /L) = 4.425x10⁻⁴ moles.

Moles of I₃⁻ produced are:

4.425x10⁻⁴ moles KIO₃ ₓ (3 moles I₃⁻ / 1 mole IO₃⁻) = 1.3275x10⁻³ moles I₃⁻

This iodine reacts with Na₂S₂O₃ and AsCl₃, As³⁺, thus:

I₃⁻ + 2S₂O₃²⁻ → 3I⁻ + S₄O₆²⁻

I₃⁻ + As³⁺ → 3I⁻ + As⁵⁺

Moles of I₃⁻ that react with Na₂S₂O₃ are:

0.0500L ₓ (0.02000mol / L) = 1.000x10⁻³ moles Na₂S₂O₃

1.000x10⁻³ moles Na₂S₂O₃ ₓ (1 mole I₂ / 2 moles Na₂S₂O₃) = 5.000x10⁻⁴ moles I₃⁻.

That means moles of I₃⁻ that react with As³⁺ are:

1.3275x10⁻³moles - 5.000x10⁻⁴moles = 8.275x10⁻⁴ moles I₃⁻. As 1 mole of I₃⁻ reacts per mole of As³⁺, moles of As³⁺ are 8.275x10⁻⁴ moles.

Molar mass of AsCl₃ is 181.28g/mol. 8.275x10⁻⁴ moles weight:

8.275x10⁻⁴ moles ₓ (181.28g / mol) = 0.1500g of AsCl₃

As the weight of the sample is 1.150g, mass percent of AsCl₃ is:

0.1500g / 1.150g ₓ 100 =

adding or remove a gaseous reactant or product changes the concentrations. if the concentration of reactant or product is increased, the system will shift away from the side in which concentration was increased (i.e. if the concentration of reactants is increased, the system will shift toward the products. if more products are added, the system will shift to form more reactants). conversely, if the concentration of reactant or product is decreased, the system will shift toward the side in which concentration was decreased (i.e. if reactants are removed, the system will shift to form more reactants. if the concentration of products is decreased, the equilibrium will shift toward the products).

explanation: