Question

To determine the concentration of a sodium thiosulfate solution as in this experiment, a student pipetted 25.0 mL of 0.0100 M potassium iodate (KIO3) solution into a 125 mL Erlernmeyer flask. Potassium iodide and sulfuric acid were added as in this experiment. The titration needed 15.21 mL of the sodium thiosulfate to reach the end point. What is the concentration of the sodium thiosulfate solution

Answer 1

0.0986M is the concentration of the Na₂S₂O₃ solution

Step-by-step explanation:

Potassium iodate, KIO₃, reacts with sodium thiosulfate, Na₂S₂O₃, as follows:

KIO₃ + 6Na₂S₂O₃ +5KI + 3H₂SO₄ → 3H₂O + 3K₂SO₄ + 3Na₂S₄O₆ + 6NaI

To solve this question we must find the moles of sodium thiosulfate that reacts as follows:

Moles KIO₃:

0.0250L * (0.0100mol / L) = 2.5x10⁻⁴moles KIO₃

Moles Na₂S₂O₃:

2.5x10⁻⁴moles KIO₃ * (6mol Na₂S₂O₃ / 1mol KIO₃) = 1.5x10⁻³ moles Na₂S₂O₃

Molar concentration:

1.5x10⁻³ moles Na₂S₂O₃ / 0.01521L =

0.0986M is the concentration of the Na₂S₂O₃ solution