Sodium thiosulfate (Na₂S₂O₃, molar mass = 158.11 g/mol) is used in photography.The purity of a Na₂S₂O₃ solution labeled as 0.2043 M is checked by redox titration.It is found that 0.100 L of this solution requires 40.21 mL of 0.246 M iodine solution to reach the equivalence point.What is the percent purity of the sodium thiosulfate solution?
I₂ (aq) +2S₂O₃² ^- (aq) $\rightarrow$ 2 I ^- (aq) + S₄O₆² ^- (aq)

Question

Sodium thiosulfate (Na₂S₂O₃, molar mass = 158.11 g/mol) is used in photography.The purity of a Na₂S₂O₃ solution labeled as 0.2043 M is checked by redox titration.It is found that 0.100 L of this solution requires 40.21 mL of 0.246 M iodine solution to reach the equivalence point.What is the percent purity of the sodium thiosulfate solution?
I₂ (aq) +2S₂O₃² ^- (aq)

\rightarrow

2 I ^- (aq) + S₄O₆² ^- (aq)

Quizplus · Accepted Answer

The moles of I2 used are 0.04021 L * 0.246 mol/L = 0.00989766 mol. According to the reaction, 1 mol of I2 reacts with 2 mol of Na2S2O3, so moles of Na2S2O3 = 2 * 0.00989766 = 0.01979532 mol. The expected moles in 0.1 L of 0.2043 M Na2S2O3 solution are 0.1 * 0.2043 = 0.02043 mol. Percent purity = (0.01979532 / 0.02043) * 100% = 96.8%.

Sodium Thiosulfate (Na2S2O3, Molar Mass = 158 →\rightarrow→ 2 I - (Aq) + S4O62 - (Aq) A)100% B)48

Sodium Thiosulfate (Na₂S₂O₃, Molar Mass = 158 $\rightarrow$ 2 I ^- (Aq) + S₄O₆² ^- (Aq)
A)100%
B)48