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97) The concentration of an aqueous solution of I3⁻ can be determined by a redox titration with aqueous
sodium thiosulfate, Na2S2O3:
2 S2O32- (aq) + I3⁻ (aq) + → S4O62- (aq) + 3 I⁻ (aq)
Assume that the black spheres in the buret represent S2O32– ions, the gray spheres in the flask represent
I3– ions, the concentration of the S2O32- ions in the buret is 0.120 M, and the volumes in the buret and the
flask are identical. What is the concentration of the I3– in the flask, and what fraction of the S2O32-
solution in the buret must be added to the flask to react with all the I3– ions?
A) 0.0400 M I3–; 1/3 of the S2O32- must be added.
B) 0.0400 M I3–; 2/3 of the S2O32- must be added.
C) 0.0600 M I3–; 1/3 of the S2O32- must be added.
D) 0.0600 M I3–; 2/3 of the S2O32- must be added.
98) The concentration of an aqueous solution of Fe2+ can be determined by a redox titration with aqueous
bromate ion, BrO3⁻:
6 Fe2+ (aq) + BrO3⁻ (aq) + 6 H⁺ (aq) → 6 Fe3+ (aq) + Br⁻ (aq) + 3 H2O (l)
Assume that the black spheres in the buret represent BrO3⁻ ions, the gray spheres in the flask represent
Fe2+ ions, the concentration of the BrO3⁻ ions in the buret is 0.120 M, and the volumes in the buret and
the flask are identical. What is the concentration of the Fe2+ in the flask, and what fraction of the BrO3⁻
solution in the buret must be added to the flask to react with all the Fe2+ ions?
A) 0.0200 M Fe2+; 1/18 of the BrO3⁻ must be added.
B) 0.0200 M Fe2+; 1/3 of the BrO3⁻ must be added.
C) 0.0400 M Fe2+; 1/18 of the BrO3⁻ must be added.
D) 0.0400 M Fe2+; 1/3 of the BrO3⁻ must be added.