The Iodine "Clock Reaction" Involves the Following Sequence of Reactions $\rightarrow$

question 87

Multiple Choice

The iodine "clock reaction" involves the following sequence of reactions occurring in a reaction mixture in a single beaker.
1. IO₃¯(aq) + 5I¯(aq) + 6H⁺(aq) $\rightarrow$ 3I₂(aq) + 3H₂O(l)
2. I₂(aq) + 2S₂O₃²¯(aq) $\rightarrow$ 2I¯(aq) + S₄O₆²¯(aq)
The molecular iodine (I₂) formed in reaction 1 is immediately used up in reaction 2, so that no iodine accumulates. In one experiment, a student made up a reaction mixture which initially contained 0.0020 mol of iodate ions (IO₃¯) . If the iodate ions reacted completely, how many moles of thiosulfate ions (S₂O₃²¯) were needed in reaction 2, in order to react completely with the iodine (I₂) produced in reaction 1?

• A) 0.0020 mol
• B) 0.0030 mol
• C) 0.0040 mol
• D) 0.0050 mol
• E) 0.0060 mol

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