Answer to Question #134730 in General Chemistry for Mel

Question

The Winkler method is used to determine the amount of dissolved oxygen in a water sample. The procedure involves the following sequence of reactions.
Step 1. 2Mn2+(aq) + O2(g) + 4OH−(aq) 2MnO(OH) (s 2 )
Step 2. MnO(OH)2(s) + 2I−(aq) + 4H+(aq) I (aq 2 ) + Mn2+(aq) + 3H2O(aq)
Step 3. I2(aq) + 2S O 2− 2 3 (aq) 2I−(aq) + S4O 2− 6 (aq)

When a 5.00 L sample of water was analysed using the Winkler method, a total of 4.00 × 10–3 mol of thiosulfate (S2O 2− 3 ) was required in Step 3.

What concentration of oxygen was present in the original sample?
A. 3.20 mg L–1 B. 6.40 mg L–1 C. 12.8 mg L–1 D. 32.0 mg L–

Answer 1

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