help Notice: Full credit given to 1 removed question. uestion 14 of 21 (1 point)

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help Notice: Full credit given to 1 removed question. uestion 14 of 21 (1 point) A method for d reactions. Balance the following chemical equations in that series under the conditlons indicated a. In basic solution the quantity of dissolved oxygen in natural waters requires a series of redox include p Indluide phases in the balanced Chemical oquation. (),(e) MnO2(s) b. In acidic solution c. In neutral solution; Cck on the (ag) bustion in the fao's to select the phase to add Phases should not be subscripted O Hint 11 12 13 14 15 16719 20 rogresS ty Grade: 22 Points Possble started. Thusda,J-11, 2015, 11 S0AM caper teet 10 percent late peniaty

Explanation / Answer

Basic medium:

Mn+2(aq) + O2(g) --> MnO2(s)

The two half reactions are

Mn 2+ --> Mn 4+ + 2e-
O2 + 4e- --> 2O2-

Balanced equation: 2Mn(2+)(aq) + O2(g) + 4OH(1-)(aq) >> 2MnO2(s) + 2H2O(l)

2. MnO2 + I- --> Mn+2 + I2   ( acidic medium)

two half reactionsa re
MnO2 --> Mn2+

Balance metal and then oxygen and hydrogen by addition of H2O and H+ respectively

MnO2 + 2e- 2+ 4H+--> Mn2+ + 2H2O

2I- --> I2 + 2e-

MnO2 + 4H+ + 2I- --> Mn 2+ + 4H+ + I2 + 2H2O

3. I2 + S2O3-2 --> I- + S4O6-2

Oxidation half-reaction:

2 (S2O3-2)2- ----> (S4O6)2-

balance out the non-hydrogen/non-oxygen atoms ,then number of electrons being lost as oxygen are alreay balanced
2 (S2O3)2- ----> (S4O6)2- + 2 e-


Now for the reduction half-reaction:

I2 + 2 e- ---> 2 I-

No hydrogen or oxygen atoms to balance
2 (S2O3)2- + I2 ----> (S4O6)2- + 2 I-

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