Chemistry- Electro Chemistry, Redox, Balancing

If some could help me with these problems i would really appreciate it. Thanks

Balance the following reaction using oxidation numbers:
K2Cr2O7 (aq) + HI (aq) -> KI (aq) + CrI3 (aq) + I2 (s) + H2O (l)
Items required:
- oxidation numbers; bridges connecting oxidation and reduction ½ reaction
- electrons equalized with visible factors
- reaction partially balanced with oxidation numbers
- reaction fully balanced via visual inspection

Describe completely the galvanic cell based on the following reaction under standard conditions:
MnO4-(aq) + I-(aq) -> I2(s) + Mn 2+(aq)
Items needed for a description of a galvanic cell:
-oxidation and reduction half reactions; halfreaction
and cell potentials; balanced cell reaction
- standard cell notation for the cell
- a cell diagram, including halfcells,
electrodes, electron flow, electrolytes & saltbridge,
and ion flow in saltbridge
- the nature of each electrode and the ions present in each compartment, including saltbridge


Determine whether the system below is a redox reaction and support your answer:
K2Cr2O7 (aq) + HI(aq) ---> KI(aq) + CrI3 (aq) + I2 (s) + H2O (l)
Items required:
- bridges connecting the elements that are oxidized and reduced, including LEO, GER and electrons involved
- oxidation numbers of the elements that are oxidized and reduced, including the sign, below/ above the element

Determine the oxidation number of each element in the following compounds, showing your work neatly
and clearly:
a) NiPO4 (aq) b) HSO4-(aq)

Silver is often found in nature mixed with other metals and their ores. Cyanide ion is often used to extract
the silver by the following reaction which occurs in basic solution:
Ag (s) + CN- (aq) + O2 (g) ---> Ag(CN)2- (aq)
Balance this equation, using the half-reaction method:
Items required:
- separate, balanced half reactions in basic solution
- equalizing the number of electrons
- overall balanced reaction


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2 K2(Cr2O7) + 28 HI > 4 KI +

2 K2(Cr2O7) + 28 HI > 4 KI + 4 CrI3 + 6 I2 + 14 H2O.

4 K+ > K+
4 I- > I-
4 Cr+6 > 4 Cr+3
6 I- > I-
12 I- > 6 I20
28 H+ > 28 H+
14 O= > 14 O=

12 electrons have moved from the 12 I- ions to the 4 Cr+6 ions to give 4 Cr+3 ions. You would do the others in the same way.

Dr. J USA H2S + HNO3 --->

Dr. J

H2S + HNO3 ---> S + NO2 + H2O what type of reaction is this? doesn't fit models of DR or SR

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