Balance Redox Reaction/Equation
Chemistry
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tool (Redox Calculator)
7.1 What is the overall reaction (equation):
Cr2O7-2 + 14H+ + 6e- --> 2Cr+3
+
7H2O
H2S --> S + 2H+ + 2e-
Solution:
Insert following equations in the half cells:
Cr2O7-2 + 14H+ + 6e- > 2Cr+3 +
7H2O
H2S > S + 2H+ + 2e-
and calculate.
7.2 What is the overall reaction (equation):
Cr --> Cr+3 + 3e-
MnO4- + 8H+ + e- --> Mn+2 + 4H2O
Solution:
Insert following half cells reactions:
Cr > Cr+3 + 3e-
MnO4- + 8H+ + e- > Mn+2 + 4H2O
and calculate.
7.3 Balance: OH- + ClO- + S2O3-2 --> Cl- + SO4-2 + H2O
Solution:
Insert following equation i one of the half cell fields:
OH- + ClO- + S2O3-2 > Cl- + SO4-2 + H2O
and calculate.
7.4 Dropping a piece of sodium in water. What is the overall reaction.
Is
this a spontaneous reaction, explain?
2H2O + 2e- --> H + 2OH- E0 = -0.83 V
Na + e --> Na
E0 = -2.71 V
Solution:
Insert following half cells reactions and potentials:
2H2O + 2e- > H + 2OH-
Na+ + e- > Na
Remember to turn second half cell reaction.
Calculate.
Spontaneous reaction? -> Investigate sign of overall reaction
potential.
7.5 What is the value of the solubility product constant (Ksp) for
AgCl?
AgCl + e- --> Ag + Cl-
E0 = 0.22 V
Ag --> Ag+ + e-
E0 = -0.80 V
---------------------------------
AgCl --> Ag+2 + Cl-
Solution:
Step 1) Insert first and second half-reaction
AgCl + e- > Ag + Cl- E0 = 0.22 V
Ag > Ag+ + e-
E0
= -0.80 V
and calculate equation and overall cell voltage.
Step 2) Insert n=1 (-n=-1) and E0 cell=-0.58 in equation: G = -n
F
E0 and calculate.
Step 3) Transfer result of G to equation: -G = R T ln K (remember to
change
sign of G) and calculate K in which represent the solubility product
constant.
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