A bit of a Review of chp . 13.2. Reminder that the Quest for chp . 13 is March 13. QUICK REVIEW Summary: Five Step method for Predicting Redox Reactions.
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Reminder that the
Quest for chp. 13 is March 13
Could copper pipe be used to transport a hydrochloric acid solution?
Since the reaction is nonspontaneous, it should be possible to use a copper pipe to carry hydrochloric acid
Redox Reactions using Half-Reactions When ½ reaction is not in data booklet (13.2c) Example #3 p.581
Rules for Writing Half-Reactions
For basic solutions only:
Chapter 13.3a Oxidation States
Each oxygen atom has 8 p+ and 8 e-. But if the oxygen atom gets to count the two hydrogen electrons (red dots) in the two shared pairs, as its own, then it has 8 p+ but 10 e-, leaving an apparent net charge of -2
Each hydrogen atom has 1 p+, but with no additional electron (since oxygen has already counted it), that leaves hydrogen with an apparent net charge of +1
x + 4(+1) = 0
x + (-4) = 0
x = -4
Mn + 4 O = -1
x + 4(-2) = -1
x + -8 = -1
x = -1 + -8
x = -7
2(+1) + x + 4(-2) = 0
2 + x + -8 = 0
So the oxidation number of sulfur is +6
0 in O2(g) to -2 in CO2(g)
Remember this example from 13.2 p. 580: Predicting Redox Reactions by Constructing Half Reactions
Note: a similar example is on p.581 (in basic solution)
-2 +1 -2 +1 +6 -2 +1 0 +1 0 -2 -2 +1 +3 +1 -2
NiO(s) + H2(g) Ni(s) + H2O(l)
Ni +2 Nio
4 Fe(s) + O2(g) Fe2O3(s)
Fe 0 Fe+3
Balancing Redox Equations Using Oxidation Numbers
Example: When hydrogen sulfide is burned in the presence of oxygen, it is converted to sulfur dioxide and water vapour. Use oxidation numbers to balance this equation. H2S(g) + O2(g) SO2(g) + H2O(g)
Example: Chlorate ions and iodine react in an acidic solution to produce chloride ions and iodate ions. Balance the equation for this reactions. ClO3-(aq) + I2(aq) Cl-(aq) + IO3-(aq)
Remember to record the change in the number of electrons per atom and per molecule or polyatomic ion.
Example: Methanol reacts with permanganate ions in a basic solution. The main reactants and products are shown below. Balance the equation for this reaction.
8 OH-(aq) +
+ 8 OH-(aq)
Balancing RedoxDisproportionation Equations using Oxidation Numbers #4 (p.592)
Example: Household bleach contains sodium hypochlorite. Some of the hypochlorite ions disproportionate (react with themselves) to produce chloride ions and chlorate ions. Write the balanced redox equation for the disproportionation.
For disproportionation reactions, start with two identical entities on the reactant side and follow the usual procedure for balancing equations.
2e- of Cl *2 = 4 4e- of Cl*1=4
Redox Stoichiometry p. 596-600
2H+(aq) + 2e- H2(g)
Cu(s) Cu2+(aq) + 2e-
2H+(aq) + Cu(s) H2(g) + Cu2+(aq)
V= 500mL m= ???g
0.500 L x0.25 molH+(aq)x1 mol Cu(s)x63.55g = 3.97 gCu(s)
L 2 mol H+(aq) mol Cu(s)
3 [Ni(s) Ni2+(aq) + 2e-]
Cr2O72-(aq) + 14 H+(aq)+ 6 e- 2Cr3+(aq) + 7H2O(l)
3Ni(s)+ Cr2O72-(aq) + 14 H+(aq) 3Ni2+(aq + 2Cr3+(aq) + 7H2O(l)
2.50 gx mol Ni(s)x1 mol Cr2O72-(aq)x __1__= 0.284 mol/L Cr2O72-(aq) 58.69 g 3 mol Ni(s) 0.0500L
Titration of 10.00mL of acidic Sn2+(aq) with 0.0832 mol/L KMnO4(aq)
According to the evidence and the stoichiometric analysis, the amount concentration of tin(II) ions in the solution is 0.258mol/L
Near the endpoint, continuous gentle swirling of the solution is important