Molarity/redox reactions

  • Thread starter pmart491
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  • #1
pmart491
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Homework Statement


What is the molarity of a NaCl solution if 18.3mL of the solution reacted with 13.6mL of 0.1M KMnO4 based on the following unbalanced redox reaction in an acidic solution?

Cl- + MnO4- yields-> Cl2 + Mn2+


The Attempt at a Solution



I did the two half reactions
Cl- -> Cl2
MnO4- -> Mn2+

Do I find the full half reactions (ie: the electrons gained/lost H2O, H+) and then do a molarity problem?
 

Answers and Replies

  • #2
Borek
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Yes - this is in fact simple stoichiometric question, just based on the redox reaction. Find full balanced reaction equation first.
 
  • #3
pmart491
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Ok I got 10Cl- + 16H+ + 2MnO4- -> 5Cl2 + 2Mn2+ + 8H2O

Next I did 13.6mL KMnO4 x .1M = .00136moles KMnO4

what i don't understand is how to find moles of NaCl through the half reaction
 
  • #4
pmart491
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well i think i got it

based on the half reaction, there are 5 times as many Cl- ions as there are MnO4- ions.
therefore there are 5 times as many moles of NaCl than there are moles of KMnO4.
5 x .00136=.0068moles NaCl

.0068moles NaCl/.0186L NaCl=.372M NaCl
 
  • #5
Borek
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OK
 
  • #6
Asian Girl
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Ok I got 10Cl- + 16H+ + 2MnO4- -> 5Cl2 + 2Mn2+ + 8H2O

Next I did 13.6mL KMnO4 x .1M = .00136moles KMnO4

what i don't understand is how to find moles of NaCl through the half reaction

well i think i got it

based on the half reaction, there are 5 times as many Cl- ions as there are MnO4- ions.
therefore there are 5 times as many moles of NaCl than there are moles of KMnO4.
5 x .00136=.0068moles NaCl

.0068moles NaCl/.0186L NaCl=.372M NaCl

I don't understand this. If we have V of NaCl is 18.3 mL, can we find M by using M=mole/V. So the ratio of NaCl and KMnO4 isn't 1:1 ?
 
  • #7
Borek
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Ratio is given by reaction equation. Take a look at stoichiometric coeffcients.
 
  • #8
Asian Girl
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Ok I got 10Cl- + 16H+ + 2MnO4- -> 5Cl2 + 2Mn2+ + 8H2O

Next I did 13.6mL KMnO4 x .1M = .00136moles KMnO4

what i don't understand is how to find moles of NaCl through the half reaction

Ratio is given by reaction equation. Take a look at stoichiometric coeffcients.

Why do we have to do 10Cl + 16H ...?

Sorry, I just don't understand your step.
 
  • #9
Borek
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Because these coefficients where necessary to balance the equation. Do you know what it means to balance the equation and why the reaction equations needs to be balanced?
 

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