If H2SO4 and HNO3 both are oxidising agent then why only H2SO4 is only preferrable in titrations?
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Why are nitric acid and hydrochloric acid not suitable for titration of sodium ethanadioate and potassium manganate (VII) solution?
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Kumaraswami Sathiavasan, MSc in Chemistry & IAS officer(retd.)
Updated Jul 1, 2016
The titration between sodium ethanedioate (sodium oxalate) and KMnO4 in the presence of a mineral acid is a redox reaction.
Nitric acid itself is a powerful oxidising agent, and so it will also react with and consume part of the oxalate ions. Therefore, in the presence of nitric acid, lesser amount of KMnO4 will be needed to reach the end point. On the other hand, hydrochloric acid (HCl) is a mild reducing agent, and so it will also consume a certain amount of KMnO4 during the titration. This will give a slightly higher value of KMnO4 consumption than the actual amount needed by the oxalate taken initially. Hence, both these two acids are avoided in redox reactions between other substances.
Dilute sulphuric acid is neither an oxidising agent, nor is it a reducing agent. So, it is preferred in redox reactions involving KMnO4.
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Tay Jason, studied Chemistry
Answered Oct 9, 2017
Generally when creating an acidic medium for titration with KMnO4, the acid of choice is H2SO4 as the S is in a +6 oxidation state and cannot be further oxidised.
HCl is not used since the Cl- can be oxidised to give Cl2. Some KMnO4 will be reacted away as such and this would give you a higher than actual end point value.
Similarly, HNO3 is not used as HNO3 itself is also an oxidising agent. Ideally,in the titration reaction, you would want KMnO4 to be the only reactant that does the oxidation so that you can do the calculations with the titration values and obtain the accurate amount of ethanedioate present. If HNO3 is present, there is a possibility that it will oxidise the reactant before titration begins, leading to a lower that actual end point value.
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Chinedu Alamezie, I taught Chemistry for senior secondary schools in Nigeria.
Answered Sep 22, 2017
This is because Nitric acid is oxidizing in nature just as potassium manganate (VII), end result will be erroneous. Hydrochloric acid on the other hand Hydrochloric acid will react (reduction) with potassium tetraoxomanganate (VII) and reduce it from Mn7+ to Mn2+, leading to another erroneous result. Dilute Tetraoxosulphate (VI) acid is an ideal acid for that redox titration as it does not alter the analyte or titrant.
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Kumaraswami Sathiavasan, MSc in Chemistry & IAS officer(retd.)
Updated Jul 1, 2016
The titration between sodium ethanedioate (sodium oxalate) and KMnO4 in the presence of a mineral acid is a redox reaction.
Nitric acid itself is a powerful oxidising agent, and so it will also react with and consume part of the oxalate ions. Therefore, in the presence of nitric acid, lesser amount of KMnO4 will be needed to reach the end point. On the other hand, hydrochloric acid (HCl) is a mild reducing agent, and so it will also consume a certain amount of KMnO4 during the titration. This will give a slightly higher value of KMnO4 consumption than the actual amount needed by the oxalate taken initially. Hence, both these two acids are avoided in redox reactions between other substances.
Dilute sulphuric acid is neither an oxidising agent, nor is it a reducing agent. So, it is preferred in redox reactions involving KMnO4.
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Tay Jason, studied Chemistry
Answered Oct 9, 2017
Generally when creating an acidic medium for titration with KMnO4, the acid of choice is H2SO4 as the S is in a +6 oxidation state and cannot be further oxidised.
HCl is not used since the Cl- can be oxidised to give Cl2. Some KMnO4 will be reacted away as such and this would give you a higher than actual end point value.
Similarly, HNO3 is not used as HNO3 itself is also an oxidising agent. Ideally,in the titration reaction, you would want KMnO4 to be the only reactant that does the oxidation so that you can do the calculations with the titration values and obtain the accurate amount of ethanedioate present. If HNO3 is present, there is a possibility that it will oxidise the reactant before titration begins, leading to a lower that actual end point value.
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Chinedu Alamezie, I taught Chemistry for senior secondary schools in Nigeria.
Answered Sep 22, 2017
This is because Nitric acid is oxidizing in nature just as potassium manganate (VII), end result will be erroneous. Hydrochloric acid on the other hand Hydrochloric acid will react (reduction) with potassium tetraoxomanganate (VII) and reduce it from Mn7+ to Mn2+, leading to another erroneous result. Dilute Tetraoxosulphate (VI) acid is an ideal acid for that redox titration as it does not alter the analyte or titrant.
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