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AS silver ions first react with Cloride ions in the sample(equivalence point) and when all the chloride ions are consumed we have to add more silver nitrate solution to increase its concentration to a level where it can precipitate chromate ions as silver chromate precipites (reddish brown ppts) this is the end point . so remove this error of equivalence point detection we take the same volume of indicator (chromate solution) in a flask labelled blank and add water into this flask (the same volume as that of sample solution) and then titrate this blank labelled flask with standard silver nitrate solution and note the volume of titrant consumed (blank volume),then calculations for real equivalence point can be made as:
equivalence point=(end point)-(blank volume)
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Why HCl is used in titration of mohr salt and potassium dichromate?
so that ferrous doesnot get converted into ferric
Why mohr method is better than volhard method?
because mohar method gives the accurate result
What is a mohr method?
Mohr method is a Precipitation titrations method which is the concentration of an unknown substance in solution is determined by adding measured amount of a standard solution such as AgNO3 that react with unknown samples to determine CL, Br in Solid and solutions samples . NaCL + AgNO3 =====> AgCL + NaNO3. Br- + Ag NO3=====> AgBr + NO3- Then the concentration of the unkown can be calculated using the stoichiometry of the recation and the number of moles of standard solution needed to reach the End point. The mohr method uses chromate CrO4 2- ion as an indicator . By Known the stoichiometry and moles consumed at end point,we can determine the mount of chloride in an unknown samples. Saeed Yousef AL-Soumali
What is mohr's salt test?
Chlorides will be dosed by titration with Silver nitrate (AgNO3) in the presence of potassium chromate (K2CrO4) as indicator. Salinity was expressed in mg NaCl/L of treated oil.
Why do we add dilute sulphuric acid to dissolve mohr's salt?
For preparation of standard solution of Mohr salt {FeSO4.(NH4)2SO4.6H2O}, it's necessary to add dilute H2SO4 to prevent the Fe2+ ions of Mohr salt solution from undergoing oxidation (to Fe3+). Just try to prepare the standard solution without adding this acid. You'll observe that your "Mohr solution" will become yellow in colour, i.e., it won't remain "Mohr salt solution" anymore, hence can't be used in titration. And while doing the titration of the Mohr salt solution with KMnO4 (or even with K2Cr2O7), you need to add dilute H2SO4. The reason is well explained by the chemical equation involved: reduction: (MnO4)- + 8H+ + 5e ----> Mn2+ + 4H2O oxidation: Fe2+ ----> Fe3+ + e net equation: (MnO4)- + 8H+ + 5Fe2+ ----> Mn2+ + 4H2O + 5Fe3+ There is involvement of H+ ions in this reaction. This redox titration requires acidic medium. Moreover, KMnO4 acts as a very good oxidizing agent in the presence of acidic medium, than in the basic and neutral medium. NOTE: Now a query may arise that for providing acidic medium, can HCl or HNO3 be used? (Let me tell you it's one of the favourite questions of external examiners) The answer is NO, because HNO3 is a very strong oxidizing agent. So, the Fe2+ present will be oxidized both by KMnO4 and HNO3, which will result in an error in determination of volume of KMnO4 reacting with Mohr salt solution. Also, HCl can't be used because Cl- from HCl will be oxidized by KMnO4: HCl (aq) ---> H+ (aq) +Cl- (aq) oxidation by KMnO4=> 2Cl- ----> Cl2 + 2e So, some extra KMnO4 will be used up because it will oxidize both- Cl- as well as Fe2+, => error in titration.
What is the equivalent weight of mohr's salt in the titration of pottasium permanganate and mohr's salt?
E Mohr salt 392/1
Why we add conc sulphuric acid in mohr salt in the titration of mohr salt against potassium dichromate?
For preparation of standard solution of Mohr salt {FeSO4.(NH4)2SO4.6H2O}, it's necessary to add dilute H2SO4 to prevent the Fe2+ ions of Mohr salt solution from undergoing oxidation (to Fe3+).
What are the limits for determination of chloride by the Mohr method?
1- done only in neutral medium. 2- all the cations which give insolublld be chromate must be absent or removed before titration. 3-titration of Ag+ with Cl- is not feasible. 4- not suitable for I- and SCN-
Why HCl is used in titration of mohr salt and potassium dichromate?
so that ferrous doesnot get converted into ferric
Why mohr method is better than volhard method?
because mohar method gives the accurate result
How can you test the percent purity of potassium chlorate?
by mohr's method
What is a mohr method?
Mohr method is a Precipitation titrations method which is the concentration of an unknown substance in solution is determined by adding measured amount of a standard solution such as AgNO3 that react with unknown samples to determine CL, Br in Solid and solutions samples . NaCL + AgNO3 =====> AgCL + NaNO3. Br- + Ag NO3=====> AgBr + NO3- Then the concentration of the unkown can be calculated using the stoichiometry of the recation and the number of moles of standard solution needed to reach the End point. The mohr method uses chromate CrO4 2- ion as an indicator . By Known the stoichiometry and moles consumed at end point,we can determine the mount of chloride in an unknown samples. Saeed Yousef AL-Soumali
Why the brown colour appear and disappear at mohr method?
because the japs attacked pearl harbor and the dropping of the atomic bomb caused radiation poisoning, therefore causing the brown color, not colour to appear and disappear at mohr method, whatever that is.
What is mohr's salt test?
Chlorides will be dosed by titration with Silver nitrate (AgNO3) in the presence of potassium chromate (K2CrO4) as indicator. Salinity was expressed in mg NaCl/L of treated oil.
How do you determine percentage purity of a salt by Mohr method?
Stop being a buttpirate and ask a real question... buttpirate!
What is principle of potassium dichromate in COD estimation?
The titer volume of the sample gives the volume of Ferrous Ammonium Sulphate required to react with the excess potassium dichromate in the solution. Similarly, the titer volume for the blank (distilled water) gives the volume of Ferrous Ammonium Sulphate required to react with the excess potassium dichromate in the blank. The equation for the titration can be expressed as: Cr2O72 -- + FeSO4 (NH4)2SO4 = Cr+ + NH4+ + Fe 3+ From above equation it can be seen that one molecule of dichromate corresponds to one molecule of Mohr's salt. Thus, the difference in volume of excess K2Cr2O7 reacting with Mohr's solution can be calculated from the expression: = (Original vol. K2Cr2O7 -- vol. of K2Cr2O7 used for oxidation) solution - (Original vol. K2Cr2O7 -- vol. of K2Cr2O7 used for oxidation) blank = (Vol. of K2Cr2O7 used for oxidation) blank - Vol. of K2Cr2O7 used for oxidation) solution Hence, the difference in the titer volume for the solution and the blank is used to find out the Chemical Oxygen Demand directly.
Why do we add dilute sulphuric acid to dissolve mohr's salt?
For preparation of standard solution of Mohr salt {FeSO4.(NH4)2SO4.6H2O}, it's necessary to add dilute H2SO4 to prevent the Fe2+ ions of Mohr salt solution from undergoing oxidation (to Fe3+). Just try to prepare the standard solution without adding this acid. You'll observe that your "Mohr solution" will become yellow in colour, i.e., it won't remain "Mohr salt solution" anymore, hence can't be used in titration. And while doing the titration of the Mohr salt solution with KMnO4 (or even with K2Cr2O7), you need to add dilute H2SO4. The reason is well explained by the chemical equation involved: reduction: (MnO4)- + 8H+ + 5e ----> Mn2+ + 4H2O oxidation: Fe2+ ----> Fe3+ + e net equation: (MnO4)- + 8H+ + 5Fe2+ ----> Mn2+ + 4H2O + 5Fe3+ There is involvement of H+ ions in this reaction. This redox titration requires acidic medium. Moreover, KMnO4 acts as a very good oxidizing agent in the presence of acidic medium, than in the basic and neutral medium. NOTE: Now a query may arise that for providing acidic medium, can HCl or HNO3 be used? (Let me tell you it's one of the favourite questions of external examiners) The answer is NO, because HNO3 is a very strong oxidizing agent. So, the Fe2+ present will be oxidized both by KMnO4 and HNO3, which will result in an error in determination of volume of KMnO4 reacting with Mohr salt solution. Also, HCl can't be used because Cl- from HCl will be oxidized by KMnO4: HCl (aq) ---> H+ (aq) +Cl- (aq) oxidation by KMnO4=> 2Cl- ----> Cl2 + 2e So, some extra KMnO4 will be used up because it will oxidize both- Cl- as well as Fe2+, => error in titration.
