Question

the difference between the Mole method and Vol d a heimation of the chloride ions in a sample ) Mon method s potassium chromate while the Volhare method Uyes potarum thiocyanate as 15 Andicator. Name the indicator for the MOHR method. [1] Potassium chromate is the indicator for the Mohr Method, VEVO Cur Name the chemical used as a primary standard in the estimation of Chloride (0) Name the secondary standard. [1] # What is the function of adding nitrobenzene to your solution 12 solution Adding nitrobenzene 10 the solution In the Volhard method what is the indicator used and give the color change atend.point (2) Potassium thiocyanate is used as an indicator பட்டி 04b. 0.12 g of sample containing chloride ions requires 20 mls of O.IM KSCN when 25 mis prepared AgNO, was added to the sample solution 25mls of prepared AgNO, requires 31.25mls of O. IM KSCN. Calculate the percent of chloride in your sample. [8] % chloride in somple In the estimation of the chloride why is excess silver nitrate added to the sample?[2] Excess of silver nitrate is added to the sample to

Answer 1

Mohr method involves the titration of chloride ion solution with silver nitrate solution in the presence of potassium chromate as indicator, which gives a red silver chromate as end point.

AgNO₃ + Cl^-$\rightarrow$ AgCl

First silver cations reacts with chloride ions present in the solution to form precipitate of silver chloride. When all chloride ions are precipitated, the excess silver ions forms silver chromate complex which is red in colour and it signifies the endpoint.

In volhard's method chloride ion solution is titrated against silver nitrate in the presenxe of free nitric acid with potassium thiocyanide or ammonium thiocyanide solution, iron(III)nitrate or iron (III)sulphate is used as indicator which gives red colour as a end point.

Here in this titration excess of silver nitrate is added to chloride solution and then after silver chloride precipitated the excess remaining amount which is left is determined by back titrating with potassium thiocyanide.

Ag⁺ + SCN^-$\rightarrow$AgSCN

Fe³⁺ + SCN​^-$\rightarrow$( FeSCN )²⁺

^{As silver thiocyanide is a less soluble salt hence thiocyanide ions may react with silver chloride and determination of chloride ions becomes difficult.}

AgCl + SCN​​​​​​^-$\rightarrow$ AgSCN + Cl^-

^{So to reduce the reaction of thiocyanide with silver chloride we will add nitro benzene, so that it coats the AgCl precipitate and remaining excess silver nitrated can be easily determined.}

To standardize silver nitrate which is a secondary standard we will use sodium chloride as primary standard.