Question

Argentometric Determination of Chloride Using Mohr's Method Experiment

25ml of a solution of AgCl (with an unknown concentration) was placed into a 250ml flask. 25ml of distilled water was then added to the flask followed by a few drops of potassium chromate indicator. This solution was then titrated with 0.1012M AgNO3.

It was found that 13ml of AgNO3 was needed to be titrated to the solution to reach the reddish/brown endpoint.

V of AgNO3 = 13.00ml, [AgNO3] = 0.1012M, V of AgCl = 25.00ml, molar mass Cl = 35.45g/mol

Reaction Equations:

Ag+ + Cl- = AgCl

2Ag+ CrO4^2- = Ag2CrO4

Calculate the concentration of chloride in both mg/L and %(w/v).

And if you can also do this: explain how the potassium indicator functions in this experiment (include an equation)

Answer 1

Moles of AgNO₃ added till end point

= 0.1012 M * 13.00 ml

= 1.3156 millimole

Moles of AgCl present in 25 ml of sample = 1.3156 millimole

Molarity of AgCl = 1.3156 millimole/25 ml = 0.0526 M

Molarity of Cl^- = 0.0526 M

Concentration of Cl- in g/L = 0.0526 mol/L * 35.45 g/mol

= 1.864 g/L

= 1864 mg/L (Answer)

For %(w/v) , i.e. g of Cl^-/100 ml

1.864 g of Cl^- is present in 1000 ml

0.1864 g will be present in 100 ml

So, w/v % = 0.186% (Answer)