Question

17
A 100 grams sample of Limestone is dissolved
in acid and Calcium is precipitated as Calcium
Oxalate. The precipitate is filtered, washed with
water and dissolved in dilute H,so, The
solution required 50 ml of 0.25N KMnO4
solution for titration Calculate the percentage
of Cao in Limestone​

Answer 1

Given: Reaction: CaC2O4 + KMnO4 --------> Mn2+ + CO2

To find: The percentage of CaO in Limestone​.

Solution:

• Now, we have

              CaCO3 + 2H+ ------> Ca2+ + CO2 + H2O

              Ca2+ + C2O4^2- -------------->CaC2O4

• Now, we have CaC2O4 + KMnO4  in presence of H2SO4 gives the following reaction:

              C2^3+   ------------->  2C4+ + 2e     and

              Mn7+ +5e  ---------------------->  Mn2+

• This is a redox changes.

• From above reactions, we can conclude that:

                  M(equivalent) of CaO = M(equivalent) of CaC2O4 = M(equivalent) of KMnO4,   because valence factor is 2 for Calcium throughout the changes occured.

• Now:

               W(CaO) / (56/2)  x 1000 = 40 x 0.25

               After calculations, W(CaO) = 0.28

• So therefore:

          percent of CaO in limestone = 0.280.56 x100 = 50%

Answer:

             Percent of CaO in limestone is 50%.