Potassium chloride was historically known as Muriate of potash. This name is occasionally still encountered in association with its use as a fertilizer. It varies in colour from pink to red to white depending on the mining and recovery process used. White potash, sometimes referred to as soluble potash is used primarily for making liquid fertilizers. This fertilizer aids in the formulation of vegetative matter and root production. Potassium chloride occurs naturally as sylvite , carnalite and potash and it can be extracted from these ores and can be manufactured by crystallization from solution, floatation or electrostatic separation from suitable minerals. Potassium in Muriate of potash is to be estimated precisely and correctly for its value added properties. That is why this gravimetric process was tried for accurate estimation of potassium as methods with flame photometer /AAS/ICP-OES is sometimes erroneous because method requires extreme dilution of the solution. All these three methods are good for low concentration and not for higher concentration because of saturation of detectors.
In a small pyrex beaker sample is treated with 70% perchloric acid three times and evaporated to dense white fumes to barely to dryness on a hot plate at a temperature not exceeding 350OC. 15-20ml mixture of equal volume of anhydrous alcohol and anhydrous ethyl acetate is added and digested near the boiling point for 2 to 3 minutes. The solution is filtered in a previously weighed gooch crucible, residue washed with solvent mixture (mixture of equal volume of anhydrous alcohol and anhydrous ethyl acetate)6 to 8 times. Original beaker along with the precipitate is dried and precipitate is brushed into gooch crucible. The crucible along with the precipitate is dried at 110OC for 15 to 20 minutes and finally heated to 350OC for 15 minutes, cooled and weighed as KClO4.
One Potassium Chloride sample (original content of K is 52.44%) has been analyzed in four times. The results are given below:
- % of K = 52.32
- % of K = 52.18
- % of K = 52.10
- % of K = 52.40
Mean = 52.45%
S.D. = 0.135
This estimation of K is extremely useful for samples containing high concentration of K like MOP. As the method is gravimetric one the accuracy of the method is high.
Contributed by: Mr. Kajal Ray under guidance of Prof. Barun Gupta