Microscale Quantitative Analysis of Hard Water Samples Using an Indirect Potassium Permanganate Redox Titration

A microscale procedure for the volumetric determination of calcium in an unknown hard water sample is reported. The experiment is accomplished via quantitative filtration and collection of calcium oxalate, which has been precipitated from the unknown sample, followed by microscale titration of the free oxalate using standardized potassium permanganate. While designed for a quantitative analysis laboratory, this experiment should also be suitable for an introductory college chemistry laboratory. Also reported are test data for the procedure, as well as data acquired by quantitative analysis students. Comparison with previous macroscale data indicates that the microscale procedure can be performed with comparable accuracy and precision, though student data indicate that the microscale procedure suffers from determinate error, most likely from loss of calcium oxalate during the filtering stage. This error leads to potential under-representation of calcium in the unknown.