Gravimetric Analysis of Calcium and Hard Water

Product Details

Students investigate six water samples, representing a wide range of potential water hardness, from 50 ppm to 500 ppm, to determine the accuracy and sensitivity of gravimetric analysis for water hardness testing.

The lab begins with an introductory activity to develop skill in the calculations and techniques of gravimetric analysis, in particular, quantitative transfer and vacuum of gravity filtration. The procedure provides a model for guided-inquiry design of the cooperative class investigation. Antacid tablets are also provided as an opportunity for further inquiry—the use of the gravimetric analysis to determine the amount of calcium in an over-the-counter medication.

Complete for 24 students working in pairs.

2024 CED Alignment:  

Unit 1 - Atomic Structure and Properties 

Topic 1.1 - Moles and Molar Mass  

Topic 4.5 - Stoichiometry 

Description of the Lab 

This classic separation experiment gives students a concrete way to apply stoichiometry and the mole concept. They precipitate calcium carbonate, isolate it by filtration, and calculate the calcium content of a water sample. The work reinforces mass relationships, procedural thinking, and precision in measurement. 

Learning Objective 

• LO 1.1.A – Calculate quantities of a substance or its relative number of particles using dimensional analysis and the mole concept. 

Skills Students Will Learn 

• 2.C – Identify experimental procedures that are aligned to a scientific question (which may include a sketch of a lab setup). 
  In this lab: Students follow a procedure to isolate and weigh precipitated calcium carbonate. 

• 2.E – Identify or describe potential sources of experimental error. 
  In this lab: Students evaluate mass loss during filtration or incomplete drying. 

• 6.D – Provide reasoning to justify a claim using chemical principles or laws or using mathematical justification. 
  In this lab: Students justify their calculated calcium levels with mole ratios and balanced equations.