1. How could you use a flame test to distinguish between hard and soft water?
2. After a period of time, your ion-exchange water softener no longer removes hard-water ions. How can you "refresh" your water softener, using a material obtained from the grocery store?
3. The deionized water in the Chemistry Department is produced by ion exchange that uses H+ ions, rather than Na+ ions, to replace the cations found in the water. Briefly, explain why the pH of deionized water is typically found to be around 6.
4. Explain why solutions of Ca2+ and Mg2+ in the presence of carbonate leave deposits (see Equation 1), but Na+ does not.
5. Write the net ionic equation for the removal of calcium ions by precipitation with carbonate in the lime-soda process. (See the introduction to Experiment 2 for a discussion of net ionic equations.)
6. Could sodium ions be removed in the same way as magnesium ions in the lime-soda process (i.e., by addition of hydroxide) for individuals concerned about their sodium intake? Briefly, explain your reasoning.
Evaluation parameters to assess the understanding of the students