Do you have your own bathroom? Then you might be familiar with soap scum, which is the result of a combination of having hard water and soap (0:44). To determine how hard water is, we can use gravimetric analysis, which is an experimental procedure used to determine the amount of a substance, for example an ion, by precipitating it from an aqueous solution (1:25). Basing off of the solubility rules (1:45), the episode describes the steps to precipitate the calcium carbonate with sodium carbonate (3:05) and briefly discusses how to calculate the water hardness (5:08) and calcium ion concentration (5:38). Experimental errors described in the episode discuss how the yield can be higher or lower than expected (6:01).
Question: Why does the sodium carbonate have to be in excess?
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