What chemical compound is used to standardize chlorine tests?

The correct choice is KMnO4, which stands for potassium permanganate. This chemical compound is widely used in analytical chemistry, particularly in redox titrations, for standardizing chlorine tests in water analysis. When testing for chlorine levels in water, potassium permanganate acts as an oxidizing agent.

During the titration process, potassium permanganate reacts with chlorine, leading to a color change that indicates the endpoint of the titration. The deep purple color of KMnO4 provides a visual cue that helps analysts determine the concentration of chlorine present in the water sample being tested. This method is preferred because it is precise and provides reliable results, which are crucial for ensuring safe drinking water standards.

In contrast, the other compounds mentioned do not serve this function. Sodium chloride (NaCl) is simply table salt and does not have redox properties relevant for standardization. Potassium chloride (KCl) also does not serve as an oxidizing agent and simply provides potassium ions in solution. Calcium carbonate (CaCO3) is another compound not related to redox titrations and is primarily used for buffering or hardness testing rather than standardizing chlorine measurements. Thus, KMnO4 is the only compound in the list