Final answer:
KI-starch paper is used to detect the presence of iodine in a solution, typically signifying the end point in iodine-related redox titrations by forming a blue-purple color.
Step-by-step explanation:
The purpose of using KI-starch paper is to test for the presence of iodine. When iodine (I2) is present, it reacts with potassium iodide (KI) in the paper to form a starch-iodine complex which turns a deep blue-purple color. This reaction is utilized in various analytical techniques, for example, in determining the endpoint of a titration involving iodine. Specifically, it is used in redox titrations where the appearance of the blue-purple color indicates the presence of excess iodine, signifying the end point of the titration. KI-starch paper is not used for detecting the presence of reducing agents, indicating the pH of a solution, identifying metal ions in a solution, or testing for the presence of alkenes.