What color does iodine test give in the absence of starch? 1. Orange or yellow 2. Brown color
The Correct Answer and Explanation is:
The correct answer is 2. Brown color.
The iodine test is commonly used to detect the presence of starch in a sample. Iodine, when in its iodine solution form (usually iodine dissolved in potassium iodide), forms a distinctive color change when it interacts with starch. When starch is present, iodine gives a blue-black color due to the formation of a complex between iodine molecules and the coiled structure of starch.
However, in the absence of starch, iodine does not form this blue-black complex. Instead, the iodine solution retains its natural color, which is typically a brownish color. The intensity of the brown color can vary depending on the concentration of the iodine solution. This brownish hue is a result of iodine being in a free state, not interacting with any starch molecules to form a complex.
This brown coloration occurs because iodine molecules themselves are brown in solution. Iodine can also appear slightly yellowish in dilute solutions, but in general, the color seen in the absence of starch is more of a brown hue rather than orange or yellow.
The test is highly specific for starch, and the color change or lack of it serves as a simple yet effective way to confirm the presence or absence of starch in a sample. Therefore, when iodine is added to a sample and no starch is present, the solution remains a brown color, indicating the absence of starch.
In summary, iodine will give a brown color in the absence of starch, with no significant color change occurring unless starch is present to form the characteristic blue-black complex.
