When performing a scientific investigation on an unknown substance, how can an indicator help you determine if the substance is a starch?
An indicator can help determine if a substance is a starch by changing color or producing a visible reaction when it comes into contact with starch molecules.
Iodine is a common indicator used to test for the presence of starch. In the presence of starch, iodine undergoes a chemical reaction that forms a blue-black complex. If a substance turns blue-black when iodine is added, it suggests that the substance contains starch. However, it is important to note that some other substances, such as cellulose, can also produce a blue-black color with iodine. Therefore, it is necessary to corroborate the results with further tests to confirm if the substance indeed contains starch.
Step 1: Obtain the unknown substance – Start by obtaining a sample of the unknown substance that you want to investigate.
Step 2: Prepare the indicator – To determine if the substance is a starch, you will need an indicator. In this case, an iodine solution is commonly used as an indicator for starch. Prepare a small amount of iodine solution.
Step 3: Perform the test – Once you have the sample and the iodine solution, follow these steps:
a. Place a small portion of the unknown substance on a white surface, such as a petri dish or a piece of white paper.
b. Add a few drops of the iodine solution onto the sample.
c. Observe the reaction – If the substance is a starch, it will produce a deep blue or black color upon contact with the iodine solution.
Step 4: Interpret the results – After applying the iodine solution to the unknown substance, observe the color change. If the substance turns deep blue or black, it indicates the presence of starch. However, if there is no color change, it suggests that the substance does not contain starch.
Remember that other indicators and tests can also be used in combination to determine the presence of starch more accurately.