A positive Molisch's test indicates the presence of a carbohydrate or any compound that dehydrates to furfural or hydroxymethylfurfural in the presence of H2SO4. A purple- or red-colored ring forming at the interface of the two liquids in the test tube indicates the positive result. Compounds other than carbohydrates cause false positives. However, a negative result is definitive in confirming the absence of carbohydrates.Know More
A Molisch's test requires mixing the test solution with Molisch's reagent. One prepares this reagent by dissolving alpha-naphthol in 95 percent ethyl alcohol. After mixing the test solution and reagent, the individual adds 2 milliliters of the test solution to a test tube and pours 2 milliliters of sulfuric acid down the side of the slanted test tube without mixing. The mineral acid is very heavy, so it forms a bottom layer.
The color change is due to a condensation reaction between the sulfuric acid and the two molecules of the phenol. While directions generally call for alpha-naphthol, other phenols, including thymol and resorcinol, also create the colored ring.
The test works for all carbohydrates, including monosaccharides, disaccharides and polysaccharides. In addition, the test is positive for nucleic acid and glycoprotein, which convert to monosacharides upon exposure to strong mineral acids.Learn More
According to Utah Valley University, a positive Tollens' test means that the substance being tested contains aldehydes, as opposed to ketones. Aldehydes are easily oxidized, while ketones are not, which causes the differing reactions.Full Answer >
Iodine is known as an indicator because it changes color in the presence of starch and several other molecules. Iodine can also be used to track iodide and iodine in its elemental form.Full Answer >
Biochemical tests are used to detect the presence or absence of gram-negative or gram-positive bacteria. These tests are commonly used in the fields of science and medicine, particularly biology. Biochemical tests are performed using a variety of methods and experimental techniques; the method of testing varies depending on whether researchers are testing for positive or negative bacteria.Full Answer >
The ninhydrin test is a test to detect proteins. According to Dr. Ian Hunt of the Department of Chemistry at the University of Calgary, it is based on the reaction between ninhydrin and amino acids containing a free amino group to give a colored compound.Full Answer >