Why is iodine used to test for starch?
Surprisingly, Wikipedia has a well-researched article on just this topic!! It's pretty short, so i'll just quote it: The Iodine test is used to test for the presence of starch. Iodine solution — iodine dissolved in an aqueous solution of potassium iodide — reacts with starch producing a purple black color. This reaction is the result of the formation of polyiodide chains from the reaction of starch and iodine. The amylose, or straight chain portion of starch, forms helices where iodine molecules assemble, forming a dark purple/black color. The amylopectin, or branched portion of starch, forms much shorter helices and iodine molecules are unable to assemble, leading the color to be of an orange/yellow hue. As starch is broken down or hydrolyzed into smaller carbohydrate units, the purple-black color is not produced. Therefore, this test can determine completion of hydrolysis when a color change does not occur. Iodine solution will also react with glycogen, although the color produced is browner and much less intense.
A test tube contains starch, hydrochloric acid, and water. The biurt test is negative. Explain?
Starch is a large chain of smaller sugars "monomers". HCl breaks the chain down into its pieces. The Benedict's test tells you if there are monomers of sugar. A positive test means sugar monomers are present. Biuret's test tells you if there are peptide bonds. These are the bonds that make proteins. A negative test tells you there are none. A negative means there is an absence of proteins.
Explain the function of the test tube with the starch suspension. What evidence does it provide?
the function of the the test tube with the starch suspension is to provide you with a comparison. the starch in the test tube accumulated at the bottom of the test tube however the solution did not change colour. this is because the test tube is impermeable. molecules cannot move through it. however the dialysis tube is semi-permeable which means that it allows only certain molecules through it. this is why the lugol's solution moved into the starch suspended dialysis tube but the starch did not move out. starch is a large molecule which can not move through cell walls, represented by the dialysis tubing. the glucose was present in the beaker because when the lugol's solution diffused into the starch suspended dialysis tube the concentration in te beaker lowered. this caused the glucose to diffuse out of its dialysis tube into the baker. glucose is a small molecule which is able to diffuse through cell walls. starch needs to be broken down into glucose molecules by the body in order to be used.
I hope this will help :What properties of starch (given its chemical structure) allow it to be used as an indicator? Davender Khera, Yale UniversityWhen starch is mixed with iodine in water, an intensely colored starch/iodine complex is formed. Many of the details of the reaction are still unknown. But it seems that the iodine (in the form of I5- ions) gets stuck in the coils of beta amylose molecules (beta amylose is a soluble starch). The starch forces the iodine atoms into a linear arrangement in the central groove of the amylose coil. There is some transfer of charge between the starch and the iodine. That changes the way electrons are confined, and so, changes spacing of the energy levels. The iodine/starch complex has energy level spacings that are just so for absorbing visible light- giving the complex its intense blue color.The complex is very useful for indicating redox titrations that involve iodine because the color change is very sharp. It can also be used as a general redox indicator: when there is excess oxidizing agent, the complex is blue; when there is excess reducing agent, the I5- breaks up into iodine and iodide and the color disappears.BTW...there is something known as GOOGLE. Next time you have such kind of doubts, please feel free to use it
Please explain Iodine test for fructose, maltose, honey. sucrose, starch, glycogen and inulin?
Honey is laid down by making use of bees as a food source. In chilly climate or whilst food components are scarce, bees use their stored honey as their source of potential[11]. by making use of contriving for the bee swarm to make its abode in a hive, human beings have been waiting to semi-cultivate the bugs. in the hive there are 3 varieties of bee: the single queen bee, a seasonally variable style of drone bees to fertilize new queens, and a few 20,000 to 40,000 worker bees[12]. the worker bees advance larvae and assemble the nectar that turns into honey in the hive. They bypass out, assemble the sugar-prosperous flower nectar and return to the hive. As they bypass away the flower, bees launch Nasonov pheromones. those enable different bees to discover their thank you to the positioning by making use of scent[13]. Honeybees additionally launch Nasonov pheromones on the front to the hive, which permits returning bees to return to the ideal hive[13]. in the hive the bees use their "honey stomachs" to ingest and regurgitate the nectar various circumstances till that's in part digested[14]. that's then stored in the honeycomb. Nectar is extreme in the two water content and organic yeasts which, unchecked, could reason the sugars in the nectar to ferment[11]. After the basically perfect regurgitation, the honeycomb is left unsealed. Bees interior the hive fan their wings, arising a reliable draft around the honeycomb which reinforces evaporation of most of the water from the nectar[11]. The alleviation in water content, which will advance the sugar concentration, prevents fermentation. Ripe honey, as removed from the hive by making use of the beekeeper, has a protracted shelf existence and could no longer ferment[11].
If you applied Benedict's test and the iodine test to a soda cracker, what should the results show?
There's certainly starch in a soda cracker, so you'd expect a positive iodine test. My box of soda crackers doesn't mention any added sugars in the list of ingredients, so I'd expect a negative Benedict's test. (However, if you chewed up a soda cracker, then spit it out, then did a Benedict's test on the result, I'd expect a positive test since the amylase in your saliva should have converted some of the starch into sugars.)
What do these results for the Benedict's Reagent Test mean? So Confused, Please Help!!!?
Background: For this Nutrient Lab we are doing in Biology we did a number of tests, one of which is known as as Monosaccharide Test where we tested substances such as Distilled Water, Glucose, Sucrose, Starch, and an unknown solution using Benedict's Reagent. In the table below given in the lab instructions it states the sugar concentration for each colour that appears: Blue --> 0% Light Green --> 0.5-1% Green to Yellow --> 1-1.5% Orange --> 1.5-2% Red to Brown --> >2% Here are the instructions for the test: 1.) Create a table to record your results for all parts of the activity. 2.) Prepare a water bath by heating 300mLof tap water in a 400mL beaker on a hot plate. Heat the water until it reaches approximately 80 degrees Celsius. 3.) Using a 10mL graduated cylinder, measure 3 mL each of distilled water, fructose, glucose, sucrose, starch and the unknown solution. Pour each solution into a separate approximately labeled test tube. Rinse the graduated cylinder after pouring each solution. Add 1mL of Benedict's Reagent to each of the test tubes. 4.) Using a test tube holder, place each of the test tubes in the hot water bath. *When you first notice a colour change in any one of the test tubes, record the colour in all test tubes. Results: The results I received were Distilled Water (Blue), Fructose (Orange), Glucose (Orange), Sucrose (Light Green), Starch (Blue), and the unknown solution (Yellow). My Problem: How do I interpret these results?! How can fructose have a sugar concentration of 1.5% - 2%. I just don't get it. Can someone please explain to me. Please help. Thank you.
Benedict's reagent is a reagent that uses the change of color (blue to red) to detect the presence of a group of carbohydrates that we collectively call Reducing Sugars.The reagent contains a copper in its +2 oxidation state in the form of copper citrate. The copper can oxidize certain sugars called aldoses, which have at least one available aldehyde group that can be oxidized to a carboxylic acid functional group. If the sugar is being oxidized (giving up electrons) then it must be reducing something else (a species that take the electrons). For this reason, sugars that can be oxidized are called reducing sugars. For example, D-glucose is an aldose that is usually in its cyclic form (all sugars are predominantly in their cyclic forms naturally) but can be in it's open chain form which is the form that reduces the cupric ion into cuprous oxide Cu2O (gives the red color).Image from: Lecture 24For sugars, as long as there is an aldose that is free, i.e., not tied up in a glycosidic linkage as it sometimes is in disaccharides, then we call the carbohydrate a reducing sugar.