Why is Starch used in an indicator in the titration of iodine with Sodium Sulphate?
959522
Starch forms a blue-black complex with iodine or triiodide.  As the Sodium sulfate reacts with the iodine, the color becomes clear.\n\nThis is called a visual indicator.
938211
Benedict's Test only tests positive for simple reducing sugars.  Starch is a polysaccharide.
602416
http://www.scienceaid.co.uk/titration.html
664759
It's Ionic if thats what you were looking for because sodium is an alkali metal (group 1) and Iodine is a halogen (group 17). Iodine forms an I- ion (this is an anion) and Na forms an Na+ ion (a cation) so they combine on a 1:1 ratio and the formula is NaI
317245
When I was growing up we used DCPIP (Di-Chloro-Phenol-Indo-Phenol) to test for Vit C.\n\nWhere did you get the OJ from? Some have added vitamins...\nHow freshly prepared was the Iodine tincture?\nDid you do your own dilutions of titrant?\nCould the Iodine have reacted with a carbohydrate present in the OJ (like it does with starch)?
981010
this works well, cation has a letter t in it, and t looks like +, so it is positive!  i never forgot this since like 10 years ago\nn_n
37924
It also depends on if you're using a chemical indicator, or a pH probe.  When I have to dump HCl down the drain but first neutralize it with NaOH, I just use a pH probe (or occasionally litmus paper), because indicators are not readily available.
179787
Starch is a polymer of carbohydrates, so it doesnt have a set molecular formula- The individual units are CH, CH2, or CH3, depending on the number of carbon bonds on each carbon.
471546
A.  Iodine is being reduced from +5 in HIO3 to 0 in I2; oxygen is being oxidized from -1 in H2O2 to 0 in O2.\n\nB.  There is no oxidation/reduction going on; this is simple metathesis, producing the barium sulfate precipitate.
164428
< < i·o·dine (ī'ə-dīn', -dĭn, -dēn') \nn.\n(Symbol I)2 A lustrous, grayish-black, corrosive, poisonous halogen element having radioactive isotopes, especially I 131, used as a medical tracer and in thyroid disease diagnosis and therapy. Iodine compounds are used as germicides, antiseptics, and dyes. Atomic number 53; atomic weight 126.9045; melting point 113.5°C; boiling point 184.35°C; specific gravity (solid, at 20°C) 4.93; valence 1, 3, 5, 7. \nA liquid containing iodine dissolved in ethyl alcohol, used as an antiseptic for wounds.\n[French iode, iodine (from Greek ioeidēs, violet-colored : ion, violet + -oeidēs, -oid) + –INE2.]\n\n\niodine (ī'ədīn, –dĭn) [Gr.,=violet], nonmetallic chemical element; symbol I; at. no. 53; at. wt. 126.9045; m.p. 113.5°C; b.p. 184.35°C; sp. gr. 4.93 at 20°C; valence −1, +1, +3, +5, or +7. Iodine is a dark-gray to purple-black, lustrous, solid element with a rhombic crystalline structure. It is the least active of the halogens, which are found in group VIIa of the periodic table. It is normally diatomic, i.e., it has 2 iodine atoms in each molecule, in the solid, liquid, and vapor states. When heated it passes directly from the solid to the vapor state (sublimation), the vapor having an intense violet color and a characteristic irritating odor. Iodine is only slightly soluble in water but dissolves readily in a solution of sodium or potassium iodide. Tincture of iodine is a solution of iodine and potassium iodide in alcohol. Iodine also dissolves in carbon disulfide, carbon tetrachloride, and chloroform, giving a deep violet solution. Iodine forms many compounds. With hydrogen it forms hydrogen iodide, which in water solution becomes hydriodic acid. It forms compounds with certain nonmetals (e.g., carbon, nitrogen, phosphorus, and oxygen) and with most metals. Iodine is displaced from its compounds by the other halogens. The element is obtained from salt deposits, as from the saltpeter beds in Chile, where it occurs in small quantities as an iodate, and from the salt brines associated with some oil wells in California and Louisiana. It is also found as an iodide in the ash of certain seaweeds. Iodine may be prepared by displacement from its compounds with chlorine. Treating an iodide with manganese dioxide and sulfuric acid sublimes the iodine. Iodine is important in medical treatment; tincture of iodine and iodoform are widely used. Iodine is employed in the preparation of certain drugs and in the manufacture of some dyes. Silver iodide, a yellow salt, is used in photography; it is water insoluble and turns black when exposed to light. Starch turns deep blue (almost black) in the presence of a small amount of iodine; this reaction serves as a test for either starch or iodine. Iodine in small amounts is essential to human nutrition; in the thyroid gland it becomes a part of the iodine-containing hormones. Goiter, a swelling of the thyroid, is often a symptom of inadequate iodine in the diet. Iodine has only one stable isotope, iodine–127; it is the only isotope of iodine occurring in nature, although 24 iodine isotopes are known. Iodine–131 is a radioactive isotope with a half-life of 8 days. It is used medically to diagnose abnormalities of the thyroid gland. It is also a component of fallout produced by nuclear explosions. Iodine was discovered in 1811 by Bernard Courtois.
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a) 0.03/200 = 3/2000\n\nno because grams are good enough and the zero's move about to make it work anyway.\n\nb) 3/2000 * 0.03 =4.5e-5g\n\nc) 3/2000 * 4.5e-5 = 6.75e-8\n\nd) method c since the carbon sulphide is no where near saturation you can split it up into smaller portions and extract far more iodine.
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When an analyte that is a reducing agent is titrated directly with a standard iodine solution, the method is called "iodimetry".\n\nWhen an analyte that is an oxidizing agent is added to excess iodide to produce iodine, and the iodine produced is determined by titration with sodium thiosulfate, the method is called "iodometry".
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You can see if it include starch, by putting iodine on it and seeing if it turns black. I found an article where they make vinegar by fermenting it, thi sis a cottage industry in the Phillipines. So it must have sugars in it as well.
1044812
Diluted potassium iodide
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to see whether the Amylase (or starch digesting enzyme you are using) is working and actually breaking down the starch
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There are many types of pH indicators which will change color withint a certain range of pH values.  Many of these indicators might be dificult for the "common person" to get a hold of though.\n\nUsing Litmus paper is an easy way to test the pH of a substance.\nBased on the color change of the Litmus paper, a general idea of the pH can be determined.\n\nOne can also use other, natural, indicators.\nFor example, red cabbage contains a natural pH indicator which can be extracted by boiling (this will STINK up your whole house, best to do it outside of possible).\nhttp://chemistry.about.com/library/weekly/aa012803a.htm\n\nYou can also get pH probles whcih work by placing an electrode into the solution to be measured and getting a reading off of the either digital display or, in the case of cheaper probles, the value the needle points to on the meter.  Some of the "good qualitity" probles can be a little expensive, but a cheap substitute is a soil pH meter.  Although soil pH metes are really not designed to be used to measure a solution's pH and only have a limited range, it can work well for many applications.\n\nIf you want to get a numeric value for the pH,\nMy advice is to go with the soil pH meter if you dont plan on measuring anything which will have pH values below roughly 3 or 4 and nothing higher than about 8 or 9.  If you do plan to, you might want to go with a "real" pH meter.\n\nIf you just want a general range of the pH (whether something is just acidic or alkiline), then go with Litmus paper or some other form of cheap indicator (cabbage juice).
211996
Well, I'll start you off.\n\nAbsorbances are additive, so you subtract the blank from the measurement (.214 - .009 = .205)\n\nSo the absorbance is .205. Now you use beer's law, which is:\n\nA = ebc\n\ne is molar absorptivity (in L/mol cm)\nb is path length (cm)\nc is concentration. \n\nYou use that equation to figure out the concentration of the complex.\n\nFrom there, you can figure out the concentration of iodine based on the amount of starch used. Unfortunately, you've not provided enough information to go beyond here.