equipment Materials 50.00 ml buret, 250.ml volumetric flask, 1.00 ml volumetric
ID: 877008 • Letter: E
Question
equipment Materials
50.00 ml buret, 250.ml volumetric flask, 1.00 ml volumetric pipet 10.0 mL volumetric pipet, 25.00 mL volumetric pipet, pipettor, 250 mL Erlenmeyer flask, 10.0 mL graduated cylinder, several beakers, several watchglasses, unkown bleach solution, 10% potassium iodide solution, 2M hydrochloric acid solution, 0.150 M sodium thiosulfate solution, 1% starch solution.
Background information regarding this experiment is as follows:
An aqueous solution of sodium hypochlorite (NaOCI) is a clear, slightly yellow liquid, and is commonly known as bleach. Aside from its uses as a bleaching agent, sodium hypochlorite solutions are also used as sterlizing agents and in water treatment. Industrial uses include agricultural, food handling, paper production, and textile production. Sodium hypochlorite is also added to waste water to reduce odors.
The concentration of sodium hypochlorite in bleach solutions can be determined by titration. Therefore, we must use a two-step method to titrate sodium hypochlorite. In the first step, sodium hypochlortie, hydrochloric acid, iodide ion, and starch are combined to form a starch-triiodide complex. In this step there are 3 reactions that take place:
The result of these 3 reactions is that when sodium hypochlorite is present the starch-triiodide complex is produced.
In the second step the starch-triiodide product is titrated by sodium thiosulfate to form a colorless solution of iodide, dithionate.
More questions all need to be answered please:
1. Calculate the volume of the reagent thiosulafte solution which would be required if you titrated a 25ml sample of the original commercial bleach instead of 25ml of the diluted solution.
2. Why would we choose a graduated cylinder to measure the HCl and KI solutions instead of a volumetric pipette? When would we use a volumetric pippette?
3. You calculated the mass percent of sodium hypochlorite in the bleach( dilute and undiluted). Now calculate the molarity of the sodium hypochlorite in the diulte and undiluted solution/
4. Use oxidation states to show that equations (2) and (4) in the introduction are redox reactions and that equation 1 is not a redox reaction. :
-(1) NaOCl(aq) + HCl(aq) yields HOCl(aq)+NaCl(aq)
-(2) HOCL (aq) + HCl(aq) + 3I(aq) yields I3(aq) + 2CL(aq) + H2O(l)
-(4) (I3) (Starch) + 2S2O3 yields 3I + S4O6 + starch
5. combine equation 1-3 to show the overall reaction for the products of the starch-triiodide complex.
-(1) NaOCl(aq) + HCl(aq) yields HOCl(aq)+NaCl(aq)
-(2) HOCL (aq) + HCl(aq) + 3I(aq) yields I3(aq) + 2CL(aq) + H2O(l)
-(3) I3 + Starch yields (I3) (Starch)
6. What standard was used in this experiment?
7. Describe the naming of NaClO and HClO. What are the names of the following compounds? NaClO2 , NaClO3, NaClO4 , HClO2, HClO3, HClO4
Explanation / Answer
1) Moles thiosulfate used = [molarity of thiosulfate]x[volume thiosulfate used]
0.15M NA2S2O3 = 158.11 G/M * V
Vt = 9.48E-4 g or ml
2) Graduated cylinders are used for measuring approximate liquid volumes. Pipets and burets are used to more precisely measure liquids volumes, such as, 1ml or more.
6) Sodium thiosulfate, Na2S2O3(aq), is not generally used as a primary standard, so it should be standardised using a suitable primary standard such as potassium iodate, KIO3(aq). A good method for the direct analysis of hypochlorite, ClO-(aq), does not exist. Therefore, the hypochlorite in the bleach solution is first reacted with an excess of iodide ion under acidic conditions. If a standard iodine solution is used as a titrant for an oxidizable analyte, the technique is iodimetry. If an excess of iodide is used to quantitatively reduce a chemical species while simultaneously forming iodine, and if the iodine is subsequently titrated with thiosulfate, the technique is iodometry. Iodometry is an example of an indirect determination since a product of a preliminary reaction is titrated.
7) NaClO: Sodium hypochlorite (whose dissolution in water is known as bleach) is a strongly oxidizing chemical compound, contains chlorine in the +1 oxidation state is strong and economic oxidant. Because this characteristic is used as a disinfectant also destroys so many dyes used as bleach.
HClO: he hypochlorous acid is the name that is given to acid resulting from the union of acid chlorine oxide with H2O. Is so called because the chlorine acts with the +1 oxidation state, which is the smallest of the four that has: +1, +3, +5 and +7.
NaClO2, Sodium chlorite
NaClO3, Sodium chlorate
NaClO4, Sodium perchlorate
HClO2, Dioxochlorous acid
HClO3, Chloric acid
HClO4, Perchloric acid
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