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19 Nov 2019

I titrated 0.02061 M Na2S2O3 with a solution of vitamin C (0.1 g), 15 mL water, 30 mL of 0.00946 M KIO3, and KI (1 g). For trials 3, it took these volumes of Na2S2O3 to reach the endpoint: 4.71 mL, 4.68 mL, and 4.66 mL. Determine the moles of vitamin C presented in the solution for each trial of the analysis and calculate the % by mass of ascorbic acid in the vitamin C sample for each trial of the analysis. Also, this equation is given: IO3 - (aq) + 8 I- (aq) + 6H+ (aq) → 3 I3 - (aq) + 3 H2O(l)

The Ksp isn't given

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Related questions

The kinetics of the reaction below were studied. The volumes of 0.040 M KBrO3, 0.040 M KI,

0.00050 M Na2S2O3, 0.040 M KCl, H2O and a buffer solution employed in each trial are shown

in the table below. One drop of 1% aqueous starch solution was also added in each trial. The

buffer solution was a pH = 4.74 solution containing 0.50 M acetic acid and 0.50 M sodium acetate; Ka = 1.8 x 10−5 for acetic acid. Each trial was performed at 25◦C. For each trial, the reaction mixture was initially colorless after combining all solutions; appearance of a blue solution color in the reaction mixture signaled that all of the thiosulfate ion initially present had reacted and marked the end of the timing period. The initial reaction rate for each trial was calculated from the change in molar concentration of thiosulfate ion from each trial; the equation for calculating Initial Rate is shown below, where Δt is the elapsed time between combining all solutions and appearance of the blue solution color. Each solution volume was measured to the nearest 0.1 mL. (ie 5 mL shown in the table is 5.0 mL.)

BrO3- (aq) + 6I−(aq) + 6H+(aq) → 3H2O(l) + Br−(aq) + 3I2(aq)

Initial rate = - 13∆S2O32-∆t

Volume (mL) Used

Trial #

KBrO3

KI

Na2S2O3

KCl

H2O

Buffer

Initial Rate (M/s)

1

10

10

5

0

0

15

5.0 x 10−6

2

5

10

5

5

0

15

2.5 x 10−6

3

10

5

5

5

0

15

2.5 x 10−6

4

10

10

2.5

0

2.5

15

5.0 x 10−6

a)Which pair of trials could be used to determine the order for I−? Justify your choice.

b)How would you determine the order for H+? Be as specific as possible.

c)What would be the value for the initial rate if 5 mL KBrO3 solution, 5 mL KI solution, 5 mL Na2S2O3 solution, 10 mL KCl solution, 15 mL pH = 4.74 buffer solution, and 1 drop of 1% starch solution were used?

d)Why do Trials 1 and 4 have the same initial rate?

e)What time was required for the color change to occur in Trial 1?

f)What was the purpose of adding 5 mL of 0.040 M KCl in Trial 2?

g)How would you experimentally verify that KCl does not cause the color change from colorless to blue? Be as specific as possible.

Direction:

Part I - Prepare and standardize a solution of Sodium Thiosulfate 1. Prepare 250 mL of a solution which is approximately 0.025 M Na2S2O3• 5H20. Because sodium thiosulfate is a hydrate, it cannot be used as a primary standard. It must be standardized in order to determine its exact concentration. (Note for Su’17: this solution has already been prepared for you). 2. Pipet 10.0 mL of 0.01 M KIO3 into a 150 mL Erlenmeyer flask. Add about 20 mL of distilled water to the flask. 3. Dissolve about 2 g of solid KI to the KIO3. The solution should turn a dark orange-brown. Add about 20 drops of 2M HCl and swirl to mix completely. 4. Calculate the approximate amount of Na2S2O3 that will be required to reach the endpoint, assuming that the Molarity of the Na2S2O3 will be approximately 0.025 M. 5. Quickly add all but about 2 or 3 mL of the volume you calculated above to the flask. 6. Add about 40 drops of a 2% starch solution. The solution should turn dark blue. 7. Continue adding Na2S2O3 dropwise until the blue color just disappears. Record the volume of Na2S2O3 in your lab notebook. 8. Repeat one more time. Calculate the concentration of the Na2S2O3 from each trial and average your results. If they differ greatly, a third trial may be necessary. Part II - Prepare a saturated solution of Ca(IO3)2 1. Combine 100.0 mL of 0.20 M KIO3 with 40 mL of 1M Ca(NO3)2 in a 150-mL beaker. Stir to mix the solutions completely. A white precipitate of Ca(IO3)2 should form. 2. Let the mixture stand a few minutes, then filter into a dry flask, through a dry filter paper using gravity filtration. Cover the solution with parafilm.

Show me part2 how to calculate the concentration of iodate ion in the filtrate. Using the equation editor, insert---> eqatuion.

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.

I do not know how to answer the following on the data sheet: (? means I do not know how to answer)

Table 1:

Mass of 1.00 ml of unknown (by tare): 10.552 g

Density of bleach: (g/ml) : 1.055 g/ml

Volume of diluted bleach used in each titration: 10.00

Concentration of sodium thiosulfate: ? (M)

Titration Data:

Initial buret reading (ml): trial1: 0.000 ml Trial 2: 0.00 ml Trial 3: 0.000ml

Final buret reading (ml): trial 1: 13.50ml Trial 2: 13.30ml Trial 3: 13.40ml

Volume delivered(ml: trial 1: ? Trial 2: ? trial 3:?

Calculations: (show clearly)

For trial 1,2,3 ???

1.Moles of Na2S2O3 in titration: ??? trial 1,2,3

2.Moles of NaOCl: ???trial 1, 2,3

3.Average moles of diluted NaOCl: (one answer) ?

4.Average moles of undiluted NaOCl: (one answer.. mol) ?

5.Standard Deviation: (one answer) (mol)

6.Average mass of NaOCl in 25.00mL of undiluted bleach: ? (g)

7.mass of 25.00 mL of undiluted bleach: ? (g)

8. Mass % of NaOCL from experiment: ? (%)

9.Actual mass % of NaOCL (from prof; student does not make an entry):? (%)

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

8 Submit a one paged (typed double spaced) report that discusses the following topics:

a. the goals or objectives of the experiment

b.your results as they relate to the goals and objectives

c. the quality of your results.

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