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18 Dec 2019

1- In the titration between potassium iodate and the sodium thiosulfate solution, if the titration is not performed immediately after the addition of the sulfuric acid, how would this likely affect the calculated concentration of your diluted sodium thiosulfate solution?

2- Why did the titrations performed need to be started immediately after adding the sulfuric acid?

3- A sample of bleach was analyzed as in this procedure. The only procedural difference is that the student weighed out the bleach solution used instead of pipetting a certain volume of bleach. The student weighed out 0.634 g of commercial bleach solution. It was found that it required 13.24 mL od 0.0732 M sodium thiosulfate solution to react with the iodine produced. What is the percentage of sodium hypochlorite in this bleach sample?

4- The active ingredient in many commercial liquid bleaches is sodium hypochlorite. The bottle lists the percentage of sodium hypochlorite as 6.0%. If the density of commercial bleach is 1.084 g/mL of 0.150 M sodium thiosulfate is required to reach the end point in a titration similar to the one performed in this experiment, if a student analyzed a 2.0 mL sample of bleach.

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Reid WolffLv2

31 Dec 2019

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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 , NaClO_3, 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.

I need help for my lab report please. It's only a-e Questions for study that I need help with, so any help or advice will be greatly appreciated! Underneath is more info on the lab if needed. Thank you!

Question for Study

1. A student performed this lab exercise, generating the following data:

Mass of H5IO6 used: 1.2320 g

Volume of thiosulfate used in blank titration: 47.93 mL

Volume of thiosulfate used in the unknown titration: 39.23 mL

a. What is the concentration of the sodium thiosulfate solution?

b. How many mmol of I3 â were present in the blank titration?

c. How many mmol of I3 â were present in the unknown titration?

d. How many mmol of glycol were present in the unknown titration?

e. What mass of ethylene glycol should be reported?

Introduction

The chemical analysis of organic compounds often presents major experimental difficulties. An accurate analysis depends upon the sample undergoing a single, well-defined reaction which quickly goes to completion. Often, organic compounds undergo several different reactions at the same time, and reaction rates are sometimes quite slow.

A functional-group analysis is one in which a particular grouping of atoms in a compound is made to react in a specific well-defined way with a particular reagent.1 In this experiment use is made of the reaction between an oxidizing reagent and an organic compound with the functional group COH-COH.

Analysis of Ethylene Glycol

Ethylene glycol reacts with periodate ion to form formaldehyde and iodate:

+ ð¼ð4 â â 2 ð»2ð¶ð +ð¼ð3 â + ð»2ð (8-1)

This oxidation-reduction reaction will proceed to completion with negligible side reactions under the appropriate set of conditions. The reaction is slow, but increases with increasing concentration of periodate. Here a known, fixed amount of periodate in excess of that needed to completely react with the glycol is added to the unknown. After the glycol has reacted, an excess of iodide is added to the solution. The iodide reacts with unreacted periodate according to:

ð¼ð4 â + 11 ð¼ â + 8 ð» + â 4 ð¼3 â +4 ð»2ð (8-2)

The iodide also reacts with the iodate produced in reaction 8-1 according to:

ð¼ð3 â + 8 ð¼ â + 6 ð» + â 3 ð¼3 â + 3 ð»2ð (8-3)

The triiodide produced in these reactions is then determined by titration with thiosulfate:

ð¼3 â +2 ð2ð3 2â â 3 ð¼ â + ð4ð6 2â (8-4)

To find the glycol content, a blank solution containing the same fixed amount of periodate but no glycol is treated similarly. The difference in the number of moles of ð¼3 â produced in the blank solution, and that produced in the sample solution, is equal to the number of moles of glycol in the sample solution.

Procedure

1. Prepare a solution from your unknown: a. Your unknown may have recently been refrigerated â make sure it is at room temperature before use. b. Transfer the vial contents quantitatively to a 250 mL volumetric flask. c. Dilute to volume with water and mix well.

2. Prepare a Periodic Acid standard solution (pronounced âpurr-eye-oh-dic acidâ): a. Weigh out 1.16-1.24 g of H5IO6 on an analytical balance. Periodic acid is very corrosive â to your skin and to metals. Do not spill any on the analytical balances. b. Quantitatively transfer the solid to a 100 mL volumetric flask, and dilute to volume with water.

3. Prepare a sodium thiosulfate solution: a. Weigh ~11.2 g of sodium thiosulfate pentahydrate. b. Transfer the solid to a 1L Pyrex bottle and dilute to 500 mL to produce an approximately 0.09 M solution. c. Add 0.10 g Na2CO3 and swirl to mix well.

4. Prepare a ~0.5 M solution of sulfuric acid: a. In a beaker (250 or 400 mL), combine 25 mL of 3 M sulfuric acid and 125 mL of water. Mix. Remember: âAcid Into Waterâ. What glassware is appropriate to measure these volumes?

5. Prepare samples for titration: a. Pipet 20 mL of your diluted unknown and 10 mL of the periodic acid solution into a 250 mL conical flask and swirl to mix. b. Wait a minimum of 45 minutes to allow complete reaction before titrating. Do the blank titrations while you wait! c. Prepare a total of 3 samples in this way.

6. Perform the sample titrations: a. Add ~1.5 g of KI to your conical flask and swirl to dissolve. b. Add 10 mL of your 0.5 M sulfuric acid (use a graduated cylinder). c. Titrate from a dark red initial colour to the first change to yellow. d. Add 2.0 mL of thiodene indicator solution. The solution will become a dark grey/violet colour. e. Finish the titration (fractional drops) to a sharp disappearance of the violet colour. 7. Perform the blank titrations: a. Pipet 10 mL of periodic acid solution into a 250 mL conical flask. b. Add 20 mL of water with a graduated cylinder. c. Add reagents and perform the titration as in Step 6 above. Calculations Report the total mass (in mg) of ethylene glycol in your unknown.

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