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12 Dec 2019

Given the following data, calculate the percent by mass Fe2+ in the unknown sample. Assume the experimental data provided is obtained using the same procedure you will be using in the lab.

Unknown sample mass = 0.1700

Absorbance (average) of unknown sample = 0.343

Beer’s Law Data: Slope = 0.2143 L/mg Fe2+

y-intercept = -0.002

Additional Information (Lab procedure):

1. Obtain and clean three 100-ml volumetric flasks

2. Weigh 0.15-0.20g of the unknown accurately into a clean 100ml beaker

3. Add about 30ml distilled water and 1ml concentrated sufuric acid. Swirl to dissolve sample and quantatively transfer into a 100ml volumetric flask. Make up the flask to the mark with distilled water and mix thoroughly

4. Pipet 10.00ml of this solution into the second volumetric flask and make up to the mark

5. Pipet 10.00ml of this diluted solution ( from step 4) into the third volumetric flask. Add 10ml saturated sodium acetate and 10ml 10% hydroxylamine hydrochloride, and wait five minutes

6. Add 10ml 0.1% 1,10 phenanthroline to the flask. Wait 10 minutes, then make up the flask to the mark with distilled water

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Lelia Lubowitz
Lelia LubowitzLv2
13 Dec 2019

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Related questions


I need help figuring out how to find the molarities of each dilution. My exact mass of pure ASA was .497 g. From that and the molar mass I found that there were .00276 moles of ASA.

Determinatrion of Iron in Vitamin

A. Prep of Iron Soln. from Vitamin

Weigh three vitamin tablets and place each tablet in separate 125-mL Erlenmeyer Flask. Add 25 mL of 2M HCL to each flask in the hood and boil the samples for 15 mins.

Set up Vacumm filter system and filter each sample serparetely and collect the filtrate(liquid). Transfer filtrate after each run to a 50 mL Volumetric flask. Rinse filter flask with DI water and transfer rinse to the vol. flask as well. Repeat for each solution.

After solutions cool, dilute it to the mark with DI water and Mix well. Transfer contents to a labeled beaker.

For each solution made, transfer 1.00 mL of the solution with a volumetric pipette and place it in a fresh 50 mL vol. flask. Then dilute it ot he mark with DI water.

B. Prep of sample Solutions

From each diluted vitamin solution a test solution sample will be made. Using a vol. pipette transfer 5.00 mL of the diluted vitamin solution(unknown molarity) to a large test tube. Then add 4.00 mL hydroquinone and 6 mL of o-phenanthroline to the test tube with a vol.pipettes. Note the volume of the test solutions. This dilution step is needed when calculate the mass of iron in the tablets.

C. Prep of Sample Solutions

One iron standard solution will be made for the class.

D. Prep of Calibration Solutions

Each student pair will make at least one calibration solution. Have the instructor assign you a solution 0-7. The entire lab section will make one calibration set by the following steps:

Label a 50.00 mL vol. flask with your assigned number (0-7)

Collect ~ 5 mL of hydroquinone and transfer it to a clean beaker. Then collect ~ 5 mL of phenathroline and transfer this solution to another clean beaker. Transfer 2.00mL of hydroquinone and 3.00mL of phenathroline using vol. pipettes to the labeled vol. flask

Collect ~5-10 mL of the standard solution and transfer it to a clean beaker. The amount of iron solution to transfer via vol. flask is equal to the assigned number (i.e. if your group was assigned #1, transfer 1.00 mL of the iron solution to the flask. Flask 0 will not contain any iron solution.

Once all three reagents have been added to a flask. Add ~ 20mL of DI water. Mix the solution by capping the flask and inverting it several times. Continue adding DI water to the mark on the flask and mix solution again by inversion.

What is the molarity of the iron in each calibration solution?

Given Info/Data

Mass of Iron in Tablet from bottle (mg) 18
Mass of Iron for Stock Soln. (g) 0.1435
Molar Mass of Fe(NH4)2(SO4)2• 6H2O (g/mol) 392.14
Molar Mass of Fe (g/mol) 55.845
Moles of Iron Stock Solution (mol) 0.000365941

Mass of Iron tablets: 1.2900g 1.2991g 1.2979

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 — were present in the blank titration?

c. How many mmol of I3 — 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:

+ 𝐼𝑂4 − → 2 𝐻2𝐶𝑂 +𝐼𝑂3 − + 𝐻2𝑂 (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:

𝐼𝑂4 − + 11 𝐼 − + 8 𝐻 + → 4 𝐼3 − +4 𝐻2𝑂 (8-2)

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

𝐼𝑂3 − + 8 𝐼 − + 6 𝐻 + → 3 𝐼3 − + 3 𝐻2𝑂 (8-3)

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

𝐼3 − +2 𝑆2𝑂3 2− → 3 𝐼 − + 𝑆4𝑂6 2− (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 𝐼3 − 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 – 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 “purr-eye-oh-dic acid”): a. Weigh out 1.16-1.24 g of H5IO6 on an analytical balance. Periodic acid is very corrosive – 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: “Acid Into Water”. 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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