Report 2 - Analysis of iron contents in an iron tablet via redox titration PDF

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Analysis of iron contents in an iron tablet via redox titration ...

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Analysis of iron contents in an iron tablet via redox titration PROJECT OBJECTIVES The purpose if this report is to do proficiency testing for the company “Super-Mega Supplements” by investigating the content of iron in iron tablets via redox titration to ensure the reported iron content in the tablets is accurate. The total content of the active ingredient, dried ferrous sulphate (FeSO4), is 325 mg per tablet (equivalent of 119 mg of elemental iron (Fe)).

MATERIALS AND METHODS Preparation of iron tablets Material

Quantity

Iron tablets 5M H2SO4

2 25mL

Deionised 25mL water Digestion tube 50mL Glass rod 1 Analysis of iron tablets Material Conical flask KMnO4 solution

Quantity 250mL

Preparation of Solution Materials beaker NH4)2Fe (SO4)2 6H2O Water 5 M H2SO4 volumetric flask Burette KMnO4 solution Conical flask Iron standard

Standard Quantity 150mL 5.0 g

20mL 25mL 250mL 1 1 25mL

Preparation of iron tablets 1. 2. 3. 4. 5.

Obtain two iron tablets and place each in a 50mL digestion tube Add 25mL of deionised water Add 25mL of 5M H2SO4 Place tubes in the digestion block in the fume hood and up tablets with a glass rod Set aside for an hour, occasionally swirling the tube (Practical 2 guidelines 2020)

Preparation of Standard Solution Note: Prior to weighing out ammonium iron (II) sulphate on the analytical balance ensure that the instrument is level by adjusting thumb screws on the feet 1. Take a clean, dry 150mL beaker and accurately weigh out 5.0 g of ammonium iron (II) sulphate- (NH4)2Fe (SO4)2-6H2O 2. Dissolve the solid in approximately 20mL of water and 25mL of 5 M H2SO4. Ensure that the solid is completely dissolved prior to transferring to a volumetric flask 3. Transfer the solution into a 250 mL volumetric flask and make up to volume. Rinsing the beaker 2-3 times to ensure quantitative transfer of the ammonium iron (II) sulphate solution. Filling the volumetric flask so as that the meniscus sits on the mark accounting for parallax error 4. Prepare a burette with KMnO4 solution. Using a bulb pipette transfer 25mL of the ammonium iron (II) sulphate solution to a conical flask 5. Standardise your permanganate solution with 25mL of the iron standard 6. Calculate the concentration of the permanganate solution and record the values in the lab notebook (Practical 2 guidelines 2020)

Analysis of iron tablets 7. Transfer each of the digested iron tablet solutions into a clean 250mL conical flask. Titrate each of the solutions against the now standardised KMnO4 8. Calculate the amount of FeSO4 and Fe in each of your tablets, record your data in your lab book (Practical 2 guidelines 2020)

RESULTS “Preparation of a standard solution” • Mass of (NH4)2Fe (SO4)2.6H2O weighed out: 5.0009 g • Molarity of the standard iron (II) solution C=n/v n = Mass / Molar mass = 5.0009g / 392.13 = 0.02275 moles C=n/v = 0.01275 / 0.25 (L) = 0.051 M

n (fe2+) C (fe2+)

0.02275 moles 0.051 M

V (fe2+) in 250mL / 0.025 L volumetric flask

• Volume of standard iron (II) solution used in titration: 25mL

Table 1: Titration volumes for the titration of KMnO4 solution Volumes (mL)

Average

10.5

= 32.0 + 10.5 + 49.0 + 30.5 + 30.0 + 30.5 = 182.5/6 = 30.4 mL

49.0

Standard Deviation: √ sum of total volume – mean)2 / N-1

30.5

= √ (182.5 – 30.4)2 / 6-1 = 68.02

30.0

Standard Error: SD / √ total number of volumes

30.5

= 62.09 / √6 = 27.78

32.0

(Observation) The colour at the end was: pink, pink, purple, pink, pink, pink • Net ionic equation for the titration reaction MnO4 -1 + 5Fe 2+ + 8 H • Molarity of KMnO4 solution Mn2+ : Fe2+ 1 : 5 C (Fe2+): 0.051 M Ratio:

Mn 2+ + 4H2O + 5Fe3+

Therefore, concentration of (KMnO4): 5 x 0.051 = 0.255M

“Analysis of iron tablets” Table 2: The mass of FeSO4 and Fe2+ (in mg) in each tablet

Fe2+ (mg) 106 115.2 103.3 106.8 111.2683 105.5 105 106.5

FeSO4 (mg)

Average:

Average:

106 + 115.2 +103.3 + 106.8 + 111.27 + 105.5 + 105 + 106.5

= 288.4 + 313.4 + 281 +290.4 + 302.669 + 287.2 + 287 + 290

= 859.57/8 = 107.45 mg

= 2340.069/8 = 292.51 mg

Standard Deviation:

Standard Deviation:

√ sum of total volume – mean)2 / N-1

√ sum of total volume – mean)2 / N-1

√ (859.57 –107.45)2 / 8-1 = 284.27

= √ (2340.09–292.51)2 / 8-1 = 773.91

Standard Error: SD / √ total number of volumes

Standard Error: SD / √ total number of volumes

= 265.91 / √8 = 100.51

= 723.92 / √8 = 273.62

• •

Tablet 1 required 36.5 mL Tablet 2 required 34.5 mL

288.4 313.4 281 290.4 302.669 287.2 287 290

DISCUSSION The purpose of this experiment was to investigate do proficiency testing for the company “Super-Mega Supplements” by investigating the contents of iron in iron tablets via redox titration to ensure the reported iron content in the tablets is accurate. The results in Table 2 to demonstrates that the average mass of Fe2+ achieved at the end of titration is 107.45 mg and 292.51 mg for FeSO4. The manufacturing team stated the total content of FeSO4, as 325 mg per tablet (equivalent of 119 mg of elemental iron (Fe)). Therefore, the aim of this experiment could not be fulfilled as the company’s claim of iron content did not match the findings of this experiment. Proficiency testing The level of consistency between chemists in bench 1 was pretty good as all the values were very close to each other and as the final concentration of KMnO4 is 0.01 approximately which shows the findings of all chemist in bench 1 are consistent. Moreover, the results that are taken from the whole class illustrates close findings of 0.01 M of KMnO4. Furthermore, looking at the findings of other chemists in other laboratories also display very consistent results compared to my bench and other classes too. As the molarity of KMnO4 in this experiment is 0.255, therefore it applies that the findings are not consistent. The level of inconsistencies in my findings compared to other people’s results could be due to a number of reasons including, systematic errors such as improper reading of the balancing scale. It was also observed that the mass of (NH4)2Fe (SO4)2- 6H2O was 5.0009 g instead of exact 5.0 g and this could be another cause of an error. Other random errors could be human error such as not pouring the solution to the exact meniscus, as the bright purple colour may have caused a misjudgement in the reading of burette. Furthermore, as seen in Table 1, the titrations were performed 6 times and the average volume is recorded in the table. While this proves the accuracy of the experiment as it was repeated several times and also the uncertainty of burette was marked as 0.05. However, the experiment cannot be considered precise as the findings are not consistent. It can be seen in Table 1, the Standard deviation (68.02) is greater than mean (30.04) which illustrates that the values are far apart and not consistent and this can also be seen through the Standard error of (27.78). This experiment could be improved by avoiding errors such as inaccurate weighing of the mass and avoiding random errors that would give more precise results.

CONCLUSIONS The purpose if this report was to perform proficiency testing for the company “Super-Mega Supplements” by investigating the content of iron in iron tablets via redox titration to ensure the reported iron content in the tablets is accurate. However, the findings of this experiment did not support the aim as the content of iron achieved (292.51mg FeSO4) was not equivalent to the company’s claim of 325 mg per FeSO4.tablet (equivalent of 119 mg of elemental iron (Fe)). The results were not precise and also not consistent with other chemist results. Therefore, the findings from this experiment are not valid enough to support the claim of the company.

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