I. Aim
The aim of this experiment is to have an accurate percentage of the total toxicity removed of a chromium buffer solution.
II. Introduction
Chromium is a chemical element with symbol Cr and is the 22nd most abundant element in Earth’s crust. Chromium is found due to erosion process in rocks and can be redistributed by volcanic eruptions.
- High melting point
- Steely-grey metal
- High corrosion and hardness
Chromium can be found in foods, wine and water. It was identified as an essential nutrient but in the form of Cr6+ can be very dangerous for the human body via ingestion but also when inhaled. Chromium human symptoms: dryness, erythema and allergic responses. A possible source of chromium exposure is waste dumps for chromate- producing plants causing local air or water pollution. Chromium can be used on many objects such as car parts, bath taps, kitchen gas burners, wheel rims and many others for the fact that chromium is very corrosion-resistant, and thus prolongs the life of the parts. It is also used in making expensive jewellery.
Materials Chromium containing "synthetic" wastewater Sulphuric acid 9 M
Iron (II) sulphate p.a. Sodium hydroxide solution 1 M
Double demineralized water 1% Nitric acid solution Methods. One volumetric flask has been used for an accurate concentration of Chromium (Cr). The first question that has been given is:
How much K2 Cr2 O7 is needed to reach 100 mg Cr for an accurate addiction?
100 (mg) / 52 (g/mol) = 1,92 mmol Cr2
1,92 (mmol Cr2)= 0,96 (mmol Cr)
0,96 (mmol) * 294,2 g/mol = 282,43 mg (K2Cr2O7)
III. RATIO: 282,43 mg = 1000 mL (Cr) 28,24 mg = 100 mL (Cr)
Add the amount of Cr in a volumetric flask (100mL) and it has been added double demi water until 100 ml. This solution is the main, which was added in most of the coming volumetric flasks. Then, 6 volumetric flasks have been used. The 1st one is filled with double demi water until 100 mL (the zero). The 2nd it has been added 2,5 mL of the buffer solution of Potassium dichromate plus double demi water until 100mL. The 3rd volumetric flask is filled with 5 mL plus demi water until 100mL. The 4th volumetric flask has been filled with 10 mL buffer solution plus double demi water until 100mL. The 5th one is filled with 15 mL of the buffer solution plus double demi water until 100mL. The last flask is has been filled in with 20 mL of buffer solution with the addition of double demi water until reaching 100 mL.
V. Results and calculations
When the graph has been made, it was possible to get the formula out from the result of the experiment. The formula is:
y = 0,0418 x
Consequently, it has been possible to calculate the x with the absorbance number (y)
First volumetric flask has an absorbance of 0,268 with the help of the formula: x = (0,268/0,0418) * 200 = 1282,29
Second volumetric flask has an absorbance of 0,480. x = (0,480/0,0418) * 100 = 1148,32
Third volumetric flask has an absorbance of 0,805. x = (0,805/0,0418) * 50 = 962,91
For an accurate calculation of Cr it is been calculated the average that equals to 1131,173 mg/L (1131,173 mg/L) / (51,9961 mol) = 21,75 mmol of Cr (21,75 mmol of Cr)*3 = 65.3 Fe2+
65.3 Fe2+ * 394.14 g/mol = 25721,6 mg/L (25721,6 mg/L) / 10 = 2572.16 mg Ammonium Iron Sulphate in 100mL 2572.16 mg * 1.1 = 2829.37 = 2.83 mg/100mL EFFICIENCY: y = 0,0418 x; 0.003= 0.041x; x = 0.075 mg/L 0,9 0,8 0,7 0,6 0,5 0,4 0,3 0,2 0,1 00 5 10 15 20 25
ppm (mg/L) y = 0,0418x R2 = 0,96441
Absorption
Efficiency = η = 1−(Cfinal/Cinitial)
Efficiency = 1 – (0.075 / 1131,173) = 0.99 = 99.93 %
VI. Conclusion
To detoxify 100 mL of the examined wastewater containing chromium, 2.83 mg of Ammonium Metal Sulphate need to be included.
The last consumption has been calculated to be 0.003. This value shows a performance of 99.9%, therefore the consequence is fulfilling and the research can be regarded achievements.
VII. Discussion
While analyzing the diluted samples the 10x dilution provided a result not reliable because it did not fit in the supposed range, therefore this result was not considered when the average mg/L of Chromium were calculated.
VIII. References
[1] Atsdr.cdc.gov. (n.d.). Chromium (Cr) Toxicity: What Are the Physiologic Effects of Chromium Exposure? | ATSDR - Environmental Medicine & Environmental Health Education - CSEM. [online] Available at: https://www.atsdr.cdc.gov/csem/csem.asp?csem=10&po=10.
[2] En.wikipedia.org. (n.d.). Group 6 element. [online] Available at: https://en.wikipedia.org/wiki/Group_6_element [Accessed 24 Jun. 2009].
[3]Agency for toxic substances & disease registry, 2008 retrieved from: https://www.atsdr.cdc.gov/csem/csem.asp?csem=10&po=11 the 21st December 2017
[4] Images-na.ssl-images-amazon.com. (n.d.). Cita un Sito web - Cite This For Me. [online] Available at: https://images-na.ssl- images-amazon.com/images/I/A1OdXp4c7aL._AC_UL320_SR24