This report deals with procedure followed while investigated the water body in which the dead business man might have been drowned. The procedure was necessary since it would help law enforcing officers in their investigations.The primary objective was to determine the water body in which the man got drowned since there were many water bodies within the location.
A body of Business Man was found dumped along the road. Autopsy revealed the man had been drowned as there was water in his lungs, clothes and hair were also wet. Police officers considered this homicide and wanted to know the specific reservoir within where the crime occurred. There are several reservoirs within the area where crime could have occurred and thus need to be objective in investigation by identifying specific location and enhance investigation. The experiment will manage to determine the phosphate concentration in each of four water bodies highly suspected to be where crime occurred.
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Phosphorous (P) is an element in period three and group V of periodic table. P is 11 th most abundant element in universe. It quantity is crucial in biochemical processes, pollution, and growth and development of living organisms. Abundance of P in our environment has increased due to human activities that discharge raw phosphorous it’s or compounds to the environment. Exhausts from locomotives, inorganic fertilizers, and waste waters from domestic and industrial sources are major source of Excess P in our environment. Though in most cases Phosphorous reacts to from less harmful compounds its presence in environment is still destructive if it exceed required quantity. In most cases phosphorous reacts forming acidic oxides react with other elements forming soluble compounds. The compounds formed dissolve in water and carried accumulate in water bodies (Pantic, 2016) .
Due to negative effects in aquatic habitat monitoring concentration of phosphorous has been a common activities in many places throughout the world since industrial era. In spectronic 20 the principal reaction is to produce yellow molybdophosphoric acid and then reducing it to phosphomolybdenum blue. The process has evolved over years on compound used to determine concentration some being; malachite green method, thiamin method, luminol method. The most advanced approach is direct spectrophotometric analysis which really on bismuthphosphomolybdate complex to measure concentration of phosphate under UV-light (Odelade & Kehinde, 2016) .
The approach has evolved over years and become more advanced in cost and efficiency. In addition the method gives more accurate, objective, and reliable results. Through analytical chemistry using UV-visible spectroscopy 'optimized' molybdenum blue methods would enable to calculate the concentration of dissolved phosphate in water sample. Orthophosphate is the major quality of water that facilitate detection of phosphate through spectrophotometric and also applicable to silicate, germinate, and arsenate. polyoxometallate species is formed when Dilute solution of phosphate, reacts with acidified ammonium molybdate to form molybdophosphoric acid which is a heteropoly acid. phosphomolybdenum blue is formed when polyoxometallate species Scheele describe this reaction in 1783 but in 1934 Keggin further revealed ‘Molybdenum blue’ refers to all phosphate compounds reduced to molybdate compounds and have phosphorous irrespective of their structure like heteroatom, heteropoly, or isopoly.
Kegging ion similar to Molybdate
Beer's Law: A = e b C
A is absorbance, e- molar absorptivity, b -path length (cm), and C- phosphate molarity. The correlation between absorbance and concentration of phosphate per mole is linear.
Materials and methods
Reagents
Phosphate standards
Phosphate Solution
Lake samples
Autopsy sample
Stannous chloride solution, cobalt nitrate, ammonium molybdate solution
Apparatus
Absorption Spectrum
Spectronic 20
Distilled water
Calibration Curve
50-mL Erlenmeyer flask, pipet, 25-mL measuring cylinder, holding cell, 100-mL graduated
Cylinder.
Activities
Day 1- preparation of standard solution and calibration of spectrophotometer
Day 2- generating calibration curve.
Day 3- Measuring absorbance of water sample for comparison purposes and conclusion.
Results
| Sample | Absorbance | concentration (ppm) |
| Woodlake | .447 | 1.582 |
| Lake Pinehurst | .759 | 2.687 |
| Seven Lakes | 1.062 | 3.759 |
| Reservoir Park | 1.274 | 4.510 |
| Autopsy | 1.325 | 4.690 |
Discussion
For the compound to be formed the are two phase of chemical reactions; formation of Keggin ion followed by reduction to deeply blue colored compound.
PO 4 3- +12MoO 4 2- + 27H + H 3 PO 4 (MoO 3 ) 12 + 12H 2 O
For the reaction to occur MoO 2- 4 , strong acid, and reducing agent must be present. Molybate must be in excess in for the reaction to occur since it influence formation of heteropoly acid and controls reduction. The pH should be maintained at 0-1 to get optimal results on colour intensity. Concentration of Molybate and that of acid determine number protons (Z) which will attach to Molybate in solution and the number range from six to nine.
The higher the concentration of acid or Molybdate the higher the rate of formation of the complex.
Spectral features
Conditions for different types of Methylated blue ions are as summarized on chart below.
Visible spectra for Phosphomolybdenum blue has seven band each representing a species. Based on Beer’s Law applies to concentration of species identified. Reduction number, protonation state, and presence of metallic reductant influence IVCT bands formed. Molybdenum blue methods should be followed articulately to avoid formation of blank reagent which occurs when there is formation of smaller Keggin structure. Extent of reduction, stability of product, and concentration of reductant influence results obtained. Linear range was constant and should be observed if all procedures are observed.
Absorption spectrum for phosphate was meant to give us the concentration of phosphates in water sample. The spectrum were collected at different wavelengths so as to get the optimal absorbance value. The results obtained were to be used to determine the water sample that matched that collected from the lungs during autopsy. The data obtained from phosphate solution analysis was used to set spectrophotometer to maximum absorption based on the wavelength as shown on the Calibration Curve. Calibration curve was used to measure absorbance of each sample which was used to collect data for beer’s equation linear graph. After conducting our analysis we found that reservoir Park sample had concentration of 4.51 ppm and Autopsy sample had 4.69 ppm. Other samples had the following results; Woodlake 1.582, Lake Pinehurst 2.687 and Seven Lake 3.759 ppm. From the results it was concluded the crime occurred at The Reservoir Park.
Errors in this methodology could arise from organic acids and chloride ions. Organic acids inhibit molybdate blue formation by forming reacting with Molybdate IV ion. Another source of error is ‘salt error’ where chloride ions react forming SnCl2 and this reduces Signal strength a good explanation for slight variation on the Reservoir Park sample and Autopsy Sample. Salt error cause reduction in formation of 12-Molybdophosphoric acid in the sample being analyzed. To minimize salt error I would prefer to use H2SO4 instead of HCl if we repeat the procedure. While chloride ions react to form SnCl2, suplhates does not and both acids are strong acids. Another source of error from the experiment could be from different time allocations while preparing the solutions on day two of the experiment. This error could have resulted into difference in reading recorded for different solutions. The error could be eliminated through allocating same time while preparing all the solutions.
The crime occurred in the Reseverior park because the concentration of phosphates in water sample matched those of samples from the lungs. Slight variations on final figures recorded could have occurred to process errors.
References
Odelade, S. O., & Kehinde, F. A. (2016). Evaluation of Phosphate Level in Water Samples (Ogbomoso Rivers) Using UV-Visible Spectrophotometric Method. International Journal of Scientific Research in Environmental Sciences , 4(4); 0102-0108. Retrieved from http://www.ijsrpub.com/ijsres
Pantic, I. ( 2016). Spectrophotometric method for the determination of phosphorus in natural waters using the bismuth-phosphomolybdate complex . Retrieved from ResearchGate : https://www.researchgate.net/publication/266880343_
