1.1 Abstract Chromium (VI) which is one of a heavy metal is classified as a strong oxidation agent and it poses a great deal of toxicity to humans and animals as well due to its carcinogenetic even at low aqueous solutions concentration. Chromium ions are found naturally in rivers, lakes, and streams. This health-risky situation has led to many studies and investigations on determining the presence and quantity of chromium in biological and environmental samples. In the present experiment, an absorption spectroscopy method was used for the determination of chromium (VI) concentration and the method is operated by tracing the presence of chromium (VI). As a result for this experiment, the concentration of Chromium (VI) in the lake water sample tested was 75 p.p.m. The experiment is completed and successfully conducted.1.2 Introduction

1.3 AimsThe objectives of conducting this experiment are :

1)To determine the Chromium (VI) content which present in simulated lake water sample using a spectrophotometer.

2)To demonstrate the proper method of diluting solution to prepare a series of standard solutions in the range of 5 to 100 parts per million (p.p.m) to be used in the calibration of the spectrophotometer.

3)To analyze whether the stimulated lake water sample tested is suitable for drinking water and agriculture purposes.

1.4 Theory Chromium is a metal found in natural deposits as ores containing other elements. The greatest use of chromium is in metal alloys such as stainless steel; protective coatings on metal; magnetic tapes; and pigments for paints, cement, paper, rubber, composition floor covering and other materials. Its soluble forms are used in wood preservatives. One source of chromium contamination in natural water is automobiles. Chromium that is deposited on roads derived from brake dusts and exhaust of automobile engine can unfavorably permeate into water streams through flowing rainwater. The most susceptible areas to be contaminated by such chromium are lakes and water streams which is nearer a congested with automobiles area.

A number of federal environment agencies are doing researches to determine its presence in many environmental samples. This is done due to the cancer-risk character and toxicity. Therefore, in this experiment absorption spectroscopy is being used to detect low level concentrations of Chromium (VI) in a lake water sample.

Colored aqueous solutions have chemical species contents which absorb significant wavelengths of light. Similarly, heavy metals can also be determined by absorption of wavelengths of light. In addition, the amount of light absorbed is linearly proportional to the concentration of the solution metal ions The amount of light absorbed by the chemical species in the sample is equivalent to the difference in the amount of light before it enters the sample and after it exits the sample. The light must be set to a specific wavelength in order to allow the light to be absorbed by the chemical species. Every chemical species absorbs distinct wavelengths of light. In absorption spectroscopy, the wavelength of light absorbed by a metal in solution are detected. In this experiment, standard solutions will be prepared by diluting 300 parts per million of Chromium (VI) standard solution. Standard solutions need to be prepared from the concentrated Chromium (VI) standard solution. The solution dilution formula can be used to calculate the dilute solutions volume:

(M1) (V1) = (M2) (V2)

Quantitative analysis using spectrophotometer is based on Beer-Lambert Law:

A = LC

A= absorbance value = molar absorbance (L/mol.com)L = path length of the cuvette in which the sample is contained (cm)C = concentration of the compound in solution (mol/L)

According to Beer-Lambert Law, the absorbance value depends on the total quantity of the absorbing compound in the light path through the cuvette. Thus we will get a straight line passing through the origin (0,0) if we plotted the graph of absorbance versus concentration of the compound solution. The molar absorbance, , is a constant for a particular substance, therefore if the concentration of the solution is halved, so is the absorbance value. A compound with a high molar absorbance is very effective at absorbing light (of the appropriate wavelength), and hence low concentrations of a compound with a high molar absorbance can be easily detected.

1.5 Apparatus Distilled water Spectrophotometer 10 millilitres square cuvette bottle Pipette 5 set of 10 milliliters of 5, 20, 30, 60, 100 p.p.m of diluted solution of Chromium (VI) 5 set of 300 p.p.m of standard Chromium (VI) solution Lake water sample

Figure 1 : Spectrophotometer

Figure 2 : Spectrophotometer

1.6 MethodologyIn this experiment, the apparatus was set up to carry out the experiment to determine the concentration of chromium (VI) by using absorption spectroscopy. Firstly, the 10 milliliters of square cuvette bottle was filled up with distilled water and placed on the spectrophotometer slot. A zeroing step was done to ensure that all the data obtained later was accurate. It followed by preparing 5 series of diluted chromium (VI) solution by using the diluted method with distilled water with the range concentration of 1 until 100 parts per million (p.p.m) solutions. Thus, for this experiment it used 5 p.p.m, 20 p.p.m, 40 p.p.m, 60 p.p.m, 80 p.p.m and 100 p.p.m solutions which were 300 p.p.m of standard Chromium (VI) solution of 0.17, 0.67, 1.33, 2.00, 2.67 and 3.33 milliliters. Each series of diluted solution was poured into square cuvette bottle and placed on the spectrophotometer slot to check the absorbance value by using the spectrophotometer. Then, all the data obtained was recorded first. This experiment continued by preparing 10 milliliters of lake water sample and poured it into the square cuvette bottle and spectrophotometer was used to determine the Chromium (VI) concentration contained in the water sample collected. Lastly, all the value was analyzed for the observation and the data obtained were recorded. The graph was plotted to figure out the value of chromium (VI) concentration.

1.7 Results

Concentration of Chromium (VI) solution (p.p.m)Volume of chromium (VI) solution (mL)Absorbance value

50.30.001

201.30.011

402.70.014

604.00.026

805.30.034

1006.70.043

Figure 1.7.1.1 Table of concentration of Chromium (VI) solution and their absorbance value

Absorbance of lake water sample = 0.031

Graph 1.7.1.2 Graph of Absorbance Value versus Concentration of Chromium (VI) in unitsof p.p.m

1.8 CalculationsTo dilute 20 milliliters standard solution of 5 p.p.m, the solution dilution formula is used in order to calculate the volume of Chromium (VI) solution.(M1)(V1) = (M2)(V2) (300)V1 = (5)(20) V1 = 0.3 mL

To dilute 20 milliliters standard solution of 20 p.p.m, the solution dilution formula is used in order to calculate the volume of Chromium (VI) solution.(M1)(V1) = (M2)(V2)(300)V1 = (20)(20) V1 = 1.3 mL

To dilute 20 milliliters standard solution of 40 p.p.m, the solution dilution formula is used in order to calculate the volume of Chromium (VI) solution.(M1)(V1) = (M2)(V2)(300)V1 = (40)(20) V1 = 2.7 mL

To dilute 20 milliliters standard solution of 60 p.p.m, the solution dilution formula is used in order to calculate the volume of Chromium (VI) solution.(M1)(V1) = (M2)(V2)(300)V1 = (60)(20) V1 = 4.0 mL

To dilute 20 mililiters standard solution of 80 p.p.m, the solution dilution formula is used in order to calculate the volume of Chromium (VI) solution.(M1)(V1) = (M2)(V2)(300)V1 = (80)(20) V1 = 5.3 mL

To dilute 20 mililiters standard solution of 100 p.p.m, the solution dilution formula is used in order to calculate the volume of Chromium (VI) solution.(M1)(V1) = (M2)(V2)(300)V1 = (100)(20) V1 = 6.7 mL

Based on the graph, the value of the gradient is :m = = = 0.0004By interpolating graph, the equation of the linear line was given by as :Y = mX + CThe y-intercept in the graph is 0.001, so, the value of C = 0.001. by substituting the value of , the equation is given as :Y = 0.0004X + 0.001X =

By substituting the value of Y with the value of the absorbance of water sample, which is 0.031 abs, the equation is given as :X = X = 75X is equivalent to the concentration of Chromium (VI) contains in the water sample, which is 75 parts per million (p.p.m).

1.9 Discussion The experiment was conducted to achieve a few of main objective in this experiment such as to determine the Chromium (VI) content which present in the water sample by using the spectrometer, to demonstrate the proper method of diluting solution, to prepare of standard solution in the range 5 to 100 p.p.m and lastly to analyze whether the water sample is suitable for drinking water and agriculture purpose. In chemistry, spectrophotometry is the quantitative measurement of the reflection or transmission properties of a material as a function of wavelength and the water sample. The water sample that have been used to examine the presence of chromium is assumed to be contaminant, the source of the water sample is the source of water sample located near a roadway where road users with automobiles use it every day. This is due to rivers, lakes or any water streams which are near to congested areas have the highest risk or most susceptible to contain heavy metals such as chromium itself and is classified as contaminated water source. The first step in this experiment is to prepare six standard solution Chromium (VI) standard solutions using serial method as mentioned in the theory section. The concentrations for standard 1, standard 2,standard 3, standard 4, standard 5 and standard 6 is 100 ppm, 80 ppm, 60 ppm, 40 ppm, 20 ppm and 5 ppm respectively. The absorbance for each six standard solutions and the lake water sample is taken by using the spectrophotometer. A graph of the absorbance is plotted against the concentration of standard solutions. Linear regression analysis is performed in order to determine the linear best fit for the absorbance versus concentration data. Graph 1.7.1.2 in results show a graph of absorbance versus concentration of six standard solutions. The line determined from the regression analysis will be in the form of y = mx + b, where y is the absorbance value and x is the concentration of the solution. Algebraic substitution of the absorbance value (y) for the unknown metal solution into the linear regression equation for the line permits the determination of the concentration (x) of the unknown solution. The value of absorbance of lake water sample is 0.031. From the graph, the concentration of chromium (IV) in water sample is apparently calculated to contain 75 parts per million.Based on the consideration of state and federal regulatory agencies, natural waters are regarded to be toxic if the concentration of Chromium (VI) is any higher than 0.05 parts per million. Natural waters whose chromium (VI) concentrations exceed 0.05 ppm may not be used for drinking water or for agricultural purposes. After doing some calculations based on the graph, the concentration of the lake water sample is determined to be at 75 ppm which is obviously not suitable for drinking water and for agricultural purposes. The lake water sample tested is then concluded to be unsafe and unhygienic for drinking water or even agricultural purposes. However, a few steps might be done erroneously which results in such an outrageous value of chromium (VI) content. First and foremost, the techniques applied to measure such a small volume of diluting substance might not be suitable. This might lead to difficulties when measuring the volume of chromium (VI) needed to dilute the standard solutions.Besides that, wrong way of holding the cuvette bottle used to contain the diluted solutions might also lead to errors. Any fingerprints or smudge imprinted on the outer surface of the cuvette can become an unfavorably interference for the solutions to absorb wavelengths of light in the spectrophotometer. Thus, the reading of absorbance by the instruments may not be accurate.In addition, the experiment conducted to determine the absorbance value of diluted solutions that contain chromium (VI) is done only once. Thus, no average value can be obtained from the results, and so the accuracy of the value taken is not much convincing.Others, the square cuvette bottle might not be cleansed properly with distilled water each time before it is used for another attempt. This will lead to inaccurate contents of either standard solutions or the chromium solution.

1.10 ConclusionBased on the experiment, it can be concluded that chromium (VI) are present in the sample water. The concentration of Chromium (VI) in the lake water sample tested is calculated to be 75 parts per million. Since it is above the level of standard allowed by the Malaysian Environmental Quality (Sewage and Industrial Effluents) Regulations of 1979 which is 0.05 ppm thus, the water is concluded as contaminated and does not suitable for drinking or agricultural purposes.

1.11 Recommendations1.Avoid leaving a fingerprints or any kind of smudge on the outer surface which will corrupt the reading of absorbance value of spectrophotometer.2.Ensure the square cuvette bottle clean thoroughly and properly so that the accurate reading can figure out.3.Use a specific wavelength where the component absorbs substantially to achieve the accurate value.4.Ensure there are no air bubbles in the nozzle of the stopper.5.Measure the volume of diluted chromium accurately and make sure read the level of solution by noting the lower level of the meniscus at eye to avoid parallax error.6.Ensure the square cuvette bottle is filled up with distilled water first and placed on the spectrophotometer slot to ensure the zeroing step is done so that all the data obtained later is accurate.

1.12 Reference/Appendix