Chromium Discussion

7/30/2019 Chromium Discussion

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Results

Absorbance band, max = 435nm

Table 1: Concentration and absorbance of standard solution

Concentration

(ppm)Absorbance

0 0.002

18.75 0.127

37.5 0.283

75 0.469

150 0.844

Table 2: The absorbance band of simulated lake water

Water sample

Absorbance

0.275


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Fig 3.1: Graph of absorbance versus concentration

Calculation

Standard Solution Calculation

Standard solution = 18.75 ppm

M1V1 = M2V2

V1 = (M2V2) / M1

V1 = (18.75 ppm x 50mL) / 300 ppm

= 3.125 mL

Standard solution = 37.5 ppm

M1V1 = M2V2

V1 = (M2V2) / M1

V1 = (37.5 ppm x 50mL) / 300 ppm

= 6.25 mL

y = 0.0055x + 0.0341

R = 0.9916

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

0 20 40 60 80 100 120 140 160

Absorbance

Concentration (ppm)

Graph of Absorbance Versus Concentration


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Standard solution = 75 ppm

M1V1 = M2V2

V1 = (M2V2) / M1

V1 = (75 ppm x 50mL) / 300 ppm

= 12.5 mL

Standard solution = 150 ppm

M1V1 = M2V2

V1 = (M2V2) / M1

V1 = (150 ppm x 50mL) / 300 ppm

= 25 mL

Y = 0.005x + 0.034

(0.275) = 0.005x + 0.034

X = (0.275 0.005) / 0.034

= 7.94 ppm

Notice that x is equivalent to the concentration of Chromium (VI) contains in the water

sample, which is 7.94 parts per million (ppm).


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Discussion

Many heavy metals, including chromium (Cr), are toxic even at low aqueous solution

concentration. Chromium ions, Cr (III) and Cr (IV) are found naturally in rivers, lakes and

streams. The main objective of this experiment is to determine the quantity of Cr (IV)present in a polluted water sample using a spectrophotometer and a set of standard

solutions. Besides, this experiment was performed to evaluate the suitability of the lake

water for public consumption. This experiment was analyzed by using the

spectrophotometer with wavelength 435 nm. Distilled water was used as the sample in

order to calibrate the spectrophotometer. Beer-Lambert Law states that absorbance

value depends on the total quantity of the absorbing compound in the light path through

the specific wavelength of the sample.

Five dilution of Cr (VI) standard solution has been prepared at concentration of

0ppm, 18.75ppm, 37.5ppm, 75ppm, and 150ppm from 300ppm of stock solution. The

result shows that the absorbance for each concentration of Cr (VI) has different value of

absorbance. As the concentration increased, the absorbance value is also increased.

From the results obtained, it shows that at blank sample, absorbance value was at

0.002, but at concentration of 150.00ppm, absorbance value was increases to the

highest values which are at 0.844. The absorbance values at the concentration of

18.75ppm, 37.5ppm, and 75ppm were 0.127, 0.283, and 0.469 respectively. This result

proved that the absorbance of a solution is directly proportional to the concentration of

the solution and this condition follows the rules of Beers Law.

After the graph of absorbance versus concentration of Cr (VI) has been plotted,

an equation of Y = 0.005x + 0.034 was obtained from the graph. R 2 from the graph

shows the value at 0.991 which is approximately to 1. The closer the R2value is to 1.00,the better the linear regression analysis fits the data. Then, the Y = 0.005x + 0.034

equation can be used to determine the concentration of chromium in the sample lake

water. The absorbance of lake water sample was at 0.275. By applying this equation, the

concentration of sample lake water was 7.94ppm.


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According to the values of concentration of chromium (VI) which is apparently

calculated to contain 7.94 parts per million, this obviously means that there is a

significant content of chromium ions in the water. 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 0.100 parts per million. The presence

of chromium (VI) even in very low concentration is highly visible and causes damage to

the environment as they are toxic to aquatic life (I.U Emmamuel et al., 2009). The impact

Cr (VI) exposure to water bodies can cause allergy reactions, dermatitis, skin irritation,

cancer and mutation both in babies (Garg et al., 2003). The lake water sample tested is

then concluded to be unsafe and unhealthy for drinking water for public consumption or

even agricultural purposes.


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Conclusion

The main purpose of this experiment is to determine the quantity of Cr (IV) present in a

polluted water sample using a spectrophotometer and by using a set of standard

solutions of known concentration. In this experiment, absorption spectroscopy will beused to determine Cr (VI) concentrations in solution with specific wavelength of 435 nm.

Chromium is a component in automobile brakes and engine parts. Chromium

deposited on highways, in the form of brake dust and engine exhaust, can leak into

lakes and streams via rainwater run-off. Lakes and streams near highly trafficked areas

are highly susceptible to chromium contamination.

The concentration of chromium (VI) in the lake sample tested is 7.94 ppm. At this

concentration of Cr (VI), it can cause the water pollution. The lake water can be very

toxic especially to aquatic life and human being. Result of this experiment shows that the

concentration of Cr (VI) is over the limit for drinking water or for agricultural purposes. At

this concentration level, the water sample could specified as toxic and prolonged

contact with some chromium compounds that can cause allergy reactions, dermatitis,

skin irritation, cancer and mutation both in babies. Since it is highest than 0.100 ppm that

been standardized by state and federal regulatory agencies, the water sample is

concluded to be contaminated and thus not suitable for drinking and agricultural

purpose.

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Chromium Discussion