chromium (iv) concentration exp

8/10/2019 chromium (iv) concentration exp

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ABSTRACT

Chromium (VI) is classified as a strong oxidation agent and i t poses a great deal

of toxicity to humans and animals as well due to i ts carcinogenetic. This health-

risky si tuation has led to many studies and investigations on determining the presence and quanti ty of chromium in b iological and environmental samples . In

the present study, an absorption method for the determination of chromium (VI)

concentrat ion is proposed and the method is operated using spectrophotometer

by tracing the presence of chromium (VI) at a wavelength of 435 nano meters.

The experiment was conducted to determine the chromium (VI) content present

in simulated lake water sample using spectroscopy. Five series of diluted

solution were prepared by using the diluted method with dist i l led water with the

range concentrat ion of 1-100 ppm solutions, (1, 20, 60, 85, and 100 ppm). After

that , 20 mL of each series of diluted solution is poured into square cuvette

bott le and place on spectrophotometer s lot to check the absorbance value. The

concentrat ion of Chromium (VI) in the lake water sample tested is 9.525 parts

per mill ion (ppm). The lake water sample used to test for presence of chromium

was believed to be contaminated as the lake was si tuated near a roadway where

road users with automobiles use i t every day. Rivers, lakes and 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 then

classified as contaminated water source. The water sample is concluded to be

contaminated and thus, not suitable for drinking or agricultural purposes.



1.0INTRODUCTION

Many heavy metals, such as chromium, are undeniably toxic at low

aqueous solution concentrat ions. Chromium ions are commonly found in ei ther

trivalent , Cr (III), or hexavalent , Cr (VI) states. Cr (VI) formation is favoured by an oxidizing env ironment and is not usually considered as health hazards ,

while Chromium (III) is favoured by a reducing environment and usually can be

toxic if ingested or inhaled. It is found that naturally alkaline rivers and lakes

have much lower risk of such heavy metal contamination of chromium ions in

comparison with naturally acidic water streams.

Chromium (VI) is known to be a strong oxidizing agent, which apparently

poses a h igh risk yet negat ive impact to humans and animals due to i tscarcinogenetic propert ies. The lethal dose of poisonous Cr (VI) compounds is

about one half teaspoon of material . Chronic exposure to Cr (VI) compounds can

cause permanent eye injury, unless properly treated. State and federal regulatory

agencies consider Cr (VI) to be toxic at concentrat ion level > 0.100 ppm.

Natural waters whose Cr (VI) concentrat ions exceed 0 .100 ppm may not be used

for drinking water or for agricultural purposes. That is why there are lots of

studies that have been done profusely in order to determine the health-risky

chromium in environmental as well as biological samples.

Therefore, i t is important to take note about the level of Cr (VI)

concentrat ions in water sources. If i t does not exceed 0.100 ppm then i t is

el igible to be consumed as for drinking water and agricultural purposes.



2.0OBJECTIVES

The objectives of this experiment are;

2.1To determine the Chromium (VI) content which present in simulated

lake water sample using a spectrophotometer,

2.2To demonstrate the proper method of diluting solution to prepare a

series of standard solutions in the range of 1 to 100 parts per mill ion

(ppm) to be used in the calibration of the spectrophotometer,

2.3To analyze whether the simulated lake water sample tested is suitable

for drinking water and agriculture purposes.

3.0THEORY

One common source of chromium contamination in natural waters is

painting and coating which is account for 62%, or can be said as the largest share of

environmental impacts during the manufacture of automobiles. In-mold painting techniques can

reduce discharges of hazardous materials such as nickel, copper, and hexavalent chromium into

the atmosphere. Chromium that is deposited on highroads originated from brake

dusts and exhaust of automobile engine can unfavorably permeate into any water

streams nearby via flowing rainwater. Lakes and water streams which is nearer a

typical congested with automobiles areas are the most susceptible areas to be

contaminated by such chromium.

Due to i ts cancer-risk character and toxicity even at mere concentrat ions,

a lot of federal environmental agencies are doing researches to determine i ts

presence in many environmental samples. Thus, in this experiment, absorption

spectroscopy will be used to detect low level concentrat ions of Chromium (VI)

in a lake water sample.

As a matter of fact , colored aqueous solutions have chemical species

contents which absorb significant wavelengths of l ight . Similarly, heavy metals

can be identified via absorption of wavelengths of l ight . Furthermore, the



amount of l ight absorbed is l inearly proportional to the concentrat ion of the

solution metal ions.

Absorption spectroscopy operates on the measuring principle of l ight

befo re and after i t passes through an aqueous metal solution. The amount ofl ight absorbed by the chemical species in the sample is equivalent to the

difference in the amount of l ight befo re i t enters the sample and after i t exits the

sample. For the purpose of l ight to be absorbed by chemical species, the l ight

must be set to a specific wavelength. Every chemical species absorbs dist inct

wavelengths of l ight . In absorption spectroscopy, the wavelengths of l ight

absorbed by a metal in solution are detected.

In this experiment, s tandard solutions will be prepared by diluting 300 parts per mill ion (ppm) of Chromium (VI) standard solution. Five standard

solutions need to be prepared from the concentrated Chromium (VI) standard

solution. To calculate the dilute solutions volume, the solution dilution formula

can be used, as what is writ ten below:

Where; M 1 : concentrat ion of given Chromium (IV) stock solution = 300ppm

V 1 : Volume of Chromium (IV) solution required to perform dilution

M 2 : Concentrat ion of Chromium (IV) solution after dilution

V 2 : Volume of Chromium (IV) solution after dilution



Quanti tat ive analysis using spectrophotometer is based on Beer-Lambert Law:

Where; A : absorbance value (dimensionless, thus no units is represented)

: molar absorbance (L / mol.cm)

L : path length of the cuvette in which the sample is contained (cm)

C : concentrat ion of the compound in solution (mol / L)

Beer-Lambert Law states that absorbance value depends on the total

quanti ty of the absorbing compound in the l ight path through the cuvette. Thus,

if we plot a graph of absorbance versus concentrat ion of the compound solution,we get a straight l ine passing through the origin (0, 0). The molar absorbance, ,

is a constant for a part icular substance, therefore if the concentrat ion of the

solution is halved, so is the absorbance value. A compound with a high molar

absorbance is very effective at absorbing l ight (of the appropriate wavelength),

and hence low concentrat ions of a compound with a high molar absorbance can

be easily detected.

4.0APPARATUS / REAGENTS

4.1Disti l led water

4.2Spectrophotometer

4.310 mill i l i t res square cuvette bott le

4.4Pipette

4.55 set of 20 mill i l i t res of 1, 20, 60, 85 and 100 ppm of diluted solution

of Cr (VI)

4.65 set of 300 ppm of standard Cr (VI) solution of 0.067, 1.33, 4.0, 5.67,

6 .67 mL.

4.7Lake water sample.



5.0METHODOLOGY

5.1 All the materials and apparatus were set up.

5.2 The 10 mL of square cuvette bott le was fi l led up with dist i l led

water and placed on the spectrophotometer slot . A zeroing step was

done to ensure that al l the data obtained later was accurate.

5.3 5 series of diluted solution were prepared by using the diluted

method with dist i l led water with the range concentrat ion of 1 unti l

100 parts per mill ion (ppm) solutions. (1 ppm, 20 ppm, 60 ppm, 85

ppm, and 100 ppm)

5.4 20 mL of each series of diluted solution was poured into square

cuvette bott le and placed on the spectrophotometer slot to check theabsorbance value by using the spectrophotometer.

5.5 All the data obtained was recorded.

5.6 20 mL of lake water sample was poured into the square cuvette

bott le and spectrophotometer was used to determine the Chromium

(VI) concentrat ion contained in the water sample collected.

5.7 All the value was analyzed; the observation and the data obtained

were recorded.



6.0RESULT

Volume of Chromium

(VI) , mill i l i t res (mL)0.067 1 .330 4 .000 5 .670 6 .670

Concentrat ion of

Chromium (VI), parts per

mill ion (PPM)

1.000 20.000 60.000 85.000 100.000

Absorbance Value 0 .008 0 .032 0 .118 0 .178 0 .195

Table 1.0: Determination of absorbance value using spectrophotometer

Lake Water Sample Absorbance Value

Trial 1 0.283

Trial 2 0.285

Trial 3 0.286

Average value : 0.285

Table 2 .0 : Determinat ion of absorbance va lue of water sample us ing spec t rophotometer



Graph 1 .0 : Graph o f Abso rbance Value versus Concen t ra t ion o f Chromium (VI) in un i t s o f p .p .m

7.0CALCULATIONS

7.1To prepare 20mL of 1ppm diluted solution, the volume of standard

solution required is;

( )( ) ( ) ( )

All the volumes of chromium (VI) solution needed to dilute each standard

solution are stated in Table 1.0.

y = 0.0299x + 0.0002

R² = 0.9933

0

0.05

0.1

0.15

0.2

0.25

0 1 2 3 4 5 6 7 8

A b s o r b a n c e

V a l u e

Concentration of Chromium (VI) in unit of p.p.m

Graph of Absorbance Value versus Concentration of Cr (VI) in ppm



From Graph 1.0, the gradient is;

By substi tut ing y with the average of absorbance value of water sample, which

y=0.285, then;

Hence, the concentrat ion of Chromium (VI) contains in the water sample, 9.525

parts per million.

8.0DISCUSSION

There are a few objectives for this experiment, first ly to determine the

Chromium (VI) content which present in simulated lake water sample using a

spectrophotometer, secondly to demonstrate the proper method of diluting

solution to prepare a series of standard solutions in the range of 1 to 100 parts

per mill ion (ppm) to be used in the calibration of the spect rophotometer, and

last ly, to analyze whether the simulated lake water sample tested ei ther suitable

for drinking water and agriculture purposes.

The lake water sample used to test for presence of chromium was believed

to be contaminated as the lake is si tuated near a roadway where road users with

automobiles use i t every day. According to the values of concentrat ion of

chromium (VI) which was calculated to contain 9.525 parts per mill ion, this

obviously means that there was a significant content of chromium ions in the

water. Based on the consideration of state and federal regulatory agencies,



natural waters were regarded to be toxic if the concentrat ion of Chromium (VI)

is any higher than 0.100 parts per mill ion. The lake water sample tested was

then concluded to be unsafe and unhygienic for drinking water for public

consumption 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 difficult ies when measuring the volume of

chromium (VI) needed to dilute the standard solutions. Besides that , wrong way

of holding the square cuvette bott le 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 unfavourably interference for the solutions to absorb

wavelengths of l ight in the spectrophotometer. Thus, the reading of absorbance

by the inst ruments may not be accurate.

In addit ion, 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. Moreover, the square cuvette bott le might not be

cleansed properly with dist i l led water each t ime before i t is used for another

attempt. This wil l lead to inaccurate contents of ei ther standard solutions or the

chromium solution.



9.0CONCLUSION

9.1The value of the concentrat ion of Chromium (VI) in the lake water

sample tested was 9.525 parts per mill ion.

9.2The proper method of diluting solution to prepare a series of standard

solutions in the range of 1 to 100 parts per mill ion (ppm) to be used in

the calibration of the spectrophotometer is by determining the amount

of stock solution required to prepare the desired amount of standard

solution first , using the formula of M 1 V 1 =M 2 V 2 , and then dilute i t with

dist i l led water.

9.3Since i t is more than 0.100 parts per mill ion as what has been

standardized by state and federal regulatory agencies, the water samplewas concluded to be contaminated and thus, not suitable for drinking

or agricultural purposes.

10.0 RECOMMENDATIONS

10.1 In order to measure the small volume of chromium (IV), the most

accurate apparatus to be used is a pipette. The reason for this is that a

volume of l iquid can be measured more accurately using a pipette than

a measuring cylinder.

10.2 The cuvette must be cleansed and dried properly. This is to avoid

inaccurate contents of ei ther solutions or the chromium solution.

10.3

The cuvette must also be held properly and wiped to avoidfingerprints or smudges on the outer surface of the cuvette because

they could become interferences for the measurements.

10.4 The experiment should be repeated thrice in order to increase

accuracy of the readings. The average value obtained from this is more

convincing than an experiment with no average.



11.0 REFERENCES

11.1 Brown, T.L., LeMay, H.E., Bursten, B.E., & Murphy, C.J. (2009).

Chemistry The Central Science . NJ: Pearson Education, Inc.

11.2 S. Silbeberg Martin, McGrow. Hill International Edit ion, Fifth

Edit ion Chemistry The Molecular Nature of Matter and Change , 1221

Avenue of the Americas, New York, 2009, pg 783-808

11.3 R. S. Khandpur, Handbook of Analytical Instruments, 2007, the McGraw-Hill

Company.11.4 Nat ional Primary Drinking Water Regulation, retrieved from

http:/ /water.epa.gov/drink/contaminants/ on 2 n d June 2014.

12.0 APPENDICES

12.1 To prepare 20mL of 20ppm diluted solution, the volume of standard


( )( ) ( ) ( )



( )( ) ( ) ( )



( )( ) ( ) ( )

http://water.epa.gov/drink/contaminants/





12.4 To prepare 20mL of 100ppm diluted solution, the volume of

standard solution required is;

( )( ) ( ) ( )

chromium (iv) concentration exp

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