lab 3(water quality)

8/18/2019 lab 3(water quality)

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ABSTRACT

Hexavalent chromium (chromium (VI), Cr (VI)) refers to chemical compounds that

contain the element chromium in the +6 oxidation state. Hexavalent chromium (Cr (VI))

compounds are a large group of chemicals with varing chemical properties, uses, andwor!place exposures. "he o#$ective of this experiment are are to determine the Chromium

(VI) content which present in simulated la!e water sample using a spectrophotometer, to

demonstrate the proper method of diluting solution to prepare a series standard solutions in

the range of % to %&& parts per million (ppm) to #e used in the cali#ration of the

spectrophotometer, and thus, to analse whether the simulated la!e water sample tested is

suita#le for drin!ing water and agriculture proposes. 'efore the experiment #egin, four series

of diluted chromium (VI) solution must #e prepared # using the diluted method with

distilled water with the range concentration of % until %&& parts per million (ppm) solutions.

In this experiment the concentration of chromium that was used are & ppm, * ppm, 6& ppm

and * ppm. "he sample is analsed # spectrophotometer in order to !now the a#sor#ance

value and the cali#ration curve is o#tained. In this experiment, the concentration of

Chromium (VI) solution in the la!e water sample cannot #e concluding #ecause of the cross

contamination.

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https://en.wikipedia.org/wiki/Chemical_compoundhttps://en.wikipedia.org/wiki/Chromiumhttps://en.wikipedia.org/wiki/Oxidation_statehttps://en.wikipedia.org/wiki/Chromiumhttps://en.wikipedia.org/wiki/Oxidation_statehttps://en.wikipedia.org/wiki/Chemical_compound


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INTRODUCTION

Hexavalent chromium (chromium (VI), Cr (VI)) refers to chemical compounds that

contain the element chromium in the +6 oxidation state. Virtuall all chromium ore is processed via hexavalent chromium, specificall the salt sodium dichromate. ther

hexavalent chromium compounds are chromium trioxide and various salts of chromate and

dichromate. Hexavalent chromium is used in textile des, wood preservation, and as anti-

corrosion and conversion coatings and a variet of niche uses. Chromium hexavalent

compounds exist in several forms. Industrial uses of hexavalent chromium compounds

include chromate pigments in des, paints, in!s, and plastics chromates added as

anticorrosive agents to paints, primers, and other surface coatings and chromic acid

electroplated onto metal parts to provide a decorative or protective coating.

Inhaled hexavalent chromium is recogni/ed as a human carcinogen. 0or!ers in man

occupations are exposed to hexavalent chromium. 1ro#lematic exposure is !nown to occur

among wor!ers who handle chromate-containing products and those who weld, grind, or

#ra/e stainless steel.

Hexavalent chromium (Cr (VI)) compounds are a large group of chemicals with

varing chemical properties, uses, and wor!place exposures. "heir properties includecorrosion-resistance, dura#ilit, and hardness. 0or!ers ma #e exposed to air#orne Cr (VI)

when these compounds are manufactured from other forms of chromium (e.g., the production

of chromates from chromite ore) when products containing Cr (VI) are used to manufacture

other products (e.g., chromate-containing paints, electroplating) or when products containing

other forms of chromium are used in processes that result in the formation of Cr(VI) as a #-

product (e.g., welding).

Chromium occurs in the environment primaril in two valence states, trivalent

chromium (Cr III) and hexavalent chromium (Cr VI). 2xposure ma occur from natural or

industrial sources of chromium. Chromium III is much less toxic than chromium (VI). "he

respirator tract is also the ma$or target organ for chromium (III) toxicit, similar to

chromium (VI). Chromium (III) is an essential element in humans. "he #od can detoxif

some amount of chromium (VI) to chromium (III).

"he respirator tract is the ma$or target organ for chromium (VI) toxicit, for acute (short-

term) and chronic (long-term) inhalation exposures. 3hortness of #reath, coughing, and

whee/ing were reported from a case of acute exposure to chromium (VI), while perforationsand ulcerations of the septum, #ronchitis, decreased pulmonar function, pneumonia, and

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https://en.wikipedia.org/wiki/Chemical_compoundhttps://en.wikipedia.org/wiki/Chromiumhttps://en.wikipedia.org/wiki/Oxidation_statehttps://en.wikipedia.org/wiki/Salt_(chemistry)https://en.wikipedia.org/wiki/Sodium_dichromatehttps://en.wikipedia.org/wiki/Sodium_dichromatehttps://en.wikipedia.org/wiki/Chromium_trioxidehttps://en.wikipedia.org/wiki/Chromate_and_dichromatehttps://en.wikipedia.org/wiki/Chromate_and_dichromatehttps://en.wikipedia.org/wiki/Anti-corrosionhttps://en.wikipedia.org/wiki/Anti-corrosionhttps://en.wikipedia.org/wiki/Conversion_coatinghttps://en.wikipedia.org/wiki/Conversion_coatinghttps://en.wikipedia.org/wiki/Chromic_acidhttps://en.wikipedia.org/wiki/Electroplatehttps://en.wikipedia.org/wiki/Carcinogenhttps://en.wikipedia.org/wiki/Chemical_compoundhttps://en.wikipedia.org/wiki/Chromiumhttps://en.wikipedia.org/wiki/Oxidation_statehttps://en.wikipedia.org/wiki/Salt_(chemistry)https://en.wikipedia.org/wiki/Sodium_dichromatehttps://en.wikipedia.org/wiki/Chromium_trioxidehttps://en.wikipedia.org/wiki/Chromate_and_dichromatehttps://en.wikipedia.org/wiki/Chromate_and_dichromatehttps://en.wikipedia.org/wiki/Anti-corrosionhttps://en.wikipedia.org/wiki/Anti-corrosionhttps://en.wikipedia.org/wiki/Conversion_coatinghttps://en.wikipedia.org/wiki/Chromic_acidhttps://en.wikipedia.org/wiki/Electroplatehttps://en.wikipedia.org/wiki/Carcinogen


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other respirator effects have #een noted from chronic exposure. Human studies have clearl

esta#lished that inhaled chromium (VI) is a human carcinogen, resulting in an increased ris!

of lung cancer. 4nimal studies have shown chromium (VI) to cause lung tumors via

inhalation exposure.

OBJECTIVES

"he o#$ectives of conducting this experiment are5

1. "o determine the uantit of Cr (VI) present in a polluted water sample using a

spectrophotometer and a set of standard solution.

2. "o determine whether the water sample is suita#le for drin!ing or agricultural

purpose.

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THEORY

Chromium (VI) is !nown to #e a strong oxidi/ing agent, posing a high ris! to humans

and animals due to its car-cinogenic and mutagenic properties. "he chromium contamination

in water are usuall comes from automo#iles as it is a part in various automo#ile #rea!s as

well as the parts of its engine. Chromium that was accumulated on the road created from

#ra!e dusts and exhaust of vehicle engine can adverse infiltrate into an water source. 0ater

sources such as la!es and rivers that are nearest too congested with automo#ile area are most

suscepti#le are to #e contaminated.

7ue to its cancer-ris! character and toxicit even at mere concentrations, a lot of federal

environment agencies are doing researches to determine its presence in man environmental

samples. "hus, in this experiment, a#sorption spectroscop will #e used to detect low level

concentrations of chromium (VI) in a la!e water sample.

4s a matter of fact, color aueous solutions have chemical species contents which a#sor#

significant wavelengths of light. 3imilarl, heav metals can #e identified via a#sorption of

wavelength of light. 8urthermore, the amount of light a#sor#ed is nearl proportional to the

concentration of the solution metals ions.

4#sorption spectroscop, commonl referred as spectrophotometer, which defined as the

analtical approach #ased on the measured amount of light a#sor#ed # a sample at a given

wavelength. 4#sorption spectroscop refers to spectroscopic techniues that measure

the a#sorption of radiation, as a function of freuenc or wavelength, due to its interaction

with a sample. "he sample a#sor#s energ, i.e., photons, from the radiating field. "he

intensit of the a#sorption varies as a function of freuenc, and this variation is thea#sorption spectrum. 4#sorption spectroscop is performed across the electromagnetic

spectrum.

4 spectrophotometer, one of the most convenient phsics la# euipment that com#ined

two devices which area a spectrometer and a photometer. 3pectrometer is used for producing

light of an selected wavelength or a color while a photometer is used for measuring the

intensit of light. "he two devices are placed at either side of a cuvette filled with a liuid.

3pectrometer produces the light of desired wavelength and it passes through the tu#e and

reaches photometer that measures its intensit. "hen the photometer produces a voltage signal

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https://en.wikipedia.org/wiki/Spectroscopyhttps://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)https://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)https://en.wikipedia.org/wiki/Electromagnetic_radiationhttps://en.wikipedia.org/wiki/Frequencyhttps://en.wikipedia.org/wiki/Wavelengthhttps://en.wikipedia.org/wiki/Wavelengthhttps://en.wikipedia.org/wiki/Absorption_spectroscopy#Absorption_spectrumhttps://en.wikipedia.org/wiki/Electromagnetic_spectrumhttps://en.wikipedia.org/wiki/Electromagnetic_spectrumhttps://en.wikipedia.org/wiki/Spectroscopyhttps://en.wikipedia.org/wiki/Absorption_(electromagnetic_radiation)https://en.wikipedia.org/wiki/Electromagnetic_radiationhttps://en.wikipedia.org/wiki/Frequencyhttps://en.wikipedia.org/wiki/Wavelengthhttps://en.wikipedia.org/wiki/Absorption_spectroscopy#Absorption_spectrumhttps://en.wikipedia.org/wiki/Electromagnetic_spectrumhttps://en.wikipedia.org/wiki/Electromagnetic_spectrum


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to a displa device, usuall a galvanometer. 4s the amount of light a#sor#ed # the liuid

changes the signal also changes. "he concentration of a su#stance in solution can #e

measured # calculating the amount of a#sorption of light at the appropriate wavelength or a

particular color.

"he spectrophotometer uantitativel compares the amount of light passing through

the standard solution and compares the amount of light reflecting from the water sample. "he

spectrophotometer must #e cali#rated #efore the water sample #eing analse and the

procedure is !nown as 9/eroing:. Cali#ration is done # using the reference su#stance and the

a#sor#encies are measured relative to the standard solution. 8ive standard solutions from the

concentrated Chromium (VI) standard solution need to #e prepared in order to measure the

a#sor#ance value. 3tandard solution is calculated # using the solution dilution euation.

In this experiment, the standard solutions will #e prepared # diluting && part per million (ppm)

of Chromium (VI) standard solution. 8ive standard solutions are need to #e prepared from the

Chromium (VI) standard solution. 8or calculate the volume of Chromium (VI), the solution dilution

formula was used. "he general euation is written5

M 1V 1= M 2V 2

ther was to find the value of a#sorption # using spectrophotometer is #ased on #eer-

;am#er ;aw 5

A=ξLC (mol.cm)

c = concentration of the compound in solution (mol>;)

8orm the euation that 'eer-;am#ert law state that to o#tain the value of the

a#sorption process is depends to the total value of the a#sor#ing compound in the light path.

In other word, a graph can #e plot which is graph of a#sor#ance versus concentration of the

5


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sample>compound solution. 4 straight line from the origin in the graph can show how the

value of the a#sor#ance versus concentration # using straight line euation. "he molar

a#sor#ance for a particular su#stance is a constant value and it will effect # the

concentration of the solution. High value of molar a#sor#ance occurred when a compound is

a#sor#ing light more during the spectroscop process.

PROCEDURE

% . 8 iv e s ta nd ar d s ol ut io n o f c hr om iu m w as p re pa re d w it h d if fe re nt

concentrat ions which are .* ppm, & ppm, * ppm, 6& ppm, and *

ppm.


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MATERIALS AND APPARATUS

MATERIALS APPARATUS

• 7istilled water • 1ipette

• Chromium (VI) solution • %& ml suare cuvette #ottle

• ;a!e water sample • 3pectrophotometer

•


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30 45 60 75

0

0.01

0.01

0.02

0.02

0.03

0.03

0.040.04

0.05

0.05

f(x) = 0.01x - 0.01

R² = 1

Graph of absorbance versus concentration of chromium

concentration (ppm)

Absorbance

Figure 15 @raph of a#sor#ance value versus concentration of Chromium (VI) soluiton in

units of ppm

SAMPLE OF CALCULATIONS

Calculation for diluting the && ppm of Chromium (VI) solution to a desired concentration in

this experiment5 M 1V 1= M 2V 2

"a#le 5 Volume of Chromium (VI) solutions

8

Concentration of Chromium (VI) solution,

parts per million

Volume of Chromium (VI) solution,

millilitres

& A%V% = A


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' interpolating the graph, the euation of the linear line o#tained is,

= &.&%x B &.&%


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"here are a few step might #e done erroneousl in this experiment that failed to

determine the third aim which is the techniue applied to measure the small volume of

diluting su#stance might not #e suita#le. Dext, the volumes of concentration chromium (VI)

solution to ma!e a standard solution was not pipette correctl and thus, effect the reading of

a#sor#ance value. 4fter that, the wrong wa of holding the suare cuvette #ottle can also ta!e

a part of a failure experiment. "his is #ecause, the fingerprints imprinted on the outer surface

of the suare cuvette #ottle can #ecome unfavoura#l interference for the solutions to a#sor#

wavelength of light in the spectrophotometer. "herefore, the reading of a#sor#ance value #

the instruments is not accurate.

CONCLUSION

"he o#$ective of this experiment is to determine the uantit of chromium exists in

the water sample. 8rom the result o#tained, the uantit of the chromium in the water sample

cannot #e determined since there is error due to cross contamination. "he water sample might

#e contaminated # the #acteria result of #eing exposed to the open air during filtration

process. In conclusions, the experiment was unsuccessful.

RECOMMENDATION

1. "he la!e water sample must #e ta!en freshl #efore conducting the experiment.


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. 4#sorption spectroscop (n. d). etrieved cto#er en.wi!ipedia.org>wi!i>4#sorptionspectroscop.

4#sorption > "ransmission > eflection 3pectroscop (n. d). etrieved cto#er www.andor.com>learning-academ>a#sorption-transmission-

reflection-spectroscop-an-introduction-to-a#sorption-transmission-reflection-

spectroscop

*. 3tanton, '., 4twood, C. F hu, ;. (4pril, Cole.

6. Chromium compounds (n. d). etrieved cto#er www.epa.gov>airtoxics>hlthef>chromium.html

. Chang, . (

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lab 3(water quality)