Experiment 10 (Chemistry)

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FOUNDATION OF CHEMISTRY II (EP103)

LABORATORY REPORT

EXPERIMENT NO.: 10

EXPERIMENT TITLE: DETERMINATION OF CONCENTRATION OF POTASSIUM

DICHROMATE SOLUTION BY UV-VIS ABSORPTION SPECTROSCOPY

OBJECTIVES

STUDENT NAME: ESHBINDER KAUR GILL

STUDENT ID.: 1000923!!

SCHOOL OF ENGINEERING

FACULTY OF ENGINEERING" ARCHITECTURE # BUILT EN$IRONMENT


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TABLE OF CONTENT

1 I%&'*+&,%

2 M-&',-/ -% '+*'

3 R*/& -% D,+*,%

C%+/*,%

! L,,&-&,% 4 E5',%&

R4'%+


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Experiment 10

Title:

Determination of concentration of potassium dichromate solution by uv-vis absorption of

potassium.

Objectives:

1) To determine the wavelength color) of ma!imum absorbance" #ma! for a potassium

dichromate solution$) To prepare and run a standard calibration curve" and determine the concentration of an

un%nown potassium dichromate solution.&) To e!amine the relationship between the absorbance and concentration of a potassium

dichromate solution.

'aterial and apparatus:

(ipette" pipette pump" *m+ and 1**m+ volumetric flas%s" bea%ers" analytical balance

Distilled water" potassium dichromate" un%nown potassium dichromate solution


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,ntroduction:

The spectrophotometer has well been called the wor%horse of the modern laboratory. ,n

particular" ultraviolet and visible spectrophotometer is the method of choice in most laboratories

concerned with the identification and measurement of organic and inorganic compounds in a

wide range of products and processes - in nucleic acids and proteins" foodstuffs" pharmaceuticals

and fertiliers" in mineral oils and in paint. ,n every branch of molecular biology" medicine and

the life sciences" the spectrophotometer is an essential aid to both research and routine control.

'odern spectrophotometers are uic%" accurate and reliable and ma%e only small demands on

the time and s%ills of the operator. /owever" the user who wants to optimie the functions of his

instrument and to be able to monitor its performance in critical areas will need to understand the

elementary physics of the absorption process as well as the basic elements of spectrophotometer

design. The molecular biologist" biochemist" geologist or the pathologist" the pharmacist or the

metallurgist - almost any scientist whose discipline involves materials analysis - may feel more

secure in his or her mastery of the mechanics of 02is absorption spectrophotometer with this

introduction to the underlying principles. 3pectrophotometer is used for both ualitative and

uantitative investigations of samples. The wavelength at the ma!imum of the absorption band

will give information about the structure of the molecule or ion and the e!tent of the absorption

is proportional with the amount of the species absorbing the light. 4uantitative measurements are

based on 5eer6s +aw


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(rocedure:

(reliminary (reparations

1) The instrument was turned on so that the light sources warmed up and stabilied. 7e!t

prepared or gathered all of the samples that needed in order to perform the e!periment.

(art 8. 3toc% solution of 9hromium 1**ppm)

1) 1**m+ volumetric flas% was used to prepare a 9r stoc% solution by pipeting .; m+ of

potassium dichromate *.*$mol2+) and diluted it to the mar% with distilled water.

(art 5. (reparation of 9alibration 3olutions of 9r

1) * ml volumetric flas%s was used to prepare five standard solutions with concentration.

$) $.ppm" ppm"


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trendline" thus the solution was diluted and measured the absorbance again. The volumes

used in the dilution were ta%en down.>) 5eer?s +aw was used and the euation of best-fit line was used to determine the

concentration of the un%nown solution. 0n%nown solution has been diluted and

calculated the concentration of the undiluted solution and reported the result. 9learly

labeled the un%nown number and its concentration as well.


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1$. *.1& &*

0n%nown *.&$ &$

A graph of absorbance versus concentration

2 4 6 8 10 12 14

0

0.1

0.2

0.

0.4

0.!

0.6

f"x# $ 0.04x % 0.0

Discussion:

1) The concentration of un%nown when"

yB*.&& of absorbance

*.&&)B *.*&) !

!B


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$) The 5eerC+ambert law relates the absorption of light to the properties of the material

through which the light is traveling. The law states that there is a logarithmic dependence

between the transmission" t" of light through a substance and the product of the absorption

coefficient of the substance" " and the distance the light travels through the material" E.

The absorption coefficient can" in turn" be written as a product of either a molar

absorptive of the absorber" F" and the concentration c of absorbing species in the material"

or an absorption cross section" G" and the number) density 7? of absorbers.&) 5lan% is defined as water that has been used as blan% in this case because water has no

wavelength and thus this ma%es wavelength from ero and able to determine wavelength

of another solution. 8n accurate value for wavelength for another solution can be

obtained by using this method.

) The 0-visible range is a thin part of the total electromagnetic spectrum" and is generally

ta%en to be from wavelengths of 1;* nm at the high energy 0 end to about


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+imitations and error:

1) 8void paralla! error while recording down the results.

$) 8lways rinse the euipment we are going to use with the solution of chromate to avoid

any residue reacting with the solution.&) Irror might occur when the reading was ta%en down due to bubbles in the water.

9onclusion:

,n conclusion" the wavelength color) of ma!imum absorbance" #ma! for a potassium dichromate

solution is from &* to &$ nm and its dar% red. The absorbance is proportion to concentration of

a potassium dichromate solution. The concentration of an un%nown potassium dichromate

solution is &$nm.


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Heferences:

1# &.'. (eller) Real *orl+ ,ualit- -stems) /levelan+) hio)2# http:gltrs.grc.nasa.govreports200232002211!05.p+f# reanor) chemistr- or+ham 7niversit- ress) 2006

Experiment 10 (Chemistry)

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