Refract Ometer

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Refractometry

Aim

The aim of this experiment is to determine the ethanol/water compositions of 3 unknown

samples which are A, B and C provided.

Introduction

In this experiment I am going use a process called refractometr to determine the 3 unknown

samples compositions ! using known sample such as "#$ ethanol / %#$ water &w/'(, 3#$

ethanol / )#$ water &w/'( , *#$ ethanol / *#$ water &w/'( , )#$ ethanol / 3#$ water &w/'(

, %#$ ethanol / "#$ water &w/'( and water, these are m known composition solutions.

The experiment involves a refractometer and water !ath in which !oth will !e switched on

from the start of the experiment. The instrument will !e cali!rated to +*o

C using -Cgrade water in other words pure water. This cali!ration will onl !e re0uired once, unless the

machine is switched off. The known samples which I have mentioned a!ove will all !e

inserted into the instrument. The instrument will then scan the li0uid and give me a refractive

index figure measured in degrees centigrade. I will do each experiment three times and then

work out an average1 this will increase the relia!ilit of m results. I will repeat this

procedure for the unknown samples as well. I will then plot a graph on the axis refractive

index units in degrees centigrade against on the x axis concentration of ethanol and water and

then draw a !est line fit and determine the concentration composition of the unknown

samples using the graph.

Hypothesis to be tested

The hpothesis of this experiment is to determine the ethanol/water composition of 3

unknown samples &A, B and C( provided using an instrument called a refractometer. B

plotting a graph refractive index vs. ethanol/ water this will let me determine the

compositions of the 3 unknown samples.

Experimental Plan

The o!2ectives of the hpothesis will !e achieved ! carring out the refractometer

experiment as accuratel as possi!le. I will tr adding the sample to the prism as accuratel

as possi!le and adding the same amount of drops for each sample I used and ! cleaning the

prism after I have used it. I will use a different pipette for each sample of the concentration of

ethanol and water to avoid contamination and to minimise the error. The graph will !e done

to maximum precision ena!ling me to achieve the accurate results that I want at the end of

the experiment. I will repeat the sample testing 3 times so that I can use the average figure

when I plot m graph. 'hen the instrument is scanning I will wait for the value of the

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refractive index to sta constant and not write down the values while the figures are still !een

calculated.

Apparatus

• 'ater !ath.

• efractometer instrument.

• -Cgrade water.

• Test tu!e filled with known water sample.

• Test tu!e filled with "#$ ethanol / %#$ water &w/'(

• Test tu!e filled with 3#$ ethanol / )#$ water &w/'(

• Test tu!e filled with *#$ ethanol / *#$ water &w/'(

• Test tu!e filled with )#$ ethanol / 3#$ water &w/'(

• Test tu!e filled with %#$ ethanol / "#$ water &w/'(

• 3 unknown samples A, B and C.

• -ipettes

• -aper towel

Labelled diagram for refractometry

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HPLC-grade water

Water bath

Unknown samples

A, B and C

Known 5 samples

onta!n!ng

ethanol"water at

d!##erent

onentrat!on

P!pettes

$e#ratometr% !nstr&ment

Paper towel



Method

". Cali!rate the prism on the automatic refractometer ! using -C water.

+. 4sing a pipette add five drops of -C water to the prism. 5hut the prism lid gentl

and let the instrument scan the water so it is cali!rated.

3. Clean the prism glass ! using the paper towel provided.

6. 7ow using the samples provided such as the first one which is "#$ ethanol / %#$ water

&w/'(, add * drops of this sample using the pipette to the prism ! lifting the prism lid

and placing the drops of sample onto the prism surface. A refractive index value will

appear on the instrument read out screen. Alwas use a fresh, clean pipette for each

sample to prevent an errors caused ! contamination.

*. 8entl lower the prism lid.

9. Allow the refractive index value to sta!ili:e for at least +#3# seconds !efore taking

the reading.

). ;nce the reading is taken the sample can !e removed from the prism ! lifting the

prism lid. 'ipe !oth the prism and the prism lid with a paper towel provided. The

instrument is now read for the next sample. epeat this techni0ue for each sample 3

times and use fresh samples to increase relia!ilit, and use the average at the end of

the experiment to plot the graph and find the unknown compositions.

<. At the end of the experiment ensure that the used pipettes are cleaned and washed.

Hazards

=thanol if drunken in large amounts can cause drowsiness, headaches, nausea etc. =thanol is

an irritant of respirator tracts which !rings a!out the same effects as a!ove. >ou can !e

expose to ethanol if inhaled it is an irritant to the skin ! repeated contact with the chemical.

If ethanol comes into contact with our ees, flush our ees immediatel with water for "*

minutes, and seek medical attention if irritation occurs. If ethanol is accidentl inhaled oringested, go to a place with fresh air, and seek medical attention if anthing unusual appears

'

Pr!sm



or if an smptoms start to appear. Also if ethanol comes into contact with our skin, wash

the place of contact.

=thanol is also highl flamma!le, so if there is a small fire or one that is increasing leave the

scene and call the person in charge to handle the situation.

Precaution and how to minimize the risk

• Alwas wear a la!, coat and safet glasses. ave a pair of heav gloves availa!le.

• Before starting the experiment alwas make sure that the apparatus is clean and

properl set up.

• All accidents such as chemical spillage or !reakages should !e reported immediatel

to the supervisor

• ?o not leave !ags and coats near the gangwas or the !enches

•=ating and drinking is prohi!ited

• 5moking is not allowed

• @now where our escapes are.

In an Emergency for all apparatus

" In the event of a solvent fire !riefl attempt to extinguish the fire with anextinguisher. If the situation worsens immediatel evacuate the la!, close the door,

and seek immediate assistance.

+ In the event of solvent spillage open the windows to aid evaporation. If a spillage isserious, immediatel evacuate the la!, and seek assistance from the la! technician, or

our supervisor.

Results and data

• 5tarting temperature staed constant at +* oC

(ol&t!ons $e#rat!)e!nde* +oC1st sample

$e#rat!)e !nde*

+oC1st sample

$e#rat!)e!nde* +oC1st sample

A)erage2dp+oC

1. ethanol " /. water+ w"W

10''/ 10''/2 10''/1 10'

'. ethanol " . water+ w"W

10'52 10'522 10'52 10'5

5. ethanol " 5. water+ w"W

10'5/3 10'5/4 10'5/4 10'3

. ethanol " '.

water+ w

"W

10'32 10'32 10'32 10'3

/. ethanol " 1. 10'32' 10'322 10'312 10'3



water+ w"W

Water 10''2 10''25 10''23 10''

Unknown sol&t!on A 10'53 10'3 10'32 10'

Unknown sol&t!on B 10'53' 10'532 10'535 10'5

Unknown sol&t!on C 10'31 10'31 10'315 10'3

A graph showing the refractive index &oC( vs. ethanol &$( concentration is drawn, pleasecheck last page.

Calculations

To find out the refractive index for the ethanol/water concentration I had to work outthe average of each sample.

For example for the 30%ethanol/70%water the value calculated was .3!. This was

calculated "# adding up all the three values in the test and dividing it "# three to work

out an average. $g .3!&0 ' .3!&& ' .3!&()/3* .3!

Discussions and interpretation

A refractometer measures the light which is !ent when it is travelling from air into a sample

and this is how the refractive index is measured. ooking at m results it shows that "#$ethanol had a refractive index of ".36, the results increase ! #.#" for the 3#$, and *#$

ethanol compositions, whereas after this the graph !ecomes stationar for *#$, )#$ and

%#$ compositions.

As a result when I cali!rated m results for the unknown concentration of ethanol m

solution A was exactl "#$water/%#$ethanol, solution B was 3#$ethanol/)#$water and

finall solution C was *#$ethanol/*#$water, e.g ".36, ".3* and ".39, m results also

produced no anomalies so I have no reason not to !elieve that the unknown solution were

exactl the same as m first three known concentrations, since the fitted perfectl on m

line of !est fit. There is also an increase in #."after each sample which matches m theor I

also !elieve m results are relia!le since I done the experiment three times for each

composition.

In m opinion I do not think I could have improved m results an more, since the were

ver good, although I do !elieve that there could have !een different since when I read the

reading of the refractometer we had to round up the last digit, so there is a possi!ilit thatrounding errors could have occurred, even though m results are good.

Conclusion and recommendations

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To conclude I !elieve that this experiment went ver well, since I met m aim, which was to

find the concentration of ethanol in three different compositions, even though m experiment

went well I would recommend other people to increase the num!er of decimal places for their

refractive index figures, this is so the have a wider range of data, and hopefull produce

close to perfect results.

Acknoled!ements

• !sher (!ent!#! UK Ltd0+21 67ater!al 8ata (a#et% (heet09:onl!ne;0 A)a!lable

#rom https<""e*tranet0#!sher0o0&k"Asmsds"msds=prod&tCode>?"3"4:Aessed / 7arh 21;

• @reenergy &els L!m!ted0+21 67ater!al 8ata (a#et% (heet09:onl!ne;0

A)a!lable #romhttp<""www0greenerg%0om"prod&ts"7(8("?thanol0pd#:Aessed / 7arh21;

• Hanson 0+2' 6$e#ratometr%09:onl!ne;0 A)a!lable #romhttp<""www20&ps0ed&"#a&lt%"hanson"labtehn!&es"re#ratometr%"!ntro0htm :Aessed 11 7arh 21;

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