Paper Chromatography: Experiment 5

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Paper Chromatography
1.0 Introduction
Experiment 5
Chromatography, which means "the graphing of colors" may be used for the separation of substances by a solvent moving on sheets or strips of a special porous paper. The paper is referred to as the stationary phase, or absorbent. The mixture of solvents used to carry the unknown substance along the paper is called the mobile phase, or solvent system. In practice, a sample of the solution containing the substances to be separated is placed on the paper and then dried. The end of the paper is lowered into the solvent so that the sample is slightly above the liquid surface. s the solvent begins to permeate the paper, capillary action causes it to rise and it transports the sample mixture upward with it. !ach component of the sample mixture is held back by the paper to a different extent. lso, each sample component has a different solubility in the solvent. These two factors combine to cause each component of the sample mixture to travel up the paper at a different rate, resulting in separation of the mixture. "nder the same conditions, the movement of each component of a sample can be characteri#ed by a constant retention factor, Rf . $y definition, %istance from the origin to center of spot &f ' %istance from origin to solvent front where the origin is the point at which the sample was originally placed on the paper and the solvent front is the line representing the farthest distance that the solvent climbs within the paper. The & f value is a characteristic property of a chemical substance. (or this experiment you will separate a mixture of iron)III*, (e +, , copper)II*, Cu-, , and nickel)II*, .i -,, ions from a mixture of their salt solutions. The colors of the ions along with their & f values will be determined by comparing them with spots of separate pure ion solution samples.
2.0 Procedure
E!R "!#E$% &'&&(E" 1) "sing a graduated cylinder and working in a fume hood, prepare the following solvent solution/ 1* m( of acetone and + m( of +, hydrochloric acid )0Cl*. 1our this solvent mixture into the beaker and cover it tightly with plastic wrap. This cover will allow the air within the beaker to saturate with the solvent vapor and help keep the solvent moving through the paper without evaporating. This will aid the chromatographic separation process. 2) 2btain a piece of chromatographic paper and prepare it as follows/ %raw a pencil -not in.) line about 3.4 cm from the long edge of the paper. This line will serve as the origin where you will place your sample spots to start. )5ee (igure 3* lso draw another short 3 cm long line about 6 cm above the origin line. This will serve to help you determine when the chromatographic process is complete.
Experiment 5
/) "sing a different capillary tu0e for each sample )careful not to mix them7* transfer a small drop of each solution listed below to the pencil origin line as shown in (igure 3. pply the six spots evenly along the origin line, but leave a / cm margin from each edge of the paper. fter applying each solution place the capillary tube College of San Mateo Chemistry Dept
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back in the sample bottle and not on the table top77 8ith a pencil, identify each spot by writing on the paper directly beneath the spot. The six solutions are/ 3* (e+, -* Cu-, +* .i-, 9* :ixture of all + ) label ;; * 4* 6* ny one of the unknowns ) label , $, C or % * nother unknown ) again label , $. C or % *
1) %ry the paper under a heat lamp. )2ften this is not necessary if the spots are given a little time and you fan the paper for a moment in the air.* 5) (orm the paper into a cylinder 8IT02"T 2<!&; 11I.= T0! !%=!5 and then fasten the paper with staples as shown in (igure -. +) 1lace the beaker on your desk where it remains undisturbed throughout the chromatographic process. Carefully, lower the paper cylinder into the solvent in the beaker and replace the plastic wrap. )(igure -* The origin must be above the surface of the solvent in the beaker when the process begins. .ow wait as the solvent moves up the paper and be very careful not to move the beaker while the separation is running. >es this means .2T turning the beaker around to see it better as it runs7 2) In this and all remaining steps, when the paper is wet, be sure not to lay it down on a surface that is not clean. 8hen the solvent front has climbed above the short line which was placed 6 cm. above the origin, remove the paper cylinder from the beaker and quickly remove the staples and mark the solvent front line with a pencil. %o this procedure before the solvent front has a chance to evaporate7 3) 8orking in a fume hood, hold the paper sample side down ?ust above a tray which contains a fe4 m( -20 or so) of concentrated 56/-a7) )also called ".0920"* being careful not to dip the paper into the ammonia solution. fter about a minute of exposure, when the spots no longer dark, spray the entire paper with a light mist of dimethylglyoxime to revel the remaining spots. It may be necessary to repeat this procedure if the spots do not develop. *) .ow dry the paper under the heat lamp or by fanning it for a moment. >ou can re@expose the paper to the ammonia if the spots are very faint or fail to develop.
Experiment 5
plastic 4rap
College of San Mateo Chemistry Dept
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Chromatography paper staple + cm line paper
"ample spots
origin solvent
#I&8RE 1 Preparing Chromatography Paper RE"8($" !59 C!(C8(!$I'5":
#I&8RE 2 $a.ing the Chromatogram
2bserve and record on the report sheet the colors of the spots for each known ion. :easure and record in millimeters the distance between the origin and where you marked the progress of the solvent front. ).ote/ If your solvent front was somewhat curved you might have to estimate the best average distance for the solvent front advance.* .ext measure the distance between the origin and the approximate C!.T!& of each sample spot. Calculate the &f values for each of these ions and record it as a decimal fraction with - significant figures. (inally, from all of the information above, determine and indicate by "yes" and "no" in the report table, the ions present in each of the two unknowns. Calculation rea for &f values /
Report "heet
Experiment 5 5!,E;;;;;;;;;;;;;;;;;;;;;;;;;;
%istance between origin and solvent front / AAAAAAAAAAAAA mm
"'(8$I'5" '# <5'
5 I'5" College of San Mateo Chemistry Dept
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"olution 1 2 / 1 Ion #e/= Cu2= 5i2= #e/= Cu2= 5i2= Color 9istance from 'rigin -mm) Rf
"'(8$I'5" '# 85<5'
5 I'5"
Enter >%> or >5> to indicate the presence or a0sence of each ion. Remem0er to record the letter for your un.no4ns. -!? @? C or 9)
"olution 5 +
8n.no4n I.9.
#e/=
Cu2=
5i2=
Report "heet
(a0oratory Auestions
Experiment 5 5!,E;;;;;;;;;;;;;;;;;;;;;;;;;;
3* 8hy should you use an ordinary black pencil, rather than ink or colored pens, for marking the chromatography paper B
-C
-* 8hy should you avoid moving the beaker while the chromatogram is being run B
+* :ake the appropriate measurements )in millimeters* and calculate the & f value for the chromatogram below.
5olvent (ront
"5pot"
2rigin
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College of San Mateo Chemistry Dept

#I&8RE 1 Preparing Chromatography Paper RE"8($" !59 C!(C8(!$I'5":

#I&8RE 2 $a.ing the Chromatogram

%istance between origin and solvent front / AAAAAAAAAAAAA mm

"'(8$I'5" '# <5'

5 I'5" College of San Mateo Chemistry Dept

"'(8$I'5" '# 85<5'

College of San Mateo Chemistry Dept

Intentional @lan. Page

College of San Mateo Chemistry Dept

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