EXPERIMENT 6: COLLOIDS COLLOIDS CHEMISTRY OBJECTIVE: a) To prepare prepare a ferric hydroxide hydroxide solution b) To study the general properties properties of a ferric hydroxide hydroxide solution, starch solution and some true solutions. INTRODUCTION A colloid is a dispersion of particles of one substance (the disperse phase) thr through oughou outt a disp disper ersi sion on mediu edium m made ade of anot anothe herr su subs bsta tanc nce. e. The The distributed substance is the disperse phase and the continuous substance is the dispersion medium. In colloidal solution, particles are dispersed or sprread sp ead thr through oughou outt the the disp disper ersi sion on su such ch as wate waterr. The The size size of coll colloi oid d partic particles les is inter intermed mediat iate e betwee between n the coarse coarse sus suspen pensio sion n and ordin ordinary ary soluti solution. on. There Therefor fore, e, colloi colloids ds are are somewh somewher ere e betwee between n a homoge homogenou nous s solution and heterogeneous mixture. The size of particles is small where random collisions keep them dispersed throughout throughout the dispersion medium and neither sinks to the bottom nor dissoles the solent. The particles of a course suspension can be seen under a microscope and will settle under the action of graity. The particles of a colloidal solution are not isible under a microscope but can be detected under an electron micro microsco scope. pe. These These parti particle cles s of a colloi colloidal dal soluti solution on may may be ery ery large large single molecules or aggregates of small molecules, atoms or ions. APPARATUS !. %. $. &. '. . . +. .
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CHEMICALS !. %. $. &. '. . .
:
:
0olid hydrat hydrated ed iron iron (III) (III) chloride, chloride, e/l e/l$ 1eio 1eioni nize zed d wat water er '2 sta starrch solu soluti tion on !2 sug sugar ar sol solut utio ion n %2 sug sugar ar sol solut utio ion n 0odium 0odium chlor chloride ide solution solution (3.! 4) 5otassium 5otassium chromate chromate solution6 potassium dichromate solution
+. ehling solution . *exacyanoferum (II) solution !3. 1ilute iodine solution !!. 0iler nitrate solution !%. 0odium phosphate solution (3.!4) !$. 0odium sulphate solution (3.!4)
PROCEDURE
a) 5reparation of ferric hydroxide solution 7as already prepared by the lab assistant b) Tyndall e8ect !. ie !33 cm$ of dry beakers was cleaned and labelled with A, ", /, 1 and 9. %. 9ach beaker was -lled with about %6$ full with the following solutions: "eaker A: !2 starch solution "eaker ": 3.3!2 starch solution "eaker /: ferric hydroxide prepared in 5art A "eaker 1: %2 sugar solution "eaker 9: potassium chromate solution (; %/r<&) $. The Tyndall e8ect of each solution was obsered by using narrow beam of light from laser pointer. The obseration was recorded. c) 1ialysis !. ie tests tube was dried and cleaned and then was -lled with ' cm$ of the following solutions: Test tube A: '2 starch solution Test tube ": sodium chloride solution 3.% 4 Test tube /: ferric hydroxide solution Test tube 1: %2 sugar solution Test tube 9: potassium chromate solution (; %/r<&) %. The mouth of all the test tubes was wrapped with pre=soak cellophane membrane and fastened tightly by using thread. The cellophane membrane was soaked in deionized water for at least %& hour before the experiment was conducted. $. The tests tubes were then inerted and dip in di8erent small beakers containing deionized water, clamped and leaed for ! hour.
The water leel in the beaker was make sure to always lower than the leel of the solutions in test tubes. &. $ cm$ of the deionized water in each beakers was then tested with a few drops of the following reagents after ! hour dialysis: 0tarch solution: dilute iodine solution /hloride solution: siler nitrate solution e$> ions solution: hexacyanoferum (II) solution 0ugar solution: ehling solution /hromate ion solution: ethanol solution '. ?ecord all the obserations. 1. 0tability of sol A !. $ test tubes were cleaned and dried. %. All the test tubes was -lled with ' cm$ of sol A and labelled with test tube !,% and $. $. % drops of an electrolyte was then added to each of the test tubes according to the table below: Test tube No. Tye o! e"e#t$o"yte %&&e& ! 0odium chloride, @a/l % 0odium sulphate, @a%0<& $ 0odium phosphate, @a$5<& &. After the addition of the electrolyte, the test tubes were shake and leaed to stand for a few minutes. The obseration was made from time to time for any changes that may take place in the solutions.
RESULTS
b. Tyndall e8ect Obse$'%t(o)s "eaker A "eaker "
5ositie light can be seen passing through the cloudy white solution scattered 5ositie light can be seen passing through the cloudy white solution scattered
"eaker /
@egatie, light passes through without scattering
"eaker 1
@egatie, light passes through without scattering
"eaker 9
@egatie, light passes through without scattering
c. 1ialysis Obse$'%t(o)s Test tube A Test tube " Test tube / Test tube 1 Test tube 9
The solutions turn from colourless to yellow solution The colourless solutions turns cloudy @o physical change The solution turns from colourless to light blue @o physical change
d. 0tability of sol A Obse$'%t(o)s Test tube !
/lear solution
Test tube %
Bittle amount of precipitate was present
Test tube $
*igher amount of precipitate present
DISCUSSION
rom the experiment, the Tyndall e8ect, dialysis and stability of sol A was obsered. Tyndall e8ect exists only in systems that are colloidal. The colloidal particles that are suspended or dispersed in the system are responsible for the scattering of the light. 7hen a beam of light passes through a colloidal solution, the path of the light beam can be seen as a cone of light when obsere at right angle. The particles in colloidal solution are large enough to scatter isible light, with some of the light being re#ected in a direction perpendicular to the original beam path. The Tyndall e8ect can also be used to di8erentiate between a colloid and true solution. Through the experiment, only beaker A (!2 starch solution) and beaker " (3.3!2 starch solution) show positie result where the light was scattered. 7hile beaker / (ferric hydroxide), beaker 1 (%2 sugar solution), and beaker 9 (potassium chromate solution) show negatie e8ect where the light passes the solution without scattering.
*UESTIONS
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A true solution is a homogeneous mixture of two or more components. The dissoling agent is the solent. The substance which is dissoled is the solute. The components of a solution are atoms, ions, or molecules, which makes them !3= m or smaller in diameter. The example of a true solution is sugar and water. "esides that, the particles in suspensions are larger than those found in solutions. /omponents of a suspension can be eenly distributed by a mechanical means, like by shaking the contents, but the components will settle out. The example of suspensions is oil and water. 7hile, colloid are particles intermediate in size between those found in solutions and suspensions can be mixed such that they remain eenly distributed without settling out. These particles range in size from !3=+ to !3= m in size and are termed colloidal particles or colloids. The mixture they form is called a colloidal dispersion. A colloidal dispersion consists of colloids in a dispersing medium. The example of colloid is milk.
3. ,-%t %$e 4e"s %)& t-e($ tyes5 o$ &(1e$e)t tye o! 4e"s e"%() t-e($ &(1e$e)#es o) &e-y&$%t(o) %)& so%7()4 $oe$t(es. Cels are the colloidal system constituting the liDuid as the dispersed phase and the solid as the dispersion medium. There are some sols that hae a high concentration of dispersed solid and change spontaneously into semi solid form on cooling. The types of gels are elastic and non=elastic gels. 9lastic gels are those gels which possess the property of elasticity they change to
solid mass on dehydration which can again be conerted into gel by addition of water followed by heating and cooling. 7hen they are placed in contact with water they absorb water and swell. This property is known as imbibitions. 9xamples of elastic gels are gelatin, agar, starch and etc.
7hile, non=elastic gels are those gels which do not possess the property of elasticity, they change to solid mass on dehydration which becomes rigid and cannot be conerted into the original form by heating with water. They do not show the phenomenon of imbibitions. The example of these gels is silicic acid. The di8erence between dehydration and soaking properties are dehydration is elastic gel leads to formation of elastic solid from which the original sols can be regenerated by addition of water. 1ehydration of non=elastic gels leads to the formation of glass powder. 7hile, soaking properties is ability to take water where elastic gel may take up water and swells, water is imbibed into the gel and that is called imbibition process. @on=elastic gels do not swell the liDuid enter the pores of the gel but it do not swell because of wall is rigid, therefore the olume of the gel does not change. 8. ,-%t 7()& o! ()!o$/%t(o) #%) be obt%()e& !$o/ "(4-t s#%tte$()4 ee$(/e)t () #o""o(&%" %$t(#"es () %9ueous so"ut(o)s5 E"%() you$ %)s2e$. 7hen light passes through a medium that contain no particles larger than about !3= m in diameter, the path of the light cannot be detected and the medium is said to be optically clear. 7hen, colloidal particle is present, some of the light is scattered and the incident beam passed through weakened intensity. The scattering is called Tyndall e8ect. 7hile, the path of the light through the medium, made isible as a result of scattering known as Tyndall beam. 0unbeam is example of Tyndall beam when light is scattered by -ne dust particles. Analysis of the scattering as a function of the angles proides aluable information about the sizes and shapes of colloidal particles. 7hen these are singles macromolecules, the techniDue is therefore useful in determining molar mass.
CONCLUSION In conclusion, the general properties of a ferric hydroxide solution, starch solution and some true solutions was determined and identi-ed.
REERENCE Aniruddha ?., (%3!3), 0urface and /olloid /hemistry 5rinciples and Applications, ?etrieed from 1ecember !3, %3!& from https:66www.scribd.com6doc6''&$&%60urface=and= /olloid=/hemistry= 5rinciples=and=Applications A. 4. *elmenstine, (%3!&), 0olutions, 0uspensions, /olloids, 1ispersions, ?etrieed !! 1ecember, (%3!&) from http:66chemistry.about.com6od6lecturenotesl$6a6colloids.htm
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4. /. 1izon, T. C. 4aglasang, Clenn 4. T., (%33), /olloids, ?etrieed from @oember %$, %3!& from https:66www.scribd.com6doc6'3!'+69xperiment='=!
