To prepare manganum dioxide (MnO2) sol. To test the chul!e " #ardy rule.
THEORY
The term $colloid% &as first introduced by Thomas 'raham (*) + colloid system consists of a dispersion phase and a dispersion medium. ,f the diameter of the dispersed particles is in a range bet&een 2- + to 2--- + then a colloid is formed. There are eight classes of common colloidal systems. These colloids are made/up of solids li0uid and gases. + colloid formed by the dispersion of a solid in a li0uid is called a sol. ols exhibit se1eral physical properties such as Tyndall effect electrical effect and molecular/collision effect. ,n general sol can be classified into t&o types The terms lyophilic (li0uid/lo1ing) and lyophobic (li0uid/hating) are fre0uently used to describe the tendency of a surface or functional group to become &etted or sol1ated. ,f the li0uid medium is a0ueous the terms hydrophilic and hydrophobic are used. Lyophilic surfaces can be made lyophobic and 1ice 1ersa. 3or example clean glass surfa surface ces s &hic &hichh are hydro hydrophi phili lic c can be made made hydro hydropho phobi bicc by a coat coatin ingg of &ax &ax con1ersely the droplets in a hydrocarbon oil/in/&ater emulsion &hich are hydrophobic can be made hydrophilic by the addition of protein to the emulsion the protein molecules adsorbing on to the droplet surfaces. Lyophilic sol can be prepared by dispersion (normally by 1igorous stirring of a solid in the form of gel or resin in a li0uid) and condensation. condensation. 4uring dispersion solids solids are disintegrated into particles of suitable si!es to form a colloid in a dispersion medium. 4uring condensation ho&e1er molecules or atoms are condensed into clusters 5 particles of suitable si!es to form a colloid. Lyophobic colloids are 1ery sensiti1e to the presence of electrolytes in &hich a small amount of added electrolytes resulted in precipitation. The precipitation of sol by electrolytes can be predicted using chul!e " #ardy rule &hich stated that $The effect of precipitation by a gi1en ion on a (lyophobic) ( lyophobic) dispersed phase of opposite charge increases by the increase of the 1alency of the ion%.
METHODOLOGY Part A: Preparation o !an"an#! $io%i$e& MnO '
< ml of <-= #2O2 > 6- ml of distilled &ater
olution prepared filled into the burette 6- ml of -.-2M 7MnO8 solution introduced into a clean and dry conical flas9 The diluted #2O2 solution added into the -.-2M 7MnO8 solution drop/by/drop &hile s&irling the conical flas9. #2O2 solution added until the color of the 7MnO8 solution turns bro&n. + drop of the bro&n/colored solution ta9en and tested using .-ml of :aCl2 solution. ,f a pin9ish solution is obser1ed some more of #2O2 added into the 7MnO8 solution until a pin9ish solution C+;;OT be further obser1ed.
4O ;OT +44 too much #2O2 to a1oid precipitate formed.
Part B: Verii(ation o t)e *()#+,e - Har$ R#+e.
2 < 8 Clean test tubes labeled
- ml of -.-M ;aCl solution added into test tube number . ml of the same solution and ? ml of distilled &ater added into test tube number 2 and then homogeni!e the solution by s&irling.
ml of the ;aCl solution from the test tube number 2 transferred into the test tube number < and then ? ml of distilled &ater added.
3urther dilution performed on the ;aCl solution in the test tube number 8. ml of the MnO2 sol added into each test tube containing the ;aCl solutions. The test tubes mildly s&irled and in 2 minutes time the one &hich form a precipitate obser1ed. The concentration of the ;aCl solution recorded.
+fter the results obtained further tests performed using ;aCl solutions &ith concentrations lo&er than the lo&est concentration that yielded a precipitate.
@olume of distilled &ater (ml) -.2.2.6 <.< 6.?.?.?.-
Minimum concentrationA -.- M
CALC0LATION Dilution of NaCl solutionA
Fsed the e0uationA M@ M2@2 3rom the e0uation M@ M2@2 (-. M) @ (-.-8 M) (-.- ml) @ 8.- ml @olume of -. M ;aCl solution been used 8.- ml @olume of distilled &ater been used *.- ml o the minimum concentration of ;aCl solution -.-8 M
Obser1ation of precipitate (B 5 D) B D D D D B D D
:y using the same method &e can determine the 1olume of ;aCl (ml) to use for preparing the concentration of ;aCl (M). ) 3or -.- M ;aCl M@ M2@2 (-. M) @ (-.- M) (-.- ml) @ .- ml 2) 3or -.-* M ;aCl M@ M2@2 (-.- M) @ (-.-* M) (-.- ml) @ E.6 ml <) 3or -.-8 M ;aCl M@ M2@2 (-.-* M) @ (-.-8 M) (-.- ml) @ *.E m 8) 3or -.-2 M ;aCl M@ M2@2 (-.-8 M) @ (-.-2 M) (-.- ml) @ 6.- ml 6) 3or -.- M ;aCl M@ M2@2 (-. M) @ (-.- M) (-.- ml) @ .- ml *) 3or -.-- M ;aCl M@ M2@2 (-.- M) @ (-.-- M) (-.- ml) @ .- ml E) 3or -.--- M ;aCl M@ M2@2 (-.-- M) @ (-.--- M) (-.- ml) @ .- ml
Dilution of CaCl 2 solution:
Fsed the e0uationA M@ M2@2 3rom the e0uation M@ M2@2 (-.-- M) @ (-.---8 M) (-.- ml) @ 8.- ml @olume of -.-- M CaCl2 solution been used 8.- ml @olume of distilled &ater been used *.- ml o the minimum concentration of CaCl2 solution -.---8 M :y using the same method &e can determine the 1olume of CaCl 2 (ml) to use for preparing the concentration of CaCl2 (M). ) 3or -.--- M CaCl2 M@ M2@2 (-.-- M) @ (-.--- M) (-.- ml) @ .- ml 2) 3or -.---* M CaCl2 M@ M2@2 (-.--- M) @ (-.---* M) (-.- ml) @ E.6 ml <) 3or -.---8 M CaCl2 M@ M2@2 (-.---* M) @ (-.---8 M) (-.- ml) @ *.E ml
8) 3or -.---2 M CaCl2 M@ M2@2 (-.---8 M) @ (-.---2 M) (-.- ml) @ 6.- ml 6) 3or -.- M CaCl2 M@ M2@2 (-. M) @ (-.- M) (-.- ml) @ .- ml *) 3or -.-- M CaCl2 M@ M2@2
(-.- M) @ (-.-- M) (-.- ml) @ .- ml E) 3or -.--- M CaCl2 M@ M2@2 (-.-- M) @ (-.--- M) (-.- ml) @ .- ml
Dilution of AlCl 3 solution:
Fsed the e0uationA M@ M2@2 3rom the e0uation M@ M2@2 (-. M) @ (-.- M) (-.- ml) @ .- ml @olume of -.-- M +lCl< solution been used .- ml @olume of distilled &ater been used ?.- ml o the minimum concentration of +lCl< solution -.- M :y using the same method &e can determine the 1olume of +lCl< (ml) to use for preparing the concentration of +lCl< (M). ) 3or -.- M +lCl< M@ M2@2 (-. M) @ (-.- M) (-.- ml) @ .- ml 2) 3or -.-* M +lCl< M@ M2@2 (-.- M) @ (-.-* M) (-.- ml) @ E.6 ml <) 3or -.-8 M +lCl< M@ M2@2 (-.-* M) @ (-.-8 M) (-.- ml)
@ *.E ml
8) 3or -.-2 M +lCl< M@ M2@2 (-.-8 M) @ (-.-2 M) (-.- ml) @ 6.- ml 6) 3or -.- M +lCl< M@ M2@2 (-. M) @ (-.- M) (-.- ml) @ .- ml *) 3or -.-- M +lCl< M@ M2@2 (-.- M) @ (-.-- M) (-.- ml) @ .- ml E) 3or -.--- M +lCl< M@ M2@2 (-.-- M) @ (-.--- M) (-.- ml) @ .- ml The minimum concentrations for the salt solution (;aCl CaCl 2 and +lCl<) are needed to precipitate MnO2 sol in 2 minutes. G;aClH A GCaCl2H A G+lCl
DI*C0**ION
Colloid and interface science deals &ith multi/phase systems in &hich one or more phases are dispersed in a continuous phase of different composition or state. Classical colloid science deals &ith dispersions for &hich at least one dimension of a dispersed phase falls &ithin about and --- nm. ,n applied colloid science the upper si!e limit is commonly extended to at least - --- to -- --- nm. ,nterface science deals &ith dispersions in &hich there is an extremely large interfacial area bet&een t&o of the phases. The dispersed phases may be particles droplets or bubbles. Colloidal particles are larger than molecules but too small to be obser1ed directly &ith a microscope ho&e1er their shape and si!e can be determined by electron microscopy. ,n a true solution the particles of dissol1ed substance are of molecular si!e and are thus smaller than colloidal particles in a course mixture the particles are much larger than colloidal particles. +lthough there are no precise boundaries of si!e bet&een the particles in mixtures colloids or solutions colloidal particles are usually on the order of -/E to -/6 cm in si!e. The tendency of colloidal dispersions in a fluid state not to separate is aided by the collisions that the dispersed particles experience from the constantly mo1ing molecules of the Isol1entJ. The erratic mo1ement of colloidally dispersed particles caused by such une1en buffeting is called :ro&nian mo1ement after cottish botanist Kobert :ro&n (EE< " 6). Colloidal dispersions that do e1entually separate are those in &hich the dispersed particles o1er time gro& too large. 1idently to prepare a stable colloidal dispersion &e must not only ma9e the dispersed particles initially small enough but must also 9eep them from oining together. The dispersed particles &ill not coalesce if they carry the same 9ind of electrical charge either all positi1e or all negati1e. ,ons of the opposite charge are in the sol1ent 9eeping the &hole system electrically neutral. ome of the most stable dispersions form &hen the surfaces of their colloidal particles ha1e preferentially attracted ions of ust one 9ind of charge from a dissol1ed salt. The dispersed particles of most sols &hich are colloidal dispersions of solids in a fluid. +lternati1ely dispersions may form &hen extremely large li9e/charged ions such as those of proteins are in1ol1ed. Colloidal dispersions of one li0uid in another are called emulsions. They are often relati1ely stable pro1ided that a third component called an emulsifying agent is also present. ,ts molecules act to gi1e an electrically charged surface to each microdroplet of the oil &hich 9eeps the microdroplets from coalescing. Nater/in/oil emulsions are also possible. 1en &hen a beam of light is focused on a starch dispersion so dilute as to loo9 as clear as &ater the path of the beam is re1ealed by the light scattered to the side. Light scattering by colloidal dispersions is called the Tyndall effect after ohn Tyndall (2- "
?<) a :ritish scientist. olutes in true solutions ho&e1er in1ol1e species too small to scatter light so solutions do not gi1e the Tyndall effect. 3rom the experiment there are some errors that may effects the results. rrors &hile using apparatus such as the measuring cylinder and pipette. 7MnO8 is dar9 in colours that may cause to inaccurate 1alue &hile measuring it. Ne also did not obser1e the changes &ithin 2 minutes. ome of the precipitate formed dissol1e after 2 minutes. Precaution teps . Fse dry an clean conical flas9. 2. +1oid o1ertitration &ith #2O2 to a1oid precipitate form. <. Obser1e the changes occurred &ithin 2 minutes only. 8. Calculate the 1olume using the concentrations.
CONCL0*ION
;aCl Minimum concentrationA -.-8 M CaCl2 Minimum concentrationA -.---8 M +lCl< Minimum concentrationA -.- M The minimum concentrations for the salt solution (;aCl CaCl 2 and +lCl<) are needed to precipitate MnO2 sol in 2 minutes. G;aClH A GCaCl2H A G+lCl
REERENCE*
. Chemistry matter and ,ts Changes
60E*TION*
. 3rom the results of this experiment determine &hether the MnO2 sol is of positi1ely or negati1ely charged. The MnO 2 sol is negati1ely charged because the solution used contains some cation such as Cl / and other anion +l<> Ca2> and ;a>. 2. :y &hat method the MnO2 sol &as prepared 2MnO8/ > 6#2O2 > *#> 2Mn2> > #2O > MnO2/ The MnO 2 sol &as prepared by condensation method. ,t refers to the formation of particles by precipitation reaction chemistry. <. upposed a soluble lyophilic sol &as added into an MnO2 sol prior to the addition of an electrolyte &hat &ould be the effect xplain your ans&er. :y adding electrolyte after lyophilic are added to MnO2. so the precipitation are MnO2 sol as &e expect. Fsing #2O2 <-= lyophilic sol charges positi1e. ,t can not occur bet&een MnO2 sols that are in negati1e charge &ith lyophilic sol that is in charge positi1e. Complete precipitation &ill done during isoelectronic point are reach.
