Group Leader: Jean Criste T. Cainila August 25, 2009 Group No.3 2, 2009 4ChE-B Marcelo,Ph.D.
Date
Performed:
Date Submitted:
September
Professor: Philipina A.
Experiment 2: Partially Miscible Liquids: Determination Determination of Mutual Solubility Solubility
I. Int Introdu roduct ctiion The objective of the experiment is to determine the solubility of two partially miscible liquids, construct the mutual solubility curve for the pair and determine their critical solution temperature. Miscibility means how completely two or more liquids dissolve in each other. It is a qualitative rather than quantitative observation—miscible, partially miscible, not miscible. Like any other solubility phenomenon, miscibility depends on the forces of attraction between the molecules of the different liquids. The rule of thumb "like dissolves like" means that liquids with similar molecular structures, in particular similar polarity, will likely dissolve in each other. (Polarity means the extent to which partial positive and negative charges appear on a molecule, because of the type and arrangement of its component atoms.) However there are some substances with varying polarity like water which will play a vital issue on how solute will dissolve in it.
Volume vs Solute
The The abov above e diagra diagram m shows shows the solub solubili ility ty trend trend mostly mostly occur occuring ing in solid solid-liq -liqui uid d solutions. The level of concentration of the dissolved solute can be classified as saturated, supersaturated supersaturated and unsaturated unsaturated solution. Saturated solution is attained when the maximum amount of solute a solvent can dissolve dissolve has already been reached. reached. The saturation saturation point of a solution is represented graphically by points along the straight line. On the other hand, unsaturated solutions are those when the maximum amount of solute dissolved is not yet reached by the solvent. The unsaturated region is represented by the lower region of the graph(be graph(below low the line).La line).Lastly, stly, a supersa supersatura turated ted solution solution is attained attained when when the maximum maximum amount of solute is exceeded and precipitation are evident. The supersaturated solution takes the section above the saturation line. This however can be altered depending on the temperature on which dissolving takes place. For solubility depends highly on temperature. For a liquid-liquid solution, it is but normal for components to be immiscible at the moment they are introduced introduced to one another another however however they will be miscible once once stirred or mixed. In some cases some liquiid-liquid solutions can be completely immiscible even if
stirring stirring and mixing and other other alteratio alteration n has already already been been made. made. Liquid Liquid systems systems that that can break up into two liquid phases are the simplest of two-component phase diagrams. Such systems are usually treated at some constant pressure high enough to ensure that no vapor can occur occur in equil equilibr ibrium ium with with the the liquid liquid phase phases s and and over over a rang range e of tempe temperat rature ures s high high enough to ensure that no solid phase appear. The region of the components signifies that there are regions of pure component A and B but there is also a region where in a part of A is dissolved in B and vice-versa. This is now characterized as the partial miscibility of a certain liquid-liquid solution. Such solutions are heated and cooled to attain at constant pressure to attain the complete homogeneity of the solution or complete miscibility. The graph below shows the trend for partially immiscible liquids that are either heated or cooled.
Partial Miscibility Plot
From From the the figure figure above above it is notic noticea eabl ble e that that a peak peak or maxim maximum um tempe tempera ratur ture e is reached by the solution but it the maximum temperature of the solution differs into some extent to the critical temperature of a solution. The critical temperature of a solution marks the point wherein the solution will be completely miscible either if the temperature is lowered or increased. More of critical temperature will be discussed on the latter part of the analysis As been stated ealier miscibility is a solubility phenomenon, thus, it can also be affected by factors which plays an important role in a substance solubility. The factors are as follows: (1) nature of solute/solvent, (2) temperature and (3) pressure. For liquid and solid solution pressure does not affect much of their solubility. Temperature on the other hand will depe depend nd whet whethe herr the the reac reacti tion on resu result lts s to an endo endoth ther ermi mic c or exot exothe herm rmic ic proc proces ess, s, if endothermic the solubility of the solution will increase with an increase in temperature. For an exothermic process, solubility will increase with a decrease in temperature. The nature of solvent and solute also take part in its solubility, such nature involves polarity and molecular size. Polarity was discussed earlier stating that “likes dissolves like”. While larger molecules are less soluble than that of the smaller ones. If the phase rule is applied in this two-phase mixture, two variables are needed to be specified to describe the system completely. The phase rule calculation is shown below. P=c–p+2 =2–2+2 =2 At cons consta tant nt pres pressu sure re,, the the rema remain inin ing g sign signif ific ican antt vari variab able les s are are temp temper erat atur ure e and and composition. The composition is uttered in percent by weight. Usually, both liquids become more soluble as the temperature temperature is increased, increased, and eventually eventually a critical solution temperature is reached above which the two liquids are completely miscible . An upper critical solution temperature temperature will be observable, the highest temperature temperature at which phase separation occurs. On the other hand, some systems show a lower critical solution temperature below which the components mix in all proportions and above which the components form two phases.
II. Method Methodolo ology gy
Prelimina Preliminary ry procedu procedures res were done before before the actual actual experime experiment. nt. The density of phenol was obtained from literature and the amount amount of water required to prepare 5% to 95% phenol at 5% increment, starting with 10 mL phenol in each proportion, was calculated. 95% phenol-5% water by weight mixture was prepared based on 10 mL phenol. The mixture was heated with mild stirring until the cloudiness disappeared, the temperature of which was recorded. The mixture was then cooled with mild stirring until the cloudiness reappeared, the temperature of which was recorded. The process was repeated until fairly constant readings were observed. Water was added to make 90% phenol and 10% water. The procedure was repeated until 55% phenol. For 5% to 50%, 5 mL phenol was initially used.
III.Discussion of Results Different changes were observed and noted in the experiment. After the 95% phenol5% water by weight solution was prepared, the mixture was heated in a water bath with mild stirri stirring ng and and record recorded ed its consta constant nt temp tempera eratu ture re until until the cloud cloudine iness ss of the solut solution ion disappeared disappeared and cooled instantly until the cloudiness cloudiness reappea r eappeared. red. It is observed that the turbidity turbidity,, which which signifie signifies s the partial immiscibility immiscibility of the liquids, liquids, is highly highly depend dependent ent on concent concentratio ration n of mixture mixture and tempera temperature ture.. If the mixture mixture is highly highly concent concentrate rated d to either either water water or phen phenol, ol, after after the mild stirri stirring ng in room room tempe tempera ratur ture e there there woul would d be no visib visible le cloudiness cloudiness observed. It is seen in the 5% and 95% phenol-water phenol-water solution that no cloudiness appeared because both exhibits almost a pure compound. In the 80, 85, and 90% it is noted that that there there was was cloud cloudine iness ss befor before e heati heating ng the mixtur mixture e and and requir required ed a certa certain in heati heating ng temperature temperature to make the mixture miscible. In the cooling process, however, it is observed that no cloudiness reappeared. The reason for this is that just a certain small amount of heat can make the solute and solvent solvent miscible but once once the equilibrium equilibrium is establis established hed,, the mixture is hard to separate into two components. An account to the said results is seen on Table I. Table I: Values of the temperature for each increment
% by Weight Phenol-Water Solution 5 10 15 20 25 30 35 40 45 50 55 60 65
HEATING Temperat ure ( C) No change 40 58 65 66 66 66 66 66 66 64 63 55 º
COOLING Temperat ure ( C) No change 38 56 63 64 65 65 65 66 64 58 58 54 º
70 75 80 85 90 95
45 41 34 30 29 No change
No No No No
42 30 change change change change
The heating and cooling temperatures gradually increase but as it reached a certain constant high temperature, it gradually decreases. It is seen on the 45% mixture that the heating and cooling temperature is the same. It is where, after heating the solution and putting in the ice bath, the cloudiness immediately reappears. The temperature versus percentage by weight phenol mixture was plotted in order to determine the critical solution temperature of the mixture and is seen in Graph 1.
Graph 1 Critical solution temperature is the temperature at which a mixture of two liquids immiscible at ordinary ordinary temperatures, temperatures, cease to separate into two distinct distinct phases. The red line symbolizes the temperature reading of phenol mixture in the hot water bath while the blue line is the temperature reading of phenol mixture in the cold water bath. To clearly see the single and double-phase double-phase regions, the lines were set to polynomial trend line forming smooth curves. The dotted lines represent the temperature at which the cloudiness of the mixture disappeared in the heating step and said to be the state where the mixture is single-phase. The dashed lines represent the temperature at which the cloudiness reappeared in the cooling step and said to be the point in which the mixture began to separate separate and became became double-ph double-phase. ase. It is seen seen in the graph graph that there would be a region region created in the intersection of the dotted and dashed line. This region is a single-phase region in which the phenol and water are miscible. Beyond this region would be a doublephase in which the mixture is said to be partially miscible or immiscible. Critical solution temperature is the temperature which will lead to separation of the mixture into two distinct liquid phases. This is denoted by the intersection of the polynomial trend line of the heating heating and cooling cooling tempera temperature ture.. The critical temperatu temperatures res at which which the lines intersect are 63 C and 66 C. º
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IV.Answers to Questions temperature,, or, 1. Two types of liquid-liquid critical points are the upper critical solution temperature which denotes the warmest point at which cooling will induce phase separation, and the lower critical solution temperature, temperature, which denotes the coolest point at which heating will induce phase separation. Based on Graph 1, the maximum temperature is 66 C and the minimum critical solution temperature is 63 C. º
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2. The The diff diffe erent rent temp temper erat atu ure read readin ings gs have have very very smal smalll diff differ eren ence ces. s. Thus Thus,, the the temperature readings were constant.
I.
3.
The high phenol phenol concent concentrati ration on of percenta percentage ge of phenol phenol-wate -waterr mixture mixture solidifie solidifies s during cooling process mainly because of phenol’s freezing point. At 41˚C, phenol forms into a solid that can be liquefied by a very small amount of water. Thus, a high concentration solution of phenol with water would solidify on lower temperatures.
4.
Given an unknown solution of the components, its concentration will be known by the use of the mutual solubility plot/graph. plot/graph. The composition composition of a layer can be determined by getting the critical solution temperature temperature experimentally and plotting the point on the graph. The weight percentage percentage could be obtained obtained at the point where in the temperature intersects the curve.
Conclusions In this this experi experimen ment, t, it is conclu concluded ded that that the solubili solubility ty of two partiall partially y miscible liquids could be determined by constructing a mutual solubility curve for the pair of liquid liquids. s. Turbi Turbidit dity y of the the mixtu mixture re signif signified ied two-ph two-phase ase mixtur mixture e and and the cloud cloudine iness ss could could disappear and reappear depending on the heating and cooling temperature at which the mixture became one-phase. The heating and cooling temperatures gradually increased but as it reached a certain constant high temperature, it gradually decreased. It is also concluded that in the plot of the mutual solubility curve, a region was enclose enclosed d and signified signified the single-p single-phase hase stage of the mixture. mixture. Beyond Beyond that that region, region, the mixture is of double-phase. double-phase. The intersection of the trend lines for heating and cooling would be the critical solution temperature of the mixture and was found to be approximately 63 C and 66 C. º
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II. Refere Reference nces s ed. ( Oxford [1] Atkins, Peter & De Paula, Julio. Atkins’ Physical Chemistry, 7 th ed. Oxford University Press Inc., New York, 2002.)
[2] Barrow, Gordon M. Physical Chemistry, 6 th ed. (The McGraw-Hill Companies Inc., USA, 1995) pp. 327-330 [3] Daniels, Farrigton and Alberty, Robert. Physical Chemistry, 2 nd ed. (John Wiley & Sons, Inc., USA, 1961) pp. 241-243 [5] http://science.jrank.org/pages/4382/Miscibility.html [4] http://www.citycollegiate.com/chapter3d.htm [6] http://www.sciencebyjones.com/solubility.htm
