Properties Of Solutions (1959)

[Music] Solutions are homogeneous forms of matter containing at least two components but they differ from elements and compounds which we've already studied in that the proportions of the two components may be varied within rather wide limits in this film we're going first to study some factors which influence solubility and which also May influence the rate of solution Solutions consist usually of a liquid solvent and a dispersed substance called the solute which may be either a solid a liquid or a gas sometimes we have solid or gaseous solvents also but these are not of concern to us today now the first important factor which influences solubility of one substance in another is the nature of the solvent and of the solute that we're attempting to dissolve in it it's an old uh rule of chemistry that like dissolves like while there are some exceptions to this uh it will be a good working basis uh for us today this means that a polar solvent is useful in dissolving a polar solute and usually that a non-polar solvent is a good choice for a non-polar solute we're going to illustrate that for you in a few minutes the rate of solution is often affected by the surface of the solute exposed to the solvent and we're going to examine that phenomena and finally the extent of solubility and the rate of solubility are often times influenced by the temperature and this will be Illustrated also we'll first uh study the effect of changing the solvent while keeping the solute constant in each of these test tubes we placed a small quantity of ordinary sugar or sucrose to the tube on the left I'll add a few milliliters of water and to the tube on the right an approximately equal quantity of ethyl alcohol we'll now stir both tubes for a few moments after a few moments we see that the sugar has completely dissolved in the water while the alcohol has not acted as a good solvent for sugar most of the sugar Still Remains on the bottom of the tube sugar then is not very soluble in pure alcohol is it soluble in a mixture of alcohol and water we can easily answer this question by adding some water water to the tube containing the sugar and the alcohol and again stirring for a few moments a few minutes of stirring has been sufficient to cause the sugar to dissolve completely in the mixture of alcohol and water this solvent system is not as good a solvent for sugar though as water is alone it's useful sometimes to have a Sol vent in which the solute is not too soluble such a solvent is useful for purposes of recrystallization for instance and if the uh correct solubility characteristics cannot be found using one solvent alone the chemist often employs mixtures of Two And even three solvents to achieve a system which has the properties he desires sometimes the procedure of mixing solvents can be carried out in the other direction in this test tube we have a small quantity of rosin this material is soluble in alcohol but is not soluble in water I'll add a few milliliters of alcohol to this rosin and stir for a few moments to hasten its solution after a few moments uh the rosin is virtually all dissolved in the alcohol this other tube we have several milliliters of water now notice what happens when we pour the alcohol solution of rosin into the tube of water you notice the Milky appearance of the mixture which is rosin which has been precipitated out of the alcohol when water mixed with the alcohol a few moments ago we saw that fire sugar wouldn't dissolve an alcohol by adding water to the alcohol we caus the sugar to go into solution now here we see the thing in reverse the rosm did dissolve in the alcohol but then when we added the alcohol to water the mixture is not a good solvent for rosin and the rosin is precipitated when a solute is not very soluble in a solvent it's often said to be slightly soluble but this this is a very inaccurate term because even many slightly soluble solutes are much more soluble than others in this test tube we've placed a few grams of calcium sulfate and in this tube some calcium carbonate to each tube We'll add a few milliliters of water and we'll stir the mixtures now I think it's obvious that neither of these materials is very soluble in water they are both then slightly soluble but of the two which is the more soluble in order to determine this we'll wait a few minutes for a solution to take place in so far as it will and then we'll filter both suspension after stirring for a few moments we've permitted the remaining solid in each tube to metal it's obvious that a considerable excess of undissolved material exists in both tubes in order to test the solubilities of these two materials we're now going to filter each solution the calcium sulfate remains on the left and the calcium carbonate on the right after the filtration operation is complete I'm then going to place a few drops of each Solution on a watch glass and evaporate the solution to dryness then we'll examine each watch glass to see if there's a residue on the watch glass on the right we placed five drops of the filtrate from the calcium carbonate uh suspension and evaporated it to dryness you can see that there is a very faint residue here on the watch glass on the left we placed five drops of the filtrate from the calcium sulfate suspension and evaporated to dryness and here we obtained a very noticeable residue from this we conclude that while both calcium sulfate and calcium carbonate are slightly soluble in water calcium sulfate on the left is still much more soluble than calcium carbonate from the residue test which we've just performed it would appear that the filtrate from the calcium sulfate suspension should contain a significant amount of dissolved calcium sulfate we can test this suspicion by treating this solution with a few drops of barium chloride because barium chloride solution reacts with any solution containing a sulfate to give a white precipitate and the immediate formation of this white precipitate with barium chloride confirms our suspicion that a significant amount of calcium sulfate did go into solution when we stirred the calcium sulfate with water we wish next to consider the solubility or lack of it of two liquids in each other when two liquids mix in all proportions they're said to be missible if they do not dissolve in each other they are then IMM missible in the this test tube I placed a few ccs of water and to this we'll add a few drops of glycerol G ol is a rather heavy thick liquid as we add it to the water the glycero sinks to the bottom but by stirring we find that glycerol and water form a solution and we can say that glycerol is missable with water the second test tube also contains water to which We'll add add a quantity of gasoline now in this case the gasoline floats on the surface of the water and even stirring will not cause the two liquids to mix so gasoline and water are imiss now to this test tube we can add a quantity of gasoline and to this gasoline we can add some carbon tetrachloride and we find that the carbon tetrachloride and the gasoline form a nice solution so they are missible now this phenomena occurs because glycerol and water chemically have much in common they both contain o groups water and gasoline chemically are very different because water is a polar solvent and gasoline is is quite non-polar but carbon tetrachloride and gasoline mix nicely because again each of these is a non-polar solvent we will now consider uh the phenomena of extraction this occurs when you have a solute and two emiss solvents and when the solute is much more soluble in one of the solvents than it is in the other in the tube on the left we have a solution of iodine in water and iodine is not very soluble in water it is however highly colored so this solution has a brownish color but it doesn't really contain very much iodine now I'm going to put portions of this iodine solution in each of these two test tubes and to the first tube We'll add some carbon tetrachloride a carbon tetrachloride doesn't mix with water but iodine is much more soluble in carbon tetrachloride than it is in water we remove the tube and Shake we find that the iodine is extracted from the Water by the carbon tetrachloride and gives the carbon tetrachloride a pink color now to this next test tube I'm going to add some potassium iodide solution a potassium iodide reacts with the dissolved iodine in the water the I minus ion from the potassium iodide reacts with the I2 molecule to give an i3 ion and this ion being charged uh is presumably not very soluble in carbon tetrachloride and in fact when we add carbon tetrachloride to this solution and Shake as before we find that the pink color in the carbon tetrachloride layer is noticeable by its absence from this tube then the carbon T was able to extract the iodine because the iodine was much more soluble in the carbon tetrachloride than it was in the water but over here when we've converted the I2 molecule to the I3 ion this ion was more soluble in the water and the carbon tetrachloride was not able to extract it one of the more obvious factors which influences the rate at which a solute dissolves in the solvent is the state of subdivision of the solute I think obviously solution takes place only at the surface of the solute Crystal and the smaller these crystals are uh the more of the solute is at the surface of the Crystal and therefore more of it is in contact with the solvent in these two tubes we've placed in each case crystals of copper sulfate this tube contains rather large crystals while in this tube the crystals have been pulverized and reduced to the form of a very fine powder now to each tube we're going to add 15 mlit of water and then we'll shake both tubes vigorously for a few seconds and then we'll replace both tubes in the clamps after a few minutes you can see that considerable quantities of Crystal still remain in the tube where we started off with large crystals in the first place while in this tube where we started with powdered copper sulfate all of the crystals have disappeared this confirms our suspicion that increasing the surface area of the solute will increase the rate at which it dissolves in this experiment we're going to study the influence of temperature on the solubility of a solid solute in the test tube we placed a few milliliters of lead acetate solution and to this tube I'm going to add four drops of dilute hydrochloric acid now in a few seconds we'll see the the appearance of a white crystallin precipitate lead chloride I think you can see this precipitate forming in the tube now lead chloride is only moderately soluble in cold water and a reasonable quantity of this material will precipitate from the solution in the course of a few seconds now we're going to warm the solution with the burner we'll continue to stir to avoid bumping in the solution I think you can see that the lead chloride is rapidly going into solution at the higher temperature it remains to be seen if we can cause it to reprecipitate by lowering the temperature in this Beaker we have some ice water we'll lower our tube of lead chloride solution into the ice water and once again stir I think perhaps already you can see the formation of some small Crystal of lead chloride in the test tube they're now present in some quantity it's obvious then that the solubility of lead chloride changes quite drastically with the temperature Le chloride is a salt which is very much more soluble in hot water than in cold there are many such salts and in fact it's a rather general property of solid solutes that they are more soluble in warm solvent than they are in cold although this is not an absolutely general rule since there are a few exceptions in this case however lead chloride is behaving normally showing much higher solubility in the warm water than it does in the coal we just seen that some solutes are much more soluble in hot solvent than they are in cold solvents that is their solubility increases as the temperature rises this uh brings us to a consideration of an interesting phenomenon called super saturation in this flask we've placed quite a large amount of the salt sodium acetate and a relatively small amount of water now sodium aetate is much more soluble in hot water than in cold so we heated this FL flas and all of the sodium acetate dissolve at the higher temperature then we very carefully cool the solution down now here we have a situation where there is much more sodium acetate dissolved in this water than can be an equilibrium with solid sodium acetate the solution is super saturated however there is no solid sodium acetate present so equilibrium is not established between the solid and the dissolved solute on the tip of this spatula I've placed a very small crystal of sodium acetate but that small Crystal will be enough so that when added to this flask it brings two phases into presence in the flask the dissolved sodium acetate and the solid sodium acetate and when that happens equilibrium must be established and a great amount of sodium acetate will be crystallized from the solution I'm now add the small Crystal to the solution in the flask so much of the sodium acetate crystallized from the solution that there's scarcely any liquid phase left as we can illustrate by tipping the flask over you can see very small quantity of liquid leaking out of the crystals here the rest of this large mass of material the solid sodium acetate which was present in the original solution in a super saturated condition we'll now proceed to examine the temperature effect which is produced when a very soluble solid dissolves in a liquid in this test tube we've placed 10 mL of water we've inserted in a thermometer in this water and we'll measure its temperature before the solute is added the temperature of the water before we add the ammonium nitrate solute is 38° we're going to use ammonium nitrate as the solute in this experiment because of its high solubility in water I've placed some crystals of ammonium nitrate on this spatula I'll remove the thermometer from the test tube and add the ammonium nitrate to the liquid then we we'll replace the thermometer in the tube and stir temperature is falling quite rapidly it's now down to 20 Mercury is now approaching the 10° Mark and seems to be stopping at about this Point therefore the temperature of this solution has been lowered from 39 to 10° by the heat absorbed by the ammonium nitrate as it went into solution we will now examine the effect of the presence of a nonvolatile solute on the vapor pressure and therefore on the boiling point of the Sol vent in this test tube we placed some water a few boiling stones in the bottom we're heating with the bunson burner we've placed a thermometer in the tube with its bulb dipping into the water and the thermometer now reads exactly 100° Centigrade the boiling point of water now to this tube we're going to add quite a large quantity of Ura as we add the Ura the boiling point uh of the solution should be raised because the presence of the non bottle Ura will lower the vapor pressure of the water I'll now add the Ura which we have on this paper of course the liquid stops boiling now because the cold Ura has uh lowered the temperature of the mixture and we'll replace the thermometer we'll now continue to heat with the burner and see at what temperature the solution now boils we're now heating the solution with the burner the temperature of the solution was lowered by the cold Ura but it's now Rising and as you can see the solution is now boiling at about 104 105 106 degre Centigrade the presence of the nonv Ura has increased the boiling point of the water from its normal 100° temperature to about 107° centigrade in this film we've examined several of the factors which influence solubility and the rate of solution with respect to 01 the nature of the solvent and solute we examine first the solution of sugar and water but found that sugar was insoluble in alcohol next we saw the rosin is soluble in alcohol but insoluble in water thirdly we saw that a solution of iodine in water is such that when carbon tetrachloride is added the iodine being much more soluble than the carbon tetrachloride is extracted by it and passes into the carbon tetrachloride layer We examined two rather insoluble solutes calcium sulfate and calcium carbonate and found that although they are each only slightly soluble it's possible to differentiate between them because calcium sulfate is more soluble than calcium carbonate with respect to liquid liquid mixtures we found that water and glycerin dissolve in each other very nicely that water and gasoline do not but that gasoline and carbon tetrachloride dissolve nicely in each other coming to point two we saw that finally divided copper sulfate dissolves in water very much more rapidly than large lumps of copper sulfate under point three we found we made some lead chlorine we found that it was very much more soluble in hot water than in cold water and we found this solution when cooled caused the lead chloride to reprecipitate and finally we found that the presence of a nonvolatile solute lowered the vapor pressure of its solvent and thereby cause the boiling point of that solvent to increase [Music]