Solutions (1959)

[Music] [Applause] 7/10 of the earth's surface is covered by water endlessly moving endlessly wearing away the land the countless streams and rivers also wear away the land as they move carrying tiny fragments Downstream into the sea if we took a sample of seawater it would show us some of this material yet even after the particles have settled a single taste tells us that there is salt in the water the salt which we know was once solid material is now invisible finer than the finest sand or Clays we'll take a little of this water and evaporate it under a heat lamp with the camera speeding the action we see crystals appear crystals of soluble minerals that were dissolved in the water minerals that were in solution in the sea the SE then is really a tremendous solution what kinds of solutions are there and how do we use them to have a working knowledge of solutions we must first learn some definitions we say that a solution has two components the sugar in this case is the solute the sub subance we will dissolve the water is the solvent that is the substance in which the solute is dissolved there are three important characteristics that will help us identify a solution the first characteristic is that solute particles become molecular or ionic in size second solute and solvent particles become and remain uniformly dispersed dispersal is homogeneous a third characteristic is different concentrations of a solution are possible unlike a compound the ratio of constituents may vary let's examine the first point solute particles become molecular or ionic in size into a container suspended in water we introduce soluble crystals of potassium permanganate almost immediately the crystals begin to to dissolve becoming ionic in size in time through the activity of the water molecules the ions are dispersed throughout the solution coloring it uniformly in a solution solute particles being molecular or ionic in size come through the finest types of filters and even through semi-permeable membranes the portion of solution we filtered called the filtrate is the same as the original solution if we divide this quantity of our solution into four exactly equal parts each part contains exactly 1/4 of the solute we originally dissolved and 1/4 of the solvent used if we had taken the same solution and divided it into 10 equal portions each portion would have contained exact 1/10th of both solute and solvent so in a solution solute and solvent particles become and remain uniformly dispersed a third characteristic of a solution is that it may vary in concentration by varying the proportion of solute to solvent here we've added a few crystals of a salt copper sulfate to water making a very dilute solution if we add a large amount of solute Ute we say we have a concentrated solution after it has dissolved and if we keep adding solute until no more will dissolve we have a saturated solution a given solvent does not necessarily dissolve all substances equally solubility varies with different solutes carbon for example a apparently does not dissolve in water careful analysis would show that about one part of carbon dissolves in 10,000 parts of water when solubility is so slight we may say that carbon is insoluble in water if we use calcium hydroxide about 2/10 of a gam dissolves in 100 G of water about one part in 500 at this ratio we say a substance is slightly soluble in this example we dissolve 12 G of sodium sulfate in 100 G of water roughly a ratio of 1 to 10 substances which dissolve in ratios of 1 to 10 up to 1 to3 we call soluble in this final example 110 G of sodium hydroxide dissolved in 100 G of water actually we have used more solute than solvent in such a case we call the substance very soluble solubility also varies with the solvent here we have a solute copper sulfate and three solvents oil petroleum ether and water for example the salt copper sulfate is soluble in water as we saw earlier now instead of water we'll try a different solvent oil copper sulfate is insoluble in oil in our next example using water again as our solvent we will try oil as the solute we see that oil is insoluble in water let's try oil with a different solvent petroleum ether oil is soluble in The Ether the chemical factors influencing solubility are complex but we can remember one general rule usually like dissolves like that is an organic substance like oil is soluble in an organic substance petroleum ether also inorganic substances such as our salt are more likely to dissolve in inorganic solvents such as water again in general like dissolves like physical factors also influence solubility one factor is the particle size of the solute here are two large crystals of the same solute we'll pulverize one crystal using equal amounts of our solvent water we place a whole Crystal into one Beaker and the finely ground Crystal into the other we can see that generally the finer the material the more rapidly it dissolves agitation is a second physical fact factor that increases speed of solution shaking or stirring a solution makes the solute dissolve faster other physical factors influence the degree of solubility generally heating a solution will increase the degree of solubility here we have a saturated solution of copper sulfate at room temperature after heating for a time not only has the excess solute dissolved but we can dissolve even more more solute than would have dissolved at lower temperature temperatures we get similar results with most solutions heating generally increases the degree of solubility of solids in liquids of liquids in liquids and of solids in solids here we are preparing to heat a soft drink which is a solution of a gas carbon dioxide in liquid as the liquid is warmed by room temperature bubbles of gas come out of solution as we heat the solution more bubbles of gas are driven off the solubility is decreased so heating decreases the solubility of a gas in a liquid another physical Factor pressure affects the degree of solubility of gases in liquids this drink is bottled Under Pressure so that more carbon dioxide gas will dissolve in the liquid increased pressure increases Sol ubility we've considered mainly Solutions of solids in liquids such as a salt in water we also saw a gas dissolved in a liquid to make a solution there are other kinds of solutions possible what about a gas dissolved in another gas we can mix chlorine in the flask with bromine Vapor for example as they mix it would be hard to say which is solute and which is solvent but the mixture fits the definition of a solution molecular sized particles uniformly dispersed in proportions we can vary another kind of solution is one we saw before oil dissolved in petrolium ether is a solution of one liquid in another liquid knowledge about Solutions can be useful in many ways that Solutions of an acid and a base when mixed can neutralize each other the exact point at which neutralization takes place depends on the concentration of each solution if the concentration of one solution is known the other can be determined by a procedure called titration with the aid of this accurate equipment an analytical balance and a buet we have prepared a normal solution of sodium hydroxide a base we Define a normal solution as one which contains one equivalent weight of a substance per liter of solution our volumetric flask contains a one normal solution exactly 40 G of sodium hydroxide in exactly 1 liter of solution 1 liter of this one normal base will neutralize one liter of one normal solution of any acid we're going to use this fact to help determine what the concentration is of this solution of hydrochloric acid first we'll fill a volumetric flask with exactly 100 ml of our hydrochloric acid we overfill then use a pipet to bring the level down to exactly 100 m the measured volume of acid is put carefully into a flask now we'll add an indicator methyl red the indicator will change color when neutralization is completed when all this acid has reacted with an equivalent amount of Base into the buet a calibrated tube used to measure milliliters and fractions of milliliters we pour the normal solution of the base sodium hydroxide we overfill and then carefully withdraw some of the base the reading is 1 and 1110th ml which we will note we release our known or standard base solution of sodium hydroxide into our acid of unknown concentration we complete the reaction cautiously drop by drop now the color changed indicates that the process of neutralization is complete now we read the differences in level to find how much base we had to add subtracting our original figure 1 and 1110th from 31 and 1110th We Know It took 30 millit of one normal base or 30 m equivalents then there must have been the same amount that is 30 mil equivalents of acid knowing the exact volume of acid we had it is possible to calculate the concentration of the acid in this case the solution is 3/10 normal this was only a simplified example of the process of titration or reacting amounts of a solution of known concentration with a solution of unknown concentration titration is an important technique in a subject called quantitative analysis which you may someday study titration is one of the many ways we put our knowledge of solutions to work another application of solutions is the use of a solution as a cleanser a solution of carbon tetrachloride for example is a solvent that will dissolve grease and so remove it from the cloth everyday Solutions include antifreeze in your car perfumes of many kinds and many common medicines sometimes we may want to separate one or more substances from several in solution in organic chemistry the process of distillation is often used to separate components of a solution a second useful method of separating Solutions is to crystallize outter solute from solution by heating the solution in the dish we can reduce the quantity of the solvent by evaporation here with the camera speeding the action we see the crystallized solute appearing the process of crystallization is used in many ways the table salt you use may have been crystallized from a salt solution this metal magnesium was produced in this plant from magnesium salts which were crystallized from seawater although Solutions have been used for centuries our in this area of science is still far from complete there is room for continued study and experimentation to increase our understanding of solutions [Music]