Acids Bases And Salts (1959)

[Music] my these three common household items represent three kinds of chemical compounds with which you will be continually concerned in your study of chemistry acids bases and salts vinegar is an acid household ammonia is a base table salt sodium chloride is one of a large number of compounds called salts what are acids bases and salts what are the relationships between them and why do they react as they do in answering these questions we will discuss briefly three of the theories that scientists have spent years in developing the classical theory of acids bases and salts which we still use in expanded form today was proposed by svante arrhenius in 1887 arrhenius knew that pure water was a poor conductor of electricity yet when certain substances were dissolved in water these liquid solutions would conduct an electric current why arenas proposed this explanation when molecules of certain substances dissolve in solution they dissociate or separate into smaller charged particles or ions which carry the current according to arrhenius theory a molecule in solution would dissociate into positive and negative ions which would be attracted to oppositely charged poles another diagram will illustrate what would happen when the current is turned on positive ions near the positive electrode will be slightly repelled from it negative ions will be attracted to it and will give up their electrons at the same time negative ions are being repelled from the negative electrode and positive ions are being attracted to it the arrhenius theory offered one explanation for the behavior of electrolytes acids bases and salts in the classical arrhenius definition a substance such as sodium hydroxide which dissociates in water to yield o h or hydroxyl ions is a base a substance such as hydrogen chloride that dissociates in water to yield hydrogen ions is an acid arrhenius believed that the hydrogen ion could exist free in solution later work indicated that this ion exists in water solution only as a hydrated hydrogen ion the hydronium ion the hydronium ion is a water molecule with attached proton it is a hydrated proton the hydrogen ion or proton is often written this way the hydronium explained why hydrogen chloride doesn't conduct electricity until it is dissolved in water and the dissociated hydronium ion and the chloride ion form concept helps explain the reaction between ammonium hydroxide and hydrochloric acid which we can express like this legislated substance water is formed this is an example of the expanded arrhenius theory which is still to introduce students to acid-base reactions in 1923 bronstead and lowry organized and enlarged the newer concepts using a definition based on the hydrogen ion or proton they define an acid as a substance which dissociates to furnish protons a proton donor a base then becomes a substance which accepts protons a proton acceptor in this concept ammonia gas can be considered a base as it will accept a proton to become an ammonium ion the electronic structure of ammonia gas shows an unshared pair of electrons in 1923 physical evidence led an american chemist gilbert n lewis to believe that a proton from an acid readily becomes attached to this unshared pair of electrons in some other molecule an acid then becomes a substance which accepts an unshared pair of electrons both the lewis and the bronsted-lowry theories explain acid-base reactions in systems other than the aqueous solution system of arrhenius of the three theories we've seen explaining acid-base reactions we'll use the arrhenius classical theory remembering that others do exist how can we tell that a solution we have is an acid the liquids in these beakers all appear to be identical colorless water clear yet one is an acid the others are not long ago chemists discovered that certain substances which we call indicators show color changes when treated with an acid litmus paper and methyl red are common indicators first we'll test these liquids with blue litmus paper this one containing acid turns the litmus paper from blue to red indicating the presence of an acid here are five more liquids this time we'll test with methyl red the middle beaker containing acid changes our indicator from yellow to red indicators by their color change indicate the presence of acids what are some of the properties of acids in aqueous solution first most common acids mix completely with water at room temperature here we are adding nitric acid to water stirring as we add acid and water form a true solution remember this important point in safe laboratory technique always add acid to water never the reverse always add acid to water it's a good safety practice a second property of acids in aqueous solution is that they conduct electricity the distilled water in this beaker is really a poor conductor of electricity but as soon as we add a little acid the bulb lights and the conductivity of the solution is evident another property of acids is that in the water system all acids contain hydrogen this can be shown by their reaction with common metals to this dilute solution of hydrochloric acid we'll add some bits of metal zinc as the zinc reacts with the acid bubbles of hydrogen are given off a further property of acids is that acids react with bases to form salts and water we'll discuss more of this property a little later how do we make an acid one way is to add the anhydride of the acid to water this anhydride is phosphoric pentoxide in water it forms phosphoric acid here we are preparing an acid by using a gas nitrogen dioxide passing nitrogen dioxide into water allows it to react with water to form nitric acid the indicator methyl red gives us the reddish color indicating an acid the acid we have made nitric acid is very important commercially another way to prepare an acid is to react the proper salt with concentrated sulfuric acid here we are adding concentrated sulfuric acid to ordinary table salt sodium chloride in the reaction the products are sodium hydrogen sulfate and gaseous hydrogen chloride which we are collecting in the jar of water to form hydrochloric acid methyl red in the solution gives us the usual acid reaction red this acid hydrochloric acid is also commercially useful these metal parts are being cleaned in an acid solution to prepare them for electroplating industries today could not exist without the water solutions we call acids equally important to us is another kind of solution a base here again we have liquids that appear to be identical but this time one of them is a base as with acids we can identify a base by its reaction upon indicators two common indicators are litmus paper which we use earlier with an acid and phenolphthalein first we'll try litmus there is no change in the litmus paper in these beakers but this solution turns red litmus paper blue showing that it is a base this time using colorless phenolphthalein we'll test for a base among five other solutions notice that the solution in the second beaker has turned pink this is one of the standard ways to identify a base earlier we said that acids react on bases to form salts and water but the reverse is equally true bases also react on acids to form salts and water this is a property of bases a second property of bases is that they too like acids conduct electricity watch the light bulb as we add a base to the water bases are electrolytes another characteristic of a base is that it feels slippery or soapy to the touch actually a tiny amount of fat from the skin has been changed by the base into soap be sure to rinse and wash your hands carefully after handling a solution such as a base or any other chemical all bases according to arrhenius theory contain in their formulas the hydroxyl ion o h minus notice that these bases contain an active metal sodium magnesium potassium calcium the modern definition of bases includes compounds such as ammonium hydroxide which does not contain a metal and methyl amine which contains neither a metal nor the o h ion in this simple preparation of a base we'll add sodium a very active metal to water first we'll add a few drops of phenolphthalein to the water there's no color change next we carefully add a small bit of sodium metal in this reaction the sodium and water combine to form sodium hydroxide a base while hydrogen is given off the phenolphthalein turns pink as the sodium hydroxide forms this is the usual indication of a base bases are useful to us in many ways for example the solution commonly called ammonium hydroxide a base is the household ammonia we use it emulsifies the greasy matter in which dirt adheres to our household things among the properties of acids and bases we mentioned earlier that they react to form salts and water in this case where we are using a dilute acid and base no visible reaction occurs if we add phenolphthalein it does not indicate a base evidently the base was changed by the acid or we can also say that the acid changed the base if each kind of compound loses its characteristic qualities in their interaction they can be said to have neutralized each other we can use the term neutralization to indicate another property that results from the interaction of any acid with a base when an acid reacts with a base hydronium ions of the acid combine with the hydroxyl ions of the base the resulting products are an ionized salt and water neither the original acid nor the base exists in the solution any longer they have neutralized each other another way to express this is to say that an acid and a base react together to form a salt and water so there is a direct relationship between acids and bases and the third kind of compound we are studying salts a simple definition is a salt is a compound other than water that results from the action of an acid and a base in aqueous solution since acids and bases are usually such active compounds we rarely find them free in nature we do however find enormous quantities of salts in nature the sea contains great quantities of various salts these chalk clips contain carbonates sulfates and other salt compounds what are some of the important properties of salts one property is that many salts such as sodium chloride are very soluble in water they dissolve readily like acids and bases many dissolved salts are electrolytes excellent conductors of electricity when we test a salt solution its conductivity is obvious in water the ions of the salt separate and the freed ions in solution conduct electricity another important property of salts is their effect on the boiling and freezing points of water here we have boiling water a boiling sugar solution and a boiling salt solution the sugar and salt solutions are of equal molecular concentrations the beaker of water boils at 100 degrees centigrade which is normal in this location in this speaker the sugar has raised the boiling point of water to more than 100 degrees centigrade however in this salt solution a salt calcium chloride has raised the boiling point of water even higher than the sugar solution the chemist calls this an abnormally high boiling point rise a salt added to water also lowers the freezing point abnormally in this comparison we can see that the water in this beaker is freezing at zero degrees centigrade normal freezing point sugar in this water has appreciably lowered the freezing point below zero degrees but salt in this water lowers the freezing point abnormally that is below the sugar solution how do we prepare a salt we've already seen that one way to prepare a salt is by the neutralization of an acid and a base but we can also prepare salts directly from their components they're metal and non-metal groups for example we'll make a mixture of this finely divided copper metal and powdered sulfur now we heat the mixture the reddish copper and the bright yellow sulfur react to form a new substance assault this black substance is the salt copper sulfide a salt can also be prepared from another and different salt earlier you remember we made hydrochloric acid by reacting sulfuric acid with sodium chloride again we have sodium chloride in concentrated sulfuric acid our products are hydrogen chloride gas and sodium hydrogen sulfate a salt different from the sodium chloride we began with sodium chloride is used in the preparation of many salts acids and bases sodium chloride is also our table salt a useful flavoring for food and vitally necessary to our diets our household sugar is processed by the use of an acid hydrochloric acid as is the gelatin in desserts and other foods lye is an impure form of a base sodium hydroxide it reacts with a grease in a sink to form soap which can be washed through the drain the mortar in which bricks are set is made in part from another base calcium hydroxide or slate lime spreading assault on ice lowers the freezing point helps to melt the ice we constantly use the properties of acids bases and salts in many ways when we take milk of magnesia to counteract stomach acidity we are using a base magnesium hydroxide an acid hydrofluoric acid is used to etch glass the glass bottles and other glass equipment you use in your chemistry lab may have been treated by hydrofluoric acid to etch the numerals into the glass among the many acids we use sulfuric acid is one of the most important the storage battery in your car contains a solution of about 40 of sulfuric acid the uses of sulfuric acid both in industry and in the lab are numerous it has been said that the amount of sulfuric acid a nation produces is one index of its prosperity but perhaps we can expand this statement and say that a nation's industrial position is related to the volume of its production of acids bases and salts [Music] you