Sulfur And Hydrogen Sulfide (1960)

[Music] the element sulfur occurs in several allotropic forms of which at least two are common and well known we are now looking at Crystals of romic sulfur these crystals have been obtained by dissolving a small quantity of sulfur in some carbon disulfide filtering the solution and then permitting the carbon disulfide to evaporate on a watch glass the two or three small crystals in the red Circle illustrate the romic form of sulfur quite clearly the romic crystals of sulfur which you just saw are the stable form at room temperature we can cause another form of crystals to be formed at somewhat higher temperature however in this test tube I've placed several grams of sulfur and have then melted this sulfur over the bunson burner the sulfur is now liquid and at a temperature somewhat above above its melting point we'll now pour this molten sulfur into this funnel we'll then permit the liquid sulfur partially to crystallize and then we'll pour off the still liquid portion and examine the crystals remaining in the funnel the liquid sulfur which we poured into the funnel cooled and solidified but before it had completely solidified we poured out the balance of the still liquid sulfur leaving this mass of sulfur which had crystallized around the edge of the funnel this Mass was then removed from the funnel and broken in half so that you could see the many needlelike crystals of monoclinic sulfur which had formed inside the funnel monoclinic sulfur is the stable form at temperatures above about 95 or 96° and since since the melid sulfur was above this temperature and began to solidify Above This temperature monoclinic crystals were formed if these crystals are permitted to stand at room temperature they slowly change to the romic form which is the stable form below 95° as this change takes place the sulfur remains in the needle likee form but the needles themselves become opaque due to the formation of many thousands of tiny crystals of romic sulfur uh which are formed from the monoclinic suf this form of sulfur then the monoclinic form that you see is only temporarily stable at room temperatures and will eventually change to the romic form it's easily identified however by means of the characteristic needle likee appearance of the crystal the sulfur in this test tube has been heated to a very high temperature in fact the sulfur is now boiling now when sulfur is heated to this high temperature and then rapidly cooled a third form of solid sulfur is formed I'm going to cool this sulfur rapidly by pouring the very hot sulfur into this Beaker of cold water the sulfur that we get by rapidly cooling sulfur near its boiling point has the appearance when chose now see this sulfur is no longer hard but is instead flexible and rather rubbery sulfur in this form is called amorphous sulfur or rubbery sulfur you can see that it has some stretch and the ability to retract C when released after being stretched this is really a super cooled liquid and it will slowly revert to the crystal form which is stable at room temperature the romic form this uh transition takes some time however and won't be complete for quite a number of days at least in the meantime the sulfur will slowly lose the rubbery properties that it has now and will become more and more brittle we turn now to the gas which is formed when hydrogen and sulfur are united hydrogen sulfide we wish to study the laboratory methods for the preparation of this gas and several characteristic reactions of it in each of these test tubes I've placed a small quantity of sodium sulfide solution sodium sulfide is soluble in water and contains a rather High concentration of the sulfide ion to the tube on the left I'm going to add a few milliliters of dilute sulfuric acid you'll notice that a gas bubbles from the solution and when we lower a piece of lead acetate paper into the region above this tube the lead acetate paper turns black this is a test as we have seen previously for the presence of hydrogen sulfide to the middle tube I'll add a few milliliters of dilute hydrochloric acid and the same result is obtained to the third tube we'll add a small quantity of acetic acid and once again the lead acetate paper is darkened this experiment shows then that hydrogen sulfide is a weaker acid than sulfuric or Hydrochloric or acetic acid since these acids liberate it from Solutions of its salt in order to prepare some hydrogen sulfide for further experiments we've set up a small generator in the Erland Meer flask I've placed some iron sulfide ferah sulfide through the thistle tube we'll add some delute hydrochloric acid you can see some bubbles rising in the flask I hen sulfide gas is being produced will pass over and be collected by the upward displacement of air since it's slightly heavier than air we will collect the total of three bottles in this way and then use them for further experiments on hydrogen sulfide the next experiment will test the solubility of hydrogen sulfide in water and in sodium hydroxide solution in this speaker we've placed some sodium hydroxide solution and some water to dilute it and I've added a few drops of phalene to impart a pink color this Beaker contains water we'll place a bottle of hydrogen sulfide in each of the beakers and agitate to bring the gas and the liquid in the beaker in contact you'll notice that the sodium hyd oxide solution rather rapidly rises in the bottle this indicates that hydrogen sulfide is an acid in the other bottle the gas has dissolved to a very limited extent you can see that water has risen into the neck of the bottle but the contrast between this bottle and the sodium hydroxide uh solution is marked from this experiment then we can can conclude that hydrogen sulfide is slightly soluble in water actually its Solutions are about 1/10 normal but that the gas because of its acid character is quite soluble in Solutions which are basic we tested Solutions of sodium sulfide with several different acids and we found that it didn't make any difference whether the acid the source of these hydrogen ions with hydrochloric or sulfuric or acetic acid in any of the three cases the acid was strong enough to cause hydrogen sulfide to be liberated from a solution of sodium sulfide we tested for the hydrogen sulfide using a solution of lead acetate on filter paper lead acetate paper turned black due to the precipitation of lead sulfide we then set up a generator utilizing the reaction between feris sulfide and hydrochloric acid to produce hydrogen sulfide and of course the ferrosi we then tested the solubility of hydrogen sulfide in water and in sodium hydroxide solution we saw that hydrogen sulfide was only slightly soluble in water but that in sodium hydroxide Solutions hydrogen sulfide dissolved rapidly because it reacted with the sodium hydroxide forming sodium sulfide and water one of the bottles of hydrogen sulfide gas gas that we collected from our generator has been placed mouth to mouth with a bottle of oxygen gas the two bottles have been allowed to remain in this position for several minutes we'll now test the reaction of hydrogen sulfide with oxygen by removing the top bottle from the bottom and then attempting to ignite the mixture in both bottles you should notice that the hydrogen sulfide oxygen mixture burned with a flash of blue flame and also that the bottles are now coated with a thin film of sulfur we will explain the appearance of this sulfur when we discuss the equations involved in this reaction a solution of hydrogen sulfide gas and water is called hydrogen sulfide water the liquid in this uh bottle has been prepared by bubbling a steady stream of hydrogen sulfide gas through distilled water this solution is very useful we will illustrate a number of its reactions I've placed a small quantity of this solution in this test tube one of the proper proper of hydrogen sulfide water is its activity as a reducing agent so we'll try it with a number of different oxidizing agents on this spatula I've placed several crystals of iodine We'll add these crystals to the hydrogen sulfide water and Shake you'll notice that the solution rapidly becomes milky in appearance the milkiness is caused by very finely divided free sulfur which is form in the reaction between the iodin and the hydrogen sulfide the other product of the reaction is hydrogen iodide we will now examine the reaction between acidified hydrogen sulfide water and potassium di chromate solution in the test tube we've placed a few milliliters of our hydrogen sulfide water which we've just prepared to this hydrogen sulfide water I'll add a small quantity of dute sulfuric acid we'll now add the pottassium D chromate solution you should notice that the D chromate ion has an orange color you should then observe the color change that takes place as the reaction proceeds first you should notice that the orange color of the potassium D chromate solution has changed to Green this greenish color is characteristic of the chromium 3+ ion you should also notice that the solution has become milky this Milky appearance is due to the presence of millions of tiny particles of Elementary sulfur which have been formed as the hydrogen sulfide was oxidized by the dichromate when we ignited the mixture of hydrogen sulfide and oxygen some of the hydrogen sulfide burned according to this equation yielding sulfur dioxide and water You observe though that this equation requires two volumes of hydrogen sulfide and three volumes of oxygen or a little more oxygen than hydrogen sulfide one and a half times as much now in our reaction we used equal volumes of hydrogen sulfide and oxygen so that not quite enough oxygen was present uh to provide the oxygen necessary for this reaction so some of the hydrogen sulfide burned according to this equation which is the equation for hydrogen sulfide burning in a deficiency of oxygen and this yields sulfur and water this equation accounts for some of the sulfur which we saw deposited on the sides of the bottle later we saw that hydrogen sulfide water reacts with iodine to produce sulfur and solutions containing hydrogen iodide and then we saw that acidified Solutions of a dichromate react with hydrogen sulfide water to produce sulfur and the green chromic ion and water You observe that there are 14 hydrogens present in the seven molecules of water eight of these came from the sulfuric acid which we added and the other six from the hydrogen sulfide this experiment will illustrate the use of hydrogen sulfide water as a precipitating agent now you know that hydrogen sulfide in water is a very weak acid this means that the concentration of sulfide ions in its solution is very low before this very low concentration of sulfide ions can react with a metal ion to form an insoluble sulfide precipitate then the metal sulfide must be very insoluble if the metal sulfide is uh compar ly soluble an insufficient quantity of sulfide ions will be present to cause precipitation in this test tube we place some cadmium sulfate solution in this tube some zinc sulfate and in this tube some nickel sulfate now to each of these tubes I'm going to add a few milliliters of hydrogen sulfide water in the tube on the left you can see the brilliant Gallow precipitate of cadmium sulfide in the tube in the middle the white precipitate of zinc sulfat in the tube containing the nickel ion however no precipitate occurs with hydrogen sulfide water this indicates that cadmium sulfide and zinc sulfide are less soluble sulfides than is nickel since obviously enough sulfide ion was present in these two tubes to cause precipitation all an insufficient quantity was present in this tube now a salt of hydrogen sulfide or hydrosulfuric acid should ionize in the normal way and provide a large concentration of sulfide ion ammonium sulfide is a soluble sulfide salt and to the tube containing the nickel sulfate solution I'll now add a few M of ammonium sulfide and instantly the characteristic black color of nickel sulfide appears when we have enough sulfide ions then as we do an ammonium sulfide solution nickel sulfide is caused to precipitate but remember that this sulfide did not precipitate with hydrogen sulfide water because an inadequate number of sulfide ions was present this experiment tells us us that nickel sulfide is more soluble than cadmium and zinc but we can't tell from this experiment which of these two sulfides is the less soluble and that determination will be the subject of the next experiment in this experiment we will examine uh Solutions of cadmium sulfate and zinc sulfate again to see which of the sulfides of these two metals is the least soluble in this tube I placed some cadmium sulfate solution and in this tube some Zin sulfate to each tube I've added a drop of methyl violet indicator this causes the purple color in the tube a methyl violet is an indicator which is purple in uh solutions that are uh less acid and about 3/10 normal it goes through a greenish color at about 3/10 normal acid and becomes yellow in solutions that are more acid than 310 Norm I'll add a two drops of hydrochloric acid to each tube and stir this produces a bluish green color in this tube and finally the green color and we can produce the same color in the zinc sulfate too the hydrogen iion concentration in these two tubes is now about 310 normal now to each tube We'll add our hydrogen sulfide water as before the cadmium sulfide still precipitate but no precipitate of zinc sulfide is obtained this result is obtained because the presence of the hydrochloric acid has so reduce the ionization of the hydrogen sulfide that very very few sulfide ions are present in the acidified Solutions in fact not enough sulfide ions to cause the precipitation of zinc sulfide cadmium sulfide however is so insoluble that an ample number of sulfide ions is present to cause it to precipitate this experiment indicates then that cadmium sulfide is the most insoluble of the three sulfides that we studied that nickel sulfide is more soluble than cadmium but less soluble than nickel and finally the nickel sulfide is the most soluble of the three hydrogen sulfide ionizes in two steps the first producing HS minus ions and hydrogen ions and then these HS minus ions ions ionized to a very small extent to produce some sulfide ions and some hydrogen ions when hydrogen sulfide is used as a precipitant it's these few sulfide ions uh that are reacting this low concentration of sulfide ions is sufficient as we saw to cause the precipitation of cadmium sulfide and of zinc sulfide so therefore the product of the concentration of the cadmium ion times the sulfide I concentration must be greater than the solubility product constant for cadmium sulfide and the same thing must be true for zinc sulfide since both of these sulfides precipitate however we saw that with the nickel ion hydrogen sulfide did not cause the precipitation of nickel sulfide therefore an insufficient quantity of sulfide ions were present and no nickel sulfide was obtained this in turn must mean that the product of the con ation of the nickel ion and the sulfide ion was less than the viability product constant for nickel sulfide then we studied the reactions of two of these ions cadmium and zinc in 3/10 normal acid solution the acid being hydrochloric acid now in a 310 normal acid solution the hydrogen ion concentration is fairly large therefore the ionization of the HS minus ions is repressed and fewer sulfide ions are present under those circumstances there was still a sufficient quantity of sulfide ion to cause the precipitation of cadmium sulfide however so this concentration of the cadmium ion times the concentration of the sulfide Ion must still have been larger than salability product constant for cadmium sulfide with zinc ion however no precipitate occurred under these conditions so that we can see that the reduced sulfide ion concentration made small by the presence of the acid was in fact so small that its concentration times the zincon concentration was now less than the cabic product constant or zinc sulfa in this film then we've studied some of the crystal forms exhibited by sulfur we've studied the preparation of hydrogen sulfide from Ferris sulfide we've examined some of its chemical and physical properties and its use as an analytical reagent