Preparation And Properties Of Hydrogen (silent)

[Music] thank you in the modern laboratory hydrogen Like Oxygen is usually obtained from a cylinder containing the gas under high pressure the hydrogen in this cylinder however was probably obtained by the electrolysis of water or sodium chloride solution on the screen you see a picture of a small Laboratory electrolyze the right hand electrode or the cathode is where the hydrogen is being liberated the left hand electrode or anode is where the oxygen is being liberated you can note that the hydrogen is being produced much more rapidly than the oxygen actually just twice as fast the liquid in the electrolyzer is water containing a small amount of sulfuric acid we will now examine the two gases produced in the electrolysis of the water which has been going on in this apparatus this tube contains the oxygen because it's been produced in just about half the quantity of the gas in this tube the hydrogen we've developed a test for oxygen before the going splint test and we'll apply it to the gas in this tube now invert a test tube or the delivery tip here Force the gas up into the tube lightest blend in the burner extinguish it and the glowing splint test is obtained so our suspicion of this gas at oxygen has been confirmed now the other gas should be hydrogen so invert a tube over this delivery tip or some hydrogen up into this test tube now hydrogen Burns so we should expect a small pop when this gas is ignited and that pop is a tank in this experiment then we've demonstrated that the electric current will separate water into oxygen and hydrogen and commercially this reaction is carried out and the hydrogen and oxygen are drawn off and Bottles in cylinders for laboratory use when metals are employed to displace hydrogen from one of its compounds the rate of reaction depends on the activity of the metal and on the availability of replaceable hydrogen in the compound of hydrogen used as a source some metals are sufficiently active to displace hydrogen from water in this Beaker we've placed some distilled water into this water I'm going to add several drops of phenolphthalein solution is an indicator which turns pinkish red in the presence of bases in this bottle we have some sodium I've removed one piece of sodium from the bottle dried off the kerosene which is covering it and place the sodium on this watch plant now we'll drop the sodium into the beaker of water containing Athena failing you should notice that the reaction is very vigorous sodium has become so hot that it's melted we have a little glob of molten sodium floating on the surface of the water hydrogen is being liberated rapidly and sodium hydroxide is the other product of the reaction and is indicated by the pink color in the thin saline solution the reaction between sodium and water was too rapid and violent to be considered a good method for the laboratory preparation of hydrogen other metals react with water more slowly however in this bottle we have metallic calcium a small piece of this calcium is on the table in the beaker we have distilled water containing a few drops of phenolphthalein solution I'll drop the calcium into the speaker and try to persuade it with the stirring Rod to be trapped beneath the bottom of the test tube so if the gas that's produced is bubbling up into the test tube filled with water you'll notice that the water in the beaker is assumed a pink color indicating the presence of a base we'll collect approximately a half a test tube full of the gas and then establish its identity as hydrogen by igniting this should be a sufficient quantity of hydrogen to unlock the calcium from the bottom of the tube move the tube from the beaker permit air to mix with the gas in two then apply the lighted splint test to this gas the sharp bark indicates that when calcium reacts with water the gas produces hydrogen the other product of the reaction is calcium hydroxide which causes the phenolphthaleine to turn red in these test tubes I have placed samples of several different metals zinc iron copper aluminum and magnesium to each tube I will add a few milliliters of dilute hydrochloric acid since these Metals do not react with water at an appreciable rate over each tube I've inverted a larger test tube to collect any gas which might be given off by the reaction we'll now wait for a few moments until a sample of gas has been collected from each reaction we'll now test the gas produced by each reaction to see if it is hydrogen this is a tube in which zinc is reacting with hydrochloric acid obviously hydrogen is formed here this is the tube in which iron is reacting hydrogen again in the center tube copper and hydrochloric acid are in contact but no reaction is taking place and no explosion is obtained copper does not replace hydrogen from hydrochloric acid this is the tube in which the aluminum is reactive hydrogen and this is the tube in which the Magnesium has reacted hydrogen well four of our five Metals then have replaced hydrogen from hydrochloric acid and only one copper has not replaced it this is because copper is below hydrogen in the activity series it's less active as a hydrogen and cannot replace hydrogen from acid on the board you see the equation for several of the reactions which we have just performed the first equation shows the decomposition of water that means an electric current to produce hydrogen and oxygen second equation shows the reaction of sodium metal with water third equation the reaction of calcium with water to produce hydrogen and calcium hydroxide then four of the next five equations are very similar these are the reactions of zinc and iron and aluminum and magnesium with hydrochloric acid to produce in each case a salt of the metal and hydrogen gas and here we have a demonstration that copper metal does not react with hydrochloric acid and does not produce hydrogen in the previous scene we showed that the choice of a metal which will react with an acid is important in the preparation of hydrogen we will now illustrate that the choice of the acid is important also in each of the test tubes I placed a small portion of metallic zinc granulated zinc metal to the first tube I'll add a small portion of hydrochloric acid dilute this is the same reaction that we saw previously hydrogen is produced at a reasonable rate to the second tube I'll add some dilute sulfuric acid hydrogen is produced at a reasonable rate here also to the third tube I'll add some concentrated sulfuric acid the fourth tomb yeah and to the fifth two some concentrated nitric acids you should observe the difference in the reaction rate the first two acids the loot hydrophoric and dilute sulfuric are satisfactory for the preparation of hydrogen from zinc because the reaction proceeds at a nice rate concentrated sulfuric acid is reacting with the zinc very slowly and If We examined the gas that is formed we'd find that it was not hydrogen but instead sulfur dioxide glut acetic acid and zinc will react to liberate hydrogen but as you can see the reaction is very small because acetic acid is a weak acid and few hydrogen ions are available in the solution concentrated nitric acid reacted rapidly with zinc but the product was not hydrogen it wasn't that the brown gas nitrogen dioxide from laboratory preparation standpoint then it would appear that blue Hydrochloric dilute sulfuric acid would be good choices for the preparation of hydrogen while the other three acids would not be good choices in these two test tubes I have placed pieces of Mossy zinc and some distilled water one tube will add a few drops of copper sulfate solution which is of course blue you'll notice that the zinc in this solution darkens this is because metallic copper is being plated out on the surface of the zinc now to each tube We'll add a few drops of concentrated sulfuric acid which will of course be diluted by the water in the tubes and you should notice the very considerable difference in the rate of the reaction of the acid with the zinc there's a good reason for this in this tube the acid reacts with the zinc liberating hydrogen but many thousands of little tiny bubbles of hydrogen stick to the surface of the zinc and prevent further reaction with the acid the zinc in this tube however was copper plated and hydrogen bubbles do not stick very effectively to Copper so in this case the hydrogen immediately leaves the surface of the copper plated tank permitting more acid to penetrate to the zinc and causing a great increase in the rate of reaction if we wish to use sulfuric acid and mossy zinc for the preparation of hydrogen then it's obvious that we should add a small quantity of copper sulfate in order to attain a better rate of reaction we've now prepared a hydrogen generator using the principles that we've developed in preceding experiments in this generator bottle I've placed several pieces of Mossy zinc we then added some distilled water some copper sulfate solution and some concentrated sulfuric acid reaction is proceeding at a convenient rate hydrogen is being produced and is bubbling into the water in the tank since this generator has been in operation for several minutes all of the air has been flushed out of the system the gas that is now being produced is essentially pure hydrogen we'll collect this gas by displacement of water in the trough indicating that it's solubility in water is very low three bottles of gas will be collected in this fashion to compare the density of hydrogen with the density of air we will now open both of these bottles of hydrogen to the air but this bottle we will keep mouth down in this bottle we will turn mouth up on the table we will now wait one minute and then attempt to light the gas in each bottle one minute later we will now apply the glowing splint test to the bottle which has been mouth up and nothing happens we'll now move to the bottle which has been mouth down we obtain of an explosion indicating plenty of hydrogen was still left in this bottle this experiment indicates then that hydrogen is much less dense than air to illustrate another property of hydrogen we will take this last bottle of hydrogen gas and put it on top of a bottle of air the two bottles mouth to mouth with the hydrogen on top and will now permit the bottles to stay in this position for about three minutes three minutes later the bottles remain in their original position you will remember that the hydrogen was originally in the bottle on the top now testing both of these bottles were the burning splint but separately we contain this result an explosion from the top bottle and an explosion from the bottom bottom this means that considerable amount of hydrogen gas must have passed from the Top Model into the bottom bottle even though we saw before that hydrogen is lighter than air this illustrates another property of gases in general and hydrogen in particular called diffusion the molecules of gas are in such rapid motion and the spaces between them are so great that gas molecules mingle with each other quite readily as you saw in this experiment quite a number of hydrogen molecules managed to penetrate down into the bottle of the heavier air we return now to our hydrogen generator which is operating as before with the zinc and sulfuric acid in the bottom of the bottle I've wrapped a towel around the generator as a precaution in case of an explosion the hydrogen is passing up this tube and through this calcium chloride tube which we've inserted in the system and which serves to pick up any spray or any water vapor in the hydrogen and the dried hydrogen gas is now leaving the generator set up through this delivery tube we will now ignite the jet of hydrogen issuing from the end of the tube the Gen of hydrogen is now burning at the end of the two you may not be able to see the flame very clearly but it's definitely there as we can show by having it ignite this wooden splint now over this burning jet of hydrogen I'm going to invert a clean dry beaker I want you to notice how the inside of the beaker becomes fogged with moisture this of course is condensing water vapor which has been formed as the Hydrogen burn we're now going to illustrate another chemical property of hydrogen its activity as a reducing agent in this test tube we've placed a quantity of copper oxide and through the tube we're passing a stream of hydrogen I'll now heat the tube at the higher temperature produced by the burner the copper oxide and the hydrogen will react the products of the reaction will be water and metallic copper copper you can soon tell is present by the color of metallic copper which will begin to appear in the tube I think perhaps you can see some water vapor condensing in the cooler portion of the tube the metallic copper color is now appearing in the area in which we've been heating the copper oxide with the burner several times we tested for the presence of hydrogen by igniting a mixture of the gas and air when hydrogen Burns this is the equation for the reaction the product being water and we saw in one experiment how this water which is produced in the form of vapor may be condensed on the inside of a coal beaker the last experiment involved the reduction of copper oxide with hydrogen with the formation of copper and water in this film then We examined several different methods for the preparation of hydrogen we've made a generator prepared several bottles full of the gas we've examined its density relative to the density of air and we've exhibited several features of its chemical behavior foreign [Music]