EXPERIMENT 4 te Preparation and Properties of Hydrogen l the MATERIALS AND EQUIP

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EXPERIMENT 4 te Preparation and Properties of Hydrogen l the MATERIALS AND EQUIPMENT t mouth to ttles an th a gas bottle b Solids: strips of oopper, magmesium, and zine, steel wool; mossy zine; wood splints. Solutions: dilute (6 M) acetic acid (HC,HO), 0.1 M copperID sulfate (CuSO), dilute (6 M) hydrochloric acid (HCD, dilute (3 M) phosphoric acid (HR.. 9 M sulfuric acid H,SO,) and dilute (3 M sulfuric acid (H SO), phenolphthalein solution. Pneumatic trough five wide-mouth (gas-collecting) bottles, five glass cover plates, pH paper DISCUSSION of oxygen Measure a bottle of nd in air. Hydrogen, having atomie number 1 and atomic mass 1.008 amu, is the simplest element. It is the ninth most abundant element in the earth's crust (about 0.9 percent by mass). At ordi nary temperatures and pressures it is a gas, composed of diatomic molecules, Ha, and is only very slightly soluble in water. Hydrogen is usually found combined with other elements Water is the most common and probably the most important compound of hydrogen. Hydrogen will not support combustion, but in the presence of oxygen it burns readily to form water: the bott on) in the wool first ntial that of air 2 Hdg) + 01g)-. 2 Hro@ This reaction is used as a simple test for hydrogen, for mixtures of hydrogen and air (or oxygen) burn explosively with a distinctive "popping or "barking sound ciden- A. Preparing Hydrogen There are several ways of producing hydrogen gas. The method used in this experiment involves the formation of hydrogen from squeous solutions containing hydrogen ions (H"). The concentration of hydrogen ions in solution is often expressed as pH. pH is a numerical scale corresponding to the acidity of a solution. Pure water at 25'C is neither acidic nor basic and is given a pH of 7 on the pH scale. pH values less than 7 indicate an acidie solution; the lower the number, the more acidic the solution. pH values greater than 7 indicate a basic solu- tion; the larger the number the more basic the solution. ned next o a bonl the light the eye by heat- ab plate pH

Explanation / Answer

5. When hydrogen is burnt in the presence of excess oxygen (present in the atomsphere), they both react to give water which arrives as vapor due to the enormous amount of heat produced. 2H2 + O2 -----> 2H2O.

6. Hydrogen is not a supporter of combustion unlike oxygen and thus does not burn by itself when heated. In the first bottle, the splinter was introduced at the mouth where an interface of atmosphere and hydrogen occurs thus burns rapidly giving a tiny "pop" as enormous heat is produced by this combustion within a very short span of time selectively heating only a very small layer of air surrounding the splint to extreme temperatures. This results in the formation of a transverse wave which travels at speeds greater than that of sound resulting in the pop.

In the second bottle however, the splint is inserted all the way in such that there is no oxygen present around the splint to support the combustion. Here, being exposed to pure hydrogen, the splint is extinguished. Again when its withdrawn to the mouth of the bottle, due to the latent heat of the splint, the hydrogen gas at the mouth starts burning but not so rapidly as the heat produced (by the splint) is an important rate-limiting factor for hydrogen combustion.

7. a) In the third bottle, the splint does not burn rapidly or go out with a pop.

b) Hydrogen gas is much less denser than air. So when the third bottle containing hydrogen was left open for a minute, all the hydrogen escapes out leaving only air inside accounting for the absence of any characteristic burning in the splint introduced.

8. a) The top bottle contains hydrogen gas and thus will make the splint burn explosively.

b) The bottom bottle will contain air which is much more denser than hydrogen and thus will not give any difference in the burning splinter after introduction into the bottle.

c) Owing to the very low density of hydrogen gas compared to air, the hydrogen in the top bottle will tend to remain there while the denser air will be in the bottom bottle thus giving the observations recorded.

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