Lesson 1 PROPERTIES OF HYDROGEN

Transcription

1 Lesson 1 PROPERTIES OF YDROGEN

2 The English chemist enry Cavendish ( ) first isolated pure hydrogen. Because the element produces water when burned in air, the French chemist Lavoisier gave it the name hydrogen, which means "water producer" (Greek: hydro, water; gennao, to produce).

3 ydrogen is one of the most important elements in the world. It is all around us. It is component of water, fats, petroleum, table sugar, ammonia, hydrogen peroxide things essential to life. ydrogen containing compounds can both be ionic and covalent in nature. Examples include acids, bases, and all organic compounds. The sun and other stars are composed largely of hydrogen.

4 Position of ydrogen in Periodic Table lightest element known having atomic number 1. Dihydrogen The position of hydrogen is anomalous in periodic table Alkali metals alogens In modern periodic table it is located in first group.

5 Elemental hydrogen exists at room temperature as a colorless, odorless, tasteless gas composed of diatomic molecules. We can call dihydrogen, but it is more commonly referred to as molecular hydrogen or merely hydrogen. Because is nonpolar and has only two electrons, attractive forces between molecules are extremely weak. As a result, the melting point (-59 C) and boiling point (-53 C) of are very low.

6 Resemblance with alkali metals 1. Electronic configuration Na K 1s s, s, p, 3s s, s, p, 3s, 3p, 4s. Electropositive character +, Na +, K + etc. 3. Oxidation state: +1

7 1. Electronic configuration: Resemblance with halogens Both contain one electron less than the nearest noble gas configuration 1 1 1s near to e 5 9F 1s, s, p near to 8Ne Cl 1s, s, p, 3s, 3p near to Ar. Non-metallic character: Typical non-metals. 3. Atomicity: Diatomic molecules.

8 4. Formation of similar types of compounds alides: CCl 4, SiCl 4, GeCl 4 ydrides: C 4, Si 4, Ge 4 5. Oxidation state: Na Na Cl

9 Isotopes of hydrogen

10 Protium ( 1 ) is the most common isotope, consisting of 99,98% of naturally occurring hydrogen. It is a nucleus containing a single proton. Deuterium ( ) is another an isotope containing a proton and neutron, consisting of only 0,015% of the naturally occurring hydrogen. Commonly indicated with symbol D, D O is called heavy water, which has a higher density, melting point and boiling point than regular water. Tritium ( 3 ) is a radioactive isotope with a 1-year halflife, which is continuously formed in the upper atmosphere due to cosmic rays. Tritium is also used in hydrogen bombs.

11 Methods for commercial production of dihydrogen 1. Electrolysis of water Water is the most common and probably most important compound of hydrogen. ydrogen is liberated when a direct current of electricity is passed through water containing a small amount of an electrically conducting substance such as sulfuric acid, SO 4. The chemical change that occurs is summarized in a chemical equation below: electrolysis O O / O

12 . Reforming with steam of natural gas Large quantities of are produced by reacting methane, C 4 (the principal component of natural gas), with steam at 1100 C. We can view this process as involving the following reactions: C 4 O 3 3. Water gas shift reaction CO When heated to about 1000 C, carbon also reacts with steam to produce a mixture of and CO gases: 673 K FeO3 CO O CO This mixture, known as water gas, is used as an industrial fuel.

13 Laboratory preparation of hydrogen 1. Preparation of hydrogen gas from metals with acids When a small quantity of is needed in the laboratory, it is usually obtained by the reaction between an active metal such as zinc and a dilute strong acid such as Cl or SO 4 : Zn dil. SO4 ZnSO4 Because has an extremely low solubility in water, it can be collected by displacement of water

14 . Preparation of hydrogen gas from active metals Several of the most active metals such as lithium (Li), sodium (Na), potassium (K), rubidium (Rb), cesium (Cs), magnesium (Mg), and calcium (Ca) will react with water to produce hydrogen gas. The net change is summarized in reaction below using the reaction of sodium metal with water as an example. The reaction produces hydrogen gas and sodium hydroxide. Na O NaO

15 Specific test for hydrogen gas The test for hydrogen is a method used to test the presence of hydrogen. This is achieved by inserting a glowing splint into the reaction tube. If it burns with a pop sound, then hydrogen is present. The pop is the sound of a small explosion, hydrogen is highly flammable.

16 Chemical properties of hydrogen ydrogen wanting to give up its single electron causes it to act like an alkali metal: e A half-filled valence shell with one electron also causes hydrogen to act like a halogen because it wants to gain Noble gas configuration by adding an electron : e Chemical properties: Not very reactive due to high bond dissociation energy ( kj mol -1 at 98. K)

17 1. Reaction with alkali metals ydrogen accepts electron from an active metal to form ionic hydrides. By forming an ion with -1 charge, the hydrogen behaves like a halogen. Ex. Li Li lithium hydride K K potassium Ca Ca calcium hydride hydride

18 . Reaction with non-metals ydrogen forms polar covalent bonds with non-metals. (a) Combustion: It burns with pale blue flame O water (b) Reaction with nitrogen directly to produce ammonia gas. This involves high temperature 3 O N N 3 ammonia (c) Reaction with sulfur: when hydrogen is bubbled through molten sulphur, hydrogen sulphide which has a characteristics rotten egg smell is formed: S S hydrogen sulphide

19 3. Reaction with metal oxides: ydrogen is a good reducing agent! ydrogen reduces oxides of less active metals to corresponding metal. CuO Cu O Fe3O 4 4 3Fe 4O

20 Atomic hydrogen (g) 370 K kj ighly reactive. (g) Atomic hydrogen alf life period is 0.3 sec. Nascent hydrogen The hydrogen produced in contact with the substance to be reduced is known as nascent hydrogen. It is very reactive form of hydrogen Better reducing agent than ordinary dehydrogen.

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22 Water. Structure of water 95.7 pm O O O O Gaseous state O Liquid state O O O O O O O O Structure of ice Vacant space

23 ard water Contains dissolved salts of bicarbonates, sulphates and chlorides of calcium and magnesium. ard water does not produce lather with soap solution. Soft water Soft water is free from bicarbonates, sulphates and chlorides of calcium and magnesium. It produce lather with soap solution easily. e.g., distilled water, rain water

24 ydrogen peroxide O ydrogen peroxide is a chemical compound of hydrogen and oxygen with the formula O. Pure, anhydrous hydrogen peroxide is a colorless, syrupy liquid. It blisters the skin and has a metallic taste. Concentrated solutions are unstable, and the pure liquid can explode violently, if heated to a temperature above 100 C. It is soluble in water in all proportions, and the usual commercial forms are a 3% and a 30% aqueous solutions. To retard the decomposition of the peroxide into water and oxygen, it is kept in dark bottles at low temperature.

25 Structure of hydrogen peroxide 95.0 pm 95.8 pm pm pm Gas phase Solid phase Structure of hydrogen peroxide

26 Methods of hydrogen peroxide preparation 1. It can be prepared by the reaction of acid with other peroxides such as those of sodium and barium Na O SO4 NaSO4 O BaO SO4 BaSO4 O Barium sulphate is filtered off leaving behind O.

27 . ydrogen peroxide is manufactured in large amounts by the electrolysis of aqueous solution of 50% SO 4 electrolysis SO 4 SO4 At cathode At Anode e SO4 S O8 e Peroxydisulphuric acid distilled 8 at reduced pressure 4 S O O O SO O distills first leaving behind the SO 4 which is recycled.

28 Chemical properties of hydrogen peroxide 1. Acid Base Properties ydrogen peroxide is a weak acid. It reacts with alkalies and decomposes carbonates. NaO O NaO O Na CO3 O NaO O CO

29 . Oxidation Reduction Properties ydrogen peroxide acts as both an oxidizing and reducing agent. a) In acidic, basic and neutral solutions hydrogen peroxide can act as an oxidizing agent. FeSO4 O SO4 Fe ( SO4 ) 3 O oxidizing agent PbS 4 O PbSO4 4 O oxidizing agent

30 b) At the presence of a stronger oxidizing agent it exhibits reduction properties. KMnO O 4 5 O reducing 3 SO4 KSO4 MnSO4 8 O 5 agent Cl O reducing Cl O agent

31 Uses of hydrogen peroxide 1. For bleaching silk, wool, hair and leather.. It is used medicinally, in the form of 3% aqueous solution, as an antiseptic and throat wash. 3. As rocket fuel. 4. Dilute solution is sold in name perhydrol