GRADE 9 CHEMISTRY SELINA LESSON 7 HYDROGEN

GRADE 9 CHEMISTRY SELINA LESSON 7 HYDROGEN

1. HYDROGEN

2. THEME: Hydrogen is an important constituent of several compounds. It is found in acids and organic compounds. It acts as a fuel which makes its study useful .

3. INTRODUCTION

4. PREPARATION OF HYDROGEN Electrolysis of water

5. PREPARATION OF HYDROGEN BY THE ACTION OF DILUTE ACIDS ON ACTIVE METALS Metals like magnesium, zinc,iron,etc react with dil.hydrochloric acid to liberate hydrogen gas along with the formation of their respective salts .

6. Laboratory preparation of hydrogen Hydrogen is prepared in the laboratory by the action of dilute hydrochloric acid or dilute sulphuric acid on granulated zinc.

7. Laboratory preparation of hydrogen

8. Precautions Do not collect the first few bubbles of hydrogen gas, since they may contain air too, which is present in the flask and delivery tube. Do not bring any flame near the apparatus, since hydrogen is inflammable. Highlight the points present in the columns in page numbers 90 and 91

9. Metals such as copper, silver and gold which are below hydrogen in the reactivity series, do not displace hydrogen from water or dilute acids.

10. METALS OTHER THAN ZINC ARE NOT USED IN THE LABORATORY PREPARATIONN OF HYDROGEN GAS, BECAUSE, i ) Sodium and potassium react with acid violently. (ii) Calcium and Magnesium are cost effective. (iii) Aluminum forms a protective coating of its oxide because of its high affinity for Oxygen. (iv) Iron has to be heated. Due to this, impurities like hydrogen sulphide and sulphur dioxide gas are produced. (v) Lead cannot be used because it reacts with dilute sulphuric acid or hydrochloric acid to form insoluble sulphate and chloride salts. (vi) Metals like copper, mercury, etc cannot be used as they come below the Hydrogen in the activity series. As, only the metals which are more reactive than the hydrogen itself can displace hydrogen from acids.

11. MANUFACTURE OF HYDROGEN BOSCH PROCESS Hydrogen is prepared on large scale by this process. It takes place within four steps.

12. MANUFACTURE OF HYDROGEN BOSCH PROCESS

13. Properties of hydrogen PHYSICAL PROPERTIES Nature: Hydrogen is a colorless, odourless and tasteless gas. It is non-poisonous in nature. Solubility: Hydrogen is sparingly soluble in water. One litre of water dissolves about 20ml of hydrogen gas at ordinary temperature and pressure. Liquefaction: Hydrogen gas cannot be easily liquefied. Only at -240 degree centigrade and at 20 atmospheric pressure, it liquefies into a colorless liquid. Density: Hydrogen is the lightest of all the gases. Air is 14.4 times heavier than hydrogen.

14. To prove that hydrogen gas is lighter than air

15. CHEMICAL PROPERTIES

16. Reactions of hydrogen with some non-metals

17. Action of hydrogen with nitrogen

18. Action of hydrogen with sulphur

19. Reactions of hydrogen with metals

20. Action of hydrogen as a reducing agent

21. Test for hydrogen

22. Uses of hydrogen 1. Oxyhydrogen flame(2800-3000)degree centigrade is used for cutting and welding of metals. 2.As a fuel: 3. For hydrogenation of vegetable oil: 4. For the manufacture of chemicals 5. As a reducing agent in the extraction of metals: 6 . For meteorological purposes

23. OXIDATION-REDUCTION REACTION

24. REDUCTION AND REDUCING AGENT

25. REDUCING AGENT