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WATER AND HYDROGEN


WATER

The uses of water include drinking, washing, cooling, generation of steam to drive turbines and as a solvent. In this subtopic we will study some of the physical and chemical properties of water.Water is very important in Chemistry. Water reacts with both metals and non metals.

SOURCES OF WATER

Water is the most abundant substance on earth. About 70% of the earth surface is covered with water.The sources of water are rain, rivers, lakes,oceans and wells.

LESSON OBJECTIVES

By the end of the lesson you should be able to

a) State the sources of water

b) Describe an experiment to show water is a product of burning organic matter

c) State the products of reactions of cold water and steam with different metals


PRODUCTS OF A BURNING CANDLE

The products of a burning candle can be investigated using the set up below. The candle is lit and the sunction pump is turned on.

Observe the following animation and carefully and note what happens.


The candle burns in air to form a colourless gas that forms a white precipitate with calcium hydroxide solution. The white precipitate is Calcium Carbonate.

The candle also produces vapour which condenses to colourless liquid in the beaker containing ice cold water.


ACTIVITY 1


 


TEST FOR COLOURLESS LIQUID

The colourless liquid can be tested by dividing it into two portions.To the first portion a few drops of the colourless liquid are added to white anhydrous Copper (II) Sulphate. To the second portion, blue Cobalt (II) Chloride paper is immersed. Observe what happens carefully and note the colour changes.

ACTIVITY


CONCLUSION

The change of colour of anhydrous Copper (II) Sulphate and dry cobalt (II) chloride paper indicate that the colourless liquid is water.

Water turns white anhydrous Copper (II) Sulphate blue.

         

The colourless gas produced forms a white precipitate with calcium hydroxide.

The gas is Carbon (IV) Oxide.

From the above observations we can conclude that candle wax is made up of hydrogen and carbon only.

REACTION OF METALS WITH WATER

Some metals react with water.The experiment below investigates the reaction of sodium with cold water. Observe what happens when Sodium metal is immersed into a trough containing cold water.Note the colour of red and blue litmus paper.


Sodium metal melts to a silvery ball, darts on the water surface and gradually becomes smaller as the reaction continues. The solution formed turns red litmus paper blue while the blue litmus remains blue. Therefore, the solution formed is alkaline. Sodium hydroxide and hydrogen gas are formed from this reaction.

Calcium reacts with cold water slowly. Observe what happens carefully

Calcium reacts with cold water to form Calcium hydroxide and hydrogen gas.

The solution is also alkaline because red litmus turns blue and the blue litmus remains blue..

Magnesium reacts with cold water very slowly to produce hydrogen and an alkaline
solution of Magnesium hydroxide.Observe what happens carefully


The red litmus paper turns blue after a few days because the reaction between magnesium and water is very slow.


ACTIVITY


ACTIVITY

 

Potassium, Sodium and Calcium react with cold water forming their hydroxides and hydrogen gas.Sodium reacts vigorously with water. Potassium reacts explosively with cold water. The solutions formed are alkaline.

REACTION OF METALS WITH STEAM

Reaction of Magnesium with steam

Magnesium reacts slowly with cold water however, it reacts vigorously with steam . Observe what happens


The reaction produces Magnesium oxide and Hydrogen gas.

Magnesium oxide dissolves in water to form an alkaline solution of Magnesium hydroxide.

Zinc reacts with steam as shown below. Observe what happens carefully.


Zinc forms a yellow solid when heated in steam which turns white on cooling.

Zinc reacts with steam much more slowly than Magnesium. Zinc Oxide and

Hydrogen gas are formed.


Iron also reacts with steam. Observe the following animation and note what happens.



Red hot Iron reacts with steam to produce tri- iron tetra oxide which is black.

NB: Zinc and Iron do not burn in steam but they glow.

Copper does not react with water.

 

CONCLUSION

Magnesium, zinc and iron react with steam. Magnesium, zinc and iron form their oxides and hydrogen gas. Aluminum is more reactive than zinc and iron but it does not react with steam. This is due to a layer of aluminum oxide which is formed when it is exposed to air.

REACTIVITY SERIES OF METALS

Lead, Copper, Mercury, Silver and gold do not react with either water or steam.

Metals can be arranged in order of their reactivity with water.

HYDROGEN

Hydrogen occurs naturally in combined states such as water acids, organic compounds e.g. petrol, wood, starch, candle wax and proteins.


QUIZ


HYDROGEN GAS

Hydrogen is prepared in the laboratory by the action of a metal on a dilute acid. Hydrogen gas is prepared by adding dilute Sulphuric acid to Zinc granules. Copper (II) Sulphate solution is added to speed up the reaction.. The Hydrogen is collected over water. Observe what happens carefully.


OBJECTIVES

By the end of the lesson you should be able to:-

Prepare hydrogen; investigate its properties and its uses.

Define oxidation and reduction.

Explain reactions of metal oxides with hydrogen in terms of reduction and oxidation.

QUIZ


Zinc granules react with dilute Sulphuric acid to produce hydrogen gas which is collected over water. During the reaction effervescence occurs.

If the gas is required dry it is passed through concentrated sulphuric acid or fused calcium chloride.

PROPERTIES OF HYDROGEN GAS

When a test tube containing hydrogen gas is inverted into a water trough the water level remains the same.This shows that Hydrogen is insoluble in water.



When moist blue and red litmus papers are put in a gas jar containing hydrogen there is no effect on the litmus papers. Therefore, hydrogen gas is neutral..

Hydrogen forms an explosive mixture with oxygen or air and a pop sound is heard. This is the confirmatory test for Hydrogen gas.During the reaction water is formed.Hydrogen is less dense than air as shown below.

BURNING OF HYDROGEN IN AIR

Hydrogen burns readily in air. A stream of pure hydrogen burn in air quietly with a blue flame. The hydrogen gas is ignited and a beaker of cold water is placed over the flame.Note that hydrogen gas should be passed through the apparatus for sometime to displace air before igniting.


A colourless liquid is collected in a beaker. .


The anhydrous Calcium chloride acts as a drying agent.

REACTION OF HYDROGEN WITH METAL OXIDES

Hydrogen gas reacts with some metal oxides. When hydrogen gas is passed through a combustion tube containing a small amount of Copper( II) Oxide which is heated a reaction takes place.


During the reaction, Copper (II) Oxide loses Oxygen. Therefore the Copper (II) Oxide is reduced to copper metal.

Hydrogen gas gains the oxygen,and is therefore oxidized to water.

Copper (II) Oxide is therefore an oxidizing agent while hydrogen gas is a reducing agent.

This reaction is known as a redox reaction because reduction and Oxidation takes place at the same time.

 

REACTION OF HYDROGEN WITH LEAD (II) OXIDE

When the experiment is repeated with lead (II) Oxide yellow Lead (II) changes to red brown on heating. When the reaction is complete, grey lead metal is left in the crucible. Note the colour change in the animation.




Reaction of Hydrogen with Iron (III) Oxide

Iron (III) Oxide can also be reduced by hydrogen gas.





CONCLUSIONS

In these reactions, metal oxides lose oxygen while hydrogen gains oxygen to form water.

The oxides are reduced to metals while hydrogen is oxidized to water.

Oxidation is the addition of oxygen to a substance.

Reduction is the removal of oxygen from a substance.

 

USES OF HYDROGEN GAS

Hydrogen burns in oxygen to produce a very hot flame with a temperature of 3020 degrees centigrade used in welding and cutting metals. This flame is called oxyacetylene flame. Click to play the video to observe how this flame is used.





Margarine
Hydrogen is used in hardening of oils into fats. This is used in the manufacture of margarine.




Rocket




Rocket fuel: Liquid hydrogen is used as a rocket fuel.

 

 

 


Haber process

Manufacture of Ammonia.



Manufacture of Hydrochloric acid


Hydrogen is also used in the Industrial manufacture of hydrochloric acid .




Weather station

In weather baloons due to its low density.

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