Self Learning Material

Submitted by –

Meenu kumari

14162051

B.Ed Program 2014-15

PREPARATION OF GASES

There are many gases in air, such as Oxygen, Carbon dioxide, Hydrogen, Nitrogen etc. All these are very important for living beings.The atmosphere of earth is a layer of gases surrounding the planet Earth that is retained by Earth’s gravity. Air is mainly composed of nitrogen, oxygen and argon.

OXYGEN

Oxygen occurs in the free state as a gas, to the extent of 21 percent by volume or 23 percent by weight in the atmosphere.

Combined oxygen also occurs

1. in water

2. in vegetable and animal tissues,

3. in nearly all rocks and

4. in many minerals

Oxygen occurs to a larger extent in the earth’s crust than any other element.

PREPARATION

The most convenient method for preparing oxygen in the laboratory involves either the catalytic decomposition of solid potassium chlorate or the catalytic decomposition of hydrogen peroxide.

1. Preparation of oxygen using potassium chlorate

Potassium chlorate decomposes at a low temperature if previously mixed with magnesium dioxide which is a catalyst for the decomposition. Only the potassium chlorate is decomposed and no perchlorate formed.

2KClO3 ===> 2 KCl + 3 O2

2. Preparation of oxygen using Potassium permanganate (KMnO4)

Potassium permanganate which is a purple crystalline solid, decomposed without fusing on heating to 240 degC, producing crackling sound forming a black powder consisting of a mixture of potassium mangnate and manganese dioxide and releasing oxygen.

KMnO4 ===> K2MnO4 + MnO2 + O2

Potassium potassium Manganese Oxygen

Permanganate mangnate dioxide

Physical Properties

Oxygen is colorless,odourless and tasteless. It is sparingly soluble in water

and helps in combustion.

Chemical Properties

1. Oxygen reacts with metal and forms out metal oxides

2Mg + O2 ---------------> 2MgO

Magnesium Oxygen Magnesium oxide

2. Oxides of metal react with water and form hydroxides of metal.

MgO + 2H2O -----------------> Mg(OH)2

Magnesium oxide Water Magnesium hydroxide

3. Oxygen reacts with non-metals and gives of non metals.

S + O2 ----------------------> SO2

Sulphur Oxygen Sulphur dioxide gas

4.Oxides of non-metals react with water and give salts.

SO2 + H2O -------------------> H2SO3

Sulphur dioxide water Sulphurous acid

Uses of Oxygen

1. Every living being makes use of Oxygen in respiration. It dissolves in

water hence creatures living under water also make use of dissolved

Oxygen for respiration.

2. Hand pumps of special types are made for the patients suffering from the

diseases like Pneumonia and Lung diseases. In this hand pump, there is

an upper valve, when it is pressed a reaction takes place between Sodium

peroxide (Na2O2) and water forming oxygen. Using the released Oxygen,

the patient gets instant relief.

3. Oxygen is used to produce flames (31000 – 33000 C). With the help of

these flames, metals can be cut or metals can be joined together.

4. Oxygen is very necessary in the production of chlorine, Nitric acid,

Sulphuric acid etc.

CARBON DIOXIDE

Carbon dioxide is anaturally occurring chemical compound composed of

two oxygen atoms each covalently doubled bonded to a single carbon

atom.Carbon dioxide dissolves in the ocean to form carbonic, bicarbonate

and carbonate.

The oceans act as an enormous carbon sink, and taken up about a third of

CO2 emitted by human activity.

Preparation

Add three spatulas full of calcium carbonate chips to the flask. Pouring

dilute hydrochloric acid into the top of the funnel; ensure that the liquid

covers the tip of the funnel in the flask. Uncover gas jar and place a lit

candle over the mouth of the jar.

CaCO3(s) + 2HCl(aq) ----------> CaCl2(aq) + H2O(I) + CO2(g)

Calcium carbonate Hydrochloric acid Calcium chloride water Carbondioxide

Physical Properties:

It is colorless, odourless and tasteless. Sparingly in water and heavier than

other gases.

Chemical Properties:

1. Take water in the bowl. Dissolve slaked lime in this water and allow it to

settle down. Remove the top layer of water from the bowl/dish and let the

precipitation of lime remain in the bowl/dish

By the reaction of Calcium hydroxide with Carbon dioxide, calcium and

water are obtained.

Ca(OH)2 + CO2 ------------------> CaCO3 + H2O

Slaked lime Carbodioxide Calcium carbonate water

2. On reacting Carbon dioxide with Calcium Carbonate and water, it

produces calcium bicarbonate.

CaCO3 + H2O + CO2 ----------------> Ca(HCO)3

Calcium carbonate water carbondioxide Calciumbicarbonate

3. On heating Carbondioxide with water at high pressure, Carbonic acid is

CO2(Calciumdioxide) + H2O (water)---------------> H2CO3(carbonic acid)

4. With the process of reaction of Carbon dioxide with metal oxides, metals

carbonates are obtained.

MgO + CO2 -------------> MgCO3

Magnesium oxide carbondioxide Magnesium carbonate

5. With the process of reaction of Carbon dioxide with sodium hydroxide,

water soluble sodium carbonate (washing soda) and sodium bicarbonate.

2NaOH + CO2 --------------> Na2CO3 + H2O

Sodium hydroxide carbon dioxide Sodium carbonate water

2Na2CO3 + H2O + CO2--------------> 2NaHCO3

Sodium Carbonate water carbon dioxide Sodium Bicarbonate

Uses of Caron dioxide:

It is used in photosynthesis by vegetation, extinguishing fire, bringing

fermentation for idli, dhosa etc, preparation of cold drinks, washing soda,

baking soda.

Solid Carbon dioxide is known as ‘Dry Ice’. It is used for cooling agent.

HYDROGEN:

Hydrogen is a chemical element with chemical symbol H and atomic

number 1. It is lightest element and the most abundant element in universe.

Preparation:

1. Hydrogen can be made by reaction of any active metal like magnesium

or zinc with a strong acid such as H2SO4 OR HCl. In a test tube,add

magnesium strip or pieces of iron nails in it. Adding hydrochloric acid on the

strip of magnesium.

Mg(s) + 2HCl (aq) ------------> H2(g) + MgCl2(aq)

Magnesium Hydrochloric acid Hydrogen Magnesium chloride

Fe(s) + 2HCl (aq) ------------> FeCl2(aq) + H2(g)

Iron Hydrochloric acid Iron chloride hydrogen

Physical Properties:

It is colorless, odourless and tasteless. Lighter than other gases and

inflammable.

Chemical Properties:

1. Some of the reactive metals like sodium, potassium, calcium etc, react

with hydrogen and give hydrides of the metals.

2Na + H2 ------------> 2NaH

Sodium Hydrogen Sodium hydride

2. With the process of reaction of non metals with hydrogen, hydroxide of

non metals are produced.

Cl2 + H2 ---------------> 2HCl

Chlorine Hydrogen Hydrochloric acid

Uses of Hydrogen:

Hydrogen gas is used as fuel and also it is used to obtain electricity. It is

lighter than air, hence this gas is used in the balloons which are used for

the study of the atmosphere above air level.

To fill balloons and airships, as it is the least dense gas. Also used in the

synthesis of ammonia.

In hardening of vegetable and animal oils.

NITROGEN:

Nitrogen, N2 is a colorless odourless gaseous non-metallic main group

element which belong to Group Vb of the periodic table.

Preparation

1. Nitrogen is prepared by heating a mixture of mixture of ammonium

chloride and sodium nitite.

NH4Cl + NaNO2 ------------> NH4NO2 + NaCl

Ammonium chloride Sodium nitrite Ammonium nitrite Sodium chloride

NH4NO2 ------------> N2 ↑ + 2 H2O

Ammonium nitrite Nitrogen gas Water

Physical Properties:

It is colorless, odourless and tasteless. It is aneither combustible nor a

support of combustion.

Chemical Properties:

1. It combines with other elements in suitable circumstances and makes

compounds.

2. Nitrogen combines with Oxygen and forms nitric oxide. Combining with

more Oxygen it produces nitrogen dioxide.

N2 + O2 ------------> 2 NO

Nitrogen Oxygen Nitric oxide

2 NO + O2 -------------> 2 NO2

Nitric oxide Oxygen Nitrogen dioxide

Nitrogen dioxide dissolves in water and Nitric acid.

Uses to Nitrogen

1. It is used to prepare chemicals like Ammonia, Nitric acid, Calcium

Cyanamide, urea etc.

2. It is used to prepare inert atmosphere e.g. On the inflammable liquid,

instead of air, nitrogen gas should be filled so that there is less possibility of

fire.

3. It decreases reactivity of oxygen (O2) in air and in films, dramas, to show

unnatural smoke or clouds, nitrogen gas is used.

4. The roots of the plants like peas make use of the nitrogen from the air

and produce food containing plenty of protein. It is filled in the tubes of the

tyres of some of the vehicles.