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Oxygen

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Symbol: O
Molecular formula: O2
Valency: 2
Position in periodic table: Group-VI A, Period-2nd
Electronic configuration: 2, 6 (1s2, 2S2 2P4)
Atomic number: 8
Atomic weight: 16
Molecular weight: 32 amu
Freezing point:-219°C
Boiling point: -183°C

Occurrence

Oxygen is abundantly occurring element on the earth. It constitutes about 47.6% of the earth's crust.

General methods for the preparation of oxygen gas

From metallic oxides:

Oxides of metals give oxygen when heated.
2HgO → 2Hg + O2

From metal peroxide:

When sodium peroxide is treated with water, oxygen is liberated.
2Na2O2 + 2H2O → 4NaOH + O2

From electrolysis of water:

Oxygen is evolved in the positive electrode during the electrolysis of acidic water in Hofmann Voltameter.
2H2O→ 2H2 +O2

Laboratory preparation of oxygen gas

Oxygen gas is prepared in laboratory by the following two methods:

  • By heating method
  • Without heating method
By heating method

Principle:
When potassium chlorate is heated in the presence of manganese dioxide in the ratio of 3:1, it decomposes at 250°C into potassium chloride and oxygen.
2KClO3 → 2KCl + 3O2

Take a mixture of powdered potassium chlorate and manganese dioxide in the ratio of 3:1 in a hard glass test tube. Fit it with a cork and a delivery tube and adjust the test-tube in a stand as shown in the figure. Insert the other end of delivery tube into the bee-hive shelf. A gas jar is filled with water and inverted over the bee-hive shelf in the pneumatic trough. Now, heat the mixture. When potassium chlorate is decomposed, oxygen is liberated. The first formed oxygen gas is contaminated with the air inside the hard glass test tube and delivery tube and is allowed to escape. Then the oxygen is collected in gas jar by downward displacement of water.

Precautions

  • The manganese dioxide (MnO2) should be pure, otherwise the particles of carbon along with MnO2 burn inside the tube and it may cause explosion.
  • Apparatus should be made airtight.
  • The test tube should be fixed in slightly slanting position.
Without heating method

Principle:
Oxygen gas can be prepared in the laboratory by hydrogen peroxide and manganese dioxide. In this reaction manganese dioxide is used as catalyst.
2H2O2 → 2H2O + O2

The apparatus is set up as shown in the figure. Hydrogen peroxide is poured in manganese dioxide and water having a conical flask with the help of a thistle funnel. Inside the flask, the decomposition of hydrogen peroxide is taking place in the presence of manganese dioxide and oxygen gas is liberated. The produced oxygen gas is collected in the gas jar by downward displacement of water.

Test of oxygen:
To test whether the produced gas is oxygen or not, introduce a glowing matchstick in the jar containing gas. This burns with bright light.

Manufacture of oxygen

From air:
By compression, cooling and sudden expansion of air, the air is changed into liquid state and is freed from moisture and carbon dioxide. The liquid air has nitrogen and oxygen only. The liquid air allowed to vaporize. Being the boiling point of nitrogen lower, it escapes first and is separately collected. The left liquid is nearly pure oxygen.

By electrolysis of water:
Oxygen can also be manufactured by the electrolysis of water as you are explained in hydrogen gas.

Properties of oxygen gas

Physical properties

  • It is neutral to the indicator.
  • It is non-combustible gas but it is combustion supporter.
  • It is slightly heavier than air.
  • It liquefies at -183°C and solidifies at -219°C.
  • Oxygen is a poor conductor of heat and electricity.
  • Oxygen is odorless gas.
  • Oxygen is tasteless gas.

Chemical properties

  • Metals like sodium, potassium, calcium and magnesium burn with a bright flame in oxygen to produce their oxides.
    4K + O2 → 2K2O (Potassium oxide)
    Ca + O2 → 2CaO (Calcium oxide)
  • Most of the non-metals like carbon, phosphorous and sulphur burn in oxygen to form oxides
    C + O2 → CO2 (Carbon dioxide)
  • Ammonia burns in oxygen gas with greenish yellow flame and procedures nitrogen and water.
    4NH3 + 3O2 → N2+6H2O
  • Iron changes into Ferro-ferric oxide when it is strongly heated in the presence of oxygen.
    4Fe + 2O2 → Fe2O4 (Ferro-ferric oxide)
    But in the presence of moisture, iron reacts with oxygen to form rust. The process of formation of rust is called rusting.
    4Fe + 3O2 + XH2O → 2Fe2O3.XH2O
  • Various organic compounds like carbohydrate, ethyl- alcohol, oil, petrol, wax etc. burn in oxygen forming carbon dioxide.
    CH4 + 2O2→ CO2 +2H2O + Heat
    C6H12O6 +6O2→ 6CO2 + 6H2O + Heat
  • We need oxygen for oxidation of our food as it oxidizes the food and releases energy during respiration which is used to perform body functions. Here, carbon dioxide and water are formed as a by- products of respiration.
    C6H12O6 +6O2→ 6CO2 + 6H2O + Energy
  • Oxygen when passed through an electric aRC struck between two copper electrodes at 3000oC, nitric oxide is formed. It is also produced during lightning.
    N2 + O2 → 2NO (Nitric Oxide)
    3000oC

Uses of oxygen

  • Oxygen is required for oxidation of food to produce energy during respiration.
  • It is used in hospitals for the artificial respiration of pneumatic patients.
  • The liquid form of oxygen is used as fuel in rockets.



  • Oxygen is abundantly occurring element on the earth. It constitutes about 47.6% of the earth’s crust.
  • Oxygen gas can be prepared in the laboratory by hydrogen peroxide and manganese dioxide.
  • Metals burn with oxygen and produce their oxides.
  • Oxygen is required for oxidation of food to produce energy during respiration.
  • Oxygen is non-combustible gas but it is combustion supporter.
.

Very Short Questions

Oxygen is the first member of the group VIA on the periodic table. It is located in period 2 and group 16.

We used oxygen for respiration as fuel and welding and cutting of metals also.

Iron changes into ferro-ferric oxide when it is strongly heated in the presence of oxygen, but in the presence of moisture iron react with oxygen to form rust. The process of information of rust is called rusting of iron.

The physical properties of oxygen are:

  • Oxygen is colorless, odourless and tasteless gas.
  • It is slightly soluble in water.
  • It is neutral to indicator.

In a laboratory oxygen gas is prepare by heating the potassium chlorate and manganese dioxide acts as a catalyst.

0%
  • What fraction of atmosphere is covered by oxygen?

    one-fourth
    one-fifth
    two-fourth
    two-fifth
  • Which does not contain oxygen?

    Fat
    protein
    vitamin
    Diamond
  • What happens when Mercuric oxide is heated?

    It produces mercuric dioxide and hydrogen gas
    It produces mercuric dioxide
    It produces oxygen gas
    It becomes red hot and starts glowing brightly
  • What is molecular formula of potassium peroxide?

    KO2
    K2O2
    (KO)2
    K2O
  • How magnesium is used to test presence of oxygen?

    Magnesium dioxide burns in oxygen giving white ash of magnesium oxide
    Magnesium ribbon burns in oxygen giving white ash of magnesium oxide
    Magnesium ribbon burns in oxygen giving black ash of magnesium oxide
    Magnesium oxide burns in oxygen giving white ash of magnesium oxide
  • What happens when hydrogen peroxide is mixed with manganese dioxide?

    It produces water
    It produces Oxygen gas
    It produces Hydrogen gas
    It produces hydroxide
  • Which is false about oxygen?

    it is very slightly soluble in water
    It is a flammable gas
    it is neutral to litmus paper
    it is colorless, odorless and tasteless
  • Which of the following reaction is not possible?

    2CO + O2 ---> 2CO2
    C + O2 ---> CO2
    C6H12O6 + O2 ---> C6H12O8
    4K + O2 ---->  2K2O
  • What is not use of oxygen?

    It is used for respiration by all organism
    Used for combustion of wood, paper and fuel
    Oxygen is used for artificial breathing to person suffering from pneumonia
    Liquid oxygen is used to freeze things owning to it's very low temperature
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ASK ANY QUESTION ON Oxygen


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Forum Time Replies Report
Alisha

How do aquatic animal get oxygen


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amrit

why oxygen is not collected by downward displacement of air instead of downward displacement of water as it slightly dissolve in water.


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ghangjen bhotia

no


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