CHE1: THE ATMOSPHERE AND OXYGEN

This unit involves the preparation of Oxygen from various substances through different experiments carried out.

What is rust?

Iron rust is a brown costing which forms on an iron article when it is exposed to dump air.

What condition favors rusting?

  1. Oxygen
  2. Water (moisture)

How would you show that those conditions are necessary for rusting to occur?

Dampair

Moisture water

Oxygen

How is rusting prevent?

To show that air is necessary for rusting to occur

Apparatus set up as follows;-

rusting

N.B

Boiling water helps to drive out air and the oil kept air from re dissolving as it cools. After 2 days on the third day the nails have not yet rusted.

To show that moisture is necessary for rusting to take place.

 

rusting1

Anhydrous calcium chloride is a drying agent therefore it keeps the air dry. After a few days the nails don’t have brown coating.

Anhydrous calcium chloride is hygroscopic because it absorbs water from the atmosphere but doesn’t dissolve in it necessarily.

Conclusion

Therefore iron reacts with oxygen +water

Hydrated Iron (III) Oxide

(4Fe + 3O2 (g) + 2XH2OCl)         2Fe2O3 XH2O(s)

That is iron rust is hydrated iron (III) Oxide

Methods of preventing rusting

  1. Painting
  2. Greasing or oiling
  3. Coating with other metals (galvanizing)
  4. Enamel platting
  5. Use of stainless steel

Air

Is a compound or mixture

O2 = 20 %

N2= 78%

Co2˃ 0.03%

H2O          vaneible

Inert gases = 1%

Pollutants        vaneibe

How would you determine the % of oxygen in the air?

Oxygen (preparation)

Hydrogen peroxide decomposes slowly formatting oxygen and water.

However in the presence of manganese (iv) oxide hydrogen peroxide decomposes quickly. Manganese (iv) Oxide is catalyst

Manganese

Hydrogen Peroxide (iv) oxide water and oxygen

2H2O2 (l) MnoO2 (g) +               2H2Ocl3

What is a catalyst?

A catalyst is a substance which changes the cater of a reception by amines chemically unchanged.

 

oxygen

Potassium chlorate

A white crystallized solid decomposes when heated giving o77 oxygen but like hydrogen peroxide, the reaction is slow. It requires manganese (iv) oxide catalyst.

(2KCLO3(s) Mno2  2KCL (2) + 3O2 (g))

Apparatus set up as follows.-

potassium chloride

Potassium permanganate ( potassium manganite vii)

Potassium permanganate when heated gives 077 oxygen.

potassium manganate

 

Mecumic oxide (red solid heat mercury

When mercuric oxide is heated it gives off oxygen

 Test

To show the gas is oxygen it must relight a glowing splint

Physical properties

smell

Lab preparation

To prepare dry oxygen

dry oxygen

N.B

To prepare that dry oxygen it can be dried using anhydrous calcium chloride then collected into a gas syringe or using concentrate sulphuric acid.

 

gas

Chemical properties of oxygen

It is neutral to litmus

Red            acids

Blue           alkalis

Burning sulphur and oxygen

It was lowered into glass jar with oxygen and it produced purple gas which when dissolved into water turned the litmus paper which was blue red

Magnesium (solid) and oxygen

It was lowered into a glass jar with oxygen. It produces a white flame, a whitish gas and arch. The arch was added to water and it turned purple.

Magnesium Ribbon was lowered into oxygen and turned water purple.

White ash in water with litmus turns purple.

Sodium is kept in kerosene to keep it from water and air. Potassium chlorate and manganese (iv) oxide are separated from sodium with gas wool. Sodium producers an orange flame which turns green after cooling. Red litmus paper in water and the green residue from sodium turns it blue.

Carbon, sulphur and phosphorus are non-metal. Non-metals react with oxygen forming acidic (cosmetic neutral) oxides

Acidic oxides react with water forming acids that turn blue litmus red.

Sodium and magnesium are examples of metals. Metal combine with oxygen farming basic (sometimes amphoteric) acids. If a base dissolves in water, the solution is called an alkaline.

Alkalis turn red litmus paper blue.

Uses of oxygen

  1. Respiration
  2. Burning and rusting

These are natural reactions that require oxygen.

  • Oxygen is used to burn fuels e.g. in space rockets
  • Oxygen is used to produce the oxy-acetylene flame used in welding
  • It is used in manufacture of steel
  • It is used by sea divers, mountain climbers, and critically sick people.

Manufacture of oxygen

By fractional distillation of liquid air

Water

  1. Formula H2O
  2. Is water an element or a compound?

It is a compound

  1. Give reasons (SPEC)
  2. It is not easy to separate (S)
  3. The components that make up water are a definite ratio ©
  • A lot of energy is required (Σ)
  1. The properties of water are different from hydrogen and oxygen

 Where is water found?

Lakes, stream, seas, oceans, rivers etc

How does it got to our homes?

This pumped from the lakes thoroughly filtered and then treated with chlorine with kills’ germs.

Is tap water pure?

Tap water is not chemically pure because it contains dissolve substances like chlorine which treats it.

 

How would you show that a given liquid could be water?

Color: colorless

Smell: odorless

Any substance that could be water should turn blue cobalt chloride paper pink. Water should be neutral to litmus paper.

How would you show that a liquid is water?

Finding its boiling point and freezing point

Physical properties of water should contain, color, taste, smell, density, taste, boiling/points. At 4oc density c water is a Ig/cc

Test

Water dissolves a lot of substances

Boiling 100oC

Freezing 0oC

Chemical properties of water

What is a hydrate?

A substance which contains water of crystallization

Examples

Fe2O3 oX H2O

FeSO4 o7HO

CuSoo SH2O

What is the efflorescence?

Efflorescence is the giving up of water of crystallization by a crystal to the atmosphere

Water in the atmosphere

Water in the air

Some substances absorb water from the atmosphere while others release it.

Deliquescent substance: absorb water from the atmosphere and dissolve in it to become wet to form a solution.

Examples of deliquescent

Sodium hydroxide, Zinc Chloride

Potassium hydroxide, Iron (III) Chloride

Calcium Chloride etc

Deliquescence

Is the process of absorbing water by a substance to form a solution or to become wet when it is exposed to air.

Attachments9

ASSIGNMENT : THE ATMOSPHERE AND OXYGEN MARKS : 15  DURATION : 1 week, 3 days

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