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?
- Water (moisture)
How would you show that those conditions are necessary for rusting to occur?
How is rusting prevent?
To show that air is necessary for rusting to occur
Apparatus set up as follows;-
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.
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.
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
- Greasing or oiling
- Coating with other metals (galvanizing)
- Enamel platting
- Use of stainless steel
Is a compound or mixture
O2 = 20 %
Inert gases = 1%
How would you determine the % of oxygen in the air?
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
Hydrogen Peroxide (iv) oxide water and oxygen
2H2O2 (l) Mno2 O2 (g) + 2H2Ocl3
What is a catalyst?
A catalyst is a substance which changes the cater of a reception by amines chemically unchanged.
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 permanganate ( potassium manganite vii)
Potassium permanganate when heated gives 077 oxygen.
Mecumic oxide (red solid heat mercury
When mercuric oxide is heated it gives off oxygen
To show the gas is oxygen it must relight a glowing splint
To prepare dry oxygen
To prepare that dry oxygen it can be dried using anhydrous calcium chloride then collected into a gas syringe or using concentrate sulphuric acid.
Chemical properties of oxygen
It is neutral to litmus
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
- 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
- Formula H2O
- Is water an element or a compound?
It is a compound
- Give reasons (SPEC)
- It is not easy to separate (S)
- The components that make up water are a definite ratio ©
- A lot of energy is required (Σ)
- 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?
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
Water dissolves a lot of substances
Chemical properties of water
What is a hydrate?
A substance which contains water of crystallization
Fe2O3 oX H2O
CuSo2 o 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
Is the process of absorbing water by a substance to form a solution or to become wet when it is exposed to air.