continuation of expriments.

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N.B. Sodium and potassium are kept under oil/paraffin since they are very reactive and react violently with both air and water.
The sodium oxide dissolves in water forming an alkaline solution of sodium hydroxide only.

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  1. Calcium
    Calcium burns in air with a bright red flame forming white solids of calcium oxide.
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The calcium oxide slightly dissolves in cold water forming an alkaline solution of calcium hydroxide. The calcium hydroxide appears cloudy due to the presence of undissolved calcium oxide.

  1. Potassium
    Potassium burns in oxygen with a lilac flame (purple flame) forming white ash of potassium oxide.
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The potassium oxide dissolves in water to form an alkaline solution of potassium hydroxide.

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  1. Iron
    Oxygen burn is oxygen ith a shower of bright sparks leaving behind blue black solids of Tri iron tetra oxide.
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The oxide of iron formed is insoluble and therefore has no effect on litmus paper.

  1. Copper
    Copper metal burns with a blue flame turning red hot, on cooling forms black power of copper (II) oxide.
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The copper (II) oxide is insoluble in water and therefore has no effect on litmus paper.

  1. Lead
    Lead melts into shinny beads and finally forming yellow powder of lead (II) oxide.
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Reaction of non metals with oxygen
Non-metals burn in air to form acidic oxides (acid andydrides). These oxides dissolve in water to form acidic solutions that turn blue litmus paper red and have no effect on red litmus paper.
An acid anhydride is an oxide of a non metal that dissolves in water to form an acid. Examples include:

  1. Carbon
    Carbon burns in oxygen with an orange flame and bright sparks forming a colorless gas that turns lime water milky (carbondioxide gas).

The carbondioxide gas dissolves in water forming a weakly acidic solution of carbonic acid. This solution turns blue litmus paper pink and not red.

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  1. Phosphorus
    Phosphorus burns in air with a bright yellow flame forming white clouds (fumes) of a oxides of phosphorus. The white fumes is a mixture of phosphorus(V)oxide and phosphorus (III)oxide.
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Phosphorus(V)oxide and phosphorus (III)oxide dissolve in water forming phosphoric and phosphorus acids respectively.

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N.B. Phoshorus is kept in water because if it is in contact with air, it smolders (burns without a flame slowly giving off white smoke)

  1. Sulphur
    Sulphur burns in air with a bright blue flame forming cloudy fumes which have a choking smell. The white fume is a mixture of sulphur dioxide and sulphur trioxide.
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The sulphur dioxide and sulphur trioxide dissolve in water forming sulphurous and sulphuric acids respectivey.

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Uses of oxygen

Oxygen is used by living things in the process of respiration.
 Oxygen is essential for combustion or burning therefore providing heat source for various activities like cooking, burning wastes e.t.c.
 It is used to aid breathing where the natural supply of oxygen is insufficient e.g. in high altitude flying or climbing, and also in hospitals for patients.
 Oxygen when mixed with ethyne produces a very hot flame (oxy acetylene flame) which is used for welding and cutting heavy metals.
 Oxygen is used in te manufacture of steel i.e. in the conversion of pig ifron to steel.
 Liquid oxygen is used as fuel in space rockets.
 Liquid oxygen can be used as explosives in mines when mixed with charcoal and petrol.
Classes of oxides
An oxide is a compound of oxygen with another element. The following are major classes of oxides (types of oxides).

  1. Basic oxides
    These are oxides of metals which react with acids to form salt and water only. E.g. magnesium oxide, copper(II) oxide and calcium oxide.
    Magnesium oxide reacts with hydrochloric acid to produce magnesium chloride (salt) and water.
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Copper (II) oxide reacts with sulphuric acid to form copper (II) sulphate (salt) and water.

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  1. Acidic oxides
    These are oxides of non metals that dissolve in water to form acids. These oxides are called acid anhydrides. E.g. Carbondioxide (CO2), sulphurdioxide (SO2), sulphur trioxide (SO3), nitrogen dioxide(NO2) e.t.c.
    Carbondioxide dissolves in water to form carbonic acid
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Sulphur trioxide reacts with water to form sulphuric acid

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These oxides react with alkalis to form salt and water. E.g. carbondioxide reacts with sodium hydroxide to form sodium carbonate(salt) and water.

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  1. Neutral oxides
    These are oxides of non metals which do not show acidic or basic properties (they are neither acidic nor basic.). I.e. they don‘t react with water to form acids and neither do they react with acids to form salts.E.g carbon monoxide (CO), nitrogen monoxide (NO),dinitrogen oxide (N2O),water (hydrogen oxide).
  2. Amphoteric oxides
    These are metallic oxides which show both acidic and basic properties. i.e they react with both acids and alkalis to form salt and water. E.g aluminium oxides(Al2O3), lead(II)oxide(PbO), zinc oxide(ZnO).
    Reaction of the amphoteric oxides with acids
    Zinc oxide reacts with sulphuric acid to form zinc sulphate (salt) and water.
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Aluminium oxide reacts wth hydrochloric acid forming aluminium chloride (salt) and water.

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Reaction of amphoteric oxides with alkalis
Zinc oxide reacts with sodium hydroxide to form sodium zincate (salt).

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Aluminium oxide reacts with sodium hydroxide forming a salt called sodium aluminate.

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  1. Peroxides
    These are oxides that contain twice as much oxygen as they would contain in their normal oxides. E.g. hydrogen peroxide (H2O2), Sodium peroxide (Na2O2).
  2. Mixed oxides
    These are oxides that react like a mixture of two simpler oxides. E.g. lead tetra oxide (Pb3O4) and Tri iron tetra oxide (Fe3O4).
    Electrochemical series (Reactivity series)

This is the arrangement of elements in the order of their readiness to react with other substances. The most reactive elements are placed at the top of the series and the least reactive elements are placed at the bottom.
Metal competition for oxygen
Metals which are higher in the reactivity series (more reactive metals) tend to remove oxygen from the oxides of metals that are lower in the reactivity series (less reactive metal). Consider the reaction below;

Magnesium is more reactive than copper and therefore removes oxygen from it.
Comparing reactivity of metals

  1. Potassium and sodium
    When potassium and sodium are freshly cut, they are silvery shiny but their surfaces rapidly tarnish in air because they react quickly with oxygen in the atmosphere to form oxides. Potassium tarnishes more rapidly than sodium indicating that it is more reactive than sodium.
  2. Magnesium
    When a piece of magnesium is polished, tinny silvery surface is exposed. The surface remains shinny for some times before turning grey due to the slow reaction of the magnesium with air forming magnesium oxide (the grey coating). Magnesium is less reactive than sodium and potassium.
  3. Aluminium and Zinc
    Aluminium and zinc are shinny metals although their surfaces get coated with thin layers of their respective oxides on exposure to oxygen. Aluminium and zinc react more slowly with oxygen than magnesium forming their oxides. Hence aluminium and zinc are less reactive than magnesium.
  4. Copper
    Copper is a brown solid and does not react with oxygen from the atmosphere but reacts with carbondioxide and water from the atmosphere to form a green solid of copper (II) carbonate. Copper is therefore less reactive than aluminium and zinc. From the aboive reactions, we can establish the reactivity series of metals.
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Reactions between metals and metal oxides

  1. Magnesium and copper
    When a mixture of magnesium and copper (II) oxide is heated, a red glow spreads through the mixture leaving a white ash and a brown solid.
    Magnesium removes oxygen from copper to form magnesium oxide. The white ash is magnesium oxide and the brown solid is copper metal.
    This shows that magnesium is more reactive than copper
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  1. Carbon and copper (II) Oxide
    When a mixture of carbon and copper (II) Oxide is heated in a test tube, a brown solid is formed and a colorless gas that turns lime water milky (C02 ) is liberated. Carbon removes Oxygen from copper (II) Oxide to form carbon dioxide is more reactive than copper.
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  1. Magnesium and Carbon dioxide
    Magnesium burns in carbon dioxide to form a mixture of white ash and black solid particles
    Magnesium removes oxygen from carbon dioxide to form magnesium oxide.
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