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F.4 Chemistry
Chapter 11 Reactivity of metals
A.
Summary11.1 The different reactivity of different metals
1.
Different metals have different reactivity.
2.
The factors comparing reactivity of metals:
(a)
The lowest temperature at which the reaction starts.
(b)
The rate of reaction.
(c)
The amount of heat energy given out during reaction.
11.2 Appearance﹝外觀﹞of metals and their storage methods
1.
Some special storing method of some metals:
(a)
Sodium is immersed in paraffin oil﹝石蠟油﹞.
(b)
Calcium is kept in airtight container﹝不透氣的容器﹞.
(c)
Gold should be locked.
2.
The table of the appearance of metals (at room temperature and pressure)
Metals
| Appearance
|
Potassium (K)
| Dull solid
|
Sodium (Na)
|
Calcium (Ca)
| Generally dull solid
|
Magnesium (Mg)
|
Aluminium (Al)
|
Zinc (Zn)
|
Iron (Fe)
|
Lead (Pb)
|
Copper (Cu)
| Reddish brown solid
|
Mercury (Hg)
| Silvery white liquid
|
Silver (Ag)
| Silvery white solid
|
Gold (Au)
| Golden yellow solid
|
3.
When freshly cut﹝新切開的﹞or polished﹝擦亮﹞, all metals look shiny. However, if the metal is exposed to air after a several time, the surface of the freshly cut piece will become dull. It is because of the metal reacts with oxygen in the air to form a oxide layer. This layer can be removed by using a piece of sand paper.
11.3 Reaction of metals with oxygen
1.
Most metals, when heated in air, the metal will react with oxygen in the air.
2.
The formula of the reaction of metals and oxygen:
Metal + Oxygen
Metal oxide (heating is needed)
3.
The observation of the reaction of metals and oxygen is shown below.
Metal
| Observation
|
Potassium
| l
Burns vigorously﹝猛烈地﹞with a lilac flame.
l
Produces an orange powder.
|
Sodium
| l
Burns vigorously with a golden yellow flame.
l
Produces a white powder.
|
Calcium
| l
Burns quite vigorously with a brick-red flame.
l
Produces a white powder.
|
Magnesium
| l
Burns with a dazzling white flame.
l
Produces a white powder.
|
Aluminium
| l
Produces a white powder.
|
Zinc
| l
Produces a powder which is yellow when hot but white when cold.
|
Iron
| l
Burns with yellow showery sparks.
l
Produces a black solid.
|
Lead
| l
Melts on heating to silvery balls.
l
Produces a powder which is orange when hot but yellow when cold.
|
Copper
| l
Its surface turns black on strong heating.
|
Mercury
| l
Forms a red powder on surface on strong heating.
|
Silver
| No visible change (No reaction)
|
Gold
|
11.4 Reaction of metals with water or steam
1.
When a metal reacts with water or steam, hydrogen gas is given off and the hydroxide or oxide of the metal is formed.
2.
The formula of the reaction of water and metals:
(Only for high reactivity metals, for example, K, Na, Ca)
Metal + Water
Metal hydroxide + Hydrogen
3.
The formula of the reaction of steam and metals:
(For the metals that the reactivity is equal to or lower that magnesium)
Metal + Steam
Metal oxide + hydrogen
4.
The observation of the reaction of metals and water / steam is shown below.
Metal
| React with
| Observation
|
Potassium
| Water
| l
It floats on water and melts to a silvery ball.
l
The ball moves quickly on the water surface with a ‘hissing’ sound.
l
It burns with a lilac flame.
l
The resulting solution is alkaline. So, the red litmus paper changes from red to blue.
l
It dissolves in water.
|
Sodium
| l
It floats on water and melt to a silvery ball.
l
Tall ball moves quickly on the water surface with a ‘hissing’ sound.
l
It burns with a golden yellow flame.
l
The resulting solution is alkaline. So, the red litmus paper changes from red to blue.
l
It dissolves in water
|
Calcium
| l
It sinks in water.
l
It reacts with water less vigorously.
l
Colourless gas bubbles are produced.
l
If tested with a burning splint, the gas in the test tube burns with a ‘pop’ sound.
l
The resulting solution is alkaline. So, the red litmus paper changes from red to blue.
|
Magnesium
| Steam
| l
It has little reaction with cold water but it reacts with hot water more vigorously.
l
Colourless gas bubbles is produced.
l
If tested with a burning splint, the gas in the test tube burns with a ‘pop’ sound.
|
Aluminium
| l
No reaction, because the surface of aluminium has a oxide layer, it prevents its reaction with steam.
|
Zinc
| l
Heated they reacts with steam in a similar way as magnesium does. However, the reaction is less vigorous for zinc, and even less for iron.
|
Iron
|
Lead
| No visible change (No reaction)
|
Copper
|
Mercury
|
Silver
|
Gold
|
5.
The experimental set-up of the experiment of the reaction of Ca and water.
6.
The experimental set-up of the experiment of the reaction of Mg and water.
(a)
Remove the delivery tube﹝導管﹞before turn off the burner. Otherwise, this causes sucking back.
(b)
On strong heating, the water in the cotton wool will be turned into steam which fills up the whole test tube and reacts with the metal.
(c)
The metal is heated instead of the cotton wool. This is to prevent the water vaporize too fast without being reacted with the metal.
11.5 Reaction of metals with acid
1.
Reactivity metals with dilute acids (expect dilute nitric acid) to produce salts and hydrogen gas. Salt means the combination of metal ion and acid root.
2.
The formula of the reaction of acids and metals.
Metal + Acid
Salt + Hydrogen
3.
The observation of the reaction of metals and hydrochloric acid is shown below.
Metal
| Observation
|
Potassium
| Explosive reaction
|
Sodium
|
Calcium
| l
The grey metal dissolves in dilute hydrochloric acid.
l
Colourless gas bubbles is produced in a moderate way.
l
If tested with a burning splint, the gas burns with a ‘pop’sound.
l
Heat is released.
|
Magnesium
|
Aluminium
|
Zinc
|
Iron
|
Lead
|
Copper
| No visible change
|
Mercury
|
Silver
|
Gold
|
Remark:
l
If the metal’s ion contains colour, the hydrochloric will also change to that colour.
l
The reaction rate decrease down the metal series.
l
Lead reacts with dilute hydrochloric acid to produce insoluble Lead (II) chloride. The chloride forms a protective layer on the metal surface that prevents the reaction between lead and the acid.
l
The reaction between lead and hydrochloric acid has no ionic equation.
4.
The observation of the reaction of metals and sulphuric acid is shown below.
Metal
| Observation
|
Potassium
| Explosive reaction
|
Sodium
|
Calcium
| l
The grey metal dissolves in dilute sulphuric acid.
l
Colourless gas bubbles is produced in a moderate way.
l
If tested with a burning splint, the gas burns with a ‘pop’sound.
l
Heat is released.
|
Magnesium
|
Aluminium
|
Zinc
|
Iron
|
Lead
|
Copper
| No visible change
|
Mercury
|
Silver
|
Gold
|
Remark:
l
Calcium formed a white solid precipitate﹝白色沉澱物﹞.
l
The reaction rate decreases down the metal series.
l
Calcium and lead reacts with dilute sulphuric acid to give insoluble Calcium sulphate and Lead (II) sulphate. The sulphates form a protective layer on each metal surface that prevents the reaction between each metal and the acid.
l
The reaction between calcium / lead and sulphuric acid has no ionic equation.
11.6 The metal reactivity series
1.
A metal higher in the reactivity series has a higher reactivity, and its atoms would lose outermost shell electron(s) to form cations more easily.
2.
Metals at the top of the series are the most reactive; those at the bottom are the least reactive.
3.
The common metals in order of reactivity could be arranged as follows:
Potassium (K)
| Most reactive
Decrease in reactivity
Least reactive
|
Sodium (Na)
|
Calcium (Ca)
|
Magnesium (Mg)
|
Aluminium (Al)
|
Zinc (Zn)
|
Iron (Fe)
|
Lead (Pb)
|
Copper (Cu)
|
Mercury (Hg)
|
Silver (Ag)
|
Gold (Au)
|
