metals Flashcards
List the general physical properties of metals
Diagram showing bonding and structure in metals
General chemical properties of Metals
The chemistry of metals is studied by analysing their reactions with water, dilute acid and oxygen.
Based on these reactions a reactivity series
of metals can be produced.
Reactivity with water
Some metals react with water, either warm or cold, or with steam.
Metals that react with cold water form a metal hydroxide and hydrogen gas, for example calcium:
Reactivity with acids
Most metals react with dilute acids such as HCl.
When acids and metals react, the hydrogen atom in the acid is replaced by the metal atom to produce a salt and hydrogen gas, for example iron:
Reactivity with oxygen
Unreactive metals such as gold and copper do not react with acids.
Some reactive metals such as the alkali metals react with oxygen.
Copper and iron can also react with oxygen although much more slowly.
When metals react with oxygen a metal oxide is formed, for example copper:
Alloys
An alloy
is a mixture of two or more metals or a metal and a nonmetal.
Alloys often have properties that can be very different to the metals they contain, for example can have more strength, hardness or resistance to corrosion or extreme temperatures.
Alloys contain atoms of different sizes, which distorts normally regular arrangements of atoms in metals.
This makes it more difficult for the layers to slide over each other, so alloys are usually much harder than the pure metal.
Alloys arrangement of a metal lattice structure
Alloys are mixtures of…
They are not …combined.
An alloy is not a…
- substances.
- chemically
- compound.
Common alloys and their uses
Brass is an alloy of copper and zinc and is much stronger than either metal.
Alloys of iron with tungsten are extremely hard and resistant to high temperatures.
Alloys of iron mixed with chromium or nickel are resistant to corrosion.
Aluminium is mixed with copper, manganese and silicon for aircraft body production as the alloy is stronger but still has a low density.
The Reactivity Series
The chemistry of the metals is studied by analysing their reactions with water, dilute acid and oxygen.
Based on these reactions a reactivity series of metals can be produced.
The series can be used to place a group of metals in order of reactivity based on the observations of their reactions with water, acid and oxygen.
The reactivity series mnemonic
“Please send lions, cats, monkeys and cute zebras into hot countries signed Gordon”.
Displacement reactions between metals and metal oxides
The reactivity of metals increases going up the reactivity series.
This means that a more reactive metal can displace a less reactive metal from its oxide by heating.
Example: Copper(II) Oxide
It is possible to reduce copper(II) oxide by heating it with magnesium.
As magnesium is above copper in the reactivity series, magnesium is more reactive so can displace copper.
The reducing agent in the reaction is magnesium:
they are all
Displacement reactions between metals and metal oxides
Displacement reactions between metals and aqueous solutions of metal salts
Any metal will displace another metal that is below it in the reactivity series from a solution of one of its salts.
This is because more reactive metals lose electrons and form ions more readily than less reactive metals, making them better reducing agents.
The less reactive metal is a better electron acceptor than the more reactive metal, thus the less reactive metal is reduced. (OIL-RIG: reduction is gain of electrons).
expalin example and write an equation for it
Example: Zinc and copper(II) sulfate
As Zinc is above copper in the reactivity series, zinc is more reactive so can displace copper from copper(II) sulfate solution:
these are all…
Displacement reactions between metals and aqueous solutions of metal salts
Thermal decomposition reactions
Some compounds decompose or breakdown when they are heated to sufficiently high temperatures.
These reactions are called thermal decomposition reactions.
A common example is the thermal decomposition of calcium carbonate (limestone), which occurs at temperatures above 800ºC:
Thermal decomposition of metal hydroxides
Most metal hydroxides undergo thermal decomposition.
Water and the corresponding metal oxide are the products formed, for example zinc hydroxide thermally decomposes as follows:
Group II metal hydroxides decompose similarly but the Group I hydroxides (apart from lithium) do not decompose due to their having a higher thermal stability.
Thermal decomposition of metal carbonates
Most of the metal carbonates and hydrogen carbonates undergo thermal decomposition.
The metal oxide and carbon dioxide are the products formed, for example magnesium carbonate thermally decomposes as follows:
Group I carbonates (again apart from lithium carbonate) do not decompose when heated.
This is due to the high thermal stability of reactive metals; the more reactive the metal then the more difficult it is to decompose its carbonate.
CuCO3 for example is relatively easy to thermally decompose but K2CO3 does not decompose.
Thermal decomposition of metal nitrates
All of the metal nitrates decompose when they are heated.
Group I nitrates decompose forming the metal nitrite and oxygen, for example sodium nitrate decomposes as follows:
Aluminium and its apparent lack of reactivity
Aluminium is a curious metal in terms of its reactivity.
It is placed high on the reactivity series but it doesn’t react with water or acids.
This is because the surface of aluminium metal reacts with oxygen in the air forming a protective coating of aluminium oxide:
Extraction of ores from the Earth’s crust
The Earth’s crust contains metals and metal compounds such as gold, iron oxide and aluminium oxide.
When found in the Earth, these are often mixed with other substances.
To be useful, the metals have to be extracted from their ores through processes such as electrolysis, using a blast furnace or by reacting with more reactive material.
The extraction of metals is a reduction process.
Unreactive metals do not have to be extracted as they are often found as the uncombined element as they do not easily react with other substances.
Extraction of metal and the reactivity series
The position of the metal on the reactivity series influences the method of extraction.
Those metals placed higher up on the series (above carbon) have to be extracted using electrolysis.
Metals lower down on the series can be extracted by heating with carbon.
The extraction of iron in the blast furnace
The extraction of iron in the blast furnace
Raw Materials:
Iron Ore (Haematite), Coke, Limestone and Air
Explanation:
Iron Ore, Coke and Limestone are mixed together and fed into the top of the blast furnace. Hot air is blasted into the bottom of the blast furnace
Describe the conversion of iron into steel using basic oxides and oxygen
Molten iron is an alloy of 96% iron, with carbon, phosphorus, silicon and sulfur impurities.
It is too brittle for most uses, so most of it is converted into steel by removing some of the impurities.
Not all of the carbon is removed as steel contains some carbon, the percentage of which depends on the use of the steel.
The molten iron is transferred to a tilting furnace where the conversion to steel takes place.
Oxygen and powdered calcium oxide are added to the iron.
The oxygen oxidises the carbon, phosphorus, silicon and sulfur to their oxides which are all acidic.
CO2 and SO2 are gaseous so escape from the furnace.
The acidic silicon and phosphorus oxides react with the powdered calcium oxide and from a slag which is mainly calcium silicate:
SiO2(l) + CaO(s) → CaSiO3(s)
The slag floats on the surface of the molten iron and is removed.
Extraction of aluminium
Aluminium is a reactive metal which sits above carbon on the reactivity series.
It cannot be extracted from its ore (bauxite) by carbon reduction, so electrolysis is used.
Recycling metals: iron, steel and aluminium
Advantages and disadvantages
Advantages
Raw materials are conserved (bauxite and haematite).
Energy use is reduced, especially in the electrolysis of aluminium.
Less pollution is produced as both processes contribute to air pollution.
Disadvantages
More transport on roads carrying used metals to recycling centres.
Energy consumed in collecting materials and sorting them per material type.
The Process of Alumium Extraction by Electrolysis
Diagram Showing the Extraction of Aluminium by Electrolysis
Raw Materials:
Aluminium Ore (Bauxite)
Explanation:
The Bauxite is first purified to produce Aluminium Oxide Al2O3
Aluminium Oxide has a very high melting point so it is first dissolved in molten Cryolite producing an electrolyte with a lower melting point, as well as a better conductor of electricity than molten aluminium oxide. This also reduces expense considerably.
The electrolyte is a solution of aluminium oxide in molten cryolite at a temperature of about 1000 °C. The molten aluminium is siphoned off from time to time and fresh aluminium oxide is added to the cell. The cell operates at 5-6 volts and with a current of 100,000 amps. The heat generated by the huge current keeps the electrolyte molten.
A lot of electricity is required for this process of extraction, this is a major expense.
The Process of Alumium Extraction by Electrolysis
Supplement:
The Process of Zinc Extraction
Uses of Aluminium
use and most important properties in the use
Uses of Copper and special properties for uses
Uses of Steel and special properties for uses
Steel Alloys and Their Properties
The amount of carbon removed depends on the amount of oxygen used.
By carefully controlling the amount of carbon removed and subsequent addition of other metals such as chromium, manganese or nickel, the particular type of steel alloy is produced.
Explain the uses of zinc for galvanising and for making brass
Zinc is used in galvanising, the process of coating a metal such as iron or steel with a protective coating of zinc to prevent corrosion or rusting.
Galvanising is an effective way of rust protection as it works even if the zinc coating becomes scratched or damaged.
The process can be done electrolytically or by dipping the metal parts into baths of molten zinc.
Zinc is also used to make an alloy called brass.
Brass contains 70% copper and 30% zinc.
The addition of zinc makes the alloy much harder and corrosion resistant than copper alone.
