Transcript C5 revision PowerPoint - Blackpool Aspire Academy

C5
Chemical of the natural environment
What is the atmosphere?
Dry air is a mixture of gases. Our atmosphere is made up of the following:
 78% Nitrogen
 21% Oxygen
 1% Argon
 0.04% Carbon Dioxide
Chemicals of air consists of atoms and small molecules. There are weak forces of
attraction between the molecules so these chemicals have low melting and low
boiling points.
Most non-metals elements and compounds of non-metals are molecular so they
have low melting and boiling points.
The atoms in a molecule are joined together by strong covalent bonds – one or
more pairs of electrons shared between atoms. Covalent bonding arises from
electrostatic forces of attraction between the shared electrons and the nuclei of the
atoms.
Pure molecular compounds cannot conduct electricity because their molecules are
not charged.
What are ionic compounds?
Seawater is a mixture of water and dissolved ionic compounds called
salts. Ionic compounds are made up of positive and negative ions. In
ionic solids, the ions are arranged in a giant three dimensional lattice to
make crystals. There are very strong attractive forces between the
oppositely charges ions. This is ionic bounding.
Ionic compounds have high melting and boiling points because much
energy is needed to break an ionic structure. A solid ionic compounds
cannot conduct electricity but when ionic compound melts or dissolves
in water, its ions are free to more independently. It can now conduct
electricity.
How can we identify ions?
There are simple tests to identify ions and work because each
ion and each compound has its own properties.
If you mix certain solutions of ionic compounds, you make an
insoluble compound forming a precipitate. E.g.
+
 Adding an alkali to a solution that contains Cu ions make a
blue precipitate of Cu(OH)2
CuCl2 (aq) + 2NaOH(aq)  2NaCl(aq) + Cu(OH)2(s)
Solutions containing some other metal ions also react with
alkalis in solution to make precipitates.
 Adding acidified a silver nitrate solution to a solution of Clions makes a white precipitate of silver chloride
AgNO3(aq) + NaCl(aq)  AgCl(s) +NaNO3(aq)
How can we identify ions?
You can use solubility data to predict chemicals
that will precipitate on mixing solutions. A
compound with a low solubility will form as a
precipitate and if both the products are soluble
no precipitate will form.
What are giant structures?
The lithosphere is the Earth’s rigid outer layer and
consists of part of mantle and crust. It is a mixture of
minerals – compounds that occur naturally.
Silicon , oxygen and aluminium are the most
common elements in the Earth’s crust and much of
the silicon and oxygen exists as a compound, silicon
dioxide – solid silicon dioxide has a giant structure
of atoms, which are held together in a huge lattice
by strong covalent bonds.
In diamond and graphite are also minerals which
both consists of carbon atoms arranged in giant
structures.
What are giant structures?
In diamond, each carbon atom is joined to four
other carbon atoms by strong covalent bonds
and the four bonds are arranged in three
dimensions around each atom.
In graphite, each carbon atoms is joined to three
other carbon atoms by strong covalent bonds
and the three bonds are arranged around each
carbon atoms, making sheets of hexagons and
between the sheets, or layers are free electrons
which help to stick the layers together.
Diamond
Graphite
What are giant structures?
Graphite
Diamond
Silicon Dioxide
Melting and
boiling points
Very high because much energy is needed to break the
strong covalent bonds in the giant structure of atoms
Solubility in water
Insoluble because much energy is need to break the
strong covalent bond
Hardness
Soft because the
forces between
the layers are
weak. A good
lubricant/
Very hard because much energy is
need to break the strong covalent
bonds between the surface of atoms.
Diamond is useful for tools and drill
tips
Electrical
conductivity
Good because
the electrons
between the
layers are free to
move
Do not conduct electricity because no
charge particles are free to move.
Why are metals useful?
Metals have many uses and their uses depend on their
properties. Metals have high melting points and are:
 Malleable
 Strong
 Good electrical conductor
Solid metals have giant crystalline structures so strong metallic
bonds hold the atoms together explaining why metals are strong
and why they have high melting points.
A metal crystal is made up of positive metal ions are arranged in
layers. When you bend a metal the layers of ions slide over
each other. The ions are held together by a sea of electrons that
are free to move. When a metal wire conducts electricity,
electrons drift from one end towards the other.
How are metals extracted?
In the lithosphere, most metals are joined to
other elements in minerals. Rocks that contain
useful minerals called ores. Copper is extracted
from the mineral copper iron sulfide and ore that
contains this mineral is copper pyrites.
Ores contain different amounts of minerals and
often, a huge amount of ore contains only a tiny
mass of a useful mineral.
How are metals extracted?
Extracting metals by heating with carbon
Iron, Copper, and Zinc are extracted from their
oxides by heating with carbon.
ZnO(s) + C(s)  Zn(s) + CO(g)
How are metals extracted?
Extracting metals by electrolysis
Reactive metal like Al2 are joined very strongly to
other elements in the minerals and cannot be
extracted by heating with carbon so they are
extracted by electrolysis.
Al2O3 is an ionic compound and when it melts,
its ions can move independently. So liquid Al2O3
conducts electricity and is an electrolyte.
Electrolytes decompose when an electric current
passes through them. This is electrolysis.
How are metals extracted?
Extracting metals by electrolysis
To extract aluminium from aluminium oxide:
 Melt aluminium oxide
 Pass an electrical signal through the electrolyte.


Aluminium forms at the negative electrode. Al3+ ions gain
electrons from the electrode to make neutral aluminium
atoms.
Al3+ + 3e-  Al
Oxygen forms at the positive electrode. O2- ions give
electrons to the positive electrode to make oxygen atoms.
O2-  O + 2eO + O  O2