Explain the terms, element, compound and
Elements are a class of a substance that cannot be broken
down into anything simpler and aren’t changed by chemical reactions. Elements
can be found on the periodic table. Elements are defined by the number of
protons they possess. There is 115 known elements. For example: CuCO3
is made up of 3 named elements: Copper, Carbon and Oxygen.
A compound is two or more elements linked together in a
specific ratio and are chemically bonded. There are 2 types of bonds that join
compounds together. These are covalent and ionic. Compounds can be broken back
down into their constituted elements. E.g. H2O is fix in the ratio
of 2:1. Each water molecule of water contains 2 hydrogen atoms bonded to one
single oxygen atom.
An atom is the smallest particle of a chemical element. An
atom defines the structure of an element an atom consists of a nucleus of
positively charged protons and electrically neutral neutrons with negatively
changed electrons orbiting the nucleus. Each atom is unique and made up
initially of itself. The number of protons identifies an atom or its element
and secures its place on the periodic table.
A thermal decomposition which is carried out
on a large scale is the heating of limestone (calcium carbonate, CaCO3).
Find out the details of the reaction, including the chemical equation, and give
some of the uses of the uses of the products from the reaction.
Thermal decomposition is the breakdown of compounds when
heated. Many mental carbonates take part in thermal decomposition reactions. It
is an example of endothermic reaction, when a reaction gains energy from its
surroundings. Thermal energy must be present constantly throughout the reaction
in order for it to keep going.
CaCO3 àheatà CaO + CO2
When calcium carbonate is heated strongly, it breaks down to
form calcium oxide, which is yellow when hot and white when cold. Carbon
dioxide is also produced though thermal decomposition. It can be detected by
using limewater. Carbon dioxide is shown by bubbles which produces a milky
suspension of calcium carbonate. When calcium oxide is reacted with water it is
turns into calcium hydroxide. CaCO3
it products can be used in building. E.g. cement, glass and in manufacturing
iron. It can be mixed with different elements/compounds to produce varied
materials. E.g. concrete is mixed with sand, water and crushed rocks. But it
can also be used in animal and pet feeds as well as fertilisers. Calcium
carbonate needs to be optimised by its different properties such as fineness,
particle size and colour in order to use it for different commercial products. (British Calcium Carbonates Federation, 2018)
Explain in detail what is occurring
during this electrolysis at the atomic level
Electrolysis is the process in which ionic substances are
broken down into smaller particle by electricity. During the process of
electrolysis gases and metals may be produced as products formed by the electrodes.
In order for electrolysis to take place, the ions must be able to move freely
when dissolved in water or melted. Electrolysis produces electrolytes which are
compounds that undergone electrolysis. Electrolytes carry current though these
by moving ions which can’t move in a solid. Ions attracted to the negative
cathode are called cation, and negative ions attracted to positive anode are
called anions. For example, copper
chloride is broken down into the ions copper and chloride, with the copper attracting
to the negative cathode due to it being positively charged, while the chlorine attracting
to the negative anode due to its positive change. The copper deposits mental
onto the cathode while the chlorine gas is shown by bubbling of the solution
and a smell of chorine. When a positively charged ion is attracted to a
negative electrode, where they gain electrons this is called reduction. While,
the negatively charged ions are attracted to the positive electrode where they
lose electrons, this is called oxidation. (BBC, 2014)
Manufacture of aluminium
Aluminium ore is called bauxite, it is impure aluminium
oxide. Its major impurities are iron oxide, silicon dioxide and titanium
dioxide. The crushed bauxite is treated and concentrated with sodium hydroxide
solution. The concentration, temperature and pressure used is dependent on the
source of the bauxite and what form of aluminium oxide it contains. The
typically temperature is from 140°C to 240°C. The high pressure are essential
in order to keep water in the sodium hydroxide solution and needs to be keep at
The aluminium oxide reacts with sodium hydroxide solution to give a solution of
Al2O3 + 2NaOH + 3H2O à 2NaAl(OH)4
The impurities found in the bauxite remain as solids. For
example: the other metals tend not to react the sodium hydroxide solution.
However, some that do react like silicon dioxide precipitates out. Once
aluminium hydroxide is separated, aluminium oxide is formed by heating the
aluminium hydroxide to a temperature of about 1100 – 1200°C.
Al2O3 + 3H2O
Aluminium oxide is the electrolysed in the solution of
molten cryolite, which is another aluminium ore that is rare and expensive.
Mostly now chemically made. The anode is made of graphite, a form of carbon.
The oxygen ions are attracted to the anode, this is where they are converted to
oxygen. The anodes are gradually worn down by oxidation. The cathode is also
made of graphite. Molten aluminium is produced there. The process requires a
lot of electrical energy. The cell operates at a low voltage of about 5-6
volts, with huge currents of 100,000 amps. The heating produced by these large
currents keeps the cell at a temperature of 1100°C.
Aluminium ions in cathode are reduced by gaining 3
electrons. Al3+ + 3e- à
Al Oxygen ions are oxidised at the anode. 2O2- à O2 + 4e-
the temperature of the cell where electrolysis takes place, the carbon anode
can burn and bond with the oxygen to produce carbon dioxide and carbon
There are a few environmental and economic effects relating
to the production of aluminium. One environmental impact is it can reduce the
landscape due to mining and processing for bauxite. As well as impacting to
surrounding towns and villages due to noise and air pollution contributing to
the greenhouse effect. An economic
impact is the energy and material used are expensive and constantly need
replacing, such as anodes.
Aluminium itself isn’t a strong metal, however joining it
with other metals or elements such as silicon, copper or magnesium. The main reasons aluminium is useful is
because it has a low density, can be strong when alloyed, and is also a good
conductor of electricity. It is also resistant to corrosion because of it
strong thin layer of aluminium oxide. Aluminium is used for aircrafts and other
transport such as ships and trains due to the fact it is light, strong abd
resists corrosion. (Clark, 2015)