Chemistry 1

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  • Created by: Esther
  • Created on: 06-12-12 22:54


a) All substances are made of atoms. A substance that is made of only one sort of atom is called an element. There are about 100 different elements. Elements are shown in the periodic table. The groups contain elements with similar properties.
b) Atoms of each element are represented by a chemical symbol, eg O represents an atom of oxygen, and Na represents an atom of sodium.
c) Atoms have a small central nucleus, which is made up of protons and neutrons and around which there are electrons.
d) The relative electrical charges are as shown:Name of particle Charge
Proton +1
Neutron 0
Electron –1
e) In an atom, the number of electrons is equal to the number of protons in the nucleus. Atoms have no overall electrical charge.
f) All atoms of a particular element have the same number of protons. Atoms of different elements have different numbers of protons.
g) The number of protons in an atom of an element is its atomic number. The sum of the protons and neutrons in an atom is its mass number.
h) Electrons occupy particular energy levels. Each electron in an atom is at a particular energy level (in a particular shell). The electrons in an atom occupy the lowest available energy levels (innermost available shells)

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The periodic table

a) Elements in the same group in the periodic table have the same number of electrons in their highest energy level (outer electrons) and this gives them similar chemical properties.
b) The elements in Group 0 of the periodic table arecalled the noble gases. They are unreactive because their atoms have stable arrangements of electrons.

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Chemical Reactions

a) When elements react, their atoms join with other atoms to form compounds. This involves giving, taking or sharing electrons to form ions or molecules. Compounds formed from metals and non-metals consist of ions. Compounds formed from non-metals consist of molecules. In molecules the atoms are held together by covalent bonds.
b) Chemical reactions can be represented by word equations or by symbol equations.
c) No atoms are lost or made during a chemical reaction so the mass of the products equals
the mass of the reactants.

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Calcium Carbonate

a) Limestone, mainly composed of the compound calcium carbonate (CaCO3), is quarried and can be used as a building material.
b) Calcium carbonate can be decomposed by heating (thermal decomposition) to make calcium oxide and carbon dioxide.
c) The carbonates of magnesium, copper, zinc, calcium and sodium decompose on heating in a similar way.
d) Calcium oxide reacts with water to produce calcium hydroxide, which is an alkali that can be used in the neutralisation of acids.
e) A solution of calcium hydroxide in water (limewater) reacts with carbon dioxide to produce calcium carbonate. Limewater is used as a test for carbon dioxide. Carbon dioxide turns limewater cloudy.
f) Carbonates react with acids to produce carbon dioxide, a salt and water. Limestone is damaged by acid rain.
g) Limestone is heated with clay to make cement. Cement is mixed with sand to make mortar and with sand and aggregate to make concrete.

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Extracting metals

a) Ores contain enough metal to make it economic to extract the metal. The economics of extraction may change over time.
b) Ores are mined and may be concentrated before the
metal is extracted and purified. c) Unreactive metals such as gold are found in the Earth
as the metal itself, but most metals are found as compounds that require chemical reactions to extract the metal. ) Metals that are less reactive than carbon can be extracted from their oxides by reduction with carbon, for example iron oxide is reduced in the blast furnace to make iron.
e) Metals that are more reactive than carbon, such as aluminium, are extracted by electrolysis of molten compounds. The use of large amounts of energy in the extraction of these metals makes them expensive.
f) Copper can be extracted from copper-rich ores by heating the ores in a furnace (smelting). The copper can be purified by electrolysis. The supply of copper-rich ores is limited.
■ phytomining uses plants to absorb metal compounds and that the plants are burned to
produce ash that contains the metal compounds
■ bioleaching uses bacteria to produce leachate solutions that contain metal compounds.
h) Copper can be obtained from solutions of copper salts by electrolysis or by displacement using scrap iron.
i) Aluminium and titanium cannot be extracted from their oxides by reduction with carbon. Current methods of extraction are expensive because:
■ there are many stages in the processes
■ large amounts of energy are needed.
j) We should recycle metals because extracting them uses limited resources and is expensive in terms of energy and effects on the environment.

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a) Iron from the blast furnace contains about 96% iron. The impurities make it brittle and so it has limited uses.
b) Most iron is converted into steels. Steels are alloys since they are mixtures of iron with carbon. Some steels contain other metals. Alloys can be designed to have properties for specific uses. Low-carbon steels are easily shaped, high-carbon steels are
hard, and stainless steels are resistant to corrosion.
c) Most metals in everyday use are alloys. Pure copper, gold, iron and aluminium are too soft for many uses and so are mixed with small amounts of similar metals to make them harder for everyday use.

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Properties and uses of metals

a) The elements in the central block of the periodic
table are known as transition metals. Like other
metals they are good conductors of heat and
electricity and can be bent or hammered into
shape. They are useful as structural materials
and for making things that must allow heat or
electricity to pass through them easily.
b) Copper has properties that make it useful
for electrical wiring and plumbing.
c) Low density and resistance to corrosion make
aluminium and titanium useful metals.

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Crude oil

a) Crude oil is a mixture of a very large number
of compounds.
b) A mixture consists of two or more elements or
compounds not chemically combined together.
The chemical properties of each substance in
the mixture are unchanged. It is possible to
separate the substances in a mixture by
physical methods including distillation.
c) Most of the compounds in crude oil consist of
molecules made up of hydrogen and carbon
atoms only (hydrocarbons). Most of these are
saturated hydrocarbons called alkanes, which
have the general formula CnH2n+2.

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a) Alkane molecules can be represented in the
following forms:
■ C2H6
■ H –– C –– C –– H
b) The many hydrocarbons in crude oil may be
separated into fractions, each of which contains
molecules with a similar number of carbon atoms,
by evaporating the oil and allowing it to condense
at a number of different temperatures. This process
is fractional distillation.
c) Some properties of hydrocarbons depend on the
size of their molecules. These properties influence
how hydrocarbons are used as fuels.

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Hydrocarbons fuels

a) Most fuels, including coal, contain carbon and / or hydrogen and may also contain some sulfur. The gases released into the atmosphere when a fuel burns may include carbon dioxide, water (vapour), carbon monoxide, sulfur dioxide and oxides of nitrogen. Solid particles (particulates) may also be released.
b) The combustion of hydrocarbon fuels releases energy. During combustion the carbon and hydrogen in the fuels are oxidised.
c) Sulfur dioxide and oxides of nitrogen cause acid rain, carbon dioxide causes global warming, and solid particles cause global dimming.
d) Sulfur can be removed from fuels before they are burned, for example in vehicles. Sulfur dioxide can be removed from the waste gases after combustion, for example in power stations.
e) Biofuels, including biodiesel and ethanol, are produced from plant material. There are economic,
ethical and environmental issues surrounding
their use.

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Obtaining useful substances from crude oil

a) Hydrocarbons can be cracked to produce smaller, more useful molecules. This process involves heating the hydrocarbons to vaporise them. The vapours are either passed over a hot catalyst or mixed with steam and heated to a very high temperature so that thermal decomposition reactions then occur.
b) The products of cracking include alkanes and unsaturated hydrocarbons called alkenes. Alkenes have the general formula CnH2n.
c) Unsaturated hydrocarbon molecules can be represented in the following forms:
■ C3H6
■ H –– C –– C == C
d) Alkenes react with bromine water, turning it
from orange to colourless.
e) Some of the products of cracking are useful as fuels.

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a) Alkenes can be used to make polymers such as poly(ethene) and poly(propene). In these reactions, many small molecules (monomers) join together to
form very large molecules (polymers).
b) Polymers have many useful applications and new uses are being developed, for example: new packaging materials, waterproof coatings for fabrics, dental polymers, wound dressings,
hydrogels, smart materials (including shape memory polymers).
c) Many polymers are not biodegradable, so they are
not broken down by microbes and this can lead to
problems with waste disposal.
d) Plastic bags are being made from polymers and
cornstarch so that they break down more easily.
Biodegradable plastics made from cornstarch
have been developed.

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a) Ethanol can be produced by the hydration of
ethene with steam in the presence of a catalyst.
b) Ethanol can also be produced by fermentation
with yeast, using renewable resources.
This can be represented by:
sugar carbon dioxide + ethanol

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Vegetable oils

a) Some fruits, seeds and nuts are rich in oils that can
be extracted. The plant material is crushed and the
oil is removed by pressing or in some cases by
distillation. Water and other impurities are removed.
b) Vegetable oils are important foods and fuels as they
provide a lot of energy. They also provide us with
c) Vegetable oils have higher boiling points than water
and so can be used to cook foods at higher
temperatures than by boiling. This produces quicker
cooking and different flavours but increases the
energy that the food releases when it is eaten.

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a) Oils do not dissolve in water. They can be used to
produce emulsions. Emulsions are thicker than oil
or water and have many uses that depend on their
special properties. They provide better texture,
coating ability and appearance, for example in
salad dressings, ice creams, cosmetics and paints.
b) Emulsifiers have hydrophilic and hydrophobic

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Saturated and unsaturated oils

a) Vegetable oils that are unsaturated contain double
carbon–carbon bonds. These can be detected by
reacting with bromine water.
b) Vegetable oils that are unsaturated can be
hardened by reacting them with hydrogen in
the presence of a nickel catalyst at about 60°C.
Hydrogen adds to the carbon–carbon double
bonds. The hydrogenated oils have higher
melting points so they are solids at room
temperature, making them useful as spreads
and in cakes and pastries.

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The Earth’s crust

a) The Earth consists of a core, mantle and crust, and
is surrounded by the atmosphere.
b) The Earth’s crust and the upper part of the mantle
are cracked into a number of large pieces
(tectonic plates).
c) Convection currents within the Earth’s mantle driven
by heat released by natural radioactive processes
cause the plates to move at relative speeds of a few
centimetres per year.
d) The movements can be sudden and disastrous.
Earthquakes and / or volcanic eruptions occur at
the boundaries between tectonic plates.

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The Earths Atomsphere

a) For 200 million years, the proportions of different gases in the atmosphere have been much the same as they are today:
■ about four-fifths (80%) nitrogen
■ about one-fifth (20%) oxygen
■ small proportions of various other gases, including carbon dioxide, water vapour and noble gases.
b) During the first billion years of the Earth’s existence there was intense volcanic activity. This activity released the gases that formed the early atmosphere
and water vapour that condensed to form the oceans.
c) There are several theories about how the atmosphere was formed.
One theory suggests that during this period the Earth’s atmosphere was mainly carbon dioxide and there would have been little or no oxygen gas (like the atmospheres of Mars and Venus today). There may also have been water vapour and small proportions of methane and ammonia.
d) There are many theories as to how life was formed billions of years ago.
e) One theory as to how life was formed involves the interaction between hydrocarbons, ammonia and lightning. f) Plants and algae produced the oxygen that is now in the atmosphere.
g) Most of the carbon from the carbon dioxide in the air gradually became locked up in sedimentary rocks as carbonates and fossil fuels. h) The oceans also act as a reservoir for carbon dioxide but increased amounts of carbon dioxide absorbed by the oceans has an impact on the marine environment.
i) Nowadays the release of carbon dioxide by burning fossil fuels increases the level of carbon dioxide in the atmosphere.j) Air is a mixture of gases with different boiling points and can be fractionally distilled to provide a source of raw materials used in avariety of industrial processes.

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