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IGCSE Chemistry

TOPIC 0

Introduction to IGCSE Chemistry

States of Matter 1.1 understand the arrangement, movement and energy of the particles in each of the three states of matter: solid, liquid and gas

Solids

As you can see, the spacing between particles is extremely small and they are close together and touching one another. Solids have a regular and repeating pattern and vibrate in their fixed positions but do not move apart. They have strong forces between the particles, which is stronger than liquids and gases.

Liquids

Liquids also have particles that are close together and touching each other, but their arrangement of particles is irregular. They move around and slide past each other. The forces between particles is not as strong as in solids.

Gases

There is a large spacing between the gas particles and the arrangement is irregular. The particles move freely and constantly collide with each other. There are no forces between particles


IGCSE Chemistry

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Introduction to IGCSE Chemistry

1.2 & 1.3 understand how the interconversions of solids, liquids and gases are achieved and recall the names used for these interconversions Solid to Liquid- (melting)

The particles gain kinetic energy and vibrate faster and faster. This allows the particles to overcome forces off attraction that holds them in place in the state of a solid. The regular pattern is broken down and the particles are free to 'slide over' each other.

Liquid to Solid- (freezing)

The particles lose kinetic energy and this allows the forces of attraction between the particles to hold them together. The particles arrange themselves into a regular pattern and cannot slide over each other.

Liquid to Gas- (boiling)

The particles gain kinetic energy and move further apart. Eventually the forces of attraction between the particles are completely destroyed and are then able to escape from the liquid.

Gas to Liquid- (condensing)

The particles lose kinetic energy and this allows the forces of attraction to bring the particles closer together. The particles eventually clump together to form a liquid.

Solid to Gas- (sublimation)

The particles gain kinetic energy and vibrate faster and faster. Eventually the forces of attraction between particles are completely broken and they are able to escape from the solid.


IGCSE Chemistry

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Introduction to IGCSE Chemistry

1.4 describe and explain experiments to investigate the small size of particles and their movement including: i dilution of coloured solutions ii diffusion experiments Dilution of coloured solutions When potassium manganate (VII) crystals are dissolved in water, a purple solution is formed. A very few tiny crystals can produce a highly intense colour. When this solution is diluted several times, the colour fades, but does not disappear until a lot of dilutions are made. This indicated that there are a large number of particles of potassium manganate (VII) in a very small amount of solid. If this is true, then the particles of potassium manganate (VII) must be very tiny.

Diffusion Particles will move to fill the space available to them. They can do this in both liquids and gases. An example is the diffusion of bromine from one flask to another. After five minutes the bromine gas has diffused into the left-hand flask. This happens because both air and bromine particles are moving randomly and there are large gaps between the particles. The particles can therefore easily mix together.

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IGCSE Chemistry

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Introduction to IGCSE Chemistry

Atoms 1.5 understand the terms atom and molecule Atoms and molecules Atoms are made up of sub-atomic particles called protons, neutrons and electrons. Most molecules are made up of two or more atoms covalently bonded together. Molecules that contain only one atom are called monatomic molecules.

1.6 understand the differences between elements, compounds and mixtures Elements, compounds and mixtures

Elements and compounds have their own chemical properties. The properties of a compound are likely to be different from the elements that have been used to make it. A mixture will have the properties of each substance been used to make it.

Elements- Only one substance, all elements are listed on the periodic table. e.g Na, O, Fe

Molecules- 2 or more elements chemically bonded e.g NaCl, MgO

Mixtures- 2 or more elements that have not been bonded together e.g Iron and sulfur

1.7 describe experimental techniques for the separation of mixtures, including simple distillation, fractional distillation (studied later in organic chemistry), filtration,


IGCSE Chemistry

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Introduction to IGCSE Chemistry

crystallisation and paper chromatography

Separation of mixtures Since the components of a mixture are not bonded together, they can be separated without using chemical reactions. Filtration- To separate an undissolved solid from a mixture of the solid and a liquid/solution (e.g. sand and water)

Evaporation- To separate a dissolved solid from a solution, when a solid has similar solubilities in both cold and hot solvent (e.g. sodium chloride from a solution of sodium chloride and water)

Crystallisation- To separate a dissolved solid from a solution, when the solid is much more soluble in hot solvent than cold (e.g. copper (II) sulfate from a solution of copper (II) sulfate in water)

Separation of mixtures


IGCSE Chemistry

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Introduction to IGCSE Chemistry

Simple distillation- To separate a liquid from a solution (water from a solution with sodium chloride and water)

[Fractional distillation- To separate two or more liquids that a miscible with each other (e.g. ethanol and water) to learn later in organic chemistry]

Paper chromatography- To separate that have different solubilities in a given solvent (e.g. different coloured inks that have been mixed to make black ink)

Separation of two or more immiscible liquids. The higher density liquid can be removed through the tap at the bottom of the separating funnel.

1.8 Explain how information from chromatograms can be used to identify the composition of a mixture.


IGCSE Chemistry

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Introduction to IGCSE Chemistry

Chromatography Chromatography can be used to separate mixtures of coloured compounds. Simple chromatography is carried out on paper. A spot of the mixture is placed near the bottom of a piece of chromatography and the paper is then placed upright in a suitable solvent, e.g. water. As the solvent soaks up the paper, it carries mixtures with it. Different components of the mixture will move at different rates, this separates the mixture out.

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Atomic Structure 1.9 understand that atoms consist of a central nucleus, composed of protons and neutrons, surrounded by electrons, orbiting in shells Protons, neutrons and electrons

As you can see from the diagram, in the centre of the atom is the nucleus, which contains protons (positive charge) and neutrons (no charge). Orbiting the nucleus is a series of shells, which hold electrons (negative charge). The electrons are much smaller than the protons and neutrons. The first shell outside the nucleus can hold 2 electrons, the second can hold 8 and the third can hold 8.

1.10 recall the relative mass and relative charge of a proton, neutron and electron


IGCSE Chemistry

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Introduction to IGCSE Chemistry

Relative mass and relative charge Neutron: Relative charge: 0 Relative mass: 1 Proton: Relative charge: +1 Relative mass: 1 Electron: Relative charge: -1 Relative mass: 1/1836

Nearly all the mass is concentrated in the nucleus. 1.11 understand the terms atomic number, mass number, isotopes and relative atomic mass (Ar ) Atomic number, mass number, isotopes and relative atomic mass

Atomic number= number of protons in the nucleus of an atom Mass number= number of protons + number of neutrons in the nucleus of an atom Isotopes are atoms that have the same atomic number but different mass numbers. This is because they contain the same number of protons but different numbers of neutrons. Relative atomic mass is calculated from the masses and relative abundances of all the isotopes of a particular element. It is usually given in the symbol Ar. 1.12 calculate the relative atomic mass of an element from the relative abundances of its isotopes Calculating the relative atomic mass


IGCSE Chemistry

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Introduction to IGCSE Chemistry

Example: Chlorine has two isotopes: chlorine-35 and chlorine-37 A typical sample of chlorine will be 75% chlorine-35 atoms and 25% chlorine-37 atoms. Total mass of 100 atoms= (75 x 35) + 5 x 37)= 3550 Mean mass of 1 atom= (3550 รท 100)= 35.5 Ar of chlorine is 35.5 1.13 understand that the Periodic Table is an arrangement of elements in order of thatomic number Periodic Table

As you can see the periodic table, shows all the elements known to man, and is arranged in periods and groups. It shows the arrangement of elements in order of atomic number.

1.14 deduce the electronic configurations of the first 20 elements from their positions in the Periodic Table Electronic configuration


IGCSE Chemistry

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Introduction to IGCSE Chemistry

The arrangement of electrons into shells for an atom is known as its electronic configuration As you are given a periodic table in the exam, you don't have to remember all of them, just be able to state them when asked. They are given in shorthand notations, e.g. Carbon has 6 electrons, so its EC would be 2.4 Aluminium has 13 electrons, so its EC would be 2.8.3 1.15 deduce the number of outer electrons in a main group element from its position in the Periodic Table. Number of electrons is the same as the group number on the Periodic Table. The outer electrons are called valence electrons As you can see (Periodic Table above), some of the columns of the table have numbers above them, this tells us how many electrons are in the outer shell of that group. It is a good idea to label this on your periodic table in your chemistry exam. 1.16 calculate relative formula masses (Mr ) from relative atomic masses (Ar) Relative formula masses Relative formula mass is given the symbol, Mr. To calculate the Mr, of a substance, all you have to do is add up the relative atomic masses of all the atoms present in the formula. Water- Hâ‚‚0 Atoms present:(2 x H) + (1 x O) Mr= (2 x 1) + 16= 18 There is 1 electron per hydrogen atom, and 2 hydrogen atoms, so that is 2 electrons. There is also 1 oxygen atom, which has 16 electrons, 2 + 16= 18 ___________________________________________________________________

Tests for Ions and Gases 2.36 describe tests for the cations: i Li+ , Na+ , K+ , Ca2+ using flame tests ii NH4 + ,


IGCSE Chemistry

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Introduction to IGCSE Chemistry

using sodium hydroxide solution and identifying the ammonia evolved iii Cu2+, Fe2+ and Fe3+, using sodium hydroxide solution Flame tests Lithium: Potassium: Calcium: Sodium:

Red Lilac Brick Red Yellow/orange

Identifying the ammonium ion Test: Add aqueous sodium hydroxide to the solid, or solution, under test and warm the mixture. Result: If ammonium ions are present then a pungent-smelling gas is produced. The gas is produced turns damp red litmus paper  blue. Identifying metal cations Copper (II): blue precipitate Iron (II): green precipitate Iron (III): brown precipitate

2.37 describe tests for the anions: i Cl- , Br- and I- , using dilute nitric acid and silver nitrate solution ii SO4 2- , using dilute hydrochloric acid and barium chloride solution iii CO3 2- , using dilute hydrochloric acid and identifying the carbon dioxide evolved

Identification of anions Test: To an aqueous solution of the solid under test, add some dilute nitric acid followed by a few drops of silver nitrate solution. chloride ion bromide ion iodide ion

white precipitate cream precipitate yellow precipitate

Sulfate ions Test: Add dilute hydrochloric acid followed by a few drops of barium chloride solution


IGCSE Chemistry

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Introduction to IGCSE Chemistry

with the sulfate ions Result: White precipitate (of barium sulfate) Carbonate ions Test: To either the solid, or an aqueous solution of the solid, under test add dilute hydrochloric (or nitric) acid Result: Bubbles of carbon dioxide gas. Test: will turn limewater milky. 2.38 describe tests for the gases: i hydrogen ii oxygen iii carbon dioxide iv ammonia v chlorine Hydrogen: Mix with air and ignite- 'squeaky pop' Oxygen: Insert glowing splint- splint relights Carbon dioxide: Bubble through limewater- limewater turns milky Ammonia: Damp red litmus paper- turns blue Chlorine: Damp litmus paper- turns white 2.25 describe the combustion of hydrogen Combustion of hydrogen Hydrogen burns when heated in the air or oxygen to form water. The product will be formed initially as water vapour, but if cooled it can be condensed to form water.

2.26 describe the use of anhydrous copper(II) sulfate in the chemical test for water Using anhydrous copper (II) sulfate to test for water


IGCSE Chemistry

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Introduction to IGCSE Chemistry

Add the liquid that you are testing to anhydrous copper (II) sulfate. The white powder will turn blue if there is water present in the liquid.

2.27 describe a physical test to show whether water is pure. Physical test to show whether water is pure Boil the liquid and measure its boiling point. If it is water, its boiling point will be 100ËšC.

2.17 describe the laboratory preparation of oxygen from hydrogen peroxide, using manganese(IV) oxide as a catalyst Preparation of oxygen Oxygen is most easily made in the lab from hydrogen peroxide solution using manganese (IV) oxide as a catalyst. The reaction is known as the catalytic decomposition (splitting up using a catalyst) of hydrogen peroxide.

2H2O2 (aq) → 2H2O(l) + O2(g)

The oxygen produced is collected in an inverted glass cylinder by the downward displacement of water in a trough.

Hydrogen peroxide, decomposes slowly to form water and oxygen. The speed of the decomposition is increased by adding solid manganese dioxide, which acts as a catalyst.


IGCSE Chemistry

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Introduction to IGCSE Chemistry

The oxygen can also be collected over water. Since oxygen is not very soluble in water, very little is lost. 2.19 describe the laboratory preparation of carbon dioxide from calcium carbonate and dilute hydrochloric acid

The reaction between any metal carbonate and an acid will form carbon dioxide. Calcium carbonate is the most commonly used metal carbonate in the lab to produce carbon dioxide. The most convenient form of calcium carbonate is marble chips. They are easy to handle and the reaction is not too fast, so the carbon dioxide is produced at a rate that makes it easy to collect. The marble chips are calcium carbonate. Remember acids react with carbonates to give a salt, carbon dioxide and water. Acid + metal carbonate → salt + carbon dioxide + water CaCO3 (s) + 2HCl (aq) → CaCl2 (aq) + CO2 (g) + H2O (l) It displaces the air as it is denser.

2.20 describe the formation of carbon dioxide from the thermal decomposition of metal carbonates such as copper (II) carbonate

Most carbonates decompose (split up) when heated to from the metal oxide and carbon dioxide. In the case of copper (II) carbonate, this is a green powder which decomposes to


IGCSE Chemistry

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Introduction to IGCSE Chemistry

give copper (II) oxide, which is a black powder and carbon dioxide when heated. CuCO3 (s) → CuO (s) + CO2 (g)

2.21 describe the properties of carbon dioxide, limited to its solubility and density Carbon dioxide is more dense than air and is soluble in water at a high pressure. 2.22 explain the use of carbon dioxide in carbonating drinks and in fire extinguishers, in terms of its solubility and density Uses of carbon dioxide ●

Making carbonated drinks. Even though carbon dioxide is not very soluble in water in normal pressures, it becomes much more soluble when it is put under high pressures. This is a method used to make fizzy drinks. When you open the bottle/can, the pressure falls and the gas bubbles out of the solution.

It is used in fire extinguishers because carbon dioxide does not support combustion. It is a dense gas, denser than oxygen and can displace it, basically pushing it out of the way so that no more oxygen reaches the fire. i.e. it 'sits' on top of the burning fuel and prevents oxygen from getting to it, thereby putting it out.

2.23 understand that carbon dioxide is a greenhouse gas and may contribute to climate change. Carbon dioxide is a greenhouse gas since it absorbs infra-red radiation given off from Earth's surface. In recent years the amount of carbon dioxide in Earth's atmosphere has increased. This is because we're burning more fossil fuels than before. Some scientists think that this is contributing to climate change.

The pH value of unpolluted rainwater is usually slightly below 7. This is because carbon dioxide in the air dissolves in rainwater to form carbonic acid, which is a weak acid. CO2 (g) + H2O (l) → H2CO3 (aq)


IGCSE Chemistry

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Introduction to IGCSE Chemistry

2.15 recall the gases present in air and their approximate percentage by volume Gases in the air Nitrogen 78% Oxygen 21% Argon 0.9% Carbon dioxide 0.04%

This is for unpolluted, dry air. Normally air contains a little water vapour too!

2.16 explain how experiments involving the reactions of elements such as copper, iron and phosphorus with air can be used to investigate the percentage by volume of oxygen in air Using copper:


IGCSE Chemistry

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Introduction to IGCSE Chemistry

An experiment was carried out to find the percentage of air that is oxygen. 100 cm3 of air was passed from side to side over copper that was being heated with a Bunsen. All the oxygen in the air will react with the copper. No air could get in or out of the system while it was passed to and fro between the syringes. As it was passed to and fro, the volume of air went down. It was passed until the volume stopped decreasing, and a few minutes later the volume of remaining air was recorded. There was 79 cm3 left. This shows that 21cm3 of the original 100cm3 of air was oxygen, because it was the oxygen that reacted with the copper to form black copper oxide. During this experiment, you should see the copper go black as it forms copper (II) oxide. copper + oxygen → copper (II) oxide 2Cu (s) + O2 (g) → 2CuO (s)

END OF TOPIC 0: Introduction to IGCSE Chemistry


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