chemistry igcse syllabus note

Question 1

Describe the meaning of exothermic and endothermic reactions

Answer 1

Endothermic (of a reaction or process) accompanied by or requiring the absorption of heat.
Exothermic (of a reaction or process) accompanied by the release of heat(or light).
(of a compound) formed from its constituent elements with a net release of heat.

Question 2

State the distinguishing properties

of solids, liquids and gases

Answer 2

gas are well separated with no regular arrangement. liquid are close together with no regular arrangement. solid are tightly packed, usually in a regular pattern.

Question 3

Describe changes of state in terms
of melting, boiling, evaporation,
freezing, condensation, deposition and
sublimation

Answer 3

Freezing: the substance changes from a liquid to a solid.
Melting: the substance changes back from the solid to the liquid.
Condensation: the substance changes from a gas to a liquid.
Vaporization: the substance changes from a liquid to a gas.
Sublimation: the substance changes directly from a solid to a gas without going through the liquid phase.
Deposition: the substance changes directly from a gas to a solid without going through the liquid phase.

Question 4

Describe qualitatively the pressure and temperature of a gas in terms of the motion of its particles

Answer 4

the higher the temperature of gas, the more pressure of the gas at constant volume

Question 5

Explain changes of state in terms

of the kinetic theory

Answer 5

The kinetic particle theory
Look at the key ideas you have met:
 A substance can be a solid, a
liquid, or a gas, and change from
one state to another.
 It has different characteristics in
each state. (For example, solids
do not flow.)
 The differences are due to the
way its particles are arranged,
and move, in each state.
Together, these ideas make up the
kinetic particle theory.
(Kinetic means about motion.)

Question 6

Describe and explain dependence
of rate of diffusion on molecular
mass

Answer 6

Graham’s law states that the rate of diffusion or of effusion of a gas is inversely proportional to the square root of its molecular weight. … Therefore the rate of diffusion of different gases is inversely proportional to the square root of their mass densities.

Question 7

Name appropriate apparatus
for the measurement of time,
temperature, mass and volume,
including burettes, pipettes and
measuring cylinders

Answer 7

stopwatches, ticker tape timer
thermometer
beam balance, electronic balance
beaker, measuring cylinder, Burette, Pipette

Question 8

Identify substances and assess
their purity from melting point
and boiling point information

Answer 8

The presence of impurities in a substance:
lowers the melting point, and
raises the boiling point of the substance.

Question 9

Understand the importance of
purity in substances in everyday
life, e.g. foodstuffs and drugs

Answer 9

Impurities may cause undesirable side effects

Question 10

Interpret simple chromatograms,

including the use of Rf values

Answer 10

Rf =distance moved by amino acid divided by the distance traveled by the solvent

Question 11

Outline how chromatography
techniques can be applied to
colourless substances by exposing
chromatograms to substances
called locating agents

Answer 11

After spraying, heat the paper in the oven for 10 minutes. The spots turn purple. So now you have a proper chromatogram.

Question 12

Describe and explain methods
of purification by the use of
a suitable solvent, filtration,
crystallisation and distillation
(including use of fractionating
column).

Answer 12

filtration (a solid from a liquid)
crystallisation (a solute from its solution)
evaporation (a solute from its solution)
simple distillation (a solvent from a solution)
fractional distillation (liquids from each other
paper chromatography( different substances from a solution)

Question 13

State the relative charges and
approximate relative masses of
protons, neutrons and electrons

Answer 13

Proton,positive. Neutron, neutral. Electron, negative.
The relative mass of a proton is 1. The relative mass of a neutron is 1. The relative mass of an electron is 1/1840 (accept 0).

Question 14

Isotopes

Answer 14

Atoms of
the same element which have
the same proton number but a
different nucleon number

Question 15

Describe the build-up of electrons
in ‘shells’ and understand the
significance of the noble gas
electronic structures and of the
outer shell electrons

Answer 15

The period shows the number of shells. The The amount of electrons increase from left to right and is shown by the group number. Group 0 or Noble gases have 0 has a full outer shell therefore nonreactive.

Question 16

Describe the differences
between elements, mixtures and
compounds, and between metals
and non-metals

Answer 16

Elements are defined by their proton number
Mixtures are different elements mixed together that are not bonded.
Compound are chemically bonded elements
While metals are good conductors of electricity and heat, non-metals are poor conductors. Unlike non-metals, metals are ductile, which means they can be stretched into wires. Another difference between metals and non-metals, is that the former has a metallic luster, while the other does not.

Question 17

Alloy

Answer 17

An alloy is a mixture of metal with other elements

Question 18

Describe the formation of ionic
bonds between metallic and nonmetallic
elements

Answer 18

Metal atoms will become positive ions because they loose electrons, whilst non-metal ions will become negative ions because they gain electrons

Question 19

Describe the differences in
volatility, solubility and electrical
conductivity between ionic and
covalent compounds

Answer 19

1 Ionic compounds have high melting and boiling points.
Ionic compounds are usually soluble in water. Ionic compounds conduct electricity, when melted or dissolved in
water.

2Molecular covalent compounds have low melting and boiling points.
Covalent compounds tend to be insoluble in water.
Covalent compounds do not conduct electricity.
A covalent liquid is usually volatile( evaporate easily)

Question 20

Explain the differences in melting
point and boiling point of ionic
and covalent compounds in terms
of attractive forces

Answer 20

This is because the ionic bonds are very strong. It takes a lot of heat
energy to break up the lattice. So ionic compounds are solid at room
temperature.
Note that magnesium oxide has a far higher melting and boiling point
than sodium chloride does. This is because its ions have double the
charge (Mg21 and O22 compared with Na1 and Cl2), so its ionic bonds
are stronger.

Question 21

Describe the giant covalent
structures of graphite and
diamond

Answer 21

In graphite, each carbon atom
forms covalent bonds to three
others. This gives rings of six atoms.
In a diamond, a carbon atom forms covalent
bonds to four others. Each outer atom then
bonds to three more, and so on.

Question 22

Relate their structures to their
uses, e.g. graphite as a lubricant
and a conductor, and diamond in
cutting tools

Answer 22

diamond hardest known substance
does not conduct
in tools for drilling and cutting
sparkles when cut for jewellery
graphite soft and slippery as a lubricant for engines and locks
soft and dark in colour for pencil ‘lead’ (mixed with clay)
conducts electricity for electrodes, and connecting brushes
in generators
silica hard, can scratch things in sandpaper
hard, lets light through for making glass and lenses
high melting point in bricks for lining furnaces

Question 23

Describe the macromolecular
structure of silicon(IV) oxide
(silicon dioxide)

Answer 23

Each silicon atom bonds covalently to four oxygen atoms. And each
oxygen atom bonds covalently to two silicon atoms. The result is a very
hard substance with a melting point of 1710 8C.

Question 24

Describe the similarity in
properties between diamond and
silicon(IV) oxide, related to their
structures

Answer 24

1) They both have a tetrahedral crystal structure which imparts a certain hardness to the material. … 4) They both have high melting points (over 1500 K) 5) They are both relatively inert (stable to chemical reactivity)

Question 25

``` Describe metallic bonding as a lattice of positive ions in a ‘sea of electrons’ and use this to describe the electrical conductivity and malleability of metals ```

Answer 25

In metals, the atoms are packed tightly together in a regular lattice. The tight packing allows outer electrons to separate from their atoms. The result is a lattice of ions in a ‘sea’ of electrons that are free to move. They are malleable because the layers can slide over each other. They are good conductors of heat and electricity because the electrons can flow freely between atoms.

Question 26

Define the mole and the Avogadro | constant

Answer 26

A mole of a substance is the amount that contains the same number of units as the number of carbon atoms in 12 grams of carbon-12. we know that 12 g of carbon-12 contains 602 000 000 000 000 000 000 000 carbon atoms the Avogadro constant. It is written in a short way as 6.02 * 10^23. One mole of a substance is obtained by weighing out the Ar or Mr of the substance, in grams.

Question 27

Use the molar gas volume, taken as 24 dm3 at room temperature and pressure

Answer 27

Avogadro’s Law 1 mole of every gas occupies the same volume, at the same temperature and pressure. At room temperature and pressure, this volume is 24 dm3.

Question 28

``` Calculate stoichiometric reacting masses, volumes of gases and solutions, and concentrations of solutions expressed in g / dm3 and mol / dm3 ```

Answer 28

The concentration of a solution is the amount of solute, in grams or moles, that is dissolved in 1 dm3 of solution.

Question 29

Calculations involving the idea of | limiting reactants

Answer 29

The limiting reagent (or limiting reactant or limiting agent) in a chemical reaction is the substance that is totally consumed when the chemical reaction is complete. The amount of product formed is limited by this reagent, since the reaction cannot continue without it.

Question 30

Calculate empirical formulae and | molecular formulae

Answer 30

The empirical formula shows the simplest ration of the atoms present Steps for Determining an Empirical Formula Start with the number of grams of each element, given in the problem. If percentages are given, assume that the total mass is 100 grams so that the mass of each element = the percent given. Convert the mass of each element to moles using the molar mass from the periodic table. Divide each mole value by the smallest number of moles calculated. Round to the nearest whole number. This is the mole ratio of the elements and is represented by subscripts in the empirical formula. If the number is too far to round (x.1 ~ x.9), then multiply each solution by the same factor to get the lowest whole number multiple. e. g. If one solution is 1.5, then multiply each solution in the problem by 2 to get 3. e. g. If one solution is 1.25, then multiply each solution in the problem by 4 to get 5.

Question 31

Calculate percentage yield and | percentage purity

Answer 31

percentage purity = mass of the pure product/ mass of the impure product obtained × 100% percentage yield = actual yield/ theoretical yield

Question 32

Define electrolysis as the breakdown of an ionic compound, molten or in aqueous solution, by the passage of electricity

Answer 32

Guidelines ●● Non-metals are produced at the anode whereas metals and hydrogen gas are produced at the cathode. ●● At the inert anode, chlorine, bromine and iodine (the halogens) are produced in preference to oxygen. ●● At the inert cathode, hydrogen is produced in preference to metals unless unreactive metals such as copper and nickel are present.

Question 33

Describe the electrode products and the observations made during the electrolysis of: • molten lead(II) bromide

Answer 33

positive lead attracted to negative terminal. Negative bromide attracted to positive terminal. Bromine vapour (orange) forms around positive terminal

Question 34

``` Describe the electrode products and the observations made during the electrolysis of: concentrated hydrochloric acid ```

Answer 34

two gases are created. Both chlorine and hydrogen would be attracted the anode. Chlorine then forms a bond with itself 2cl ->cl2 + 2el- hydrogen bonds with the electrons and is attracted to cathode.

Question 35

``` Describe the electrode products and the observations made during the electrolysis of: concentrated aqueous sodium chloride ```

Answer 35

When the current flows, the chloride ions, Cl−(aq), are attracted to the anode. Chlorine gas is produced by the electrode process. This leaves a high concentration of sodium ions, Na+(aq), around the anode. The hydrogen ions, H+(aq), are attracted to the cathode and hydrogen gas is produced. This leaves a high concentration of hydroxide ions, OH−(aq), around the cathode. The sodium ions, Na+(aq), are drawn through the membrane, where they combine with the OH−(aq) to form sodium hydroxide, NaOH, solution.

Question 36

Describe the electrode products and the observations made during the electrolysis of: dilute sulfuric acid

Answer 36

Dilute sulfuric acid H2SO4 (aq). It contains water (H2O) as well. The ions present are H+, SO42- and OH-. There is only one positive ion that can discharge at the cathode and that is hydrogen. Hydrogen will undergo reduction (gain electrons) to become hydrogen atoms. 2H+ + 2e– ——————-> H2At the anion, OH will be discharged, as it is less reactive than the sulfate. OH will undergo oxidisation to lose electrons and become water and oxygen. 4OH2- – 4e– ————————> 2H2O +O2

Question 37

On which electrode ( anode or cathode) are metals, hydrogen and non-metals formed?

Answer 37

There is a general principle that metals or hydrogen are formed at the negative electrode (cathode), and that non-metals (other than hydrogen) are formed at the positive electrode (anode)

Question 38

Describe the electroplating of | metals

Answer 38

Electroplating is a process that uses an electric current to reduce dissolved metal cations so that they form a thin coherent metal coating on an electrode. ... A power supply supplies a direct current to the anode, oxidizing the metal atoms that it comprises and allowing them to dissolve in the solution

Question 39

Outline the uses of electroplating

Answer 39

Electroplating is primarily used to change the surface properties of an object (such as abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities), but may also be used to build up thickness on undersized parts or to form objects by electroforming.

Question 40

``` Describe, in outline, the manufacture of: • aluminium from pure aluminium oxide in molten cryolite (see sub-topic 10.3) ```

Answer 40

``` Bauxite treated with sodium hydroxide pure aluminium oxide is dissolved in molten cryolite put it in electrolysis tank aluminium goes to the cathode oxygen goes to anode ```

Question 41

``` Describe, in outline, the manufacture of: • chlorine, hydrogen and sodium hydroxide from concentrated aqueous sodium chloride ```

Answer 41

When the current flows, the chloride ions, Cl−(aq), are attracted to the anode. Chlorine gas is produced by the electrode process. oxidation chloride ions 2Cl−(aq) chlorine molecules Cl2(g) + + electrons 2e− This leaves a high concentration of sodium ions, Na+(aq), around the anode. The hydrogen ions, H+(aq), are attracted to the cathode and hydrogen gas is produced. hydrogen ions 2H+(aq) + + electrons 2e− hydrogen molecules H2(g) reduction This leaves a high concentration of hydroxide ions, OH−(aq), around the cathode. The sodium ions, Na+(aq), are drawn through the membrane, where they combine with the OH−(aq) to form sodium hydroxide, NaOH, solution.

Question 42

Describe the meaning of exothermic and endothermic reactions

Answer 42

Endothermic (of a reaction or process) accompanied by or requiring the absorption of heat. Exothermic (of a reaction or process) accompanied by the release of heat(or light).

Question 43

Describe bond breaking as an endothermic process and bond forming as an exothermic process

Answer 43

When chemical bonds are formed, heat is released, and when chemical bonds are broken, heat is absorbed. Molecules inherently want to stay together, so formation of chemical bonds between molecules requires less energy as compared to breaking bonds between molecules, which requires more energy and results in heat being absorbed from the surroundings.

Question 44

Draw and label energy level diagrams for exothermic and endothermic reactions using data provided

Answer 44

The energy stored in the bonds is called the enthalpy and is given the symbol H. The change in energy going from reactants to products is called the change in enthalpy and is shown as ΔH (pronounced ‘delta H’). ΔH is called the heat of reaction.

Question 45

Describe the release of heat | energy by burning fuels

Answer 45

methane + oxygen = carbon dioxide + water + energy

Question 46

State the use of hydrogen as a | fuel

Answer 46

It doesn't make waste. It just creates water. an almost unlimited amount can be made by eletrolysis. The only problem is that it is costly.

Question 47

Describe radioactive isotopes, | such as 235U, as a source of energy

Answer 47

Nuclear fission happens when one neutron hits a 235U causing it to split and produce three more neutrons. This starts a chain-reaction which releases a lot of energy. It produces waste which is extremely radioactive, hard to store and hard to dispose of.

Question 48

Describe the use of hydrogen as a fuel reacting with oxygen to generate electricity in a fuel cell

Answer 48

The aqueous NaOH electrolyte is kept within the cell by electrodes which are porous, allowing the transfer of O2, H2 and water through them (Figure 6.25). As O2 gas is passed into the cathode region of the cell it is reduced: O2(g) + 2H2O(l) + 4e− → 4OH−(aq) The OH− ions formed are removed from the fuel cell by reaction with H2: H2(g) + 2OH−(aq) → 2H2O(l) + 2e− The electrons produced by this process pass around an external circuit to the cathode.

Question 49

``` Describe and explain the effect of concentration, particle size, catalysts (including enzymes) and temperature on the rate of reactions ```

Answer 49

For reaction to take place collision must happen. Concentration means that there are more atoms per cm^3 and therefore a higher chance of collisions. The bigger the particle the bigger the surface area and the bigger the chance of collision and faster rate of reaction. Catalyst speed up the rate of reactions. A catalyst increases the rate of a chemical reaction by providing an alternative reaction path which has a lower activation energy. A catalyst does not increase the number of collisions between the reactant particles but only causes more of the collisions to become successful collisions, so increasing the rate of the reaction. The higher the temperature the faster the particles and the higher chance of collision.

Question 50

``` Describe the application of the above factors to the danger of explosive combustion with fine powders (e.g. flour mills) and gases (e.g. methane in mines) ```

Answer 50

With fine powder there is a lot of surface area and high chances for collision. This can cause explosive reactions. with methane in mines. there is not really anywhere for the flammable gas to go do it stays concentrated in the tunnels. If one of the miners makes a spark, then it can set alight the whole mine.

Question 51

``` Demonstrate knowledge and understanding of a practical method for investigating the rate of a reaction involving gas evolution ```

Answer 51

A gas evolution reaction is a chemical process that produces a gas, such as oxygen or carbon dioxide. In the following examples, an acid reacts with a carbonate, producing salt, carbon dioxide, and water, respective.

Question 52

Describe and explain the role of light in photochemical reactions and the effect of light on the rate of these reactions

Answer 52

Some chemical reactions are affected by light. When particles absorb light energy, the energy can be used to break bonds, overcoming the activation energy of the reactions and causing a chemical reaction to occur faster (see p. 105). Reactions which occur as a result of the absorption of light are known as photochemical reactions.

Question 53

Demonstrate knowledge and understanding of the concept of equilibrium

Answer 53

``` equilibrium noun *a state in which opposing forces or influences are balanced. *a state of physical balance *a calm state of mind. ```

Question 54

Define oxidation and reduction in | terms of oxygen loss/gain.

Answer 54

oxidation is oxygen gain, reduction is oxygen loss

Question 55

Define redox in terms of electron | transfer

Answer 55

A handy way of remembering it is OIL RIG | Oxidation Is Loss, Reduction Is Gain of electrons

Question 56

Define oxidising agent as a substance which oxidises another substance during a redox reaction.

Answer 56

An oxidising agent is a substance which oxidises another substance during a redox reaction

Question 57

Define reducing agent as a substance which reduces another substance during a redox reaction.

Answer 57

An reducing agent is a substance which reduces another substance during a redox reaction

Question 58

``` Describe the characteristic properties of acids as reactions with metals, bases, carbonates and effect on litmus and methyl orange ```

Answer 58

An acid is a substance that dissolves in water to produce hydrogen. Acids are sour in taste and are corrosive nature. Examples: hydrochloric acid (found in our stomachs), citric acid (found in ‘citrus’ fruits such as oranges and lemon) and ethanoic acid (found in vinegar) acids have pH values from 0 to 6, 0 being the strongest acids and 6 being the weakest acids. If the blue litmus paper turns red or if red litmus paper stays red the solution must be acidic .

Question 59

Describe and explain the importance of controlling acidity in soil

Answer 59

: Soil is used to grow crops, so it is important for it to be neutral. If it is too alkaline or acidic, the crops won’t grow properly. Acidity is usually the problem for soil, so a base can help neutralise it. Bases like limestone, slaked lime, or quick lime are usually sprayed in the soil to neutralise it before planting crops.

Question 60

Define acids and bases in terms of proton transfer, limited to aqueous solutions

Answer 60

* an acid as an H+ ion (or proton) donor | * a base as an H+ ion (or proton) acceptor.

Question 61

Describe the change from metallic to non-metallic character across a period

Answer 61

left of the dark line under boron is metals and right of it is non metals.

Question 62

``` Describe and explain the relationship between Group number, number of outer shell electrons and metallic/nonmetallic character ```

Answer 62

The group number usually is the same as the number of electrons in the outer shell. The more right you go in the periodic table the more the element has non metal characteristics.

Question 63

Describe lithium, sodium and potassium in Group I

Answer 63

a collection of relatively soft metals showing a trend in melting point, density and reaction with water

Question 64

``` Describe the halogens, chlorine, bromine and iodine in Group VII, as a collection of diatomic non- metals showing a trend in colour and density and state their reaction with other halide ions ```

Answer 64

Any of a group of five nonmetallic elements with similar properties. The halogens are fluorine, chlorine, bromine, iodine, and astatine. Because they are missing an electron from their outermost shell, they react readily with most metals to form salts. As you go down the group this outermost extra electron is further from the nucleus. It will, therefore, be held less securely, and the resulting reactivity of the elements in Group VII will decrease down the groupI2(aq) orangebrown 2I−(aq) colourless + Cl2(g) green

Question 65

``` Describe and explain the relationship between Group number, number of outer shell electrons and metallic/nonmetallic character ```

Answer 65

The group number usually is the same as the number of electrons in the outer shell. The more right you go in the periodic table the more the element has non metal characteristics.

Question 66

Describe the transition elements

Answer 66

``` a collection of metals having high densities, high melting points and forming coloured compounds, and which, as elements and compounds, often act as catalysts ```

Question 67

Describe the noble gases, | in Group VIII or 0,

Answer 67

unreactive, monoatomic gases and explain this in terms of electronic structure

Question 68

State the uses of the noble gases in providing an inert atmosphere, i.e. argon in lamps, helium for filling balloons

Answer 68

Argon, for example, is the gas used to fill light bulbs to prevent the tungsten filament reacting with air. Neon is used extensively in advertising signs and in lasers. Further uses of these gases are discussed in Chapter 11, p. 176. Helium is separated from natural gas by the liquefaction of the other gases. The other noble gases are obtained in large quantities by the fractional distillation of liquid air (Chapter 11, p. 174).

Question 69

List the general physical | properties of metals

Answer 69

high melting point good heat/electricity conductors ductile malleable

Question 70

Explain in terms of their properties why alloys are used instead of pure metals

Answer 70

When a metal is alloyed with a second metal, the different sized metal atoms make the arrangement of the lattice less regular. This stops the layers of metal atoms from sliding easily over each other when a force is applied. Thus an alloy is stronger and harder than a pure metal. This is why alloys are used rather than metals for industrial uses. One very common alloy is the brass. It is an alloy made of copper and zinc. It is stronger than copper but still malleable, so is used in making musical instruments and ornaments. Another very common alloy is stainless steel, made from iron, chromium and nickel. Iron rusts easily but the alloy doesn’t, so it can be used to make car parts, cutlery, surgical instruments etc.