chemistry igcse syllabus note Flashcards
Describe the meaning of exothermic and endothermic reactions
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.
State the distinguishing properties
of solids, liquids and gases
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.
Describe changes of state in terms
of melting, boiling, evaporation,
freezing, condensation, deposition and
sublimation
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.
Describe qualitatively the pressure and temperature of a gas in terms of the motion of its particles
the higher the temperature of gas, the more pressure of the gas at constant volume
Explain changes of state in terms
of the kinetic theory
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.)
Describe and explain dependence
of rate of diffusion on molecular
mass
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.
Name appropriate apparatus for the measurement of time, temperature, mass and volume, including burettes, pipettes and measuring cylinders
stopwatches, ticker tape timer
thermometer
beam balance, electronic balance
beaker, measuring cylinder, Burette, Pipette
Identify substances and assess
their purity from melting point
and boiling point information
The presence of impurities in a substance:
lowers the melting point, and
raises the boiling point of the substance.
Understand the importance of
purity in substances in everyday
life, e.g. foodstuffs and drugs
Impurities may cause undesirable side effects
Interpret simple chromatograms,
including the use of Rf values
Rf =distance moved by amino acid divided by the distance traveled by the solvent
Outline how chromatography techniques can be applied to colourless substances by exposing chromatograms to substances called locating agents
After spraying, heat the paper in the oven for 10 minutes. The spots turn purple. So now you have a proper chromatogram.
Describe and explain methods of purification by the use of a suitable solvent, filtration, crystallisation and distillation (including use of fractionating column).
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)
State the relative charges and
approximate relative masses of
protons, neutrons and electrons
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).
Isotopes
Atoms of
the same element which have
the same proton number but a
different nucleon number
Describe the build-up of electrons in ‘shells’ and understand the significance of the noble gas electronic structures and of the outer shell electrons
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.
Describe the differences
between elements, mixtures and
compounds, and between metals
and non-metals
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.
Alloy
An alloy is a mixture of metal with other elements
Describe the formation of ionic
bonds between metallic and nonmetallic
elements
Metal atoms will become positive ions because they loose electrons, whilst non-metal ions will become negative ions because they gain electrons
Describe the differences in
volatility, solubility and electrical
conductivity between ionic and
covalent compounds
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)
Explain the differences in melting
point and boiling point of ionic
and covalent compounds in terms
of attractive forces
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.
Describe the giant covalent
structures of graphite and
diamond
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.
Relate their structures to their
uses, e.g. graphite as a lubricant
and a conductor, and diamond in
cutting tools
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
Describe the macromolecular
structure of silicon(IV) oxide
(silicon dioxide)
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.
Describe the similarity in
properties between diamond and
silicon(IV) oxide, related to their
structures
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)
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
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.
Define the mole and the Avogadro
constant
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.
Use the molar gas volume, taken
as 24 dm3 at room temperature
and pressure
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.
Calculate stoichiometric reacting masses, volumes of gases and solutions, and concentrations of solutions expressed in g / dm3 and mol / dm3
The concentration of a solution is the amount of solute, in grams or
moles, that is dissolved in 1 dm3 of solution.
Calculations involving the idea of
limiting reactants
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.
Calculate empirical formulae and
molecular formulae
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.
Calculate percentage yield and
percentage purity
percentage purity = mass of the pure product/ mass of the impure product obtained × 100%
percentage yield = actual yield/ theoretical yield
Define electrolysis as the
breakdown of an ionic compound,
molten or in aqueous solution, by
the passage of electricity
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.
Describe the electrode products
and the observations made during
the electrolysis of:
• molten lead(II) bromide
positive lead attracted to negative terminal. Negative bromide attracted to positive terminal. Bromine vapour (orange) forms around positive terminal
Describe the electrode products and the observations made during the electrolysis of: concentrated hydrochloric acid
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.
Describe the electrode products and the observations made during the electrolysis of: concentrated aqueous sodium chloride
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.
Describe the electrode products
and the observations made during
the electrolysis of:
dilute sulfuric acid
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
On which electrode ( anode or cathode) are metals, hydrogen and non-metals formed?
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)
Describe the electroplating of
metals
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
Outline the uses of electroplating
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.
Describe, in outline, the manufacture of: • aluminium from pure aluminium oxide in molten cryolite (see sub-topic 10.3)
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
Describe, in outline, the manufacture of: • chlorine, hydrogen and sodium hydroxide from concentrated aqueous sodium chloride
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.
Describe the meaning of
exothermic and endothermic
reactions
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).
Describe bond breaking as an
endothermic process and bond
forming as an exothermic process
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.
Draw and label energy level
diagrams for exothermic and
endothermic reactions using data
provided
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.
Describe the release of heat
energy by burning fuels
methane + oxygen = carbon dioxide + water + energy
State the use of hydrogen as a
fuel
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.
Describe radioactive isotopes,
such as 235U, as a source of energy
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.
Describe the use of hydrogen as
a fuel reacting with oxygen to
generate electricity in a fuel cell
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.
Describe and explain the effect of concentration, particle size, catalysts (including enzymes) and temperature on the rate of reactions
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.
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)
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.
Demonstrate knowledge and understanding of a practical method for investigating the rate of a reaction involving gas evolution
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.
Describe and explain the role of
light in photochemical reactions
and the effect of light on the rate
of these reactions
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.
Demonstrate knowledge and
understanding of the concept of
equilibrium
equilibrium noun *a state in which opposing forces or influences are balanced. *a state of physical balance *a calm state of mind.
Define oxidation and reduction in
terms of oxygen loss/gain.
oxidation is oxygen gain, reduction is oxygen loss
Define redox in terms of electron
transfer
A handy way of remembering it is OIL RIG
Oxidation Is Loss, Reduction Is Gain of electrons
Define oxidising agent as a
substance which oxidises another
substance during a redox reaction.
An oxidising agent is a substance which oxidises another substance during a redox reaction
Define reducing agent as a
substance which reduces another
substance during a redox reaction.
An reducing agent is a substance which reduces another substance during a redox reaction
Describe the characteristic properties of acids as reactions with metals, bases, carbonates and effect on litmus and methyl orange
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 .
Describe and explain the
importance of controlling acidity
in soil
: 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.
Define acids and bases in terms
of proton transfer, limited to
aqueous solutions
- an acid as an H+ ion (or proton) donor
* a base as an H+ ion (or proton) acceptor.
Describe the change from metallic
to non-metallic character across
a period
left of the dark line under boron is metals and right of it is non metals.
Describe and explain the relationship between Group number, number of outer shell electrons and metallic/nonmetallic character
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.
Describe lithium, sodium and potassium in Group I
a collection of relatively soft metals showing a trend in melting point, density and reaction with water
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
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
Describe and explain the relationship between Group number, number of outer shell electrons and metallic/nonmetallic character
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.
Describe the transition elements
a collection of metals having high densities, high melting points and forming coloured compounds, and which, as elements and compounds, often act as catalysts
Describe the noble gases,
in Group VIII or 0,
unreactive, monoatomic gases
and explain this in terms of
electronic structure
State the uses of the noble gases
in providing an inert atmosphere,
i.e. argon in lamps, helium for
filling balloons
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).
List the general physical
properties of metals
high melting point
good heat/electricity conductors
ductile
malleable
Explain in terms of their
properties why alloys are used
instead of pure metals
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.
