nota kimia
TRANSCRIPT
NOTA KIMIAChemistry Form 4 Definition List
1. Element – a substance consists of one type of atom.
2. Compound – a substance consists two or more elements that are chemically
bonded(molecule or ions).
3. Atom – smallest particle of an element.
4. Molecule – a group of two or more atoms.
5. Ion – a positively charged / negatively charged particle.
6. Isotopes – atoms of the same element with same proton number but different
nucleonnumbers.
7. Relative atomic mass of an element = the average mass of one atom of an
element/((1/12) x the mass of one carbon-12 atom)
8. Relative molecular mass of an element = the average mass of one atom of an
molecule/((1/12) x the mass of one carbon-12 atom)
9. Molecule formula – compound shows the actual number of atoms of each element
that are present in a molecule of the compound
10.Empirical formula – compound shows the simplest whole number ratio of atoms
of each element in the compound
11.Mole – amount of substance that contains as many particles as the number of
atoms inexactly 12 g of carbon-12 the symbol of mole is mol.
12.One mole – Avogadro constant – 6.02 x 1023
13.Group (Periodic Table) – vertical columns of element (similar chemical properties).
14.Periods (Periodic Table) – horizontal rows of element.
15.Valence electrons – electrons that occupy the outermost shell.
16.Ionic bond – bond formed through the transfer of electrons between atoms
of metal andnon-metal to achieve the stable octet electron arrangement.
17.Ionic compound – consist of positive ions and negative ions which are held
by strong electrostatic forces of attraction.
18.Covalent bond – bond formed through the sharing of non-metal electrons to
achieve the stable duplet or octet electron arrangement.
19.Covalent compound (also simple molecular structure) – consists of neutral
molecules which are held by weak intermolecular forces (Van der Waals).
20.Alkali (base) – chemical substance which ionizes in water to produce hydroxide
ions, OH-.
21.Acid – chemical substance which ionizes in water to produce hydrogen ions, H+ or
hydroxonium ions, H3O+.
22.pH – degree of acidity or alkalinity of a solution. Scale ranges from 0 to 14.
23.pH value – measure of the concentration of hydrogen ions, H+.
24.Strong alkali – ionises (dissociates) completely in water to form hydroxide ions,
OH- of high concentration.
25.Weak alkali – ionises (dissociates) partially in water to form hydroxide ions, OH- of
low concentration.
26.Strong acid – ionises (dissociates) completely in water to form hydrogen ions,
H+ of high concentration.
27.Weak acid – ionises (dissociates) partially in water to form hydrogen ions, H+ of
low concentration.
28.Polymer – long chain molecules made up by monomer (repeating unit).
SPM Form 4 – Terminology and Concepts: The Structure of the Atom
Important Terms
Matter – anything that occupies space and has mass.
Compound – a substance consists two or more elements that are chemically
bonded (molecule or ions).
Element – a substance that cannot be made into anything simpler by chemical
reaction.
Atom – smallest particle of an element.
Molecule – a group of two or more atoms.
Ion – a positively charged / negatively charged particle.
Cations – positively-charge ions. Example: H+, K+, NH4+ and Mg2+
Anions – negatively-charge ions. Example: Br-, OH-, O2- and S2O32-
Velocity of the particle increases when
Temperature increases
Kinetic energy increases
Diffusion – movement of particles from a region of high concentration to a region
of lowconcentration.
Changes in the States of Matter
1. Freezing / Solidification – liquid -> solid
2. Melting – solid -> liquid
3. Evaporation – liquid -> gas / vapour
4. Condensation – gas / vapour -> liquid
5. Sublimation – gas / vapour -> solid
6. Sublimation – solid -> gas / vapour
(Sublimation – iodine, ammonium chloride and solid carbon dioxide)
Important Scientist and Their Contributions
Berry Berry Teacher thinks that it will be good if students can link the contribution of
each great scientists to their findings. This will allow a chronological understanding of
the discoveries (for easier understanding) and to appreciate the work of these fine
scientist.
John Dalton (1808) – atomic theory
1. Atoms – small indivisible particles.
2. Atoms – neither created nor destroyed.
3. Atoms – an element are alike.
4. Atoms – it combine in simple ratio.
5. Atoms – chemical reactions result from combination / separation of atoms.
J. J. Thomson (1897)
1. Electrons – negatively-charged particles.
2. Atoms – positively-charged sphere.
Ernest Rutherford (1911)
1. Atoms – consists of a positively-charged nucleus with a cloud of electrons
surrounding nucleus.
2. Protons – positively-charged particles.
Niels Bohr (1913)
1. Electrons – surrounding the nucleus (orbit).
James Cadwick (1932)
1. Neutrons – electrically neutral subatomic particles.
2. Neutrons – mass almost the same with a proton.
3. Nucleus of an atom – consists of protons and neutrons.
Concepts of the Atomic Model
Modern Atomic Model
1. Nucleus of an atom – consists of protons and neutrons.
2. Electrons – moving around the nucleus (orbits / electron shells/ quantum shells)
Proton number / Atomic number / Number of protons
1. Number of protons in its atom.
2. Number of electrons (neutral atom).
Nucleon number / Mass number / Number of nucleon
1. Sum of the number protons and neutrons.
Isotopes – atoms of the same element with same proton number but different
nucleonnumbers.
(Further clarification on isotopes as there are still students who are confused with this
concept – Isotopes for any elements simply means that it is another element with the
same number of proton and electron but different number of neutrons. It is important
to note that the atomic number of isotopes are the same, although the mass number is
different. If you can understand this concept, you should be okay)
SPM Form 4 – Terminology and Concepts: Chemical Formulae and Equations –
Part 1
1. Relative atomic mass, Ar is the atomic mass of an atom when compared to
a standardatom
2. Standard atom:
Hydrogen scale: hydrogen is the lightest atom of all and the mass of one hydrogen
atom was assigned 1 unit.
Weakness of Hydrogen scale:
not too many elements can react readily with hydrogen,
the reactive masses of some elements were not accurate,
hydrogen exists as a gas at room temperature and
has a number of isotopes with different masses.
Helium scale: the second lightest atom of all and the mass of one helium atom was
assigned 1 unit.
Weakness of Helium scale:
Mass of 1 helium atom = 4 times the mass of a hydrogen atom
So, mass of 1 helium atom = 4 times 1/12 mass of a carbon atom
helium exists as a gas at room temperature and
helium is an inert gas.
Oxygen scale: chose as the standard atom to compare the masses of atoms
Weakness of Oxygen scale:
the existence of three isotopes of oxygen were discovered,
natural oxygen (containing all the three isotopes) as the standard (Chemist) and
used the isotopes oxygen-16 as the standard (Physicists).
Carbon scale: standard atom of comparison internationally.
a carbon-12 atom is 12 times heavier than an atom of hydrogen,
used as the reference standard in mass spectrometers,
exists as a solid at room temperature,
most abundant carbon isotope, happening about 98.89% and
carbon-12 is close to the agreement based on oxygen.
3. Relative molecular mass, Mr of a substances is the average mass of
a molecule (two or more atoms) of the substances when compared 1/12 with of the
mass of a carbon-12 atom.
4. Relative formula mass, Fr is for ionic compound which is calculated by adding up
therelative atomic masses of all the atoms.
5. Example:
Relative atomic mass, Ar of helium = 4
Relative molecular mass, Mr of CO2 = 12 + 2(16) = 44
Relative formula mass, Fr of NaCl = 23 + 35.5 = 58.5
Relative formula mass, Na2CO3·10H2O = 2(23) + 12 + 3(16) + 10 [2(1) + 16] = 286
Try to solve some of the examples without looking at the answers. If you can
understand this, then stay tune and log in again for Part 2 of this topic’s notes. If you
cannot understand the examples, try and try and try and try and try again until you are
good with it. Till then.
Italian physicist Amedeo Avogadro (Name at birth: Lorenzo Romano Amedeo Carlo
Avogadro)
Born: 9 August 1776
Birthplace: Turin, Piedmont, Italy
Died: 9 July 1856
Best Known As: The guy they named Avogadro’s number after
1. Avogadro constant / Avogadro’s number is 6.02 x 10 23
2. Atomic substances
Elements – all the particles are atoms.
Example: zinc (Zn), sodium (Na), aluminium (Al) and all noble gases, argon (Ar),
helium (He) and neon (Ne).
RAM (Relative Atomic Mass) of Na = 23
3. Molecular substances
Covalent compounds – the particles are molecules.
Example: carbon dioxide (CO2), water (H2O) and non-metal elements, iodine (I2),
nitrogen (N2) and oxygen (O2).
RMM (Relative Molecular Mass) of I2 = 127 + 127 = 254
4. Ionic substances
Ionic compounds – the particles are ions.
Example: sodium chloride (NaCl), hydrochloric acid (HCl) and potassium iodide
(KI).
RFM (Relative Formula Mass) of HCl = 1 + 35.5 = 36.5
5. Avogadro’s Law / Gas Law states that equal volumes of all gases contain the same
numberof molecules under the same temperature and pressure.
Example: equal volumes of molecular hydrogen and nitrogen would contain the
same number of molecules under the same temperature and pressure.
6. Volume of gas (dm3) = Number of moles of gas x Molar volume
7. Room temperature and pressure (r.t.p.) = 24 dm3 mol-1 (25°C and 1 atm)
Example: What is the volume of 5.0 mol helium gas at s.t.p.?
Volume of gas = Number of moles x Molar gas volume
= 5.0 mol x 24 dm3 mol-1
= 120 dm3
8. Standard temperature and pressure (s.t.p.) = 22.4 dm3 mol-1 (0°C and 1 atm)
Example: What is the volume of 5.0 mol helium gas at s.t.p.?
Volume of gas = Number of moles x Molar gas volume
= 5.0 mol x 22.4 dm3 mol-1
= 112 dm3
9. Mass (g) = Number of moles x Molar mass
10. Number of particles = Number of moles x Avogadro constant
11. Volume (dm3) = Number of moles x Molar volume
SPM Chemistry Form 5 Definition List:
1. Effective collision (Collision theory) – collision that results in a chemical reaction
where the particles collide with the correct orientation and are able to achieve
the activation energy.
2. Homologous series – organic compounds (families) with similar formulae and
properties.
3. Catalyst – a chemical that alter the rate of reaction.
4. Positive catalyst – increases the rate of reaction & lower the activation energy.
5. Negative catalyst – decreases the rate of reaction & higher the activation energy
6. Organic compounds – carbon-containing compound. Carbon atoms
form covalent bonds.
7. Inorganic compounds – compounds from non-living things which do not contain
the element carbon.
8. Saturated hydrocarbons – hydrocarbons containing only single bonds between all
carbon atoms.
9. Unsaturated hydrocarbons – hydrocarbons containing at least one carbon-
carbondouble or triple bond.
10.Esterification – esters are produced
11.Vulcanisation – process which makes the natural rubber harder and increases its
elasticity by adding sulphur.
12.Redox reaction – chemical reactions involving oxidation and reduction occurring
simultaneously.
13.Flavouring – improve the taste or smell of food and restore taste loss due to food
processing.
14.Stabilisers – help to mix two liquids that usually do not mix together so that they
form an emulsion.
15.Thickeners – substances that thicken food and give the food a firm, smooth and
uniform texture.
16.Precipitation – the heat change when one mole of a precipitate is formed from
their ions in aqueous solution.
17.Displacement – the heat change when one mole of a metal is displaced from its
salt solution by a more electropositive metal.
18.Neutralisation – the heat change when one mole of water is formed from the
reaction between an acid and an alkali.
19.Combustion – the heat change when one mole of a substance is completely
burnt in oxygen under standard conditions.
SPM Form 5 – Terminology and Concepts: Rate of Reaction
Chemical reaction can be observed by
1. Volume of gas liberated (Laboratory Work 1.2, Experiment 1.1)
2. Pressure changes
3. Precipitate formation (Experiment 1.2)
4. Change in the concentration of a liquid reactant
5. Change in the pH value
6. Change in mass during the reaction
7. Colour changes / Change on the colour of intensity
8. Temperature changes (Experiment 1.3)
Rate of reaction is the measurement of the speed which reactants are converted into
products in a chemical reaction.
Average rate of reaction is the average value of the rate of reaction over
an interval of time.
Instantaneous rate of reaction / Rate of reaction at a given time are
the actual rate of reaction at that instant.
Factors Affecting the Rate of Reaction
1. Total surface area of solid reactant
2. Concentration of reactant
3. Temperature of reactant
4. Use of catalyst
5. Pressure of gaseous reactant
Effect of total surface area of solid reactant on the rate of reaction
1. Smaller the size (increase the total surface area), cm3, of the solid reactant,
the higher the rate of reaction, cm3 s-1 or cm3 min-1.
Effect of concentration of a liquid reactant on the rate of reaction
1. Higher the concentration, mol dm-3, of a liquid reactant, the higher the rate of
reaction, mol dm-3 s-1 or mol dm-3 min-1.
Effect of temperature on the rate of reaction
1. Increase in temperature, the higher the rate of reaction.
Effect of catalyst on the rate of reaction
1. Alters the rate of reaction
2. It is specific in its action. It can only catalyse a particular reaction
3. Does not change the quantity of products formed
4. Only small amount of catalyst is needed to increases the rate of reaction. (An
increase in the quantity of catalyst will increase the rate of reaction but only a very
slight increase.)
5. Catalyst remains chemically unchanged but may undergo physical changes.
Effect of pressure on the rate of reaction
1. Increase in pressure, the higher the rate of reaction (reversible reaction and
gaseous reactants and gaseous product).
Collision Theory and Activation Energy
Collision theory states a reaction occur when the particle of the reactant collide with
each other with the correct orientation and achieve activation energy.
Effective collision is the particles collide with the correct orientation
and achieve activationenergy which result in a reaction.
Ineffective collision is the particles that collide with energy less than activation
energy orwrong orientation.
Activation energy, Ea, is the minimum kinetic energy that colliding particles of
the reactantsmust possess. It can be visualised by energy profile diagram.
Keywords: frequency of the collision; frequency of effective collision, rate of reaction
Common Mistakes (SPM Form 5 – Rate of Reaction)
Never use word: ‘faster the rate of reaction’ or ‘ slower the rate of reaction’. (use
word such as ‘ increases’, ‘decreases’, ‘ higher’ or ‘lower’.
Average rate of reaction is berry different from instantaneous rate of reaction.
(Instantaneous can be determined by drawing a tangent on the graph’s curve).
Time reading: 1 decimal point. (It also depends on the measurement apparatus
either a normal stopwatch or digital stopwatch) Example: 21.0 seconds and 45.5
seconds.
Measuring cylinder reading: 1 decimal point. Example: 5.0 cm3 and 4.5 cm3.
Burette reading: 2 decimal points. Example: 50.00 cm3 and 45.25 cm3.
Pipette reading: 1 decimal point: Example: 25.0 cm3 and 10.0 cm3.
Important Tips – SPM – Rate of Reaction
Rate of Reaction will be Berry Important Topic (BIT) for the Paper 2 (essay) and Paper
3 that young berries could not skip as one of your revision routine. Do take notes on
the graphs and these few experiments that listed below.
Experiment 1.1 Effect of surface area on the rate of reaction.
Experiment 1.2 Effect of concentration on the rate of reaction.
Experiment 1.3 Effect of temperature on the rate of reaction.
Experiment 1.5: Effect of the amount of catalyst on the rate of reaction.
Activity: Factors affecting the rate of reaction.
SPM Chemistry Form 5 – Terminology and Concepts: Carbon Compounds
1. Organic compounds – carbon containing compounds with covalent bonds.
2. Inorganic compounds – non-living things and usually do not contain carbon but
few carbon containing inorganic compounds such as CO2, CaCO3 and KCN.
3. Hydrocarbons – organic compounds that contain hydrogen and carbon atom only.
4. Non-hydrocarbons – organic compounds that contain other elements (oxygen,
nitrogen, iodine, phosphorus)
5. Saturated hydrocarbons – only single bonded (Carbon-Carbon) hydrocarbons.
6. Unsaturated hydrocarbons – at least one double / triple bonded (Carbon-Carbon)
hydrocarbons.
7. Complete combustion – organic compounds burn completely which form CO2 and
H2O.
Example: C2H5OH (l) + O2 (g) –> 2CO2 (g) + 3H2O (l)
8. Incomplete combustion – organic compounds burn with limited supply of
O2 which form C (soot), CO, CO2 and H2O.
Homologous Series
Homologous series – organic compounds with similar formulae and properties. It
have thephysical properties that change gradually as the number of carbon atoms in a
molecule increases.Carbon Compounds
General Formula Functional group
Alkane CnH2n+2 n = 1, 2, 3, … Carbon-carbon single bond- C – C -
Alkene CnH2n n = 2, 3, 4, … Carbon-carbon double bond- C = C -
Alkynes CnHn n = 2, 3, 4, … Carbon-carbon triple bond- C = C -
Arenes CnH2n-6 n = 6, 7, 8, … - C = C -delocalised / free to move around the ring
Alcohol CnH2n+1OH n = 1, 2, 3, … Hydroxyl group- OH
Carboxylic Acids
CnH2n+1COOH n = 0, 1, 2 Carboxyl group- COOH
Esters CnH2n+1COOCmH2m+1 n = 0, 1, 2, …m = 1, 2, 3, …
Carboxylate group- COO -
Sources of Hydrocarbon:
1. Coal – from the lush vegetation that grew in warm shallow coastal swamps
or dead plantsslowly become rock. Mainly contains of hydrocarbon and
some sulphur and nitrogen. It is used to produce: fertiliser, nylon, explosives and
plastics.
2. Natural gas – from plants and animals and trapped between the layers of
impervious rocks (on top of petroleum). Mainly contains of methane gas and other gas
such as propane andbutane. It is used for: cooking, vehicle and generate electrical
power.
3. Petroleum – from plants and animals and trapped between the layers of
impervious rocks. It is a complex mixture of alkanes, alkenes, aromatic
hydrocarbons and sulphurcompound. These compounds can be separated by
using fractional distillation.
< 35°C – petroleum gas
35°C – 75°C – Petrol (gasoline)
75°C – 170°C – Naphtha
170°C – 230°C – Kerosene
230°C – 250°C – Diesel
250°C – 300°C – Lubricating oil
300°C – 350°C – Fuel oil
> 350°C – Bitumen
SPM Chemistry Form 5 – Terminology and Concepts: Carbon Compounds (Part
2)
A) IUPAC ( International Union of Pure and Applied Chemistry ) – is used to
nameorganic compound.
Organic compound is divided into three portions which is Prefix + Root + Suffix.
1. Prefix – name of the branch or side chain.
General formula: CnH2n+1 –Where n = 1, 2, 3, … (n = number of carbon)Formula Branch or name of groupCH3 - methylC2H5 - ethylC3H7 - propylC4H9 - butylC5H11 - pentyl
2. Alkyl group signifies that it is not part of the main chain.
3. Two or more types of branches are present, name them in alphabetical order.Number of side chain Prefix2 Di-3 Tri-4 Tetra-5 Penta-6 Hexa-
4. More than one side chains are present, prefixes are used.
5. Root – the parent hydrocarbon (denotes the longest carbon chain).Number of carbon atoms Root name1 meth-2 eth-3 prop-4 but-5 pent-6 hex-7 hept-8 oct-9 nan-10 dec-
The longest continuous (straight chain) carbon chain is selected.
Identify the number of carbon.
6. Suffix – functional group.Homologous series Functional group SuffixAlkane - C – C - -aneAlkene - C = C - -eneAlcohol – OH -ol
Carboxylic acid – COOH -oicEster – COO – -oate
7. Example: 4-methylhept-2-ene.
8. Prefix + Root + Suffix
B) Family of Hydrocarbon – Alkane
1. General formula: CnH2n+2
Where n = 1, 2, 3, … (n = number of carbon)
2. Each carbon atom in alkanes is bonded to four other atoms by single covalent bonds.
Alkanes are saturated hydrocarbon.Name of alkane Molecular formula of alkaneMethane CH4
Ethane C2H6
Propane C3H8
Butane C4H10
Pentane C5H12
Hexane C6H14
Heptane C7H16
Octane C8H18
Nonane C9H20
Decane C10H22
Molecular formula is a chemical formula that shows the actual number of atoms of
each type of elements
present in a molecule of the compound.
Example: molecular formula of butane is C4H2´4+2 = C4H10
Name Condensed structural formula of alkaneMethane CH4
Ethane CH3CH3
Propane CH3CH2CH3
Butane CH3CH2CH2CH3
Pentane CH3CH2CH2CH2CH3
Hexane CH3CH2CH2CH2CH2CH3
Heptane CH3CH2CH2CH2CH2CH2CH3
Octane CH3CH2CH2CH2CH2CH2CH2CH3
Nonane CH3CH2CH2CH2CH2CH2CH2CH2CH3
Decane CH3CH2CH2CH2CH2CH2CH2CH2CH2CH3
Structural formula is a chemical formula that shows the atoms of elements are
bonded(arrangement of atoms) together in a molecule by what types of bond.
3. Physical properties of alkanesName Molecularformul RMM Density(g Physical state at
a cm-3) 25°CMethane CH4 16 - GasEthane C2H6 30 - GasPropane C3H8 44 - GasButane C4H10 58 - GasPentane C5H12 72 0.63 LiquidHexane C6H14 86 0.66 LiquidHeptane C7H16 100 0.68 LiquidOctane C8H18 114 0.70 LiquidNonane C9H20 128 0.72 LiquidDecane C10H22 142 0.73 Liquid
Alkanes with more than 17 carbon atoms are solid.
Solubility in water – all members in alkanes are insoluble in water but soluble in
many organic solvent (benzene and ether).
Density of alkane – the density of water is higher than density of alkane.
When going down the series, relative molecular mass of alkanes is higher due to
the higher force of attraction between molecules and alkane molecules are packed
closer together.
Electrical conductivity – all members in alkanes do not conduct electricity.
Alkanes are covalent compounds and do not contain freely moving ions.
Boiling and melting points – all alkanes in general have low boiling points and
melting points.
Alkanes are held together by weak intermolecular forces.
4. Chemical properties of alkanes
Reactivity of alkanes
Alkanes are less reactive (saturated hydrocarbon).
Alkanes have strong carbon-carbon (C – C) bonds and carbon-hydrogen (C –
H) bonds.
All are single bonds which require a lot of energy to break.
Alkanes do not react with chemicals such as oxidizing agents, reducing agents,
acids and alkalis.
Combustion of alkanes
Complete combustion of hydrocarbons
CxHy + (x + y/4) O2 –> xCO2 + y/2 H2O
CH4 + 2O2 –> CO2 + 2H2OIncomplete combustion
occurs when insufficient supply of oxygen
CH4 + O2 –> C + H2O
2CH4 + 3O2 –> 2CO + 4H2O
Substitution reaction of alkanes (Halogenation)
Substitution reaction is one atom (or a group of atoms) in a molecule
is replaced by another atom (or a group of atoms).
Substitution reaction of alkanes take place in ultraviolet light.
Example:
Alkanes react with bromine vapour (or chlorine) in the presence of UV light.
CH4 + Cl2 –> HCl + CH3Cl (Chloromethane)
CH3Cl + Cl2 –> HCl + CH2Cl2 (Dichloromethane)
CH2Cl2 + Cl2 –> HCl + CHCl3 (Trichloromethane)
CHCl3 + Cl2 –> HCl + CCl4 (Tetrachloromethane)
The rate of reaction between bromine and alkanes is slower than the rate of
reaction between chlorine and alkanes.
SPM Chemistry Form 5 – Terminology and Concepts: Carbon Compounds (Part
3)
Family of Hydrocarbon – Alkene
1. General formula: CnH2n
Where n = 2, 3, 4 … (n = number of carbon)
2. Alkenes are unsaturated hydrocarbons which contain one or more carbon-carbon (C
= C) double bonds in molecules.
3. The functional group in alkenes is carbon-carbon double (C = C) bond.
Name of alkene Molecular formula of alkeneEthene C2H4
Propene C3H6
Butene C4H8
Pentene C5H10
Hexene C6H12
Heptene C7H14
Octene C8H16
Nonene C9H18
Decene C10H20
Molecular formula is a chemical formula that shows the actual number of
atoms of eachtype of elements present in a molecule of the compound.
Example: molecular formula of butene is C4H2x4 = C4H8
4. Physical properties of alkenesName Molecularformul
aRMM Density(g
cm-3)Physical state at 25°C
Ethene C2H4 28 0.0011 GasPropene C3H6 42 0.0018 Gas
Butene C4H8 56 0.0023 GasPentene C5H10 70 0.6430 LiquidHexene C6H12 84 0.6750 LiquidHeptene C7H14 98 0.6980 LiquidOctene C8H16 112 0.7160 LiquidNonene C9H18 126 0.7310 LiquidDecene C10H20 140 0.7430 Liquid
Solubility in water – all members in alkenes are insoluble in water but soluble in
many organic solvent (benzene and ether).
Density of alkene – the density of water is higher than density of alkene.
When going down the series, relative molecular mass of alkenes is higher due to
the higher force of attraction between molecules and alkene molecules are packed
closer together.
Electrical conductivity – all members in alkenes do not conduct electricity.
Alkenes are covalent compounds and do not contain freely moving ions.
Boiling and melting points – all alkenes in general have low boiling points and
melting points. Alkenes are held together by weak attractive forces between
molecules (intermolecular forces) van der Waals’ force. When going down the
series, more energy is required to overcome the attraction. Hence, the boiling and
melting points increases.
5. Chemical properties of alkenes
Reactivity of alkenes
Alkenes are more reactive (unsaturated hydrocarbon).
Alkenes have carbon-carbon (C = C) double bonds which is more reactive than
carbon-carbon (C-C) single bonds. All the reaction occur at the double bonds.
Combustion of alkenes
Complete combustion of hydrocarbons (alkenes)
CxHy + (x + y/4) O2 –> xCO2 + y/2 H2O
C2H4 + 3O2 –> 2CO2 + 2H2O
(Alkenes burn with sootier flames than alkanes. It is because the percentage of
carbon in alkene molecules is higher than alkane molecules and alkenes
burn plenty of oxygen to produce carbon dioxide and water)
Incomplete combustion occurs when insufficient supply of oxygen
C2H4 + O2 –> 2C + 2H2O
C2H4 + 2O2 –> 2CO + 2H2O
(The flame in the incomplete combustion of alkenes is more smoky than alkanes)
Polymerisation reaction of alkenes
Polymers are substances that many monomers are bonded together in a repeating
sequence.
Polymerisation is small alkene molecules (monomers) are joined together to form
a long chain (polymer).
nCH2 = CH2 –> -(- CH2 – CH2 -)-n
ethene (monomer)(unsaturated compound) –> polyethene polymer (saturated
compound)
It must be carry out in high temperature and pressure.
Addition of hydrogen (Hydrogenation)
Addition reaction is atoms (or a group of atoms) are added to each carbon atom of
a carbon-carbon multiple bond to a single bond.
C2H4 + H2 –> C2H6 (catalyst: nickel and condition: 200°C)
Example: margarine (produce from hydrogenation of vegetable oils).
Addition of halogen (Halogenation)
Halogenation is the addition of halogens to alkenes (no catalyst of ultraviolet light
is needed).
Alkene + Halogen –> Dihaloalkane
C2H4 + Br2 –> C2H4Br2
In this reaction the brown colour of bromine decolourised (immediately) to produce
acolourless organic liquid.
Bromination is also used to identify an unsaturated (presence of a carbon-carbon
double bond) organic compound in a chemical test.
Addition of hydrogen halides
Hydrogen halides (HX) are hydrogen chlorine, hydrogen bromide, hydrogen iodide
and etc. This reaction takes place rapidly in room temperature and without
catalyst.
CnH2n + HX –> CnH2n+1X
C2H4 + HBr –> C2H5Br (Bromoethane)
(There are two products for additional of hydrogen halide to propene. The products
are 1-bromopropane and 2-bromopropane).
Addition of water (Hydration)
Alkenes do not react with water under ordinary condition. It can react with
a mixture ofalkene and steam pass over a catalyst (Phosphoric acid, H3PO4). The
product is an alcohol.
CnH2n + H2O –> CnH2n+1OH
C2H4 + H2O –> C2H5OH
Additional of acidified potassium manganate(VII), KMnO4
CnH2n + [O] + H2O –> CnH2n(OH)2
C2H4 + [O] + H2O –> C2H5(OH)2
The purple colour of KMnO4 solution decolourised immediately to
produce colourlessorganic liquid. Also used to identify the presence of a carbon-
carbon double bond in a chemical test.
SPM Form 5 – Terminology and Concepts: Carbon Compounds
1. Comparing (Similarities and Differences) Properties of Alkanes and
AlkenesPhysical Properties
Alkanes Alkenes
Physical state Physical state changes from gas to liquid when going down the series.
Same with alkanes.
Electrical conductivity.
Do not conduct electricity at any state.
Same with alkanes.
Boiling points and melting points
Low boiling points and melting points (number of carbon atoms per molecule increases).
Same with alkanes.
Density Low densities (number of carbon atom per molecule increases).
Same with alkanes.
Solubility in water
Insoluble in water (soluble in organic solvent)
Same with alkanes.
Chemical Properties
Alkanes(Substitution reaction)
Alkenes(Addition reaction)
Reactivity Unreactive ReactiveCombustion Burn in air and produce
yellow sooty flame.Burn in air and produce yellow and sootier flame compare to alkanes.
Reaction with bromine solution
No reaction. Decolourise brown bromine solution.
Reaction with acidified potassium manganate(VII) solution
No reaction. Decolourise purple acidified potassium manganate(VII) solution.
2. Isomerism
Isomerism – phenomenon that two or more molecules are found to have
the same molecular formula but different structural formulae.
Isomerism in alkanesMolecular formula Number of isomers Structure nameCH4 - (no isomer) MethaneC2H6 - (no isomer) EthaneC3H8 - (no isomer) PropaneC4H10 2 Butane2-
methylpropaneC5H12 3 Pentane2-
methylbutane2,2-dimethylpropane
Isomerism in alkenesMolecular formula Number of isomers Structure nameC2H4 - (no isomer) EtheneC3H6 - (no isomer) PropeneC4H8 3 But-1-eneBut-2-ene2-
methylpropeneC5H10 5 Pent-1-enePent-2-ene2-
methylbut-1-ene3-methylbut-1-ene
2-methylbut-2-ene
SPM Form 5 – Terminology and Concepts: Carbon Compounds (Part 5)
Non-Hydrocarbon – Alcohol
1. General formula: CnH2n + 1OH
Where n = 1, 2, 3 … (n = number of carbon)
2. Alcohols are non-hydrocarbons which contain carbon, hydrogen and oxygen atoms.
3. The functional group in alcohols is hydroxyl group, – OH.
Name of alcohol Molecular formula of alcohol
Methanol CH3OHEthanol C2H5OHPropanol / Propan-1-ol C3H7OHButanol / Butan-1-ol C4H9OHPentanol / Pentan-1-ol C5H11OHHexanol / Hexan-1-ol C6H13OHHeptanol / Heptan-1-ol C7H15OHOctanol / Octan-1-ol C8H17OHNonanol / Nonan-1-ol C9H19OHDecanol / Decan-1-ol C10H21OH
4. Physical properties of alcoholName Molecular
formulaMelting point (°C)
Boiling point (°C)
Physical state at 25°C
Methanol CH3OH -97 65 LiquidEthanol C2H3OH -117 78 LiquidPropanol C3H5OH -127 97 LiquidButanol C4H7OH -90 118 LiquidPentanol C5H9OH -79 138 Liquid
Solubility in water – all members in alcohol are very soluble in water (miscible
with water).
Volatility – all alcohols are highly volatile.
Colour and Smell – alcohols are colourless liquid and have sharp smell.
Boiling and melting points – all alcohols in general have low boiling points
(78°C).
5. Chemical properties of alcohol
Combustion of alcohol Complete combustion of alcohol. C2H5OH + 3O2 –>
2CO2 + 3H2O (Alcohol burns with clean blue flames. Alcohol burns plenty of
oxygen to produce carbon dioxide and water. This reaction releases a lot of heat.
Therefore, it is a clean fuel as it does not pollute the air.) Other example: 2C3H7OH
+ 9O2 –> 6CO2 + 8H2O
Oxidation of ethanol In the laboratory, two common oxidising agents are used for
the oxidation of ethanol which are acidified potassium dichromate(VI) solution
(orange to green) and acidified potassium manganate(VII) solution (purple to
colourless). C2H5OH + 2[O] –> CH3COOH + H2O Ethanol oxidised to ethanoic acid
(a member of the homologous series of carboxylic acids – will be discussed in Part
6). Other example: C3H7OH + 2[O] –> C2H5COOH + H2O
Removal of water (Dehydration) Alcohol can change to alkene by removal of
water molecules (dehydration). It results in the formation of a C=C double bond.
CnH2n+1OH –> CnH2n + H2O C2H5OH –> C2H4 + H2O Two methods are being used to
carry out a dehydration in the laboratory. a) Ethanol vapour is passed over a heated
catalyst such asaluminium oxide, unglazed porcelain chips, pumice stone or porous
pot. b) Ethanol is heated under reflux at 180°C with excess concentrated sulphuric
acid, H2SO4. Other example: C3H7OH –> C3H6 + H2O
6. Uses of Alcohol
Alcohol as a solvent (cosmetics, toiletries, thinners, varnishes, perfumes).
Alcohol as a fuel (fuel for racing car, clean fuel, alternative fuel).
Alcohol as a source of chemicals (polymer, explosives, vinegar, fiber).
Alcohol as a source of medical product (antiseptics for skin disinfection, rubbing
alcohol).
7. Misuse and Abuse
Depressant drug
Alcoholic drinks
Addictive drug
