YEAR 10 SCIENCE
SEMESTER 2 – 2011
EXAM REVISION
CHEMISTRY
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UNIT 2.1 – CHEMISTRY – THE STORY SO FAR
REVISION
1.
In order to understand chemistry questions in the exam, you need to
understand what each of the following words means.
For each word write a sentence explaining what it means:
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pure substances
elements
states of matter
solutions
solvent
dilute solutions
ions
properties of metals
covalent bonding
monatomic molecules
covalent network
physical change
chemical reaction
reactants
law of conservation of matter
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mixtures
compounds
standard laboratory conditions (SLC)
solutes
aqueous solutions
concentrated solutions
polyatomic ions
properties of ionic compounds
discrete molecular substances
diatomic molecules
reaction types
chemical change
types of reactions
products
law of conservation of mass
2. Structure of matter
You must know how matter is structured and the names used to describe matter.
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3. States of matter
Chemicals can exist as solids, liquids or gases.
Their physical state may be indicated by using the appropriate subscript :
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(s) – for a solid substance
(g) – for a gas
(l) – for a pure liquid
(aq) – for a solution dissolved in water)
4. Physical properties vs chemical properties
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5. Standard laboratory conditions (SLC)
The state of substances will depend upon both temperature and pressure
conditions.
Standard laboratory conditions are specified as being :
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Temperature :
Pressure
:
250C
1 atmosphere (ie. Normal air pressure at sea level).
6. Solutions
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A solution consists of one or more solutes dissolved in a liquid solvent.
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Solutions in which water is the solvent are called aqueous solutions.
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Dilute solutions contain a small quantity of solute in a relatively large volume of
solvent.
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Concentrated solutions contain a large quantity of solute in a relatively small
volume of solvent.
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Structure and bonding
All pure substances cab be classified in one of the following ways :
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metallic
ionic
discrete molecular
covalent network
7. Metals
The bonding within metals is called metallic bonding.
When metals bond, the electrons in the
outer shell of the atom (valence
electrons) are free to move through the
lattice.
These wandering electrons are called
delocalised electrons.
Metals are lustrous due to these
delocalise electrons.
Properties of metals
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8. Ionic compounds
Ions are charged particles.
Ions have an unequal numbers of protons and electrons.
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Cations ( positively charged ions) - have more protons than electrons.
eg. Na+ and
Pb2+
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Anions (negatively charged ions) – have more electrons than protons
eg. Cl- and O2-
Polyatomic ions
Polyatomic ions is a charged particle made up of more than one atom.
eg,. NH4+ and CO32-
Properties of ionic compounds
9. Ionic bonding
Ionic bonding is the electrostatic attraction between oppositely charged ions.
eg. Common salt : sodium chloride (NaCl)
Ionic compound have high melting and boiling points, making them crystalline solids at
SLC.
The formula for an ionic compound is not a molecular formula, since ionic compounds
form crystal lattices, not molecules.
eg. Ionic compound Magnesium oxide has a formula of MgO
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WRITING IONIC FORMULA
Use the valence sheet on the previous page to help you write formula for the following :
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PRACTICE - NAMING IONIC COMPOUNDS
(Solutions on next page)
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PRACTISE – WRITING THE FORMULA FOR IONIC COMPOUNDS
(Solutions on next page)
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10. Covalent bonding
Covalent bonding is the sharing of pairs of electrons and occurs between non-metal
atoms such as carbon and oxygen,
a). Discrete Molecular substances
A molecule is a group of non-metal atoms covalently bound and represented by a
chemical formula.
Examples of discrete molecular substances are : CO2 and H2O
Monatomic molecules - atoms of Group VIII – noble gases.
Diatomic molecules – atoms like H2, O2 and N2.
b). Covalent network structures
– like Carbon (C) and Silica SiO2
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Many inorganic covalent compounds are named using Greek prefixes :
1- Mono
2- Di
3-Tri
4- Tetra
5- Penta
6- Hexa
7- Hepta
8- Octa
9- Nona
10-Deca
Examples :
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CO2
CO
H2S2
SF6
carbon dioxide
carbon monoxide
dihydrogen disulfide
sulfur hexafluroide
11. Reaction Types
Physical change is one in which no new substance is formed, such as ice melting.
Chemical change is one in which a new substance is formed.
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Signs that a chemical reaction or change has occurred.
1. a permanent colour change
2. a gas given off
3. energy produced or absorbed (ie.
change in temperature).
4. a precipitate forms
5. one metal deposited on another
metal.
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12. Reaction Types
Hints on how to spot the reaction type
1. Combustion reaction - look for O2 on the LHS of equation.
2. Displacement reaction – look for as metal (solid) on the RHS of equation.
3. Neutalisation reaction – look for OH or the acids in the LHS of the equation.
4. Displacement reaction – look for a precipitate – ie. a solid on RHS of equation
5. Combination reaction – look for two compounds on LHS producing a single
product on the RHs.
6. Decomposition reaction – look for one compound on LHS breaking into two
compounds on RHS of equation.
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13. Balancing chemical equations
LHS
Reactants
→
RHS
Products
Law of conservation of matter
“ Matter can only be changed, not created or destroyed.”
Therefore the number of atoms of each element at the beginning of the reaction must still
be the same after the reaction.
PRACTICE PROBLEMS FOLLOW – WITH ANSWERS
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HOW TO BALANCE CHEMICAL EQUATIONS
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ANSWERS
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ANSWERS OVER PAGE
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ANSWERS
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MORE PRACTICE BALANCING CHEMICAL EQUATIONS
(answers next page)
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UNIT 2.2 – MORE AND FASTER : RATE AND YIELD
REVISION
1. In order to understand genetics questions in the exam, you need to understand
what each of the following words means.
For each word write a sentence explaining what it means:
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Rate of reaction
homogeneous
yield
 Collision theory
 heterogeneous
2. Measuring the rate of a reaction.
The rate of a reaction is inversely proportional to time :
3. Collision Theory
The collision theory of chemical reactions states that :
1. The reactants must collide.
2. The reactants must collide with sufficient energy to react.
3. the reactants must collide in the correct orientation.
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4. Changing rate of reaction
The rate of a chemical reaction can be changed by :
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Increase concentration.
Increase surface area
increase temperature
effect a catalyst
All these things make it more likely for molecules of the reactants to collide with
each other and cause a chemical reaction
Problems from your textbook. P67 / 68
1. How are the rate of reaction and time taken to react related?
2. Describe in terms of collision theory how a decrease in concentration can change the
rate of a precipitation reaction.
3. How are temperature and kinetic energy related?
4. What is a catalyst?
5. What are the three things that must happen before a reaction will occur?
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UNIT 2.3 – CHEMISTRY – STRICTLY ORGANIC
REVISION
1. In order to understand genetics questions in the exam, you need to understand
what each of the following words means.
For each word write a sentence explaining what it means:
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organic chemistry
inorganic compounds
double covalent bonds
hydrocarbons
homologous series
fractional distillation
alkynes
functional group
complete combustion
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organic compounds
single covalent bonds
triple covalent bonds
alkanes
refined oil
alkenes
hydroxyl group
fermentation
incomplete combustion
2. Organic chemistry.
A large part of organic chemistry involves only four elements :
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Carbon
–C
Hydrogen – H
Oxygen
-O
Nitrogen - N
Organic compounds usually contain carbon bonded to hydrogen. They can also contain
Oxygen, Nitrogen and other non-metallic elements.
Compounds carbon dioxide (CO2) and carbon monoxide (CO) are considered to be
inorganic compounds.
When carbon forms compounds it usually has eight shared electrons.
Living or once-living organisms are the source of many carbon compounds , which is why
the term organic chemistry is traditionally applied to this branch of chemistry.
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3. Multiple Bonds
The bonding between non-metal atoms can be either :
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Single covalent bonds - 1 shared pair of electrons.
Double covalent bonds – two shared pairs of electrons.
Triple covalent bonds – three shared pairs of electrons.
Each carbon atom can form :
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Four single bonds
Two double bonds
A single and a triple bond
One double and two single bonds
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4. Hydrocarbons
The simplest organic compounds are hydrocarbons.
These are compounds that consist only of carbon and hydrogen. Hydrocarbons play an
important role in our everyday life. Cars run on hydrocarbon fuels and their engines are
lubricated by other hydrocarbon compounds. Many plastics are also derived from
hydrocarbons.
5. Types of Hydrocarbons
a). ALKANES
Alkanes are hydrocarbons that only contain single bonds between carbon atoms.
They have the general formula :
CnH2n + 2
Molecules that have formulas differing by one or more CH2 units form homologous series.
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The first two members in the homologous series of alkanes are methane( CH4) and
ethane (C2H6).
The first part of the name indicates how many carbon atoms are in the chain. The prefixes
used for naming are listed below.
The second part of the name indicates what type of compound it is. For alkanes, the name
ends in “ – ane”.
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b). ALKENES
Alkenes contain a double bond and have the general formula :
CnH2n
This means the number of hydrogen atoms in the molecule is exactly double the number of
carbon atoms. The two smallest alkenes are ethane and propene.
Alkenes names end in “ – ene”.
The biggest use for alkenes is making plastics.
c). ALKYNES
Alkynes contain triple bonds and have the general formula :
CnH2n-2
The number of hydrogen atoms in an alkyne is equal to double the number of carbon
atoms minus two.
The simplest alkyne is ethyne, commonly called acetylene.
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d). ALCOHOLS
Alcohols are not hydrocarbons because they contain oxygen in addition to carbon and
hydrogen.
All alcohols contain the hydroxyl group, - OH.
Ethanol is the best known of the alcohols, being found in beer, wine and spirits such as
whisky and brandy. Ethanol is also used as a solvent and is found in many glues, paints
and inks. It also used as a reactant to make rubbers and flavourings.
Alcohol can be made by fermenting fruit or vegetable matter.
6. Combustion of hydrocarbons and alcohols.
Complete combustion occurs when hydrocarbons or alcohols are burnt in excess
oxygen, producing carbon dioxide and water as the products.
Incomplete combustion occurs if the oxygen supply is limited.
Incomplete combustion is inefficient in that it produces less heat and energy than complete
combustion. Incomplete combustion also creates unwanted products such as carbon
monoxide gas.
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UNIT 2.4 – GREEN CHEMISTRTY
REVISION
2.
In order to understand genetics questions in the exam, you need to understand
what each of the following words means.
For each word write a sentence explaining what it means:
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green chemistry
supercritical carbon dioxide
critical pressure
 biodegradable
 critical temperature
 supercritical fluid
3. Green chemistry
Green chemistry is a philosophy that encourages chemists to consider the consequences
of using certain reactants such as chlorine.
There are twelve principles for green chemistry. You must rember at least six of them for
the exam.
The Twelve Principles of Green Chemistry*
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4. Problems caused by the chemical industry
5. Examples of green chemistry
a).
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b).
Biodegradable
Biodegradable means that over time the material can be broken down by microorganisms and not pose a threat to the environment.
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c).
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