O Level – Combined Science

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Salt Preparation

Preparation of salt by reaction between acid and an insoluble base.

Example: Preparation of copper(II) sulfate from copper(II) oxide(insoluble base)

Step 1: Put sulfuric acid in a beaker.

Step 2: Add copper(II) oxide until no more can dissolve.
Copper(II) sulfate solution & unreacted copper(II) oxide

Step 3: Filter to remove the excess copper(II) oxide

Step 4: Collect the filtrate.

Step 5: Heat up the filtrate to evaporate the water to about 1/3 the original volume.

Step 6; Allow the filtrate to cool to room temperature so that copper(II) sulfate crystals.

Step 7: Wash the crystal with a little cold distilled water.

Step 8: Dry the crystal with filter paper

For more key points and exam based questions with full worked solutions please contact Mr Ong @98639833

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Oxidation and Reduction

Oxidation
– Gain of oxygen
– Gain of oxidation number
– loss of hydrogen
– loss of electron

Reduction
– loss of oxygen
– loss of oxidation number
– Gain of hydrogen
– Gain of electron

1. A redox reaction is a reaction involving oxidation and reduction.

2. An oxidising agent is a substance that causes oxidation on another substance.

3. An reducing agent is a substance that causes reduction on another substance.

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Metals

Important Definitions

1. An alloy is a mixture of metal with one or a few other elements.

2. The reactivity series is a series of metals arranged in the order of their chemical reactivity, from the most reactivity to the lease reactivity.

3. Displacement reaction of metals is a redox reaction in which a more reactive metal displaces a less reactive metal to form its salt solution.

4. Galvanising is the coating of iron or steel on zinc for protection against corrosion.

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Key Points – Electromagnetic Waves

1. Electromagnetic waves are transverse waves. They transfer energy from one place to another without the need for a material medium.

2. The speed of the electromagnetic waves in vacuum is 3 x 10^8 m/s

3. Electromagnetic waves can be reflected and refracted.

4. Velocity of the wave = frequency x wave length

5. Electromagnetic Spectrum
Frequency in the ascending order
Radio waves
Microwaves
Infrared radiation
Visible light
Ultraviolet rays
X-rays
Gramma rays

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The Periodic Tables

Important Definitions

1. A group is a vertical column of elements in the Periodic Table.

2. A period is a horizontal row of elements in the Periodic Table.

3. A metalloid is an element that has the properties of both a metal and a non-metal

4. An alkali metals are the Group I elements.

5. The halogens are the Group VII elements.

6. The noble gases are the Group 0 or Group VIII elements.

7. The transition elements are a block metallic elements between Group II and II in the Periodic table.

8. A catalyst is a substance that increases the speed of chemical reaction.

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Key Points – Sound

1. Sound is a longitudinal wave produced by a vibrating source in a medium. It comprises compression and rarefaction.

2. Unlike electromagnetic waves, sound waves cannot travel through vacuum. They requires a medium to propagate.

3. The speed of the sound depend on the type of medium it travels in. Sound travels faster in solids, followed by liquids and travels the slowest by in gases.

4. The speed of sound is 330 m/s

5. The speed of sound increases when the temperature of the air increases.

6. The loudness of the sound increases as the amplitude increases.

7. The pitch of the sound wave increases as the frequency increases.

8. When sound is reflected after striking a hard surface, an echo is formed.

For more key points and exam based questions with full worked solution, please contact Mr Ong @9863 9633

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2014 Secondary 4 Preparatory Course

11-Nov Mon 10.30am to 12pm 1.5 hrs Chemical Bonding 1

12-Nov Tue 10.30am to 12pm 1.5 hrs Chemical Bonding 2

13-Nov Wed 10.30am to 12pm 1.5 hrs The Mole 1

14-Nov Thu 10.30am to 12pm 1.5 hrs The Mole 2

15-Nov Fri 10.30am to 12pm 1.5 hrs Chemical Calculation 1

18-Nov Mon 10.30am to 12pm 1.5 hrs Chemical Calculation 2

19-Nov Tue 10.30am to 12pm 1.5 hrs Acids and Bases 1

20-Nov Wed 10.30am to 12pm 1.5 hrs Acids and Bases 2

21-Nov Thu 10.30am to 12pm 1.5 hrs Salts 1

22-Nov Fri 10.30am to 12pm 1.5 hrs Salts 2

If you need help in the above topics, please contact Angie @96790479 or Mr Ong 98639633

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Power Revision

O Level Chemistry – 2 hrs Each Lesson

1. Atomic Structure/Ionic, Covalent and Metallic Bonding – 2 lessons
2. Formulae & Equation Writing – 1 lesson
3. Mole & Chemical Calculations – 2 lessons
4. Acids and Bases – 1 lesson
5. Salts – 1 lesson
6. Chemical Analysis – 1 lesson
7. Metals – 2 lessons
8. Periodic Table – 2 lessons

Power Revision

O Level Physics – 2 hrs Each Lesson

1. Kinematics – 2 lessons
2. Dynamics – 2 lessons
3. Forces – 1 lesson
4. Turning Effect of Forces – 1 lesson
5. Work Done, Energy & Power – 1 lesson
6. Thermal Physics – 2 lessons
7. Light – 2 lessons
8. Current Electricity/DC Circuits/Practical Electricity – 3 lessons

If you need help in the above topics, please contact Angie @96790479 or Mr Ong @98639633

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Speed of Reaction – Important definitions

1. the speed of reaction is the amount of reactant used up or the amount of product obtained per unit time.

2. Activation energy is the minimum energy that the reacting particles must possess for a reaction to occur.

3. An effective collision is a collision that successful in producing a chemical reaction.

4. A catalyst is a substance that increases the speed of a chemical reaction.

5. An enzyme is a substance that catalyses biochemical reactions.

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Key Points – Static Electricity

1. Protons and electrons have electric charge. A proton positively charged while and electron is negatively charged.

2. SI unit of electric charge is the coulomb (C)

3. The electric force is the attraction between unlike charges or the repulsion between like charges.

4. In electrical conductors, there are electric charges (usually electrons) that can move freely within the object.

5. Electrical Insulators are materials in which the electric charges cannot move freely.

6. Electric charges is due to the transfer of electrons from one object to another.
– solid insulators can be charged by rubbing.
– solid conductors can be charged by induction.

7. Discharging is the process of neutralising a charged object by removing excess charges.

8. An electric field is a region in which an electric charge experience an electric force. The direction of the electric field line represents the direction of the force experiences by a small positive test charge within the electric field

If you need help in the above topics, please contact Angie @96790479 or Mr Ong @98639633

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Ammonia – Important Definitions

1. A reversible reaction is a chemical reaction that can proceed in both the forward and reverse directions.

2. Haber process is an industrial process for making ammonia from nitrogen and hydrogen.

Operating conditions in the Haber process
Temperature – 450 deg C
Pressure – 200 – 300 atm
catalyst – Finely divided iron

If you need help in the above topic, please contact Angie @96790479 or Mr Ong 98639633

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Key Points – Current Electricity Part 1

1. Electric current I is the rate of flow of electric charge through a cross section of a conductor

I = Q/t

Q = amount of charge in coulomb (c)
t = time in second (s)

2. SI unit for electric current is Ampere (A)

3. The direction of conventional current is from the positive end of a cell or battery to the negative end. The directional of conventional current is opposite to that of electron flow.

4. Electromotive force (e.m.f.) e of an electrical energy source is defined as he work done W by the electrical energy source in moving a unit charge around a complete circuit.

e = W/Q

5. Potential difference (p.d.) V between two points in a circuit is defined as the work done W in moving a unit charge between these two points.

V = W/Q

6. SI unit for e.m.f. and p.d. is volt (V)

If you need help in the above topics, please contact Angie @96790479 or Mr Ong @98639633

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The Atmosphere and Environment – Important Definitions

1. Air pollution is the condition in which air contains substances that are harmful to living things or the environment. These substances are known as air pollutants.

2. A photochemical reaction is a chemical reaction caused by light or ultraviolet radiation.

3. Acid rain is rainwater with pH 4 or less than 4

4. Flue gases are waste gases produced when fossil fuels undergo commutation.

5. Chlorofluorocarbons CFCs are compounds containing the elements carbon, fluorine and chlorine.

6. The carbon cycle is the movement of carbon from carbon dioxide in the in the air through living things and back to the air again.

7. Greenhouse effect is the absorption of infrared radiation by some gases in the air which leads to atmospheric warming.

8. Global warming is the gradual warming of the Earth’s atmosphere due to the increased concentration of greenhouse gases in the atmosphere.

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Key Points – Current Electricity Part 2

7. Resistance R of an electrical component is the ratio of the potential difference V across it to the electric current I going through it.

R = V/I

8. SI unit of resistance is ohm

9. Ohm’s law states that the current I passing through a conductor is directly proportional to the potential difference V across it when the physical conditions are unchanged.

I is proportional to V

10. Conductors that obeys Ohm’s Law are said to be ohmic. Their resistance remains constant under constant physical conditions an their I-V graphs are linear.

11. Non-ohmic conductors do not obey Ohm’s Law. Their resistance varies.

12. Resistivity p is a measure of how much a material opposes the flow of electric current.

13. The resistance R of a wire is directly proportional to its length, inversely proportional to its cross-sectional area A, and directly proportional to the reisitivity p of the material.

R = (pl)/A

If you need help in the above topics, please contact Angie @96790479 or Mr Ong @98639633

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1. Organic compounds are compounds that contain the element carbon.

2. A hydroarbon is an organic compound that contains only carbon and hydrogen.

3. A homologous series is a family of organic compounds with the same general formula and similar chemical properties.

4. A functional group is an atom or group of atoms that gives characteristic properties to an organic compound.

5. Petrochemicals are chemical made from petroleum or natural gas.

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