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Chapter 14 – Metal

1. The physical properties of metals are as follows:
– Usually have high densities, melting points and boiling points.
– Can be bent, stretched or beaten into very thin sheets without breaking
– Good conductors of heat and electricity

2. Any alloy is a mixture of a metal with one or few other elements

3. There are four main reasons for making alloys
– To improve the strength and hardness of metals.
– To improve the appearance of metals.
– To improve the resistance of metals against corrosion.
– To lower the melting points of metals.

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Chapter 15 – Electrolysis

1. An electrolyte is a compound that conducts electricity in the molten state or in aqueous state.

2. A cathode is a negatively charged electrode. An anode is a positively charged electrode.

3. Positively charged ions are called cations and negatively charged ions are called anions.

4. The decomposition of a compound by electricity is called electrolysis.

5. During the electrolysis, cations move towards the cathode while the anions move towards the anode.

6. Redox reactions take place at the electrodes. Oxidation occurs at the anode and reduction at the cathode

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Chapter 18 – Atmosphere and Environment

Greenhouse Gases

Carbon dioxide is released to the atmosphere when solid waste, fossil fuels (oil, natural gas, and coal), and wood and  wood products are burned.

Methane is emitted during the production and transport of coal, natural gas, and oil. Methane emissions also result from the decomposition of organic wastes in municipal solid waste landfills, and the raising of livestock.

Nitrous oxide is emitted during agricultural and industrial activities, as well as during combustion of solid waste and fossil fuels.

What are the effects of global warming?
1. Heat waves and periods of unusually warm weather
2. Sea level rise and coastal flooding
3. Glaciers melting
4. Arctic and Antarctic warming
5. Spreading disease
6. Earlier spring arrival
7. Plant and animal range shifts and population declines
8. Coral reef bleaching
9. Downpours, heavy snowfalls, and flooding
10. Droughts and fires

What is causing the depletion of ozone?
1. Chlorofluorocarbon compounds are also known as CFCs – made of  chlorine, fluorine and carbon.
2. These compounds are unreactive and do not burn.
3. They are compressed to form liquids which are used in aerosol  propellants and as coolant fluids for refrigerators and air conditioners.
4. When an aerosol can is utilised, the CFC molecules are released into  the air. At higher altitudes in the atmosphere, these molecules are  decomposed by sunlight to produce chlorine atoms.
5. The chlorine atoms react with the ozone molecules and thus destroy  the ozone layer which protects the earth from the direct rays of the  sun.
6. Exposure to direct radiation of the sun can cause skin cancer to  humans and also destroy the agriculture.

Effects of Ozone Depletion
1. There is an increase in the temperature due to the ozone depletion as more UV rays are entering the earth’s surface.
2. There would be a no.of skin cancers.3.Crop yields would be adversely affected.Vegetation land becomes dessert.
4. North and South Pole melts causing the ocean level to rise and flood the low-lying countries such as Netherlands.5.Rapid evaporation would occur and cause droughts especially in India.Thus, CO2 dissolved in the oceans rise into the atmosphere adding further to the greenhouse effect.

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Stop and Think, are the following questions True or False

1. Temperature, volume and mass are physical quantities.

2. All measurements in chemistry are made using SI units.

3. It is not possible to measure precise volumes of liquids.

4. Clocks and watches are accurate to only 1 second.

5. Many physical quantities can be measured with senors connected to
computers.

Ans: TFFFT

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Kinetic Particle Theory – Common Error

Wrong Concept
During melting, the temperature rises because heat is absorbed

Correct Concept
During melting, the temperature remains constant at the melting point because the heat absorbed is used to overcome the attractive forces between the particles.

Wrong Concept
Diffusion does not occur in solid

Correct Concept
Diffusion does take place in solids, it occurs extremely slowly in solids because the solid particles are less energetic and move with less speed

For more common errors please contact Mr Ong @98639833

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Experimental Techniques – Key Points

1. Fractional distillation is used to separate a mixture of liquids with different boiling points

2. The starting line in paper chromatography should be drawn with pencil and not ink. Ink contains dyes that will dissolve in the solvent.

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

O Level Chemistry Tuition Singapore/Chemistry O Level Tuition/Tutor

Chapter 5 – Atomic Structure

1) Atoms are made up of protons, neutrons and electrons.
2) Proton number or atomic number is the number of protons in an atom.
3) Nucleon number is the number of protons and neutrons in an atom.
4) Isotopes are atoms of the same element with the same number of protons but different number of neutrons.

From : O Level Chemistry Tutor