Question 1

                   

Purification Tablets – Cheap, requires about half an hour to purify. To be used on water without sediments.

                           

Filtration Straws – Cheap, instantaneous usage. But has to be replaced after a certain amount of uses.

Boiling of Water – Requires fuel, takes about 15mins to boil. Has to be filtered before the start of boiling to reduce the amount of sediments.

Purification methods of municipal water supplies consist of:

Filtration Systems, similar to Filtration Straws
A water filter is a device which removes impurities from water by means of a physical barrier, chemical, and/or biological process.

Distillation Systems, similar to Boiling which involves heat
Distillation is a process in which impure water is boiled and the steam is collected and condensed in a separate container, leaving many of the solid contaminants behind.

Disinfection, similar to Purification Tablets, Boiling
Disinfection is a physical or chemical process in which pathogenic microorganisms are deactivated or killed. Examples of chemical disinfectants are chlorine, chlorine dioxide, and ozone. Examples of physical disinfectants include ultraviolet light, electronic radiation, and heat.

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Question 2

Desalination of water requires a lot of energy. Salts dissolves very easily in water, forming strong chemical bonds, and those bonds are difficult to break. Energy and the technology to desalinate water are both expensive, and this means that desalinating water can be pretty costly.  Also, the residue is very saline brine, which must be disposed of without causing too many environmental problems.

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Question 3

(a)

The corrosion from the piping used to transport water.

(b) No, the research activities carried out in the chemistry building do not account for the elevated lead levels found in the drinking water. The drinking water pipeline and the pipeline used for research purpose are totally different pipelines. They are not interlinked, so water used in the research activities will not contaminate the drinking water.

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Question 4

Water soluble vitamins are polar. They contain polar groups such as -OH which can interact with other polar water molecules, via hydrogen bonding. Fat soluble vitamins are non-polar. They have few or no polar group, thus they tend to interact with the hydrophobic fatty acid tail found in lipids.

Question 1

Even though the amount of energy emitted from the surface is more than double the amount received from the sun, Earth does not cool rapidly. The surface of Earth absorbs a large amount of energy from the atmosphere. The presence of greenhouse gas will also trap radiation within the atmosphere, resulting in higher temperatures in the atmosphere. Hence, inhibiting the rapid cooling of the Earth.

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Question 2

The statement is incorrect. The sea levels are still rising even in the polar climates, for example, in the Northern and Southern Hemisphere.
The observation is too narrow to explain the global phenomenon. While the said cartoon could apply to that specific region/zone, the effects of global warming is still omnipresent and continues to affect the other parts of the world.
As illustrated in the cartoon, the water levels are still rising, yet Pepper and Salt are oblivious and choose to ignore the warning signs of global warming.

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Question 3

The use of microwave radar devices during WWII was not a feasible idea. Water in the atmosphere would absorb the microwave radiation which triggers the rotation of the molecules, thus reducing the efficiency of the microwave radars as energy is not fully transmitted.

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Question 4

In the short run, air quality (Unit 1) poses the most serious problem in the short run. It creates the most immediate effect compared to the other two units. This is because when the air quality is compromised, mankind has to wear masks to reduce the inhalation of particulate matter, which could induce immediate effects on oneself, such as breathing difficulties, shortness of breath, etc.
In the long run, global warming (Unit 3) has the greatest impact on the world. Effects include melting ice caps resulting in higher sea levels, which causes the loss of habitat for animals such as polar bears. There will be increase in average global temperature, which could indirectly implicate mankind by loss of homes due to flooding. Low lying land areas will be submerged.

Question 1

1. Exothermic. It is a combustion reaction.
2. Endothermic. Liquid water molecules absorb energy to overcome the intermolecular forces between h20 molecules to become gaseous vapour.
3. Endothermic. When solid ice melts into water, energy is absorbed, increasing kinetic energy of its molecules, explaining its liquid state.

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Question 2

To make a good explosion, the total amount of energy in reactants should be much, much greater than the final total amount of energy in its products, so that the enthalpy change (-ΔH/ energy released) will be huge.

Therefore, bond strength in reactants has to be very strong as compared to bond strength in products (weak).

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Question 3

Temperature is an objective measurement of the amount of heat energy present in a body, which is represented using units like the Kelvin scale (for absolute temperature) and Celcius/Fahrenheit.

eg. “It is hot and sunny outside. The weather forecast says it would be 37 degrees Celcius.”

Heat refers to the total energy of all molecular motion inside an object. The hotter an object, the more rapid the molecules move inside it. Heat is also defined as the transfer of kinetic energy from one body to another.

eg. “Put the pack of ice next to the frozen food we bought, not next to the hot food, or else the ice will melt faster from the heat.”

eg. Heating a beaker of water over a bunsen burner with a thermometer.

eg. Chemical energy from burning of gas is converted to thermal energy to heat the water, which results in the bubbling of water and a rise in surrounding air temperature. The amount of heat energy converted is measured by the thermometer in the water.

Heat can be physically felt, temperature cannot. Heat energy depends on the size and type of object on how it conducts heat; temperature not dependent.

eg. A metal plate and a book in the same set-up, both are at same temperatures, however the heat we perceive when we touch them are different.

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Question 4

(a) Octane rating of 98: knocking characteristic of 98% isooctane & 2% heptane. The higher the octane number, the more compression the fuel can withstand before igniting. It is a measure of the ability of gasoline to burn smoothly without knocking (resistance).

(b) Octane rating provides no information about the presence of oxygenates.