Q1) How can you purify your water when you are hiking? Name two or three possibilities. Compare these methods in terms of cost and effectiveness. Are they any of these methods similar to those used to purify municipal water supplies? Explain.

Method	Cost	Effectiveness
Sedimentation	No cost	Straightforward method however it may take a longer time for particles and dirt to settle
Boiling water	Need for source of heat/fire	Easy to obtain pure, potable water (with bacteria removed etc)
Water purification droplets or tablets	Can be costly	Straightforward and kill bacteria and viruses quickly
Evaporation trap	Materials needed are not very costly	Time consuming and require a lot of effort to construct the evaporation trap

Municipal water purification methods include fluoridation, chlorination, coagulation, sedimentation and filtration to name a few. When hiking, the several methods available for us to obtain pure water follow the same approach as the municipal purification method.

For example, using sedimentation to obtain purified water is similar to the setting process in the municipal purification process. After sedimentation, filtration is required as well in order to separate the water from impurities.

Q2) Explain why desalination techniques, despite proven technological effectiveness, are not used more widely to produce potable drinking water.

Desalination involves removes ions from seawater, namely NaCl. NaCl is an ionic compound that consist of both Na⁺ and Cl^– ions. When dissolved in water, the ions will form ion dipole attractions with the water molecules as shown below.

These attractions are very strong and would require high amounts of energy to overcome. Energy consumption for the desalination process would hence be high making the process very costly in addition to the high cost of the technology used. Furthermore, the brine residue results in environmental concerns when being disposed.

Q3) Water quality in a chemical engineering building on campus was continuously monitored because testing indicated water from drinking fountains in the building had dissolved lead levels above those established by NEA.

a. What is the likely major source of the lead in the drinking water?

Major source of the lead is likely to come from corroded lead and iron pipes that distributes water to those drinking fountains. Due to the corrosion, lead seeps into the moving water and thus resulting in higher levels of dissolve lead in them.

b. Do the research activities carried out in this chemistry building account for the elevated lead levels found in the drinking water? Explain.

No, the research activities carried out in the chemical building may have nothing to do with the elevated lead levels found in the drinking water. There are several factors that may cause corrosion in the lead and iron pipelines, such as pH of the water, the amount of oxygen in the water, temperature of the water and the velocity of the water.

Q4) Some vitamins are water-soluble, whereas others are fat-soluble. Would you expect either or both to be polar compounds? Explain.

Both the water soluble and fat soluble vitamins would be polar compounds. The reason why water soluble vitamins are polar is because it has many polar parts such as -OH and C=O-O as seen in Figure 1, in which there are lone pairs in the O. Hence these areas are very electronegative, which results in the net dipole moment of the water soluble vitamins to be more negative than fat soluble vitamins. As such,more inter molecular hydrogen bonds can be formed between the hydrogen from one of the –OH with the lone pair from the oxygen from the another polar part such as –OH and C=O-O.

Figure. 1

Figure. 2

Fat soluble vitamins are also polar,just that it is less polar than water soluble vitamins.

As seen in Figure 2,the fat soluble vitamins usually have a long chain of carbon and hydrogen bonds,which is non polar.Hence the only polar areas in fat soluble vitamins would be those with –OH. Hence,the overall dipole moment of fat soluble vitamins are less negative as compared water soluble  vitamins. Therefore, it is not very soluble in water since it does not form much inter molecular hydrogen bonds in water.

Q1) Understanding Earth’s energy balance is essential to understanding the issue of global warming. For example, the solar energy striking Earth’s surface averages 168 watts per square meter (W/m^₂), but energy leaving Earth’s surface averages 390 W/m^₂. Why isn’t Earth cooling rapidly?

Even though the energy leaving Earth’s surface is more than twice that of the solar energy striking the Earth’s surface, Earth isn’t cooling rapidly because of Earth maintain her energy balance.

The emitted energy does not go directly out into space, but instead it is reabsorbed by clouds and gases in the atmosphere. Majority of the energy are reabsorbed by greenhouse gases such as methane, nitrous oxides, carbon dioxide etc. These greenhouse gases will constantly emit energy back into the atmosphere and keep the Earth a habitable temperature.

Ultimately, most of the energy will make its way out back into space and those that doesn’t are the ones responsible for the phenomenon known as global warming.

Q2) Decide and explain whether the statement is correct or incorrect. Explain.

The statement is incorrect. The winter mentioned in the cartoon is not due to the effect of higher average temperature caused by global warming but as a result of the effect of extreme weather and climate changes caused by global warming. Therefore, the issue of global warming is still more present than ever and we should not rest on our laurels.

Q3) One of the first radar devices developed during World War II used microwave radiation of a specific wave range that triggers the rotation of water molecules. Why was the design not successful?

Water molecules will absorb the the microwave radiation and hence it the water molecules will rotate.However,this design is not successful during the WWII as the water molecules will interfere with the intended content that the radar device is suppose to detect.

Q4) Now that you have studied air quality (Unit 1), stratospheric ozone depletion (Unit 2), and global warming  (Unit 3), which do you believe poses the most serious problem for you in the short run (pick one and explain)? In the long run (pick one and explain why)?

In the short run, air quality poses the most serious problem. Its effects can be seen in days. Even now, industrialised countries with many factories like China are already facing air pollution issues, with air quality reaching hazardous levels. People are already facing health problems and premature deaths due to air pollution. In Singapore, when mass burning of forests occur in Indonesia every year, air quality in Indonesia & neighbouring countries can reach dangerous levels and people fall ill as a result. Air pollution’s adverse effects on people’s health and productivity can be seen even now.

In the long run, I think that global warming poses the most serious problem. An increase in global temperatures can disrupt ecosystems. Rising sea levels also have the potential to lead to entire countries and islands becoming submerged under the sea. Extreme weather conditions can also pose threats to safety across the world. The agricultural sector may be the most affected because it is the most reliant on external weather conditions, which will lead to even more food source problems across the world on top of affecting the livelihood of many families depending on agriculture for a living.