Month: February 2017

This week, we talked about water in class.

Here are our answers for AE5.

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Question 1

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 any of these methods similar to those used to purify municipal water supplies? Explain.

Boiling

Chemicals 

Filtration/Purification

Cost (cheapest to most expensive): boiling –> filtration –> chemicals

Effectiveness (most effective to least effective): chemicals = filtration –> boiling

Distillation and chlorination are done to purify municipal water supplies.

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Question 2

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

There is high energy consumption during desalination to remove salt from seawater. This is very expensive and not cost-effective. There are cheaper alternatives such as finding sources of potable water (groundwater, lakes, etc.)

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Question 3

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.

• What is the likely major source of lead in the drinking water?
• Do the research activities carried out in this chemistry building account for the elevated lead levels found in the drinking water? Explain.

The likely sources of lead are solder from lead pipe joints or lead pipes themselves.

No, the research activities carried out in the building do not account for the elevated lead levels found in the drinking water. Many experiments carried out in the building have been redesigned to exclude the use of lead and toxic chemicals. Also, the building is likely to have a waste disposal system that is separate from water sources.

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Question 4

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

Polar compounds have bonds that are of high electronegativity difference. Non-polar compounds have bonds that are of lower electronegativity difference. Water-soluble vitamins are polar compounds while fat-soluble ones are non-polar. 

Polar compounds can form hydrogen bonds with water. Since water-soluble vitamins are polar compounds, they are able to dissolve in water.

Non-polar compounds cannot form hydrogen bonds with water. The weak interactions they form with water are not strong enough to break the intermolecular forces between fat-soluble compounds. Thus, they cannot dissolve in water.

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This week, we covered Unit 3: Global Climate Change. 

Here are our answers for AE 4.

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Question 1

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/m2), but the energy leaving Earth’s surface averages 390 W/m^2. Why isn’t Earth cooling rapidly?

Although the energy leaving the Earth is greater than the energy absorbed by the Earth’s surface, the Earth does not cool rapidly as the atmosphere retains some of the energy emitted by the Earth’s surface.

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Question 2Decide and explain whether the statement is correct or incorrect. Explain.

The statement is incorrect. The people in the cartoon are questioning why it is getting colder when everyone is concerned about global warming. They believe that the colder than usual winter is evidence to disprove global warming.  

However, global warming is actually an increasingly concerning phenomenon. Not only has it led to extreme temperatures, it has also led to rising sea levels, increasing occurrences of droughts and hurricanes. 

The main problem with this comic is that the people are confused between the terms “weather” and “climate”.

Weather is the day to day condition of the atmosphere. This includes temperature, rainfall and wind. Climate is the average weather conditions of a place, usually measured over one year.

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Question 3

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?

The radar device was designed to detect radiation reflected back onto the device. However, it did not work.

Microwave radiation has lower energy than infrared radiation. Water molecules can absorb microwave radiation and interfere with the detection of intended objects.

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Question 4

Now that you have studies 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)?

The most serious problem in the short term is the air quality. It directly affects the air we breathe and can cause respiratory problems.

In the long term, we have to worry about global warming. Melting ice caps and rising sea levels can lead to the submergence of many low-lying coastal regions such as Singapore. Global warming is not an immediate concern as it takes time for ice caps to melt and temperatures to rise before the Earth becomes inhabitable.