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Solutions to 2009 Monthly Questions
The question was:
Ammonium nitrate, NH4NO3, was used as a fertilizer before people realized that it was potentially explosive. Between 1911 and 1921, a German company BASF was producing a mixture of ammonium sulfate and ammonium nitrate in the town of
The equation representing the explosion is
2 NH4NO3(s)--> 2 N2(g) + 4 H2O(g)+ O2(g)
Two solid molecules produce a total of seven gaseous molecules, causing the sudden increase in pressure responsible for the explosive character.
But upon close inspection, the reaction is bizarre. How could an oxidizing agent like nitrate(NO3-) produce an even stronger electron-thief like oxygen? What’s going on?
Answer
The equation actually represents an overall reaction, which hides the short-lived sequence of ammonium nitrate’s decomposition.
First NH4NO3 contains both a reducing agent(NH4+) and an oxidizing agent(NO3-). With the proper activation energy, the fertilizer will decompose into dinitrogen monoxide (nitrous oxide or laughing gas) and water.
NH4NO3(s)
N2O(g) + 2 H2O(g)
Although the following may not be the actual mechanism, it can be rationalized as follows:
H2O + 2 NH4+
N2O(g) + 8e- + 10H+ (reduction
half reaction)
2 NO3- + 10 H+ + 8e-
N2O(g) + 5 H2O (oxidation half
reaction)
(1) Overall : 2 NH4NO3(s)
2N2O(g) + 4 H2O(g)
In fact, this is how laughing gas is produced. But when temperature exceeds 240 oC, N2O(g) decomposes
(2) 2N2O(g)
2N2(g) +O2(g)
If you combine (1) and (2) , the net equation is
2 NH4NO3(s)
2 N2(g) + 4 H2O(g)+
O2(g)
Solution to February 2009 Question of the Month
The question was:
Compact fluorescents work like conventional fluorescents. Electricity excites mercury atoms that exist in the gas-form within the light bulb. When electrons fall back from higher energy levels, ultraviolet light is emitted. The energy excites phosphors on the glass, and we get visible light. Both the glass and the phosphor supposedly block UV light, and none leaks out. But Health Canada launched a study in December 2008 to test compact fluorescent bulbs for emission of ultraviolet rays - less than two months after British health officials issued a public warning that the bulbs release UV rays. They advised people not to work in close proximity of the bulbs.
How can the average consumer test compact fluorescents for ultraviolet light?
Answer
PULS cards can be obtained from the American Chemical Society. They contain a photochromic chemical which absorbs UV light and changes colour. The intensity of the colour produced is proportional to the amount of UV absorbed. I used the card to measure UV from natural lighting, a compact fluorescent, a conventional fluorescent bulb and from outdoors. In each case I used a one minute exposure and then photographed what the card looked like. The results are shown below:
Indoor natural light
1 minute exposure 2 mm under compact fluorescent 1 minute exposure 2 mm under conventional fluorescent 1 minute exposure in shade. Part of snow-covered deck in sunshine, 2: 15 PM January 22 at 45o latitude You can see that some UV is indeed emitted by compact fluorescents, more than what is released by conventional fluorescents but less than what bounces off snow on a winter afternoon.
Compact fluorescents have become popular, but I see this as a third arguable strike against them.
The first is that each compact contains 5 mg of mercury and creates a disposal problem.
The second is that although they are more efficient than tungsten bulbs, in a cold climate, this is irrelevant 9 months of the year. In tungsten bulbs, the electricity that is not converted into light is converted into heat, and that is certainly not wasted energy when you are trying to keep your home above outdoor temperatures.
Solution to March 2009 Question of the Month
The question was:
Felix Hoffman synthesized three seemingly different drugs: the anti-diarrheal drug Tannig; aspirin and heroin. Yet they all have something in common from a chemical synthetic point of view. What molecule, serving as a common add-on, was used to produce all three substances?Answer
Acetic anhydride was used in all cases to convert tannic acid, salicylic acid and morphine into Tannig; aspirin and heroin, respectively.
Solution to April 2009 Question of the Month
The question was:
I thought of this question while using a globe to explain latitude and longitude to my grade 6 daughter.
Extra Question.
This one was also inspired by my daughter's homework.
You have a set of cards, one for each of the first 20 elements of the periodic table. You flip over the first card, and out comes hydrogen. The next card is placed at the bottom of the deck. The next card flipped over is atomic number 2, helium. The third card is placed at the bottom of the deck, and the next one to be flipped is atomic number 3, lithium. The pattern continues until all twenty elements are revealed in the correct order.
How do you arrange the cards so they come out in order of increasing atomic number? It is not as obvious as it seems. Trial and error could lead to frustration, but a simple experiment or a bit of logic will tremendously facilitate the task.
The solution will be posted in early April, but you should think of the experiment. It's a lot more fun than sneaking a peek at the solution.
Answer
There are 360o of longitude in all. Half of that is 180o. To get from
To locate the antipode, look for 40o S. and 176E on a globe. That will take you to close to
Wikipedia has a nice map showing antipodes for any point on Earth. Notice that the antipodes for all of Africa and
http://en.wikipedia.org/wiki/File:Antipodes_LAEA.png
Solution to Extra Puzzle
There are at least two ways of obtaining the sequence. You can simply number 20 cards 1 to 20. Flip them alternately, with each second card going at the bottom of the deck and they will come out in the following sequence:
1,3,5,7,9,11,13,15,17,19,2,6,10,14,18,4,12,20,16,8
That means that 1H should be placed first, 2He third, 4Be fifth and so on all the way to 20Ca which should be arranged eighth before beginning to flip them.
Here is the list as it should be arranged according to the above:
H, Na,He, S, Li, Mg, Be, Ca, B, Al, C, Cl, N, Si, O, K, F, P, Ne, Ar.
The sequence can also be deduced as follows. Since we flip the cards alternately, it is obvious that the odd cards will be revealed first : 1,3,5,7,9,11,13,15,17,19. The remaining cards will be:'br" 2,4,6,8,10,12,14,16,18, 20.
But the alternating sequence will continue, so after skipping the 20th card, 2 will come next, skip one to 6, skip one to 10, skip one to 14, skip one to 18. We skip the 20thcard again(2 is already gone) bringing us to 4, skip one(namely 8; 6 and 10 are gone already) to 12, skip the 16th to get to 20, skip the 8th to get to 16, and finally the 8th card will be the last to be revealed.
Solution to May 2009 Question of the Month
The question was:
There is a classic high school demonstration in which a few drops of the glycerin(CH2OHCHOHCH2OH) are poured on top of a pile of potassium permanganate(KMnO4) powder. At first nothing seems to happen, which of course begs the question: "Sir, what's supposed to happen?" which in turn begs the cliche-reply, "Good things come to those who are patient." Then just as the chatter of disinterest begins to break the silence, white smoke appears, and within seconds, a spectacular violet flame erupts, leaving behind a crusty residue and a harsh smell that, in the absence of a fumehood, grates on the throat and lungs.
It is often said that science allows both young and old adults to regain the curiosity of childhood. Good demonstrations lead to numerous questions. Why is the start of the reaction delayed? Why does it start at all without any mixing or heating? Why does the steam appear before the flames? Why is the flame violet? Are there any practical applications of this reaction?
Answer
The activation energy, the energy that must be absorbed in order to get the reaction going, is small, which is why it proceeds unaided. But although relatively small. But small does not imply nonexistent, so it still borrows some heat from the air. The appearance of steam before that of flames suggests that this is not a one-step affair. The mechanism probably goes through more than one intermediate.
The equation is just a summary of the overall reaction, giving no hints of what ensued behind the scenes.
14 KMnO4(s) + 4 C3H5(OH)3(l) -->7 K2CO3(s) + 5 CO2(g) + 16 H2O(g) + Mn2O3(s) In the late 1950's gentlemen named Kenneth B. Wiberg and Klaus A. Saegebarth investigated the mechanisms of permanganate oxidations, in case you want to pursue the matter.The flame is violet due to the excitation of the electrons of the potassium ion. Delayed Aerial Ignition Devices (DAID), which shoot a stream of flaming ping-pong balls, make use of this reaction when controlled fires are deliberately set from helicopters.
Solution to June 2009 Question of the Month
The question was:
A patient suffering from impotence consults a doctor. Good doctors are also good scientists, so instead of immediately prescribing Viagra, the doctor asks his patient to perform a simple experiment with a strip of conventional postage stamps. The doctor wants to establish whether the cause of the impotence is psychological or physiological. What non x-rated experiment does the doctor have in mind?
Answer
In rapid eye movement (REM) sleep, active dreaming occurs. Heart rate, blood pressure, and body temperature become much more variable. Men often have erections during this stage of sleep(source:Society of Neuroscience). So if a male glues a roll of postage stamps around his penis before going to bed and then finds them detached in the morning, there is a good chance that he experienced an erection in REM sleep. If this happens repeatedly, then the source of the impotence is psychological.
Solution to July 2009 Question of the Month
The question was:
Long-term exposure to concentrated vapors of hydrochloric acid, HCl, may cause erosion of teeth. This is consistent with self-inflicted damage to teeth caused by an aqueous form of hydogen chloride. When does this happen?
Answer
The majority of people with bulimia nervosa engage in self-induced vomiting. This constantly exposes the inner side of teeth to hydrochloric acid from the stomach, and according to the Journal of the American Dental Association, (Vol 133, No 12, 1689-1691),
"People who have engaged in bulimic activity for a moderate period of time (from months to a few years) have severe erosion on the lingual surfaces of the maxillary anterior teeth."
Here is a graphic representation of that damage:
Solution to August 2009 Question of the Month
The question was:
According to biologist Stuart Kauffman, autocatalytic reactions played an important role in the origin of life. In such reactions some molecules can play a dual role: they can be a product of a reaction and also act as a catalyst. Can you draw a flow chart of two hypothetical molecules, A and X, that react to form AX, which then catalyzes the reaction between A and X?
Answer
Reference: Kauuffman, Stuart At Home in the Universe. Oxford University Press.1996
Science Question for September 2009
In the past year, scientists at Albert Einstein College of Medicine of Yeshiva University in New York have proposed a new theory of autism that suggests that the brains of people with autism are structurally sound but unregulated. This implies that symptoms of the disorder might be reversible.
According to the theory, autism is a developmental disorder caused by impaired regulation of a bundle of neurons that processes sensory signals from all areas of the body. Where in the brain is this important bundle?
By the way, one of the observations that inspired the theory is the temporary but positive impact of fever on the behaviour of autistic individuals. The brain area in question is responsible for controlling our fever response.
The bundle of neurons is found in the brain stem, specifically in the locus coeruleus-noradrenergic (LC-NA) system. These neurons also provide the entire central nervous system with noradrenaline, a neurotransmitter and stress hormone.
Here’s the abstract of the actual research paper from
BRAIN RESEARCH REVIEWS 59 (2009) p. 388–392 by Mark F. Mehler and Dominick P. Purpura
Some children with autism spectrum disorders (ASD) exhibit improved behaviors and enhanced communication during febrile episodes. We hypothesize that febrigenesis and the behavioral-state changes associated with fever in autism depend upon selective normalization of key components of a functionally impaired locus coeruleus-noradrenergic (LC-NA) system. We posit that autistic behaviors result from developmental dysregulation of LC-NA system specification and neural network deployment and modulation linked to the core behavioral features of autism. Fever transiently restores the modulatory functions of the LC-NA system and ameliorates autistic behaviors. Fever-induced reversibility of autism suggests preserved functional integrity of widespread neural networks subserving the LC-NA system and specifically the subsystems involved in mediating the cognitive and behavioral repertoires compromised in ASD. Alterations of complex gene–environmental interactions and associated epigenetic mechanisms during seminal developmental critical periods are viewed as instrumental in LC-NA dysregulation as emphasized by the timing and severity of prenatal maternal stressors on autism prevalence. Our hypothesis has implications for a rational approach to further interrogate the interdisciplinary etiology of ASD and for designing novel biological detection systems and therapeutic agents that target the LC-NA system's diverse network of pre- and postsynaptic receptors, intracellular signaling pathways and dynamic epigenetic remodeling processes involved in their regulation and functional plasticity.
Science Question for October 2009
In a 250 ml Erlenmeyer water was added along with two drops of phenolphthalein. In a second flask we added about 5 ml of ammonia. We covered the water-filled flask with a wet filter paper and inverted it. We then placed it over the ammonia flask.
After a few seconds, in the water-filled flask, we noticed a thin fuchsia-coloured funnel forming in the center of the liquid. It elongated progressively until it reached the top of the liquid, which gradually turned a deep shade of fuchsia. The base of the upper flask had a similar colour change, and a chaotic swirling pattern emerging from the funnel eventually coloured the entire upper flask. The lower flask remained clear.
Why was there a colour change?
Why did we get a "funnel" shape? A swirling pattern?
Suggested Additional Experiments:
Experiment |
Results |
Add litmus to the smelly liquid |
It turns blue |
Add NaOH to phenolphthalein |
The solution turns deep pink. |
Put wet filter paper on top of ammonia liquid and nothing else. |
We can still smell the gas. |
Measure the temperature above the ammonia. |
The temperature drops. |
Repeat the experiment without ammonia liquid. Instead use a drop of NaOH solution on the filter paper. |
We get similar observations—with the thin pink funnel, but everything seems to happen more slowly. |
Answer
You might be thinking,” Enough already with this ammonia demo!” But the beauty of this so-called constructivist activity is that by showing others what was on our minds, we kept learning from each other. By that I certainly include myself because if it had not been for your hypotheses and suggested experiments, I probably would not have given as complete an explanation as what many of you offered on the lab test. So here is a summary of all your best thoughts and reflections.
1. How did it all start?
Ammonia is an aqueous solution of NH3 gas and water. The gas can free itself from water’s bonds and come out into the air. How do we know? We can smell it. That’s what the ammonia did in the lower flask.
2. What’s the connection between diffusion and translations?
When the ammonia first begins to pop out of the water, it tends to be momentarily concentrated near the surface of the water. Here the molecules are more likely to bump into their own kind than into air molecules. But the translations and collisions take them a little beyond the crowd, and as they start to bump into air molecules, they slowly get surrounded by more air molecules. That’s what we mean when we talk about diffusion being a movement from a high concentration (original crowded ammonia area at the surface of the water) to a lower concentration (where there was mostly air).
3. What evidence did a temperature drop provide?
A student suggested that we measure the temperature of the air above the ammonia in the lower flask. It would drop slightly because evaporation has a cooling effect. Ammonia steals heat from the air and uses the energy to free itself from water’s grasp.
4. What happens with the filter paper?
The NH3 gets back into the water because
the filter paper is wet. NH3, when dissolved in water, actually
reacts with H2O to make NH4+ (aq) and
5. Why did a pink colour appear in the upper flask?
Phenolphthalein is a pH indicator. When it bonds to
6. Why did the pink colour rise?
Phenolphthalein is less dense than water;
that’s why the pink colour rose to the top. Many
students thought the NH3 was rising through the water, but others
realized that it is the phenolphthalein that turned pink when the NH3 and water produced OH-.Moreover, when the same experiment was
repeated without ammonia but with a drop of NaOH on filter
paper instead, a rising pink projection still occurred.
With the NaOH version, everything was slower and less intense because the only NaOH present was in the drop. But NH3 keeps
hitting the filter paper and keeps providing more
7. Why did we observe a chaotic pattern?
It was the result of Brownian motion, which is caused by the random rotations of water molecules as they collide into rising phenolphthalein molecules. It is similar to what you see if you place a drop of food coloring into a flask of water. It will send coloured offshoots in every direction, and just like the water and phenolphthalein, it will seem to slowly stir on its own. The flask will be entirely mixed and uniformly coloured.
Science Question for November 2009
The idea for this question came from James Trefil's A Scientist in the City.
Greenhouse effect aside, even at night, closed windows allow heat into an air conditioned home, and in the winter they let heat out. How does this happen at the molecular level, even if no air can escape?
Answer
Summer: Excited air molecules hit the glass from the outside. Glass molecules get excited very easily(poor insulating properties). On the other side of the glass, the cooler air molecules from the air conditioned inside pick up energy from the excited glass. As they pick up speed, these air molecules are now at a higher temperature. Electricity bills get bigger.
Winter: Excited air molecules hit the glass from the heated interior of the home. Again because glass molecules get excited very easily. with this transfer of energy, the air molecules from inside the house now move slower. On the other side of the glass, the glass molecules make contact with the colder air molecules from outside the house. They pick up energy at the expense of the glass and the home's interior.
Science Question for December 2009
On April 25, 1953, in the journal Nature, Watson and Crick wrote, "If the sequence of bases on one DNA chain is given, then the sequence on the other chain is automatically determined." They realized that this is how genetic messages are copied with so much fidelity when chromosomes duplicate during cell division. The DNA molecule unzips to form two separate strands, each of which serves as a template for the synthesis of a new strand. 
But as obvious as the mechanism seemed to the two theorists, the evidence only came in 1957-58 from the experiments of Meselson and Stahl. How did they use radioactive isotopes to support the idea that DNA unzips and doubles each strand?
Answer
They used a centrifuging technique that allowed them to separate DNA containing a heavier isotope of nitrogen(15N) from DNA that had a lighter one.(14N). They grew E.coli bacteria for many generations from a medium that had only 15N (using tagged ammonium chloride) to ensure that each DNA strand would only have bases with 15N. They then switched to a medium that had only the lighter isotope and also let it replicate for one generation. After extracting DNA from the bacteria, they observed that the DNA was a hybrid containing both isotopes.
| 15N | 15N | ||
| medium | 14N | 15N14N | 15N14N |
| 14N | 15N14N | 15N14N |
By letting the bacteria continue to grow in a 14N medium, the DNA extracted after each generation showed a progressively lower amount of hybrid DNA and a higher amount of lighter DNA. The table shows 2nd generation DNA daughter molecules.
| 15N | 14N | ||
| medium | 14N | 15N14N | 14N14N |
| 14N | 15N14N | 14N14N |
Diagram taken from Original paper
from Proc Natl Acad Sci U S A. 1958 July 15; 44(7): 671–682