11 Sept - Reflections about Projects Day

This year for Projects Competition, I did a Category 1 Project – experimental research. The project was titled: Removing heavy metal ions from water using marine algae. After grueling rounds of judging and countless obstacles, the Project Competition is finally over. I believe that it is important that I reflect on the Project Competition, especially since I am the leader for the project group.

I believe that the most important element to a good project is a good topic. Some topics are more difficult to do and yet less appealing to the audience. Others are easy to do, very feasible and have a wide range of applications. Such topics have a strong appeal from the audience. Such topics often concern the environment. Environmental destruction is a very hot topic, very intensely debated and very urgent. Thus, my group and I decided to focus on solving an environment problem. We sourced through the seemingly endless list of past projects and found a few topics which are quite suitable to do. One of them which interested us was about heavy metal pollution. A few hundred years ago, people heavy metal pollution was completely unheard of and not seen at all. However, only recently due to the rapid increase in industries such as mining, metal plating, pesticides etc, is the problem of heavy metal pollution becoming a serious one. Such heavy metals such as mercury can even be toxic at parts per million concentrations. Many other heavy metal ions are also known to be carcinogenic. Heavy metal ions are also easily absorbed by plants and animals and can accumulate in organisms and in the food chain. Due to such a strong need to solve heavy metal ion pollution, we decided to investigate ways to solving it.

There are many ways to removing heavy metal ions: chemical precipitation, ion-exchange, adsorption and filtration. Chemical precipitation refers to causing the metal ions to form insoluble compounds and precipitate out of the solution. Hydroxide precipitation and sulfide precipitation are amongst the most common forms. Metal precipitation, however, produces lots of toxic metal sludge which needs to be disposed of somewhere else. Ion exchange is something like the double displacement reactions we learn in chemistry. Heavy metal ions in the solution would replace the cations on the ion exchange resins and bind to the resins. While ion exchange is very effective for concentrated solutions, it is expensive for dilute solution. Adsorption is the result of inter-molecular bonding such as dipole-dipole bonding between the pollutants and the adsorbent. Adsorption is especially useful for removing organic pollutants but is ineffective for removing ions. Filtration involves passing solutions through a membrane. Reverse osmosis is one such example and it is very effective. However, to pump water to such great pressure through a semi-permeable membrane, it is also very expensive.

One possible solution is bioadsorption, which means using biological material to adsorb metal ions. It is different from bioaccumulation whereby the living things take in trace mineral while they are alive. Bioadsorbants are cheap and widely available. Hence, we decided to hunt for various materials which are suitable for adsorption. We found marine algae, or put simply seaweed. And that was how we found such a good topic.

Soon, we arrived at our first obstacle, Prelims. It was an easy obstacle though. By following closely to the judging rubrics, we eased past it. However, the judges did point out a few mistakes. One of them was that we were not specific in our hypothesis. After the Prelims, we quickly reviewed through our hypothesis and addressed the problem.

Right after our first problem, we arrived at our second. We found out that obtaining marine algae was not easy as it appeared. At first, we thought we could order them. However, many suppliers sold them in quantities which were either too big (1 metric ton) or too small (those samples which are for looking under a microscope). Eventually, we decided to settle for the most unwanted solution – sourcing for marine algae along the beaches. At first, we thought that there would have been very little to find as we thought that marine algae would be found in deep waters. However, we were wrong. Marine algae were everywhere. Some of the rocks were even completely covered by marine algae. They had all been washed up on the shore. In the end, we managed to collect a lot of marine algae.

Then, it came to the actual doing part. The doing part was not as easy as it appeared. I had to go down to the laboratory at least 3 times a week to do the experiment. It was very time consuming. Many of my group members were frustrated that they had go down to the laboratory many times. I told them to just persist on – that the fruit of their labour would be sweet. They eventually agreed and their frustration vanished.

However, things got messier when the school term started. People started to have their hectic schedules – from CCA to ACE project. My group members started to lose focus. To make matters worse, we had come to our second judging round: the semi-finals. This was the most important round as it was worth 30 marks which was 60% of the total project marks. It could make or break us. I stressed its importance to my group members. We worked hard, rehearsed many times for it and hoped for the best. Eventually, our efforts paid off and we scored 24 marks, which was the third highest amongst the Sec 2s. I could tell that my group members be very elated. On the contrary, I was not, because the battle may be over but the war was not. We still had to go through the finals round. I did not want to get complacent and neither did I want my group members to get complacent.

Then, one month later, came our last and toughest battle: the finals. Last year, I did not go into the finals round and thus was completely unsure of how difficult it was or what we needed to do. I was clueless and so were my other group members. It was like we did not know what to expect. For example, on the last day of the webreport submission, we were almost late as we did not expect the uploading to be so problematic. For example, we realised that chemical formulas appeared as H2O instead of H₂O. Some of our pictures could not be displayed properly. We all became very stressed out and very worried. A few days later, when our mentor told us a piece of bad news, the pictures still could not be displayed correctly. And it was too late to change. We learned an important lesson: always finish your work ahead of time to prevent last minute cramming and avoid making unnecessary mistakes.

Before we knew it, the day of oral judging arrived. I was quite nervous. I could even feel my arms trembling, but I told myself that there was no use being nervous and took a deep breath. Our oral presentation went smoothly but what killed us was next. During the Q and A session, the judges attacked us ruthlessly with questions. One of the most difficult questions to answer was: Could you show us the photographs of you guy collecting the marine algae? I could not answer as we did not take any photos. I was stunned. I thought that we would definitely do badly. I tried to look on the bright side. At least now I know that we need to include as many pictures as possible to proof that we really did the experiments.

A week later, the results were out. We had scored 8 out of 10 marks. I was overjoyed. We were also the top in the Sec 2 cohort for our category. It turned out that our efforts and persistence have paid off.

From this project, I learned many important values. I learned about persistence. We faced setback after setback, but we did not give up. At first, we thought that we had no way of obtaining marine algae, but we eventually did. We spent a lot of time at the laboratory, so much that sometimes we felt like forgetting about the project completely. We did not. We decided to persist on. We also learned to communicate our ideas with clarity and precision using pictures. A picture tells a thousand words. A picture is proof of our work. Most of all, we learned the Hwa Chong motto of 自强不息. Even though we did well for the semi-finals, we did not settle for that score. While other groups chose to slack after the semi-finals, we pushed ourselves to the limit. That was how we got 42 points in total – the highest amongst all of the Sec 2 experimental research projects. Now, presenting the link to our web report. I hope that you will enjoy it.

http://projectsday.hci.edu.sg/2011/15-FinalsWeb/Cat-01/1-022/Home.html

28 Aug - Reflections of Term 3 Performance

It has come to the end of the third term for Secondary 2. It is so amazing that time flies so fast. Soon, I would be about to take the EOY exams. I better start revising for the EOY exams. But first, I should reflect on my Term 3 performance. As usual, I would be reflecting about my term test, about the various topics and comparing them with Term 2. However, since the EOY exams are coming already, I shall also include my plan to study for EOY exams – for Science only of course.

Term 3 test reflections

I scored 36 out of 40 for this test – which is 90% exactly. I felt that I did not do very well for this test. I was ranked 4^th position – out of top 3 – which I feel is quite unacceptable as I am supposed to be quite good at science. 36 out of 40 was the worst score I had for all of my Sec 2 science tests. I must have made quite a number of mistakes which I shall review through them. The first mistake is as follows:

Is Savanna a habitat, population, community or ecosystem? Explain your answer.

I know that the Savanna consists of more than one species of living things so it is no a population. It could be a habitat, community or ecosystem. However, the question mentions about the climate, the plants and the animals. This tells us that the Savanna is more than just a habitat or a community; it is in fact both or an ecosystem. I managed to get the first part correct but failed to explain that the Savanna is a habitat to the community which consists of the various plants and animals. Here, I lost 0.5 marks.

The next question which I made mistakes was a graph about the populations of plants, grasshoppers and lizards over the years. I was asked to describe and explain the changes on the graph – which I failed to explain a few and thus lost 1.5 marks. I do not believe this was a careless mistake nor was it a conceptual error. Instead, it was more like an almost unavoidable one. Perhaps the only thing I can do to avoid making such a mistake again is by practicing graph interpretation. This is a skill and a skill can only be sharpened by practicing.

The next question was drawing a ray diagram for lenses. Here, I did not draw arrowheads after the lens and also drew the real image using dotted lines. A real image is real so it should be drawn using solid line; a virtual image on the other hand should be drawn using a dotted line.

Finally, I come to the last question. I asks where should an object be placed in front of a converging lens if the lens is to be used as a magnifying glass. I wrote that the object should be placed at less than 2F from the lens. Apparently, I had got confused. While an object placed at less than 2F would appear magnified, it may not be upright. Thus, only when the object is placed between F and the lens, would the object be both upright and magnified.

In this test, I lost 2.5 marks from conceptual errors and this is 6.25% of the total marks. I feel that this is a lot of marks lost from conceptual errors which also means that I am not very strong in my science concepts. I need to revise through what I have learnt thoroughly and ensure that I know my facts well. The remaining 1.5 marks lost were quite difficult to avoid. However, I will try my best to avoid making such a mistake in later tests and exams.

Various topics covered in Term 3

The topics taught in this term were slightly harder than the topics in the previous two terms. They require a deeper understanding and there are lots of facts to remember too. The first topic is lenses. I find the main difficulty in this topic is remembering the various types of images formed by a lens based on the object’s distance from the lens. There are a total of 6 different cases and 3 different variables (real or virtual, upright or inverted, and lastly the size of the image).  In addition, we also need to know the uses for the various cases. This means there is a lot of memorizing to do. But memorizing is just the tip of the iceberg. We also need to draw ray diagrams.

The next topic is and easy topic. It is about the colours of light. As we know, there are white light consists of three primary colours: red, blue and green. Once we understand how the addition and subtraction of these colours form other colours, learning this topic becomes a breeze.

The third topic is a very demanding topic: ecology. Firstly, it is a very big topic, consisting of abiotic factors, biological interactions, feeding relationships, conservation, addition and removal of certain species, natural cycles and environmental protection. Secondly, ecology requires students to know many biological terms such as habitat, community, commensalism etc. However, it may not be as hard as it looks. In order to remember so many facts, I can try and link them together in maps, or use charts and tables to organize information.

Finally, we come to the last topic: sexual reproduction. This topic might pose a level of difficulty. For this topic, we are required to memorize the names and functions of various organs such as the ovaries, oviduct and so on. Furthermore, there is the complicated topic on the menstrual cycle, which for boys who do not experience it, can be quite a challenge.

Comparison with Term 2 and Term1

I find the topics taught in Term 3 more difficult than the topics in Term 1 and Term 2. However, this should not be an excuse for not doing well this test. I did not just do badly in terms of marks, but also in terms of positioning. This term test, I made many conceptual errors. I think I need to brush up on my facts.

EOY study plan

I have dedicated Thursday as my science study day. During that day, I would do intensive science revision. First, I would be revising on the facts learned. Facts are the foundations and if we do not even know the facts, we can forget about moving deeper. Next, I would practise some specific skills which are drawing electronic configurations, chemical equations, ray diagrams for reflection, refraction and lenses, and lastly graph interpretation. By covering both the skill and the knowledge, I should be able to do well in science.

3 June - Light’s Particle-wave Duality

What is light? Light is a form of electromagnetic energy that enters our eyes and enables us to see things. It is the fastest thing in the universe, travelling at 3 x 10⁸ m/s. Light has what is called wave-particle duality which means that it behaves either like a wave or a particle but not both. Light travels in approximately a straight line although it tends to spread out as it moves away from the source.

One of the biggest controversies about light was whether it is a wave or a particle. In 1974, Isaac Newton came up with the idea that light was made up of countless tiny particles travelling at enormous speed. This explains why light travels in a straight line and casts shadows. Light would follow Newton’s law of forces. It reflects off a mirror like a tennis ball bouncing off a wall. Most significantly, the corpuscle theory would explain how light travel through a vacuum like the way we see stars.  

However, a Dutch scientist named Christiaan Huygens argued that light travels in waves and not as particles. His theory shows why light is refracted. Imagine a line of soldiers marching in perfect step. If the line hits a muddy patch at an angle, the soldiers at one end step into the mud and are slowed down. The others carry on at the old speed until they too hit the mud. The effect makes the line veer round. Huygen’s wave theory explains the spectrum of light. Each colour has a unique wavelength.

Newton’s particle theory explains why light reflects, why light travels in a straight line and how light travels in a vacuum. However, it does not explain refraction and the spectrum, both which Huygen’s wave theory explains. Hence, the long debate about whether light is a wave begins.

However, in 1801, the tables began to turn towards the wave theory. That year, a brilliant amateur scientist named Thomas Young performed a very famous experiment: the double slit experiment. He shone a beam of light on to two slits in a piece of card. Light shining through the slits created an intriguing pattern on a piece of paper.

If light was streams of particles, we should simply get two bars of light on the piece of paper. Instead, Young saw bright and dark bands, like a fuzzy barcode. Young concluded that the light beyond the two slits interfered with each other. Constructive interference gave bright bands while destructive interference gave dark bands. Thus, Young could conclude that light behaved like a wave rather than a particle.

Another piece of evidence supporting the wave theory was a phenomenon of light known as diffraction. Diffraction had been identified in 1665 by Fancesco Grimaldi. He noticed that objects don’t block off light as completely as one might think. Sometimes light, very strong light such as sunlight in particular, appears to creep around the edge of objects in its path, creating a slight ‘halo’. If light were straight-moving particles, it would not show such an effect. Diffraction occurs because the peaks and the troughs of the light waves curve over the object.

In 1832, a famous scientist named Michael Faraday said the electricity and magnetism are one and the same. He named this force electromagnetism and said that light was part of electromagnetism. Later, a Scottish scientist named James Clerk Maxwell proved that was true.

However, just when light appeared to be a wave, the particle theory suddenly made a comeback. A German science Max Planck came up with an equation to find out the amount of energy in light at based on its wavelength. Yet this equation only worked if light is emitted in particular bite-size chunks of energy and not in a continuous array as scientist had expected. Planck called these packets of energy ‘quanta’. Later, a scientist named Gilbert Lewis called these energy packets photons.

However, a few scientists still believed that light must be a wave and that photons were just tricks of mathematics. Then in 1923, an experiment performed by Arthur Compton proved that photons were real. X-rays, a kind of invisible light, were fired at graphite, causing light to shoot up in a way that showed that it must be particles. Light appeared to be both a particle and a wave!  Scientists all could not make sense of that.

However, Werner Heisenberg, an ingenious German physicist realised why. He discovered that one could measure the momentum and wavelength of a photon of light – moving, wave side of its personality. One could also measure its position – when it strikes a target as a particle. However, one can never be sure of both at the same time, because light can only be either a particle or wave at one time but not both. Put simply, a photon sets out and arrives as a particle but travels as a wave.

At last, the puzzle is solved. Light has traits of a particle and a wave. From such an intense debate about light, we can learn that science is forever changing. This is one aspect of science that never ceases to amaze me. Looking at the rapid change in science, who knows, one day light might even be neither a particle nor a wave!

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References

1.      Farndon, J. (2007). From Newton’s Rainbow to Frozen Light: Discovering Light. London, UK: Heinemann Library.

2.      Smuskiewicz, A. (2008). Light. London, UK: Heinemann Library.

Picture sources

1.      http://t2.gstatic.com/images?q=tbn:ANd9GcRtbPCwJG7fYO3CZmsxXy12tqNmFwX4mu6uIfS4N4E2Fg1cXA0erg

20 May - Reflections of Term 2 Performance

It has finally come to the end of the second term and as usual, it is time to reflect about my science experience so far. Just like my Term 1 reflection, I would be reflecting about my test results and about the various topics covered thus far. However, I have decided to include one more component: comparing my performance this term with last term.

Term 2 test reflections

For this test, I got 37 out of 40 which was quite good a score. When converted into percentages it is 92.5%. I am somewhat satisfied with the results. In this test, I think I did better in the physics component rather than the chemistry component. I was quite surprised. I thought that I was better at chemistry than physics. I would be reflecting through the conceptual mistakes which I have made. The first mistake is as follows:

In a space shutter, the carbon dioxide build up inside the spacecraft was removed by the use of canisters packed with solid potassium hydroxide. Explain the chemistry in this reaction. Write a chemical equation for the above reaction.

At first I was quite shocked. I recalled that in the science lab, we used calcium hydroxide to absorb carbon dioxide. So, I thought that the chemical reaction for potassium hydroxide would be similar to that of calcium hydroxide. However, then the problem came. I did not know why calcium hydroxide reacted with carbon dioxide. But I did know that the product of the reaction between calcium hydroxide and carbon dioxide would be calcium carbonate. But the reaction for potassium hydroxide was slightly different because potassium is an alkali metal while calcium is an alkaline earth metal. In the end, I decided to just write out the chemical reaction to find out the truth. I wrote

KOH + CO₂ à KHCO₃

However, I was marked wrong. This was what the answer wrote:

Carbon dioxide is an acidic gas [1/2] will be neutralized [1/2] by the basic [1/2] potassium hydroxide to form salt and water [1/2].

The chemical equation is as follows:

CO₂ + 2KOH  à  K₂CO₃ + H₂O

I seemed quite easy to comprehend. On the contrary, it is not free of problems. One of the problems is that carbon dioxide is not acidic on its own. It needs water to show its acidic properties. The question stated that the potassium hydroxide was “solid potassium hydroxide” thus it can be inferred that no water was present. Thus, we might need to perform an actual experiment to find out if this reaction really works. From this question, I lost 2.5 marks which was 6.25% of the total marks. The other 0.5 marks were lost through carelessness, which accounts for 1.25% of the total marks.

Various topics covered in Term 2

Now, I shall go through the various topics individually. They are mainly: acids and bases, reflection of light and refraction of light. Acids and bases is a rather difficult topic because there are many different acids and bases available. Hence, the number of reactions is over a hundred. However, I believe that by understanding the general reactions such as acid and base react to produce salt and water, acids and bases can become a rather easy topic. However, some questions can be quite tricky, for example:

The pH of a lake polluted with acid rain can be raised by adding

A.      Calcium carbonate

B.      Hydrochloric acid

C.      Potassium hydroxide

D.     Sodium chloride

We obviously know that hydrochloric acid and sodium chloride do not help raise the pH. We are left with calcium carbonate and potassium hydroxide, both of which can neutralise acids. However, potassium hydroxide is an alkali and when added in access, might cause the pH to rise to high (above pH 7). Calcium carbonate would neutralise the acid and not cause the pH to rise over pH 7 because it does not release hydroxide ions.

Other questions require some background understanding which is not directly stated in the textbook:

Sulfuric acid reacts with substance X to produce a colourless solution. No other products are seen. What substance could be X?

A.      Magnesium

B.      Zinc carbonate

C.      Copper (II) oxide

D.     Sodium hydroxide

Sulfuric acid will react with magnesium to produce hydrogen gas. Sulfuric acid reacts with zinc carbonate to produce carbon dioxide. Both A and B will produce effervescence which can be seen. Sulfuric acid reacts with copper (II) oxide to produce copper (II) sulfate and water. Copper (II) sulfate solution is blue in colour and thus isn’t colourless. Therefore, we are left with option D (sodium hydroxide).

For the topics on reflection, I might have missed some important lessons due to competition, thus it was initially quite hard for me to keep up. However, after looking through the notes, I was soon able to get the rough idea. For reflection of light, I managed to grasp the idea of angle of incidence equals angle of reflection. Just by understanding this simple concept, I was able to draw ray diagrams for reflections rather easily. The formulas in physics are often easy to understand. However, it is the application of the formulas that is difficult and there are a wide range of applications.

I also found the idea of a virtual image and a real image quite confusing. At first, I thought that all images were virtual because we cannot touch them. However, I soon realise the difference. The notes said that images are virtual because they cannot be captured on a screen as the light rays do not pass through the image. I thought of another way of understanding the difference between real and virtual images. A virtual image is an image perceived by the brain – an illusion basically.

The next topic is about the refraction of light. I find this topic quite interesting because refraction causes many optical illusions such as the bending straw trick. Yet, I find refraction a little difficult to understand. Why is it that light bends? Why is it that when a light ray travels from an optically less dense medium to an optically denser medium, it is refracted towards the normal? Why not the other way round? Sometimes, I get confused with the other case whereby light travels from an optically denser medium into an optically less dense medium. I needed a distinct way to differentiate. Eventually, I thought of a rather ingenious way of distinguishing the two cases. I imagine a car. When a car travelling on a road (less friction to slow down) hits a sandy area (more friction to slow the car down), the car would swerve towards the sandy area.  By replacing the car with light rays, the road with the optically less dense medium and sandy area with the optically denser medium, I can understand how light refracts.

Comparison with Term 1

Finally, I shall compare my Term 2 performance with my Term 1 performance. In Term 1 test, I scored 37.5 marks; in Term 2 test, I scored 37 marks. Hence, it appears that I did not perform as well as in the first term, with a difference of 0.5 marks. However, it is a mere 1.3% difference and may not be significant. Last term, careless mistakes cost me 1.5 marks; this term, careless mistakes cost me only 0.5 marks. Thus, this test I have been more careful. However, it also means that I made more conceptual errors this test compared to last term. Thus, I believe that I need to do more revision for Science, particularly chemistry where I made more mistakes, so that I can brush up on my understanding. In addition, this term I had my National Schools competition and missed a few lessons, thus experienced a little difficulty coping. But eventually by looking through the notes again and again, I managed to keep up eventually. I believe that competition should not be used as an excuse as for not doing well academically. I believe that with time management and discipline, one can continue to excel academically. For example, at the competition site, I do not idle time away. Instead, I read through my notes so that I would not be lost when I return.

29 Apr - Reflections about Term 2 Science ACE

This term for science, I did a few ACE projects. They are mainly about chemistry. Chemistry is a very big and interesting topic given that there are over one hundred elements which give rise to millions of compounds. Of course, the other two sciences are just as big and interesting as chemistry. The most captivating part about chemistry is seeing how various chemicals react – whether a violent combustion or perhaps even an endothermic reaction which takes in heat. However, in order to understand chemical reactions, it is crucial that we understand the basics about chemistry, which forms the basis of the few science ACE which I have done this term.

The changing model of the atom

https://skydrive.live.com/?sc=documents&cid=56f5581b60bd808c#!/view.aspx?cid=56F5581B60BD808C&resid=56F5581B60BD808C%21269

The first project was about the ever changing model of the atom. At first, in the ancient world, nobody understood anything about the atom. In fact, nobody even knew what an atom was. One day, a man named Democritus asked a question: What happens when you keep cutting an object into smaller and smaller bits? What do we get? He said that we would arrive with a particle that could not be further cut. He named the particles atoms. Many people thought that he was simply crazy and dismissed his idea. Then, a renowned philosopher named Aristotle, who said that all objects in the world was made up of four basic elements: water, earth, fire and air. Of course we now know that all of the objects in the world were not made of just water, earth, fire and air. Instead, they are made up of atoms.

In 1897, Joseph John Thomson discovered the electron. Since the electron was negatively charged, he thought that the rest of the atom had to be positively charged. Thus, he envisioned the atom to be like a plum pudding where electrons were stuck on the atom like plums on a pudding.

In 1911, Ernest Rutherford performed an experiment which shocked the whole scientific world. He fired alpha particles at a gold foil. At first, he expected most of the alpha particles which were positively charged helium nuclei to bounce back from gold atoms. However, most of the alpha particles passed right through the gold foil, some of the alpha particles changed course, and only a few of them bounced right back as if they hit something dense. That was when he discovered the proton. He realised that Thomson’s model was wrong and proposed that the atom was like our Solar System. It was mostly empty space with a positively-charged core in the centre and electrons orbiting the core like planets orbiting the Sun.

In 1913, Danish physicists Niels Bohr had been investigating the behavior of electrons when they gained and lost energy. When electrons gained energy, they emitted a flash of light. Bohr suggested that the electrons were arranged in energy levels around the nucleus. These levels are arranged in shells around the nucleus. Bohr suggests that each level could only accommodate a certain number of electrons. Evidence for this arrangement of electrons came from the chemical properties of the elements.

Bohr’s model of the atom was easy to understand and it is the model taught in school today. However, in 1924, French scientist Louis de Broglie realised that electrons could exist as both a particle and a wave. So instead of having electrons orbit the nucleus, the electrons move around like a wave.

By the 1920s, physicists had realised that the existing rules used to describe forces such as gravity could not be applied to atoms. The new rules they devised were called quantum theory. One of the rules states that it is impossible to measure exactly both the position and velocity of subatomic particles. This theory was published by Werner Heisenberg. This reminds me about a joke:

One day, Heisenberg was caught speeding. A traffic police asked him to pull over and said, “Do you know how fast you have been driving?” Heisenberg replied, “No, but I know exactly where I am.”

In the late 1920s, Heisenberg published the idea that the orbit of an electron was neither a circle nor a wave. Instead, it was a cloud covering the area where the electron was most likely to be. This allowed us to understand about various types of inter and intra molecular bonds such as dipole bonding.

Finally in 1932, the missing particle of the atom had been discovered – the neutron – by James Chadwick.

Here, we see that the model of the atom has been continuously changing and up till date, it still continues to evolve. I believe it is the same for science. Every day, new discoveries are being made. Old theories are being proven wrong. In the past, a famous chemist John Dalton thought that atoms were unbreakable. Scientists now are able to split the atom using nuclear fission. Science is always evolving and we should not only adapt to the change, we should also be part of the change. We should be the ones making the change.

A case study on covalent bonding

https://skydrive.live.com/?sc=documents&cid=56f5581b60bd808c#!/view.aspx?cid=56F5581B60BD808C&resid=56F5581B60BD808C%21268

This ACE project deals with why aluminum chloride and beryllium chloride are covalent compounds and not ionic compounds.  We know that a covalent bond is a bond formed by the sharing of a pair of electrons. We also know that ionic bonds are formed between metals and non-metals. The metal loses its electrons to the non-metal so that both can possess the electronic configuration of a noble gas.

Aluminum is a metal and chlorine is a non-metal. However, aluminum chloride seems to exhibit a more covalent nature rather than ionic nature. Anhydrous aluminum chloride sublimes, something strange for an ionic compound. Ionic compounds tend to have high melting and boiling points. For example, sodium chloride has a melting point of 801^OC and boils at 1413^OC. Aluminum chloride is soluble in organic solvents such as ethanol, unlike most ionic compounds.

So why is it that aluminum appears to behave like a covalent compound rather than an ionic compound? At first, I was actually quite puzzled. However, I read about electronegativity. Electronegativity describes how well an atom attracts electrons. Strongly electronegative elements such as chlorine tend to attract electrons and form negatively-charged ions. Weakly electronegative elements tend to lose their electrons and form positively-charged ions. Thus, elements with high difference in electronegativity tend to form ionic compounds and elements with low difference in electronegativity tend to form covalent compounds. Scientists estimate that elements with a difference of less than 1.7 will form covalent compounds.

Now we go back to our original question. Aluminum chloride has an electronegativity difference of 1.55 which is less than 1.7, thus aluminum chloride is a covalent compound. However, aluminum chloride does look like a salt and isn’t entirely covalent. As such, we classify it as a polar covalent compound. A polar covalent compound means that the electron isn’t shared very fairly: the electrons tend to stay on the chlorine side and not the aluminum side. This is because chlorine is more electronegative.

The same is for beryllium chloride. Beryllium chloride has an electronegativity difference of 1.59, thus it is a covalent compound just like aluminum chloride.

From doing this ACE project, I have learned that sometimes science is not as direct as it seems. There are often a few exceptions. I believe that in learning science, we have to be flexible and learn to accept new findings and integrate them with the old.

27 Mar - Reflections about Term 1 Lab Lessons

Lesson 1: Properties of Acids and Alkalis

In this lesson, I learned about some basic properties of acids and alkalis, as stated in the title. I learned that universal indicators and natural indicators change colour based on the pH of the solution they are in. I also learned about the effect of acids and alkalis on Methyl Orange and Phenolphthalein. I read that such indicators have a sharp change in their colours and are used in a kind of volumetric analysis known as titration. Universal indicator is not good for titration because its change in colour at the end point of titration is not sharp. One of the 16 Habits of Mind states the need for accuracy and precision. If the change in colour is not sharp, we cannot get an accurate end point. I read that the error for titration is only 0.1ml thus a sharp change is needed.

Lesson 2: Strength of Acids and Alkalis

In this lesson, I learned about how the strength of acids and alkalis affect its electrical conductivity. Strong acids and alkalis disassociate and ionize completely in water. For example, the gas hydrogen chloride ionizes completely in the presence of water:

HCl (aq) à H⁺ (aq) + Cl^- (aq)

Weak acids and alkalis disassociate and ionize partially in water. Such acids and alkalis prefer remain as molecules rather than ions. Organic acids in particular behave this way. For example, hydrogen ethanoate ionizes partially and some of hydrogen ethanoate remain as molecules:

CH₃COOH (aq) ↔ CH₃COO^- (aq) + H⁺ (aq)

It is quite easy to grasp the concept that strong acids and bases ionize more easily. However, how do ions such as the hydrogen ion (H⁺) and hydroxide ion (OH^-) conduct electricity. I would like to find out more.

Lesson 3: pH Changes

Here we performed a down-sized form of titration on hydrochloric acid using sodium hydroxide. The concentration of both hydrochloric acid and sodium hydroxide is 0.1M or 0.1mole/litre. I read that one mole is about 6 × 10²³ molecules. Another experiment was performed: copper (II) oxide was added in access to hydrochloric acid. This time, an interesting observation was made. The pH increased till pH 7 where no increased was observed no matter how much copper (II) oxide was added. Later, I learned that copper (II) oxide is not soluble in water and thus is not an alkali. It does not release hydroxide ions. However, it does “absorb” H⁺ ions by reacting to form water.

Lesson 4: When Dilute Acid Meets Metals…

Finally after all of the basics, comes the most interesting part – chemical reactions. We know that acids react with metals (metals which are more reactive than hydrogen) to form a salt and hydrogen gas. But how does it work? This is basically a Redox reaction. A Redox reaction is also known as an oxidation-reduction reaction. Oxidation is the loss of electrons by a substance while reduction is a gain of electrons by a substance. A Redox reaction basically has both happening at the same time. For example, hydrochloric acid reacts with magnesium metal to form magnesium chloride and hydrogen gas.

Firstly, we can express the reaction in a chemical equation:

2HCl (aq) + Mg (s) à MgCl₂ (aq) + H₂

Then, we convert it into an ionic equation (Cl^- ions are omitted because they do not change in their oxidation state):

Mg (s) + 2H⁺ (aq) à Mg²⁺ (aq) + H₂ (g)

In the reaction, magnesium loses its electrons and thus is oxidized:

Mg à Mg²⁺ + 2e^-

Hydrogen gains electrons and is oxidized:

2H⁺ + 2e^- à H₂

The next interesting part is with the testing of hydrogen gas. Place a burning splint (yes burning and not just lighted) into the test-tube containing the gas. If the flame is extinguished with a ‘pop’ sound, the gas is hydrogen gas. The reason is because when hydrogen gas mixes with oxygen gas found in the atmosphere, it forms an explosive mixture. The burning splint ignites the explosive mixture and the shockwave from the explosion puts out the flame. At the same time, one hears the ‘pop’ sound.

Finally, the last interesting part is about why copper does not react with acids. What I was told was that copper is less reactive than hydrogen, that is copper is “not willing” to “take over” the chloride ions from hydrochloric acid. But I am a little unsure if we use a more concentrated acid like 4mol/dm³. I have read that in the past, alchemists used aqua regia or ‘royal water’ (which is in fact a mixture of concentrated hydrochloric acid and nitric acid) to dissolve gold. And we all know gold is even less reactive than copper.

Lesson 5: When Dilute Acid Meets Carbonates…

In this lesson, we perform one of the oldest science experiments – the volcano. I recall that when I was young, I mixed vinegar and baking soda together to produce a messy fizz. Today, I know the vinegar is a kind of acid – ethanoic acid – and baking soda is actually sodium hydrogen carbonate. Below is their reaction:

CH₃COOH (aq) + NaHCO₃ (aq) à CH₃COONa (aq) + H₂O (l) + CO₂ (g)

Lesson 6: When Acid Meets Alkali…

I find this one of the more boring experiments as there isn’t much reaction happening – no effervescence, no precipitation and no colour change. In fact, not many of the ions change during neutralization:

H⁺ (aq) + OH^- (aq) à H₂O (l)

However, no matter how pathetic it looks, it is the basis of a more complex volumetric analysis. Titration. I believe that everything we learn today is in preparation of what we would be learning tomorrow. That is why I always learn the most I can every day.

Lesson 7: When Alkali Meets Ammonium Salts…

This experiment is in fact somewhat similar to that of adding acid to carbonate salts. Both of these reactions liberate a gas – one of them is acidic and the other is alkaline. Both the gases form weak acids/alkalis as both gases prefer to remain as covalent compounds instead of forming ionic compounds. It seems that these two reactions are quite similar. In fact, I am considering a kind of salt – ammonium carbonate. Water is an amphoteric substance (it behaves both like an acid and an alkali) and when mixed with ammonium carbonate, will it liberate carbon dioxide and ammonia gas? Below is the possible equation:

H₂O (l) + (NH₄)₂CO₃ (aq) à 2H₂O (l) + 2NH₃ (g) + CO₂ (g)

Then again, this could just be my imagination running wide.

Lesson 8: Preparation of Soluble and Insoluble Salts

These two methods use the idea of filtration either to remove the insoluble reactant or to extract the insoluble product. The first method works when the reactant (metal, metal oxide and metal carbonate) is insoluble. The second method works when the salt produced is insoluble. However, what happens if both the reactants and salts are soluble? Then we need to use titration to determine the end point or such that both reactants are used up completely and not leftover. For example, what if we want to prepare sodium nitrate? We know that we need sodium cations and nitrate anions. The sodium cations can come from sodium hydroxide while the nitrate anions can come from nitric acid. Below is the reaction:

NaOH (aq) + HNO₃ (aq) à NaNO₃ (aq) + H₂O (l)

At the end point of titration, sodium hydroxide and nitric acid would have been completely used up leaving only sodium nitrate solution left, which can be obtained through crystallization. Salts are very useful substances. Salts such as sodium chloride can be obtained from the sea easily. However, not all salts are available in nature. For such salts, we need to prepare them ourselves.

14 Mar - Applications of Acids and Bases

            When ever we mention the word acid, people of visualise the image of an extremely corrosive liquid eating up everything in its path. Acid appears to be scary and frightening. However, in truth, acids and bases are not as scary as those we see in movies. In fact, they can be found in our daily life. However, in the science laboratory, acids and bases just like all other chemical should be treated with caution. 

            First, let us recall about what acids and bases are. Acids are substances which ionize in water to produce a hydrogen ion (H⁺). Take hydrochloric acid for example.

HCl (aq) à H⁺ (aq) + Cl^- (aq)

A base is any metal oxide or metal hydroxide. Alkalis are soluble bases. Alkalis ionize when they dissolve in water to form hydroxide ions (OH^-). Take potassium hydroxide for example.

KOH (aq) à K⁺ (aq) + OH^- (aq)

            We also recall the various reactions with acids and bases:

1.      Acid + Metal (more reactive than hydrogen) à Metal salt + Hydrogen gas

Take the reaction between sulfuric acid and magnesium as an example:

H₂SO₄ (aq) + Mg (s) à MgSO₄ (aq) + H₂ (g)

2.      Acid + Base à Salt + Water

Take the reaction between nitric acid and copper (II) oxide as an example:

 

2HNO₃ (aq) + CuO (s) à Cu(NO₃)₂ (aq) + H₂O (l)

3.      Acid + Carbonate compound à Salt + Carbon dioxide gas + Water

Take the reaction between hydrochloric acid and sodium bicarbonate as an example:

HCl (aq) + NaHCO₃ (aq) à NaCl (aq) + CO₂ (g) + H₂O (l)

4.      Alkali + Ammonium compound à Salt + Ammonia gas + Water

Take the reaction between sodium hydroxide and ammonium chloride as an example:

NaOH (aq) + NH₄Cl (aq) à NaCl (aq) + NH₃ (g) + H₂O (l)

There we have it, just 4 types of reactions. Yet, these 4 types of reactions give way to a whole lot of applications.

            One such application is using the Kipp’s apparatus. The Kipp’s apparatus, also known as the Kipp’s gas generator, is laboratory equipment used for generating gases such as carbon dioxide, hydrogen, hydrogen sulfide and other gases. A Kipp’s gas generator is made of 3 connected glass bowls sitting one on top of the other. The top glass bowl is removable and has a long tube that reaches through the middle bowl and into the bottom bowl. To produce hydrogen sulfide gas, the top bowl is removed and pieces of iron (II) sulfide are placed in the centre bowl of the Kipp’s apparatus. The top bowl is then replaced. Hydrochloric acid is poured into the top bowl. The acid flows down the long tube into the bottom bowl. The bottom bowl is connected to the middle bowl, thus when the bottom bowl is filled, the acid begins to fill the middle bowl and covers the iron (II) sulfide. Hydrogen sulfide is produced in the reaction between iron (II) sulfide and hydrochloric acid:

FeS (s) + HCl (aq) à FeCl₂ (aq) + H₂S (g)

Once gas production begins, a stoppered valve in the centre bowl allows the chemist to control how much gas escapes. When the valve is opened, the hydrogen sulfide gas can be collected. When it is closed, gas pressure builds up in the apparatus and forces the acid out of the centre bowl and stops gas production. The gas production can be restarted by releasing the built-up gas. Hydrogen sulfide is often used in analytical chemistry. Carbon dioxide and hydrogen gas can also be produced by placing a carbonate compound or metal respectively into the middle bowl instead of iron (II) sulfide.

            Another use of acids is in making fire extinguishers. One kind of fire extinguisher is the water extinguisher – what an irony. It works by using high pressure to blast water at the fire. The water extinguisher has a glass vial that contains sulfuric acid. The extinguisher’s body contains baking soda solution. When the operator pushes the plunger down to break the vial, the two chemicals react, and water and carbon dioxide are produced:

H₂SO₄ (aq) + 2NaHCO₃ (aq) à Na₂SO₄ (aq) + H₂O (l) + CO₂ (g)

As the gas pressure (carbon dioxide) inside the extinguisher increases, it pushes a jet of water out of the extinguisher’s nozzle.

            Another use for acids (more specifically sulfuric acid) is in car batteries. Car batteries are a type called a lead-acid storage battery. In a lead-acid battery, the negative electrode is a plate made out of the metal lead. The positive electrode is made of lead (IV) dioxide. The electrolyte is sulfuric acid which ionizes in water:

H₂SO₄ (aq) à 2H⁺ (aq) + SO₄^2- (aq)

At the negative electrode, the sulfate ions (SO₄^2-) oxidize lead to produce electrons:

Pb (s) + SO₄^2- (aq) à PbSO₄ (s) + 2e^-

At the positive electrode, lead (IV) dioxide reacts with electrons from the negative electrode, together with hydrogen and sulfate ions, and is reduced to lead (II) sulfate and water:

Pb⁴⁺ (aq) + 2O²⁺ (aq) + 4H⁺ (aq) + SO₄^2- (aq) + 2e^- à PbSO₄ (s) H₂O (l)

 By combining these two half equations, we get:

Pb (s) + 2SO₄^2- (aq) + Pb⁴⁺ (aq) 2O²⁺ (aq) + 4H⁺ (aq) à 2PbSO₄ (s) + 2H₂O

This is a redox reaction as there is a transfer of electrons from lead atoms to lead (IV) ions. This is a transfer of electrons produces electricity.

            Perhaps one of the well-known uses of bases would be using calcium hydroxide to test for the presence of carbon dioxide. Below shows the reaction between calcium hydroxide and carbon dioxide:

Ca(OH)₂ (aq) + CO₂ (g) à CaCO₃ (s) + H₂O (l)

Calcium carbonate (CaCO₃) is insoluble in water and precipitates out, which turns the calcium hydroxide “cloudy”.

            Ammonia is a base (more specifically an alkali) and has many uses. Ammonia (NH­₃) might not appear like an alkali because it does not contain the hydroxide ion. However, when mixed in water, in forms ammonium hydroxide:

NH₃ (g) + H₂O (l) ↔ NH₄OH (aq)

One might notice the double arrow. That means that while some ammonia molecules are being converted to ammonium hydroxide, a few of the ammonium hydroxide molecules are being converted back to ammonia molecules. Hence, ammonia is a weak alkali. However, ammonia especially when concentrated is nonetheless corrosive. Ammonia evaporates easily and if concentrated vapors enter one’s lungs, it might burn through his lung cavity. Despite its dangers, ammonia is a well known cleaner.

            Ammonia is also used to make nitric acid. It sounds contradicting, using an alkali to make an acid, however it is possible. Ammonia is first made to react with oxygen in the presence of metal catalyst to form nitric oxide:

4NH₃ (g) + 5O₂ (g) à 4NO (g) + 6H₂O (l)

The nitric oxide is then oxidized to form nitrogen dioxide:

4NO (g) + 2O₂ (g) à 4NO₂ (g)

The nitrogen dioxide is bubbled through water with oxygen gas to form nitric acid:

4NO₂ (g) + 2H₂O (l) + O_­2 (g) à 4HNO₃ (aq)

Nitric acid is an extremely useful acid. It can be used to make fertilizers such as ammonium nitrate which is rich in nitrogen. Plants need nitrogen to grow. Ammonia reacts with nitric acid to produce ammonium nitrate:

NH₄OH (aq) + HNO₃ (aq) à NH₄NO₃ (aq) + H₂O (l)

            It seems the acids and bases, while dangerous, can be very useful. It all depends on how much we understand about acids and bases. For example, someone who lacks acid and base knowledge might just add water to concentrated acid and cause his face to get burned. Knowing a bit about acid-base chemistry can help us understand the benefits and dangers of these chemicals. Who knows, one day acids and bases might even be the solution to global warming!

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References

1.      Lew, K. (2009). Acids and bases. New York, USA: Infobase Publishing.

Picture sources

1.      http://users.humboldt.edu/rpaselk/MuseumProject/Instruments/Kipp-Noyes/image2.gif

2.      http://www.gravitaexim.com/images/Lead-acid-battery.jpg