Separation Techniques: Distillation

Distillation is used to separate the solvent from a solution of solutes. It can also be used to purify water. In fact, many industries use distillation to manafacture clean water, hence the name distilled water.

How to carry out simple distillation:

Step 1 - Set up the bunsen burner

Step 2 - Clamp the distillation flask in position

Step 3 - Place the three way connector into the distillation flask

Step 4 - Place the thermometer into the top of the distillation flask

Step 5 - Place the receiving flask

Step 6 - Attach the tubing to the water inlet and water outlet condenser

Step 7 - Ensure all joints are not under stress

Step 8 - Turn on cold water supply to the condenser (and check for water leaks)

Step 9 - Add the liquid to your distillation pot and then the boiling stones to ensure smooth boiling

Step 10 - Start heating the liquid and collect product in the flask

How does it work?

As the temperature rises, substances with a lower boiling point rises first, allowing us to isolate different components of the mixture. Since different substances have different boiling points, and by using the thermometer to take accurate temperature readings, we can determine which substance will be received by the flask. Once the vapor comes into contact with the cooler surface of the condenser, the substance then condenses into its liquid state and drips into the receiving flask.

Hence, distillation is based on the principle of evaporation and condensation.

What is it used for?

Distillation is used in Desalination plants such as NeWater, to obtain pure drinking water. It is also used in oil refineries to separate crude oil from petroleum.

e collecting at any given stage of the distillation as we do not want to be collecting any harmful substances

Separation Techniques: Paper Chromatography

There are several methods to separate substances from each other, such as: filtration, chromatography, distillation and fractional distillation, evaporation, crystallization, magnetization and the separation of immisicible liquids.

But today, we shall only focus on chromatography.

Paper chromatography is used to separate mixtures of solutes with different solubility and degree of absorption such as ink dyes or sugar mixtures.

How to carry out paper chromatography:

Step 1 - Draw a pencil line 2cm from the edge of the chromatography paper

Step 2 - Place a drop of the mixture on the line. Wait for awhile before dripping about 2 more times, this is to ensure there is a concentration of the mixture

Step 3 - Dip the chromatography paper in a suitable solvent, and make sure the pencil line does NOT touch the solvent

Step 4 - Observe the solvent "run" up the chromatography paper

Food coloring "running" up chromatography paper

Step 5 - Remove the chromatography paper from the solvent once it has reached the solvent front

Step 6 - Calculate the Rf value

What is Rf value?

Rf value stands for retention factor. It is the distance moved by substance over the distance moved by solvent. This means substances with a higher Rf value are less easily absorbed, and smaller Rf values means the substance is more stongly absorbed.

How does it work?

As the solvent travels up the paper, the dyes are dissolved. Some dyes are more soluble, hence they travel faster up the paper, whilst others are less soluble and are absorbed strongly on the paper. This is all based on the principle of solubility.

The difference of solubility of the substances allows separation. The more strongly absorbed substances  travel slower.

What is it used for?

Paper chromatography is used to separate and identify compounds in a mixture. It can also be used for testing the purity of substances.

Compound and Mixture

What's the difference between a compound and mixture?

A compound made up of two chemically combined elements, and are only formed by a fixed ratio. The compound will also most probably lose the inital properties from its constituents and they can only be separated by chemical means.

A mixture, however, is made up of two physically combined elements. They can be mixed in varying ratios and do not have fixed properties like compounds. The properties of a mixture are the same as the properties of its constituents.

To prove the difference between the two, we conducted an experiment using iron fillings and sulfur.

MAGNETIC TEST

Firstly, to prove that mixtures can be separated by physical means, we:
1. Mixed one teaspoon of each element on a piece of filter paper using a stirrer
2. Used a magnet, placed below the filter paper and tried to separate the iron fillings (since it is magnetic) from the non-magnetic sulfur

It was a success, because eventually the iron fillings were completely separated. Then, we moved on to prove that the property of a mixture is the same as its constituents.

WATER TEST

Since sulfur cannot float, we:

1. Mixed the iron fillings and sulfur together using a stirrer on a piece of filter paper

2. Poured the mixture into a test tube filled with water

3. Used a clean stirrer to mix the mixture in water and left it to settle for about 45sec

4. Observe the elements in the test tube

What we observed:

After the whole thing, we observed that the sulfur floated while the iron fillings sank

Since sulfur alone will indeed float and iron filllings alone would sink, we could more or less confirm our findings, but of course we had to be fair and try it with a compound.

Firstly, we had set up our bunsen burner and poured one teaspoon of sulfur and half a teaspoon of iron fillings into a crucible, which we had then placed on top of the bunsen burner for 10 minutes. Example of our set-up below:

After the 10 minutes, let it cool for about a minute then use the tongs to transfer the compound onto a piece of filter paper. 

The compound

"Transfer the compound onto a piece of filter paper"

Next, repeat the Magnetic test. We had observed that the compound was no longer magnetic. Only iron fillings were attracted to the magnet (as we had put too much). This proves also that a compound is only formed by a fixed ratio.

We had also conducted the water test. Now the compound sunk to the bottom of the test tube. Hence, we can conclude that the compound will also most probably lose the inital properties from its constituents.

Lithium

So we were doing collaborative work and I was assigned to research on lithium. 

Here's what I found out:

Lithium is a metal with a silvery appearance, though it turns black when it comes into contact with air. It is under Alkali metals and is ductile. The boiling point is 1347°C and the melting point is 180.54°C. Lithium is both a heat and electrical conductor and it's chemical symbol is "Li".

Lithium is used for various purposes like:
- Batteries
- Fireworks
- Coolants
- Nuclear fusion
- Making cellphones
- Combined with other metals to make airplane parts
- Air purifyers in submarines and spacecrafts
- Mood stabilizers

REAL LIFE CASE STUDY:

Recently I came across an article called "Dreamliner becoming a financial nightmare" in the Straits Times about lithium.

It talks about a Dreamliner having to do an emergency landing due to a battery fire. The Boeing 787 Dreamliner depends in part on lithium-ion batteries, which provide them with quick powerful charges, but can also overheat and catch fire.

A lithium-ion battery works like most other chemical batteries. A particle with an electric charge moves to one terminal when energy is applied, and the other terminal when energy is drawn. They have a higher energy density, which means they can store more kilowatt hours of work per unit of weight and volume than other chemistries.

But they have drawbacks.

One is that while all batteries get warm, which makes some of their parts expand, the chemical soup in which the ions in a lithium-ion battery swim - the electrolyte - expands more than the electrolytes of other chemistries, experts say. Because a lithium-ion battery is always sealed, it has to take the pressire of the expansion. Otherwise, it will break open or break internally.

All batteries generate heat on charging and discharging. No re-chargeable chemical batteries are 100% efficient. In other words, they never give back quite as much energy as was put into them. The energy that does not make the round trip ends up as heat.

When the lithium-ion batteries were first produced commercially, in the early 1990s, they were small, for hand-held devices. Now, though, as they move into cars and airplanes, they are much bigger. The ones on Boeing 787 are 50 to 100% larger than the lead-acid battery typical in car. The battery packs in electric cars are far bigger than that.

Info taken from Straits Times, "Dreamliner bceoming a financial nightmare". 

Sub-atomic Particles

What are Elements

Elements are either made up of atoms of molecules. Atoms can be further divided into sub-atomic particles and depending on the number of particles, it determines where the element ends up on the periodic table. 

Today we shall focus on the sub-atomic particles which are made up of protons, neutrons and electrons. Protons and neutrons, or nucleons for short, can be found in the nucleus of an atom. There are also electrons circling the atoms in areas called shells or orbitals. 

Each proton carries one positive charge, while each electron carries a negative charge. Neutrons, well they don't carry any charge. Anyways, in each atom, there will be an equal number of protons and electrons so they cancel each other out and the atom will be electrically neutral. 

This explains why you don't get electric shocks everywhere you go. If an atom doesn't have an equal number of protons and electrons, you can call them ions. This means the atom is charged, and depending on whether you have more protons or electrons, your atom will either be negatively or positively charged. 

Ions can be dangerous when inhaled, because when negatively charged ions and positively charged ions come into contact, it leads them to stick to things, including your lungs and throat, which can lead to build-up over time and exacerbate conditions like asthma attacks, blisters in lungs, blocked passages from particles and even permanent lung damage. (Taken from eHow.com)

Particles in an atom are very light. One proton weighs approximately 1.67 x 10^-27, which is 0.000000000000000000000000000167kg. So to make things simpler, our wonderfully lazy scientists came up with the standard unit "amu" or "atomic mass unit". This is also known as "relative mass".

I do have one question though...

Why is it that electrons don't "fall" into the nucleus?

Apparently, I've been reading up and this has to do with the uncertainty principal. The electron cannot have a defined position in the nuclei of atoms means that it must occupy every other space within the atom in a wave of possibilities. If the electron was positioned with great certainty within the nuclei of atoms, their momenta becomes infinitely uncertaint. But instead, they seem to have energy-orbits inside of atoms which determine the chemical struture of the universe. Another interesting thing to note is that electrons could not be in the center of atoms, because if they where, matter would drastically sink in size. 

We already know of nature objects which undergo this process, and they go by the name of neutron stars. In classical mechanics, electrons couple so strongly with protons that they should collapse all the time; and would in classical physics mean that every nucleus of every atom would gobble up the electrons in about 100 microseconds.

[Taken from: http://www.thenakedscientists.com/forum/index.php?topic=26362.0]

I know the above explanation is kinda confusing so I decided to give an analogy. It's like coasting along on a skateboard at a constant speed, and you see something to your right that you are attracted to, maybe a cute puppy. You start to turn towards it, but your forward your motion will carry you past it. If the conditions are right, you'll keep turning, but your forward motion will keep making you miss them. You'll just circle them, always turning toward them, but never getting there. It's like that for the electrons and planets too. They can't slow down, so they just keep turning and overshooting, forever circling the object.

The Periodic Table

This complicated table has stumped millions across the globe...

THE PERIODIC TABLE

How do you read the table? Well, firstly, the horizontal numbers (the roman numerals), those represents the period the element is in. Whilst the vertical numbers represent the group it's in. The arrangement of the elements are in increasing atomic number.

Elements can be divided into the metals, non-metals, metalloids and the oh-so-mighty... Noble gas, depending on the elements' properties. An element is made up of ONE type of atom and each element has different atoms or molecules. Elements have a certain way of being labelled, their first letter must always be capital.

I really like the analogy given in class...

Elements is like a string of linked paper clips. When you separate the links, you get one paper clip, representing an atom. Sure, you can still break the paper clip up into smaller pieces, but it can no longer retain its function. Likewise, if you break up the protons, electrons and neutrons in an atom, the atom is no longer part of the element.

This is because the atom is the smallest particle of an element that retains the chemical properties of an element. Even the arrangement of the atoms can affect the state of the element. Which brings to the difference between atoms and molecules...

Atoms are the smallest particle of an element that retains the chemical properties of the element. Meanwhile, molecules are two or more atoms bonded together. Of course, the noble gas, being oh-so-noble, have very low chemical reactivity as they are very stable.

MORE...

How to define if something has a high/low boiling point and melting point?
If the melting point of an element is below 0 degrees celsius, it has a low melting point. And if elements have boiling points of more than a 100 degrees celsius, they are considered to have a high boiling point. In general, just compare everything to water!

What are metalloids?
Metalloids are elements which have properties of both metals and non-metals. For example, silicon has chemical properties similar to non-metals but exhibit properties such as electrical conductivity like metals.

How to Use a Bunsen Burner (And More)

Which part of the flame is hottest?

Today we had a lab session and we had to find out which part of the flame (from the bunsen burner) is the hottest. My lab partner and I had hypothesized that the inner blue core of the flame would be the hottest since it was nearest to the core, meaning it should have a higher temperature.

But of course to even start the experiment, we had to learn how to use the bunsen burner SAFELY.

So here are the steps:

1. Connect the rubber tubing to the gas tap
2. Check that the air holes are closed (*Leaving air holes open could be dangerous)
3. Turn the gas tap on
4. Position the lighter above the barrel and light it up
5. Adjust the gas tap accordingly
6. Open the air holes to about halfway

And ta-da! There you have it, a working bunsen burner. To turn it off, close the air holes, then turn off the gas tap.

*Leaving the air holes open when lighting up the bunsen burner could result in a strike back. You don't want to know what it is, but it could be dangerous. So don't do it.

Anyways, back to the experiment...

So to test which part of the flame would be the hottest, we had divided the flame into three parts: the outer orange/yellow flame, the outer blue flame and the inner blue core. Below are the steps we took:

1. Turn on bunsen burner

2. Use metal tongs to hold copper wire at the centre of the orange/yellow part of the flame

3. Use a stopwatch to time how long it takes for the copper wire to glow red

4. Record the time

5. Repeat steps 2-4 with the copper wire held at the outer blue flame and the inner blue core.

And this is our results...

From the results tabulated above, we can see that the copper wire heated up fastest at the outer blue flame. In other words, this means that the hottest part of the flame is actually at the outer blue flame, so our hypothesis had been wrong.

Reflections...

After completing the whole experiment, there was one thing I was curious about. Why did we use a copper wire and not any other wire, or even sewing needles! Apparently, this is because copper is an excellent conductor of heat due to Metallic Bonding, and the fact that it's valence electrons are loosely arranged. Interesting...

Safety and Sketching

Lab Safety

The Do's and Don't's in the Lab

First post of the year and we shall cover lab safety!

Here are more of the more important rules highlighted:

- Do not enter the lab unless a teacher is present

- Long hair must be tied up, long fringes must be pinned up

- Do NOT wear PE shorts, it is important that you are fully covered

- Wear your goggles at ALL times (even those with specs)

- No eating or drinking in the lab at all times

- Used, mixed chemicals cannot be put back into the original container

- Do not use your hands to pick up broken glass

- Cleanliness is important

- Acid into water, never the reverse

- Do not heat anything in a closed container

Of course, there is more to it, but these are the main few. For more information, refer to the lab safety agreement passed out. That's all so far for lab safety, can't wait to get on to the practical on Friday!

Other than that, we had also done up a few sketches of scientific diagrams. The most important thing about drawing diagrams is that they have to be:

- 2D

- To scale

- In bold lines, no sketchy lines

- Labelling cannot have arrows

Why do you think we need to learn how to draw diagrams?

Personally I feel we learn this so that our drawings can be more easily communicated. As Mr Foo said, "If a scientist cannot communicate his ideas, it is also useless". Therefore, through drawing these diagrams, we have yet another way to express our ideas, and also we can impart these ideas in a clearer manner. So we have to pay attention even if the lesson might seem boring and we are just revising basic skills. However, they are called "basic skills" for a reason!

So, yeah, stay tuned!