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.