Lab session 3

Separation techniques

Today, we did chromatography! (as promised.)

EXPERIMENT TIME!!! XD

Purpose: To separate the dyes in green food colouring

Materials used:

-Capillary tube

-Green food colouring

-Chromatography paper

-Boiling tube

-Pencil

-Ruler

-Distilled water

-Clothes peg

Step 1: Draw a line across the chromatography paper 1.5cm from the edge with a pencil:

Step 2: Using the capillary tube, dot at most 3 drops of Green food coloring on the same spot in the middle of the line. 

Step 3: Fill the boiling tube with distilled water (Just 1.5cm^3 of water will do). 

Step 4: Making sure that there is no water on the sides of the boiling tube touching the chromatography paper, carefully place the chromatography paper into the water, with the water below the pencil line (Use the clothes peg to secure the chromatography paper): 

(Okay, I put more than 1.5cm^3 of water.)

Step 5: Watch the dyes move up! :D (It's really cool)

Step 6: After about 10-15 minutes or so, take out the chromatography paper. Let it dry. I got this:

But most, if not all of my classmates got this:

(I hope I didn't get it wrong. :p)

Mark the solvent front. Now, calculate the Rf values.

What are Rf Values?

Retention Factor (Rf) 

Unknown substances separated by chromatography can be identified by Rf values.

So basically, Rf value = Distance moved by substance / Distance moved by solvent. It should always be less than 1, or else something's wrong.

So... 

Here are my results:

So, yep.

TAKEAWAY FROM LESSON: Paper chromatography separates a mixture of solute with different solubility and degree of adsorption. 

e.g. The more adsorbent the solute, the further up the paper it travels, vice versa. 

!!!!NOTE!!!!

Adsorbent does NOT mean Absorbent. 

Adsorbent: (of a solid) hold (molecules of a gas or liquid or solute) as a thin film on the outside surface or on internal surfaces within the material:charcoal will not adsorb nitrates | the dye is adsorbed onto the fiber.

Absorbent: take in or soak up (energy, or a liquid or other substance) by chemical or physical action, typically gradually: buildings can be designed to absorb and retain heat | steroids are absorbed into the bloodstream. 

(Taken from dictionary)

Entry 3

21/1/13

Mixtures and Compounds

Mixtures and compounds can be differentiated by:
-separation
-properties
-energy change
-composition

An alloy is a mixture of metals with other elements. They tend to be stronger than pure metals.
Some must-know alloys...

-Steel --> Iron+carbon
-Stainless Steel --> Iron+carbon+chromium+nickel)
-Brass --> Copper+zinc
-Bronze --> Copper+tin

Separation Techniques

-Chromatogram (refer to earlier post)
-Distillation
-Crystallization
-Filtration
-Magnetic attraction
-Evaporation
-Sublimation
-Separating Funnel

Mixtures are separated into pure substances for:

-Characterization

-Identification

-Production of useful substances like medicine.

All these separation methods make use of the properties of the substances.
We should be able to:
-Apply these skills to daily life
-Suggest separation techniques that are useful when given a situation
 (We will be doing a practical on this soon, so something to look forward to ^^)

Lab session 2

Before I start, let me do an intro onto Compounds.

A compound is a pure substance that contains 2 or more elements chemically combined. It is made up of different elements chemically combined in a fixed ratio (will digress on this point later).

So the practical of today.

Part 1: Investigating a mixture of elements

In this practical, we're using the two elements, iron and sulfur. (I forgot to take pics of them individually. >< but you should know how they look like)

Appearance of iron filings: Silvery grey, powder form

Appearance of sulfur: Yellow, powder form

Placing a spatula of iron filings and another spatula of sulfur on a piece of filter paper, we mix them together to form a mixture:

And so we try to use the first method of separation: Using a magnet to attract the iron filings:

The iron filings are attracted to the magnet underneath the filter paper. We were able to use the magnetic property of iron and non-magnetic property of sulfur to separate the iron filings from the sulfur. 

Next: Adding the iron and sulfur mixture into a test tube of water, we carried out the next method of separation. 

As you can see, we are making use of the densities of the elements to separate the mixture. Iron is denser than sulfur, hence, sinking to the bottom of the test tube and sulfur floating on the surface of the water. Although they do separate, there is still some sulfur that remains unseparated from the iron filings at the bottom. 

Learning points:

-The substances in a mixture can be mixed in any proportion.

-When a mixture is formed, heat and light are not usually taken in or given out.

-The mixture can be separated by physical means.

-The mixture has the properties of its constituent substance. 

Part 2: Compounds

1. Mix one spatula of sulfur and half a spatula of iron filings in a crucible. 

2. Cover the crucible with a lid and heat for 10 mins using a strong flame. 

(This is where lighting the Bunsen Burner gets handy.)

Note: Sulfur is flammable and produces a poisonous gas (sulfur dioxide). It is, on its own, poisonous so beware when handling. (If you've been to a geothermal park, you'll know that sulfur can smell quite bad.) 

And so the wait begins...

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3. After 10 minutes, allow the crucible to cool for a while before removing it. (Use tongs!)

Open the lid and examine the residue left. 

The residue left should no longer be in powder form, but solid. Do some tests on it. Does the residue separate into iron and sulfur with a magnet? Does the residue separate when in water? If you have done the experiment properly, your answers should be no, as now, the iron and sulfur have become a compound called iron sulfide (you can see where the name came from). 

(Closer look)

Now, you may notice the grey powder. That is excess iron filings. As promised, I shall digress. Compounds are made up of elements chemically combined in a fixed ratio. As there is excess iron filings, this proves that all the sulfur has already been spent reacting with the iron filings to make iron sulfide, and the excess, unreacted iron filings are left behind. Hence, proving that compounds are formed of elements combined in a fixed ratio. 

The chemical reaction takes place when a compound is formed due to an energy change, in this case, is heating. 

My thoughts on the practical:

This practical has enhanced my understanding on how compounds are formed, and even solid elements can become compounds (I used to think that only liquid chemicals can form compounds. XD sounds VERY silly now. Very. Very. Silly. ) 

[And I'm sort of glad that I had a blocked nose then. XD I went to a geothermal park in New Zealand once, and you could smell the sulfur from the car. It was really cool though.] 

Entry 2

14/1/13

Elements, Compounds, Mixtures

Okay, to start off, here are some terms used to describe the properties of elements (I didn't know them previously, so):

Malleable: Bendable (Basically if the material can bend without breaking)

Ductile: Can be drawn into thin wires

These are usually used to describe metals. 

An element (classified into metals, metalloids and non-metals), is a pure substance made up of entirely one type of atom.

Some of you may ask, "What's the difference between atoms and molecules?"

A very important question. 

An ATOM is the smallest particle of an element that retains the chemical properties of that element. 

A MOLECULE is a group of 2 or MORE atoms CHEMICALLY COMBINED. (Most elements exist as molecules)

That brings us to the Periodic table. 

THE PERIODIC TABLE

The periodic table is a list of elements arranged in order of the increasing proton numbers. The vertical rows of the periodic table are called groups and are numbered - get this - in ROMAN NUMERALS. The horizontal rows are read as periods:

(Also a clearer pic of the periodic table I drew XD)

Just for laughs:

I found this song a really long time ago. Back then I didn't really understand. :p
(But it's catchy. XD)

Okay, I know this isn't very relevant, but still. If you're interested on how the earth was made and all, this song briefly explains it. (I like the Big Bang Theory. XD)

Lab session 1

The Bunsen Burner

Today for half of our lesson, we learnt how to light a Bunsen Burner and the the hottest to the coolest part of the flame.

DO NOTE TO WEAR GOGGLES AT ALL TIMES WHEN USING THE BUNSEN BURNER. (And tie your hair up)

How to light a Bunsen Burner?

1. Attach the rubber tubing to the gas tap firmly.
2. Close all air holes.
3. Turn the gas tap on completely (Anti-clockwise. You should be hearing a hissing noise)
4. Strike the lighter near the mouth of the barrel of the Bunsen Burner.
5. Slowly open the air holes until they are half open.

There are three types of flame:

1. Luminous flame: The yellow/orange flame
2. Non-luminous flame: The blue flame (part of it is almost invisible)
3. The strike back/roaring blue flame: When there is too much air (i.e., air holes fully opened), the fire burns inside the barrel. (If you encounter this situation, immediately turn off the Bunsen Burner and let it cool.)

What we did:

DETERMINING THE HOTTEST/COOLEST PART OF THE FLAME: HEATING A METAL WIRE UNTIL IT GLOWS AT VARIOUS PARTS OF THE FLAME.

The various parts of the flame we're testing:

(Credits to Classmate Ding Yichen for pic)

Table of results:

Therefore, we can conclude that the hottest part of the flame is the tip of the blue flame. 

NOTE: The flame should not be changed; i.e., you should not adjust the air holes such that you can easily see certain parts of the flame. 

The second part of the lesson...

For the second part of the lesson, we had to do some research on the elements we had "adopted" earlier. So my element is phosphorus: 

(So that it's easier for you to find)

Here are some facts that I've found out so far:

List of sources:

http://www.ehow.com/about_5377208_properties-phosphorus.html

http://chemistry.about.com/od/elementfacts/a/phosphorus.htm

http://www.chemicool.com/elements/phosphorus.html

http://www.merckgroup.com/en/company/discover_merck/periodic_table_of_elements.html * 

*Teacher's recommendation 

My thoughts on today:

I found the Bunsen Burner activity rather interesting as it is the first time that I've used the Bunsen Burner (When the flame came on on my first strike of the gas lighter I got a shock. XD My friend had to take a few tries so I thought I would need a few tries too). It will prove to be a useful skill as quite a number of activities require heating, including my upcoming Research Studies project on E. coli, the Bunsen Burner will be needed to culture the E. coli. (I'll put up the link later on when the experiment gets approved)

Phosphorus proves to be an interesting element and I've learnt more about it, and with this prior knowledge, if there's ever a need to handle phosphorus, I'll know what precautions to take (phosphorus is highly reactive and poisonous). 

Entry 1

7/1/2013

First official Chemistry lesson!

Today we had a brief apparatus drawing exercise.
We were supposed to draw:
-Conical flask
-Test tube
-Boiling tube
-Evaporating dish
-Tripod stand
-Measuring cylinder
-Beaker
-Bunsen Burner
-Filter Funnel

Here are some rules to note about drawing apparatus:

1. No "furry" lines (this is not sketching)
2. No discontinued lines (lines must be smooth without any gaps left between them)
3. Apparatus must be drawn to scale (e.g., the boiling tube has to be drawn bigger than the test-tube)
4. Labels must be straight lines (no arrows)
5. The markings (on a measuring apparatus) must be drawn to scale (as in evenly put out)

This skill is useful for experiment designing, as you will need to know the proper way of drawing the setup for your experiment when you're designing it.

(We learnt a bit of it in the biology module last year but I forgot quite a bit. :P)

Some notes I've made during the December Hols...

During the long December holidays, I've been pre-reading on the topics that we are going to learn. According to the scheme of work, the stuff that I've read about so far are relevant to the module. Yay!
So, here are the stuff that I've studied so far...

1. Determining purity (5/12/12)
-Chromatography
2. Elements, Compounds and Mixtures (7/12/12)
-Atoms and Molecules
-Naming compounds
-Fixed compositions of compounds
-Chemical formula of a compound
-Decomposition of compounds

And preparing for a diagnostic test in class:

1. History of the model of the atom (19/12/12)
2. Structure of an atom (19/12/12)
3. Isotopes (21/12/12)
4. Electronic configuration (21/12/12)  <--- yep...even on the so called "end of the world" XD

I've also been crazy enough to draw out the whole periodic table by hand and memorize the first few elements. XD (Though I forgot quite a few. :P)

So, I'll fill in on some of the notes I've taken so far. My references are Tan, Y.T, Chen, L.K., Chemistry Matters for GCE 'O' Level, Federal by Marshall Cavendish, 2006 and Briggs, J.G.R., Chemistry Insights, Longman, SIngapore, 2000.

This is roughly the scheme of work that I will be covering during the module:

1. Elements, Compounds and Mixtures
2. Separation techniques
3. Kinetic particle theory - Physical changes
4. Kinetic particle theory - Chemical changes
5. Kinetic particle theory - Rate of changes
6. Nomenclature and Chemical compounds

And so the journey begins...

Determining purity

A PURE substance is made up of only ONE substance and NOT mixed with any other substance. 

A MIXTURE is a substance that contains two or more substances that are NOT chemically combined. 

e.g. White diamonds are pure carbon, but coloured diamonds are impure as they contain substances other than carbon. (Some advice on choosing jewelry. ;) )

Why is it important to determine the purity of a substance?

It is important as impurities may cause undesired effects, for example, certain medicines may contain harmful impurities that may cause undesired side effects.

Having an impure substance will affect certain properties of the substance as listed below:

Melting point

-The melting point is lower (The more impure the substance, the lower the melting point)

-Melting takes place over a range of temperatures (e.g., it may melt between xºC to yºC.)

Pure solids have FIXED melting points.

Boiling point

-The boiling point is increased (The more impure a substance, the higher the boiling point)

-The liquid will boil over a range of temperatures. 

Pure liquids have EXACT and CONSTANT boiling points.

Pressure has its effects on boiling points too!

-The greater the pressure, the higher the boiling point.

-The lesser the pressure, the lower the boiling point. 

Chromatography

Chromatography is the technique of using a solvent to separate a mixture into its components.

Paper chromatography is one of the most commonly used methods. 

EXPERIMENT TIME!!! (Okay, I didn't do it, but it's an example.)

Separating dyes of food colouring

1. A spot of food coloring is applied to the chromatography paper.

2. The chromatography paper is dipped in ethanol (which is the solvent) and it soaks up the ethanol.

3. The ethanol dissolves the dye. The ethanol continues to travel up the paper, carrying the dyes along. 

             -Dyes that are very soluble in ethanol will be carried very far up the paper.

             -Dyes that are not very soluble in ethanol will not be carried very far up the paper

4. Coloured spots are left in different places on the paper at the end of the experiments.

There's your chromatogram. 

HOWEVER

If there is only one colored spot on the chromatography paper, the substance is pure. 

Here's a diagram I drew:

(Sorry if it isn't very clear ><)

Now, the positions of the solvent front and spot on a chromatogram depends on the duration of the experiment that the chromatography paper was allowed to soak.

BUT

The ratio between the distance travelled by the substance and the distance travelled by the solvent is CONSTANT. We call this ratio...... the Rf value.

Formula for Rf value of substance:

Rf = Dist. travelled by substance
        Dist. travelled by Solvent

Elements, Compounds and Mixtures

Some definitions:

Elements

A pure substance that cannot be split up into two or more simpler substances by chemical processes or by electricity.

Elements are made up of tiny particles called atoms. Atoms are the smallest particles of an element that contains the chemical properties of the element. To show an atom of an element, chemists use its chemical symbol as shown in the periodic table (all known elements and their symbols are recorded in the periodic table).

DIFFERENCE BETWEEN ATOMS AND MOLECULES

Atoms are individual particles. Molecules however, are a group of 2 or more atoms chemically joined together. E.g., The chemical symbol of water is H2O, that means that there are 2 hydrogen atoms and one oxygen atom that are chemically combined. (This proves that water is not an element. Neither is air, fire or earth.) 

Classification of elements

There are 2 major groups of classification: Metal and Non-metal. Some elements, known as metalloids, have properties of both metals and non-metals. (This will be more detailedly covered later on in the module)

Compounds
A compound is a pure substance that contains 2 or more elements that are chemically combined.
E.g., When magnesium burns in oxygen to obtain magnesium oxide: 2Mg(s) + O2(g) --> 2MgO(s)

History of the model of the atom

Here's a timeline of what happened:

1803 - Dalton viewed atoms like small solid balls that cannot be broken. However, in the late 19th Century, scientists began to obtain experimental evidence, which proved that atoms are not like solid balls and that they could be broken. 

1897 - J. J. Thomson, and English physicist, did experiments that led to the discovery of the electron. Thomson showed that 1, an electron carries negative charge and; 2, atoms contained electrons. 

1903 - Thomson proposed a new model of the atom. He described the atom as a positively charged sphere with electrons pushed into it (something like a cake studded with raisins with the raisins being the electrons). 

1910 - This model was soon modified by New Zealand physicist, Ernest Rutherford. He carried out a simple but clever experiment that proved that the atom had a nucleus. In this experiment, Rutherford used small positively charged alpha particles to bombard a thin sheet of gold foil. (Looks something like this: 

(I will be continuously updating this post as I go along when I have time to. Meanwhile, I'll be posting about my Chemistry lessons. :) )

Welcome to the blog!

Hello there! This is my Chemistry E-journal. If you've been following me, my last blog was on the Physics module (you can check it out at http://10304joycechancs.blogspot.sg/). With a new year comes new lessons, and it's time for... the Chemistry module!!! Yay!! XD