Lab session 4

Crystallization

As promised, today we did an experiment on crystallization. In this practical, we formed Copper (II) Sulfate crystals. 

 Materials needed:
- Copper (II) Sulphate (powder form)
-Distilled water
- Spatula
- Filter funnel
- Filter paper
- Boiling tube
- Evaporating dish
- Beaker
- Bunsen Burner
- Tripod stand + wire gauze
- Glass rod
- Peg / tongs

Step 1: Pour 20ml of distilled water into the beaker. Setting it on the wire gauze on the tripod stand, heat the water to a boil. Stop heating when the water starts to boil.

Step 2: Pour 1 spatula of Copper (II) Sulphate into the hot water. Stir with the glass rod until all of the powder has dissolved.

Repeat step 2 until the Copper (II) Sulfate cannot be dissolved.
Step 4: Filter the solution into the evaporating dish. Use the glass rod to help.

Step 5: Heat the solution in the evaporating dish over the bunsen burner. Stop heating when half of the solvent has evaporated from the solution. DO NOT HEAT TO DRYNESS. (If a crust forms on the surface, add distilled water to dissolve the crust. Stir with glass rod.)

Step 6: Using a pair of tongs, carefully grip the evaporating dish and pour its contents into the boiling tube. Since we're doing slow cooling, leave the boiling tube to cool.

(You can see the crystals starting to form already. :D)

(My friend accidentally spilt a bit on the table and it crystallized immediately. XD)

Now, we'll leave it for a week or so to wait for the crystals to develop. Stay tuned! :)

After a two week wait, here are the crystals formed:

Some Demos: 

IODINE SUBLIMATION: Separating iodine from sand

(Heating of mixture of solid iodine balls and sand)

(As can be seen, the dark purple gas is the iodine gas. Sublimation is the transformation from solid directly to gas.)

Separation funnel

Separating oil from colored water

The separation funnel is used to separate liquids of different densities. Since water is denser than oil, water is collected first, then oil. The separating funnel is controlled by a tap.

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)