Chemical and Physical Changes

In this practical, we did loads of heating using the bunsen burner, which is really fun. I like bunsen burners. You get to see both chemical and physical changes of a substance.

What are the differences between a chemical change and a physical change?
The difference is that there is a change in energy (energy taken in or given out) in a chemical change, but not in a physical change. Also, new substances are formed and the process is irreversible. However, no new substances are formed when there is a physical change and that you can still obtain the original state of the substance using other physical means.

Firstly, we heated two different substances: sodium chloride and copper (II) carbonate. The change in the sodium chloride was really really really slow. For my pair, we could not see the change because there wasn't sufficient time for us to see what happens. By right, we should see a clear liquid while melting and a while solid after it is left to cool.

For the copper (II) carbonate, the change was really fast from a green solid to a black solid.

Sodium chloride on the left, copper (II) carbonate on the right.

Heating up the sodium chloride, but nothing happened :(

Copper (II) carbonate after the chemical change.

Next, we heated up a magnesium ribbon. Before the change, it was a silvery-gray metallic strip but after heating, it became white powdery ash. While heating, it actually gave off a really bright white light! So cool! Here's a video of the change, sit back relax and enjoy! :)

Ready for heating! 

Yup that's it for this cool practical! I really enjoying heating all those stuff 8D.

Investigating Diffusion of Gases and Liquids

Diffusion

My definition of diffusion (as learnt in Biology!) is the movement of particles from a region of higher concentration that of a lower concentration until equilibrium is reached.

Diffusion can be explained by an assumption of the Kinetic Particle Theory, which is that particles are always in constant and random motion.

In today's laboratory lesson, we were given a demonstration on diffusion of two highly corrosive substances, hydrochloric acid and ammonia gas. We were not allowed to handle these substances by ourselves. It felt really scary when a cloud of fumes appeared immediately after the lid of the container was lifted.

So these two acids were each soaked with cotton wool and then placed at opposite ends of a tube. After a while, a white cloud was observed near the cotton wool with hydrochloric acid. The particles of the ammonia gas had diffused with the hydrochloric acid, forming the white cloud. The reason the cloud was formed nearer to the hydrochloric acid is that the molecular mass of hydrogen chloride is heavier than that of ammonia gas. Heavier particles move and travel slower than lighter particles.

After that, we did our own experiment which was very simple actually. Firstly, we poured 50cm³ of sand and 50cm³of beans into two separate measuring cylinders. Next, we just mixed them together. The resulting volume of the mixture is not 100cm³ but around 80cm³ (we all had varying values around  there). Based on my prior knowledge, my prediction to the volume of the mixture was correct.

Our experiment! 

This experiment proves that there are actually spaces in between the beans (and really tiny ones between the sand particles). The amount of space between the particles is about 20cm³.

The next experiment we did was to mix the same amount of ethanol with the same amount of water (I didn't take any pictures for this though). Ethanol and water are two miscible liquids - they can mix with each other. We put the two liquids in a tube and Cindy (my lab partner) sealed the tube with her thumb. When she shook the tube to mix them, there was a vacuum created inside the tube, causing her thumb to look all weird like it was being sucked into the tube. The resulting volume was lower than what we expected it to be. The mixture also felt quite warm.

I felt quite surprised that the volume of the mixture was lower than I expected but I was glad I learnt that the volume actually decreases when you mix them together, as they take up the space between particles.

Till next time! :)

Update on my crystals!

I finally got to see the results of my crystallisation experiment. (Refer to my old post). Hurray!

So these are my (and Cindy's) crystals.

TA-DA! 

I think they are not bad and really pretty! Though there are much nicer ones like Min and Min Chi's. But really there aren't any model answers to this. Each crystal is special! And it was a pity we weren't allowed to take them home.

Anyway, I declare our crystallisation experiment a SUCCESS! :)

Sublimation

We learnt about sublimation while waiting waiting for crystals to form. We did not get to do a practical on sublimation but we saw a demonstration of the process.

Sublimation is used to separate a substance that sublimes from one that does not and has a high melting point. For the demonstration, the substance that sublimed was iodine. See the purplish vapour? That's the gaseous state of iodine. My classmates are photobombing over here.

Iodine subliming

I managed to catch sight of the flask being removed from the evaporating dish briefly but I could not take a picture because it was too quick. When the flask was removed, there was a beautiful purple "cloud" from the bottom of the flask. Felt really mysterious. :o 

I find sublimation really cool because you don't usually see something skip the liquid state. And as you can see from the picture, we all forgot to wear our safety goggles. (How could we?!) We must keep that in mind next time!

Crystallisation

Crystallisation is the most common method to purify soluble solids. It is preferred over evaporation to dryness as many substances decompose upon strong heating. Also, when all the water is removed during evaporation, any soluble impurities will be left on the crystals (eg. sugar decomposes to become carbon when it is heated strongly). The shape and size of crystals can be controlled by controlling variables such as cooling rate and evaporation rate.

In crystallisation, water is removed by heating the solution. Heating stops when a hot saturated* solution is formed. The resulting solution is left to cool and the dissolved solid will then be formed as pure crystals. This is because the solubility of the solute decreases as the temperature drops. At a lower temperature, less solute can be dissolved in the solution.

*A solution is saturated when it contains the maximum amount of dissolved solute at a given temperature. (When no more solvent can be dissolved in the solute). To test if a solution is saturated, a glass rod is placed into the solution and if there are tiny crystals formed when the rod is removed, the solution is saturated.

Analogy time! (A short short one)
Imagine the solute is your brain and then the solvent is information. When your brain is filled with too much information that whatever remaining information cannot go in, your brain is saturated. :D

For crystallisation to take place, several conditions must be met:
1. The solid must be soluble in water.
2. The solubility of the substance should change with the changing temperature.
3. Solution must be saturated with the solute.

For our practical, we were tasked to purify copper (II) sulphate crystals and investigate the effect of cooling rate on the size of crystals obtained.

My group is making crystals by slow cooling.

Steps:
1. Heat 20cm³ of water in a beaker and stop when the water boils.
2. Add one spatula of copper (II) sulphate into the hot water and mix until all the copper (II) sulphates dissolves.
3. Repeat step 2 until the solution is saturated.
4. Filter the solution to remove solid impurities.
5. Heat the solution in an evaporating dish.
6. Stop heating when about half the solvent has evaporated.
7. Pour the solution into a boiling tube and allow it to cool slowly. Leave overnight if necessary.

Step 1. Heating the water

Step 2 and 3. Adding copper (II) sulphate into the water

Step 4. Filtering the solution.

Step 5. Heating the solution.

Okay there is another step but I'm still currently stuck at Step 7 because crystals don't take that quick to form so we are supposed to review it next week. I will update my observations when I see the crystals that are formed.

My takeaways from this practical:
Crystals formed by rapid cooling are smaller and more irregular than crystals obtained by slow cooling. To obtain more crystals, one can add more water and apply slow cooling instead of rapid cooling. We should stop heating before all the solvent has evaporated as it prevents the solute from decomposing and soluble impurities will be left behind.

Chromatography and Distillation

As seen on the title, this practical is about chromatography and distillation. 

(This is a loooooooong post)

CHROMATOGRAPHY

A technique used to separate soluble mixtures of substances with different solubilities into individual components. It is used to find out the components of a mixture and they can be identified by comparing their chromatogram with those of known substances. It also determines the purity of a substance. (When there is only one spot observed on the chromatogram, there is no separation so the substance is pure) It can work with very small amounts. 

There are several forms of chromatography. They are: paper chromatography, thin-layer chromatography, gas chromatography and high-pressure chromatography. The one in our practical is paper chromatography. They all have a stationary phase and a mobile phase. 

In paper chromatography, the stationary phase is a very uniform absorbent paper and the mobile phase is a suitable liquid solvent, or a mixture of solvents. It works with the mobile phase travelling up the stationary phase, carrying the mixture with it. The components of the mixture will separate on the stationary phase depending on how strongly they are absorbed by the stationary phase and how much they dissolve in the mobile phase. 

What we did:

During this practical, we did our own paper chromatography experiment to separate the dyes in green ink. It's an individual task actually because the process is very simple and manageable to do alone.

Firstly, I drew a line 1.5cm from the bottom of the chromatography paper slip (the stationary phase) using a pencil. Using a pen will affect the results of the chromatography as it is basically ink and ink contains dyes, and it will mix with the ink that is supposed to be separated. 

Then, I used a capillary tube to transfer a few drops of green ink onto the center of the line. Next, I put distilled water into a boiling tube (around 1.5cm from the bottom). I inserted the chromatography paper into the boiling tube, using a clothes peg to secure it. The drop of ink is not supposed to touch the water or else it will dissolve in the water instead of travelling up the chromatography paper. So all there was left to do was to wait for the results. In the meantime, we learnt about distillation (I'll touch on that later!)

Fast forward.

TA-DA!

Waiting, waiting...

I removed the chromatography paper from the boiling tube and used my pencil to mark the spots of the dyes and the solvent front (where the water has travelled to). But, I made a mistake. As we did not have time on our hands, I hurriedly removed it without waiting for the solvent front to be within 1cm-2cm of the clothes peg. 

Actually, I find that it will not affect the result very much as the position of the dyes are relative to the solvent front. And then after marking, the position of the solvent front and dyes kept moving up! :O

See what I mean?

Okay, so other than comparing the chromatograms, there is a more systemic way to go about finding out the components in a mixture, which is the calculation of R_f values. R_f stands for retention factor. It is basically taking the distance moved by the substances divided by the distance moved by the solvent. 

Taken from Google Images

R_f values should be expressed in decimals. They should never exceed the value of 1, as substances will never travel beyond that of the solvent. 

R_f values can be affected by the type of solvent, type of paper used and the temperature. Different papers have different absorption levels and different solvents have different solubilities. As temperature increases, the solubility increases.

In the case of my chromatogram, the blue spot travelled the same distance (8.3cm) as the water. Therefore, the R_f value is 1. The yellow spot travelled 7.8cm, so the R_f value is 0.94. 

Conclusion:

The green ink is made up of blue and yellow dye. 

(I wish my chromatogram was more colourful, lol) 

SIMPLE DISTILLATION

Is used to obtain a solute from its solvent. 

Below is a set up of simple distillation.  The thermometer measures the temperature of the vapour to identify the distillate by its boiling point. In the round-bottomed flask where the mixture is, there are boiling chips (or boiling stones) to make boiling smooth. Without boiling chips, boiling will be very vigorous and the apparatus may spoil. Water enters the condenser from the bottom instead of the top to ensure that most of the water vapour is condensed and collected as liquid. If cold water enters from the top, it will not fill the condenser. 

Taken from Google Images

We did not try to do distillation on our own as the setup involves many apparatus. So we watched Mr Foo demonstrate the distillation of Coca-Cola. It's supposed to be smelly, but why didn't I smell a single thing?! It was pretty interesting seeing coke getting separated into pure water and sugar with caffeine.

Other than simple distillation, there is fractional distillation to separate two miscible liquids of different boiling points. There is a fractionating column in the setup. The liquid with the lowest boiling point will be distilled first.

Both distillation methods are similar as they both require heat and involve boiling and condensation. 

Reflection:

I've really learnt a lot in this practical. For chromatography, I learnt that the most soluble substance will travel the furthest on the paper. I think I should work on my time management in practicals and I will be more patient in the future for better accuracy.

Theory Lesson: Separation Techniques Introduction

So we are gonna learn a new topic, about using physical methods to separate mixtures. Yay! :)

Notes taken in class!
In nature, almost all substances are mixtures.

Mixtures need to be separated into pure substances for
-Characterization
-Identification
-Production

It is impossible to obtain a 100% pure substance.

DETERMINING THE DEGREE OF PURITY
-the melting points and boiling points of elements are unique
-chromatography

PAPER CHROMATOGRAPHY (eg. separates dyes from ink)
-separate a mixture of solutes with different solubility and degree of absorption
-uses a solvent moving over a porous or absorbent medium

Hi there

I got locked out of my previous chemistry journal because I accidentally revoked my own administrative rights and I practically could not edit anything besides old blog posts. Silly careless me. So I shall create a new one over here and I'm gonna shift my old posts over to this one. I hope it works. :/ Hope it's as good as the old.

Atomic Structure (18/1/13)

In yesterday's theory lesson, I learnt about the atomic structure and the subatomic particles that make up an atom.

Atoms are the smallest particle that retain an element's chemical properties but they can be divided into smaller particles known as subatomic particles. When looking at the subatomic particles, elements are no longer identifiable.

We were given an analogy in class to better understand this statement:
(YAY analogies again I love analogies!)

There are two coin banks, A and B. One has only ten cent coins while the other has only twenty cent coins. When all the coins are crushed into smaller pieces and put together, you can no longer tell if the crushed pieces belong to Bank A or Bank B.

So it's the same for elements. When you put the subatomic particles together, you cannot tell which element it is from. The subatomic particles are namely:
-Protons (p)
-Neutrons (n)
-Electrons (e)

My own digram, sorry it's messy

Protons and neutrons are known collectively as nucleons as they make up the nucleus of the atom. Electrons are found in shells that circle around the nucleus. Actually, I learnt that electrons don't circle really obediently. In fact, they move about randomly but for the purpose of studying them, we take them as orbiting around the nucleus.

PROTONS
-have an electrical charge of 1
-have a relative mass* of 1
-attract electrons
-found in the nucleus of an atom

NEUTRONS
-have no electrical charge (electrically neutral)
-have a relative mass* of 1
-found in the nucleus of an atom

ELECTRONS
-have an electrical charge of -1
-have a negligible mass of ¹⁄₁₈₄₀ 
-are attracted to protons
-circle the nucleus

Acronym: PEN

*Relative mass:
All the subatomic particles are very light that it is inappropriate to express them in grams or kilograms. Instead, they are measured against a standard unit, called the atomic mass unit (amu).
1 amu = 1.67 × 10^-27

Protons and electrons attract each other because of their opposite charges. That's why the electrons "circle" around the nucleus. All atoms are electrically neutral as the number of protons and electrons in an atom are equal.

Next, I learnt about what atomic number and mass number are.

ATOMIC NUMBER (Z)
-also known as proton number
-is the number of protons in an atom (since the number of electrons are the same in an atom, it also represents the number of electrons an atom has)
-is unique to every element; no two elements have the same atomic number

MASS NUMBER (A)
-also known as nucleon number*
-is the total mass of an atom in amu (electrons are left out of the calculation as their mass are negligible)
-is basically the number of protons and neutrons in an atom

*Mass number and nucleon number are actually two different things, although they have the same value. Mass number is the total mass of an atom in amu while nucleon number is the total number of nucleons.
For example, carbon has an atomic number of 6 and a mass number of 12. That means that there are 6 neutrons and 6 protons. The nucleon number is therefore 6 + 6 = 12. As each nucleon has a relative mass of 1, the mass number will be (1 × 6) + (1 × 6) = 12.

I used to think that these two terms meant the exact same thing, and I'm glad I've learnt otherwise!

You can find out the number of protons and electrons by looking at the atomic number. To find the number of neutrons in an atom, you take A − Z.

This is how we represent elements with the atomic and mass numbers.

(taken from Google Images)

That's so fast we are almost (or maybe already) done with this topic. It's so interesting to discover the smallest particles that make up everything around us! :) 

To end off this post, here's a lame joke taken from the internet relevant (or maybe not) to this topic:


A proton and a neutron are walking down the street.
The proton says, "Wait, I dropped an electron help me look for it."
The neutron says "Are you sure?" The proton replies "I'm positive."

Okay not very funny. Bye.

Practical: Comparing Element, Compound and Mixture

This is my first Chemistry practical lesson since I was absent during last week's practical. So I was actually very excited for the session!

-Focus Question: What are some common characteristics of mixtures and compounds that can be used to distinguish them?

-Hypothesis: Mixtures can be separated by physical means but compounds cannot be separated by physical means.

-Conclusion: My hypothesis is correct! (but not complete)
To add on, the substances in a mixture can be mixed in any proportion. No energy change takes place when a mixture is formed. A mixture has the properties of its constituent substances.
On the other hand, properties of a compound have different physical properties from its constituent substances. A compound cannot be separated by physical means. A chemical reaction takes place when a compound is formed when there is energy change.

WHAT WE DID
(here I took pictures of our investigation in progress with my lousy camera phone! :P)

Here are some of the materials we used for the whole investigation.

Shown in the picture on the left are iron fillings, sulfur powder, thongs, test tubes, crucibles, filter paper, magnets and bunsen burner.

We also used a tripod stand for heating and a stirrer for stirring the mixture and compound with water.

Of course, we had to put on our safety goggles (shown in picture) as a safety measure.





PART A:
We recorded our observations of the two substances, iron fillings and sulfur powder after putting them on a piece of filter paper.
The iron fillings appeared silvery-grey while the sulfur powder appeared bright yellow.
Then, we mixed the two substances together.
We then felt the bottom of the filter paper to feel if it was warm but it was just cold.
Next, we tried to separate the iron fillings from the mixture using a magnet and it worked!
We then put the mixture into a test tube filled with water. What we observed was that both substances were insoluble in water and that the sulfur powder is suspended near the surface of the water while the iron fillings sank to the bottom of the test tube. This was because the density of iron fillings is higher than that of sulfur powder.

Sulfur and iron.

Mixing them! 

Iron fillings being attracted by the magnet at the bottom of the filter paper.

PART B:

We mixed one spatula of sulfur powder and half a spatula of iron fillings in a crucible. Then, we set up the bunsen burner and left the crucible covered with a lid to heat for 10 minutes under a strong flame. As I missed last week's practical, I did not know how to use a bunsen burner at all and I was pretty lost. Luckily my partner patiently explained to me the steps involved in setting it up, making me feel much more confident of using it. 

After heating, we allowed it to cool, and we got a black hard solid substance in the crucible. 

The compound did not separate iron from sulfur when we used a magnet. Neither did the two constituent substances separate when placed into the test tube with water. The black compound was also insoluble in water. 

Heating up the mixture under a strong flame

After 10 mins of heating

Along the lesson, I came to learn that this compound is known as iron sulphide and I actually googled for it's chemical formula, just out of curiosity. So it's FeS. Then I got really confused. I came across another term, iron sulphate. I have not the slightest idea which is which and how they are different but I think I will probably find out soon. 

Extra stuff I've learnt also include that adding too much iron will cause the final compound to have excess iron fillings. 

Some reflections I have for the day...

I feel that reading instructions carefully is very important. Another group in class added one spatula of iron fillings into the crucible instead of the half spatula which was specified. Although it was good that everyone could learn something out from their mistake (about how the final compound would be affected if there were more iron fillings), it could be really dangerous if there was a harmful chemical reaction that would take place whenever there were excess substances. I also think that I should be more accurate and alert while doing the experiment. While setting the crucible to heat, I did not take note of the time we started heating but luckily, we quickly realised that we forgot to watch the time and tried to start counting from where we left off. I think it's always better to be accurate and precise.

I've learnt so much from such a simple science practical and I could finally try it out for myself to make compounds and mixtures. I'm looking forward to the next science practical! 

Theory Lesson on 14/1/13

Today in class I learnt about what elements, atoms and compounds are. 

Elements are made up of only one type of atom while atoms are the smallest particle that retains the chemical properties of the substance. Compounds are made up of two or more atoms chemically bonded together. 

In addition, I learnt that the Periodic Table is classified into groups and periods. Groups are the vertical columns and they number from I to 0/VIII. Periods are the horizontal rows that number from 1 to 7. 

Actually, although I've heard of what elements, atoms and compounds are, I was really confused at the start. I was not sure of what exactly was the difference between the elements and atoms, since both have got to do with atoms, I would mix the two up, thinking that they are almost the same thing. However, after being given an analogy in class today, all my confusion were cleared at once.

The analogy was that each paperclip is an "atom". When they are connected together, the string of paperclips is an "element". 

I find this analogy really helpful, and I feel that by using analogies, I can understand much better. So I hope that there will be more interesting analogies in class to aid my understanding in Chemistry.

Introducing Me

Hello I am Eleanor from Class 203 :D
Welcome to my Chemistry journal where I record down my reflections and what I've learnt.

Taken from Google Images.

There, here's a funny meme. I think it's funny. I hope Chemistry is fun. I find Chemistry interesting :D I'm looking forward to learn more stuff about Chemistry!