Crystallisation

Crystallisation is another technique for separation of substances. It is the most common method use to separate solutes from solvents (purify soluble solids). In order for crystallisation to take place, several conditions must be met. Firstly, the solid in question must be soluble in water. Secondly, the solubility of the substances should change with changing temperature (e.g. solubility increases as temperature increases). Thirdly, the solution used should be saturated with the solute.

Typically, the solution is heated to form a hot, saturated solution  The heating allows for excess solvent to be removed via evaporation. As the hot saturated solution cools, the dissolved solid appears as crystals as the solubility of the solute decreases the decreasing temperatures. This means that as the temperature of the solution drops, less solute can be dissolved in the solution. The excess solute will then appear in the solution in the form of crystals.

Procedure:

1) Heat about 20cm3 of water in a beaker. Stop heating and remove from the tripod stand once bubbles are observed im the water to when the water boils.
2) Add one spatula of copper (II) sulphate into the hot water
3) Stir the mixture until all the copper (II) sulphate dissolves before adding another spatula of copper (II) sulphate.
4) Repeat step 3 until no more copper (II) sulphate can be dissolved.
5) Filter the solution if there are any solid impurities
6) Heat the copper (II) sulphate in an evaporating dish.
7) Stop heating when about half the solvent has evaporated from the solution. DO NOT HEAT TO DRYNESS.
8) Pour the solution into a clean small boiling tube and cool it in ice-cold water
9) Measure the time taken for crystals to appear

Copper(II) Sulphate

Mixing the Copper(II) Sulphate into the hot water

Filtering the mixture to get rid of solid impurities.
Photo credits to Alanna

Heating the evaporating dish

Using rapid cooling on the mixture!

When my partner and I finished the experiment, crystals did not really form. I think we had too much mixture in our boiling tube so maybe it will take a longer time to form.

Questions to consider:

1) How can you obtain more crystals from the cooled copper (II) sulphate solution?

-Add more water to dissolve the copper sulphate

-Gradual cooling instead of rapid cooling

2) Suggest 2 reasons why in crystallisation method we should stop heating before all the solvent evaporates

-Prevents decomposing of copper sulphate

-Soluble impurities will be left behind.

Practical #3- Paper Chromatography

We did a practical regarding Paper Chromatography. Paper Chromatography is a separation technique which is used to separate a MIXTURE of solutes with different solubility and degree of adsorption. This method uses a solvent moving over a porous or adsorbent medium (e.g. paper or jel) to separate a mixture of solutes. In the practical we use rectangular strips of filter paper.







The aim of the experiment is to separate the different dyes in the green food dye.

Apparatus used:

-Capillary tube

-Green Food Colouring

-Chromatography paper (Filter paper_

-Boiling tube

-Pencil and Ruler

-Distilled Water

-Clothes Peg

-Test tube rack

Steps:
1) Draw a line 1.5cm away from the end of the paper with a pencil and ruler
2) Using the capillary tube, drop 3 drops of green food dye on the middle of the starting line.
3) Fill the boiling tube with water until the water fills about 1.5cm from the bottom of the tube
4) Make sure that there is no water at the sides of the boiling tube that can touch the paper. (This may result in the substances getting separated at other parts of the paper, resulting in inaccurate observations.
5) Clip the paper in place with a clothes peg
6) Watch the dye run up the paper
7) Leave the paper there for 10 minutes.
8) Take the paper out of the test tube and let it dry
9) Mark the solvent front and tips of the different colour of dyes.

This was the result I got after the experiment. Evidently, the blue dye has travelled further the yellow dye.

Conclusions made based on the observation:
-The blue dye is more soluble in the solvent (Distilled water) than yellow dye
-The yellow dye is possibly better adsorbed by the filter paper than the blue dye.








Calculating the Rf value

Rf is short for retention factor. Unknown substances separated by chromatography can be identified by Rf values.

Rf values = Distance moved by substance/Distance moved by the solvent

Identical dyes have the same Rf when separated under the same experimental condition (Temperature, Pressure)

In this case, the results appear as a spectrum instead of individual dots. We were then told to take a reference point for each substance. I took the top of each dye.

Component	Distance moved by sport/cm	Distance moved by solvent/cm	Rf
Blue dye	6.9	12.4	0.556
Yellow dye	5.3	12.4	0.427

Some questions to consider...
1) Is it possible to separate a mixture of colourless chemicals by chromatography? Explain your answer.
Yes. A locating agent can be used to convert a colourless chemical into coloured substances.

2) What factors could affect the Rf value of a chemical? How would these factors affect Rf values?
a) Temperature affects the solubility of substances, the higher the temperature , the higher the solubility of the substances.
b) Type of paper affects the distance travelled. If the dyes are more easily absorbed by the paper, the Rf value is lower.
c) Type of solvent affects because dyes may be more soluble in ethanol than water or vice versa.

Second Practical- Elements, Compounds and Mixtures

We had our second practical in the Laboratory and this time it was about Elements, Compounds and Mixtures.

We had 2 elements, sulfur powder and iron fillings.

Firstly we had to mix them together on a filter paper. It was on a filter paper basically because the paper is white and Mr Foo said that to get a clear observation, it is normally done on a white surface. Our question was:

Does the bottom of the filter paper paper feel warm after mixing? (i.e, there is heat produced in the mixture of sulfur and iron?)

This is a picture of the mixture of sulfur (Yellowish powder) and Iron fillings (Grey powder) on a filter paper. It has been thoroughly mixed using the glass rod shown.

At first all of us were expecting warmth to be felt under the paper so we desperately mixed it as we thought something was wrong.

Turns out,

No reaction was supposed to occur. OUR LIFE IS A LIE.
Okay, so basically because this is just a mixture, the elements are NOT chemically bonded, thus there would not be any chemical reactions occurring.

The next step we did was kind of like a head-start to the next chapter- Separation Techniques. We used a magnet and place it at the bottom to the filter paper to see if we would attract the iron fillings so as to separate the iron fillings from the sulfur powder. All of us had fun looking at the iron powder move haha.

So we can conclude that when a non-magnetic element is put together with a magnetic element, a magnet can be used to separate them!

Photo credits to Eleanor :) ---->

The next activity was to see if we could separate the elements when they are put in water.

As you can see, most of the sulfur is actually floating on the water and the iron fillings have sinked to the bottom. This shows that iron is denser than water and that sulfur is less dense than water and iron.

Although it seems like water is a technique to separate these two elements, it is not the best method since some of the sulfur is actually at the bottom together with the iron.
Plus, both elements are not soluble in water so it is not very convenient if we use this way to separate them. Using water to separate requires an insoluble element and a soluble element.


The most exciting part of the practical was when we actually chemically combined sulfur and iron through heating and we got Iron Sulfide. (Mr Foo please correct me if I'm wrong).

This is when we were heating the Iron + Sulfer.

There was this STINKY gas released and it was called sulpher dioxide and the worksheet claimed it was POISONOUS.

OMG.

And then everyone was like running around to escape the gas but since everyone was heating the Compound I don't think it really helped.

Then Mr Foo was so helpful he said the effect would take place over the years. ARE YOU JOKING MR FOO I HOPE YOU ARE.

And this

is the legendary

Iron Sulfide

Done by ME
(and my partner Divyya)

Oh yeah.

It is so cool

Like me ;)

Cool people heat up cool stuff.


This new compound has been chemically bonded. The physical properties of a compounds is different from its constituent elements, which in this case is Sulfur and Iron. There is also a change in appearance. Chemical reaction takes place when a compound is found when is a change in energy.
The new compound still cannot dissolve in water though.

Krypton

This was the second part of the lesson after we studied about Bunsen Burners.

We were supposed to each "adopt" an element of our choice. I adopted Krypton since it's like "Kryptonite", which was in the song "One Thing" by One Direction. OH YEAH. After everyone has decided on their elements, we were supposed to research on the element that we have chosen. The website that Mr Foo provided us with was: http://www.merckgroup.com/en/company/discover_merck/periodic_table_of_elements.html

It's a pretty good website. I like how they designed the Interactive Table Of Element and it was really easy to navigate through the whole website.

This is the information I have gathered for Krypton:
Krypton is a non-metal. It is a colourless and odorless gas. It is classified under "Inert Gas". Before knowing about Krypton, the only Inert Gas I knew was Argon. Solid krypton is white and crystalline. The boiling point for Krypton is -153.3 °C and the melting point for Krypton is -157.2 °C. The temperatures are pretty close! Krypton is a poor conductor of both electricity and heat and it's density at room temperature (in this case, 20°C), is 3.48 g/l. Krypton is used in lighting products (light bulbs). It is an important use is in high-powered, flashing airport runway lights. Ionized krypton gas appears whitish, which makes krypton-based bulbs useful as a brilliant white light source in high speed photography. It's chemical symbol is Kr. It's electronic configuration is 18,4. And coincidentally, 18,4 is my birthdate!

Krypton FTW

Bunsen Burner

Today was our first lab lesson of the year for the Chemistry module. We kicked this lesson off by studying about Bunsen Burners.

Previously, I have seen my primary school teachers lighting bunsen burners but never really tried to light one myself. Mainly because I wasn't given very clear explanation and it seemed really scary at first. I wasn't really sure about the closing and opening of the air holes and when to light the fire etc.

However, after today's lesson, I can definitely say that I have become more confident regarding the lighting of the bunsen burner. Mr Foo gave explicit explanation on how to light it correctly and I got to try it a couple of times.

The following are the steps to lighting the bunsen burner safely:

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 ip

5) Open the air holes SLOWLY to about halfway and even fully, depending on which type of flame you want.

*Leaving the air holes open when lighting up the bunsen burner may result in a strike back.

The next step of the activity was to identify which part of the flame is the hottest

Here'a a picture to give you some idea of how the flame looks like.

When a flame is ignited with a closed air hole, the flame is yellow/orange (A,B). However, as you slowly open the air hole, the flame turns into flame C. The flame in C is called the non-luminous flame. It is really hot.

The parts of the flame we had to measure was the part slightly above the tip of the blue flame (part of the orange flame), tip of the blue flame and the core of the blue flame.

This is the non-luminous blue flame. When I lit it up it produced a noise that was quit loud but it was really really cool.

I am not sure but I actually opened the air hole fully, is it dangerous?

So you can see the tip of the blue flame and the orange flame too. Those are the positions where I used to carry out the experiment.










This was the procedure to carrying out the experiment:

1) Turn on the bunsen burner
2) Use metal tongs to hold copper wire just slightly above the tip of the blue 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

This is the results I got:

Thus, the part just above the blue flame is the hottest.

The constant variables for this experiment are:
-The flame itself
-The copper wire

The independent variable is:
-The position of the flame where the copper wire would be placed at

The dependent variable is:
-The time taken for the copper wire to glow red on respective sections of the flame

Mr Foo said that the assumption of this experiment is that the thickness of the copper wire stays the same, since the copper wire would expand when heated!

 This is a picture I took while the copper wire was being heated. You can see that the copper wire actually glows!

The copper wire was melting when I was heating it! There was also a flame on top of it.















Overall, it was a really enriching experience and I got to know more about the process of lighting bunsen burners. It was also really cool to see the copper wire getting heated!

Safety in the Laboratory

Today we talked about laboratory safety. I feel that it is really important to ensure our own safety in the laboratory, especially because in the Chemistry module, we would be handling lots of different chemicals such as acids which are often corrosive.

Although it often seems like common sense not to do certain things in the Laboratory, there are times when these rules are neglected unknowingly. For example, we may not notice that the bunsen burner is near our belongings sometimes and this is rather dangerous . Thus we need to be situationally aware at all times.

Some of the important rules listed:

1) Do not take apparatus or chemicals out of the Laboratory without the permission of a teacher
2) Always wear safety goggles when mixing, heating or handling chemicals that could be harming the eyes
3) Long hair must be tied while in the Laboratory. Long fringes must be pinned up. PE short are not to be worn in the Laboratory
4) Never taste chemicals or other materials. No eating and drinking is allowed in the laboratory at all times
5) Always carry out reactions involving poisonous gases in the fume cupboard
6) Chemicals once removed from bottles, must not be put back into the bottles unless instructed to do so by the teacher. When using a dropper to add a reagent into a rest tube of chemical, do not put the dropper into the test tube so as to avoid contamination of the reagent
7) Do not litter in the laboratory
8) Remove broken glass from your bench or floor with a broom and a pan. Place the broken glass in the broken glass bin provided
9) Keep a lighted burner away from clothing, books or other combustibles. Lean away from top of Bunsen burner while it is being lit.
10) To smell the contents of a container, use a "wafting" action of the hand as demonstrated by your teacher
11) Always add acids to water slowly, carefully and with a gentle stirring action (solid glass rod only). This should generally be done in a large open beaker. Avoid overheating which often accompanies too rapid mixing. Acid into water, never the reverse.
12) Dispose waste chemicals properly according to instruction. Solid chemicals should be disposed into the bin. Organic, or toxic liquid chemicals should be disposed in the waste chemical bottle.

That's all!