Poly Density Bottle

Another group of student who is entering the same competition are doing another experiment. Their experiment is based on the different density of the solid and liquid. We really have a difficult time to find the appropriate plastic solid that has the correct density.

In the tube shown in the video, it contain 2 solutions of different density. One is acetone which has a density of 0.81g/cm3, another is saturated salt solution (normal household salt) which has a density of 1.2g/cm3. Both solution are immiscible so they will separate when mixed.

The theory is that you can use a plastic that has a lower density and another with a higher density than the solution when mixed. Example now both solution when mixed and divide by 2, it should gives a density of 1. So if you have a plastic material density that is between 1.1 - 1.9g/cm3, it should sink when mixed. Then if you have another plastic material density that is between 0.82 - 0.99g/cm3, it should float when mixed.

So when you leave it to stand and allow these 2 solutions to separate back to their normal properties. The one with the density of 1.1-1.9g/cm3 (which is the white plastic in the video) will start to float since it is less dense than salt water. Then the one with the density of 0.82-0.99g/cm3 (the green plastic in the video) will start to sink since it is denser than acetone but less dense than salt water. Then the plastic that has a density of around 1g/cm3 (the blue solid) will float in between when mixed.

End up what you can observed is the green plastic float when the solution is mixed then sink down, the white plastic will sink when mixed and then float up. The blue plastic will remain in the middle.

Honestly, I am not sure what kind of plastic I am using but I can let you know where my material come from. The green one is from the seal of a chemical bottle, the blue one is from a mineral bottle cap and the white one is from those white colour disposable spoon (see pic).

You can try it out yourself. Actually in the link, they uses rubbing alcohol (Isopropyl alcohol). I bought a 70% isopropyl alcohol from Guardian however it is miscible with salt water so both solution cannot separate when it is mixed (same for 95% ethanol). So I do not know how the kit that they sold works. If you ever tried it before please tell me the procedure for that.

Hope you will like my sharing if you really found out that iso propyl alcohol and salt water do not separate.

The effect of the colour light on glow in the dark item

My school student was doing on a project on the effect of temperature on glow in the dark item. Initially, I gave them magnetic stirrer that come with hot plate. So one will remain in room temperature and the other one will be heated to 70 degree celsius (controlled by the hot plate).

We observe that the glow in the dark star in hot water discharge faster than the one in room temperature.

After that then I realise that the apparatus used for this Amazing Science Challenge project will be kept by the Science Centre people so we cannot give them such expensive equipment like magnetic stirrer to them. So my lab tech and I are finding ways to heat up the glow in the dark star.

Firstly we used a mug warmer, however it does not warm the water at all. So we tried to invert a beaker wrapped with aluminium foil over a light bulb which gives off heat. It indeed can heat up my water on top (which contain the star) however I realise the heat is so hot that it melts my bulb holder. Finally, we have to give up the idea using heat. Instead, we will try whether different colour light will affect the glow of the star.

We saw in the net that red colour light does not charge the particles in the glow in the dark item (you can refer to the link for info). So we compare red light with normal fluorescence light, indeed it does not charge the star and when I off the light only the star in fluorescence light glow.

My experience of lasik surgery

This time I am not going to write about experiment but just want to share my experience of the lasik surgery. I did a Intralase custom lasik at The lasik surgery clinic just 2 days ago. Now I can see perfectly with no side effect. They even recommend me to put eye drop every hour but I am so comfortable that I did not put it every hour as I don't think I need it.

The clinic I went to has a lot of patient doing lasik. At first I really doubt how they can manage with so many patient but everything was fast and I did not need to wait too long. Their skill is also good, maybe they are expert in doing lasik since they have so many patient everyday.

On the day of my surgery, I reach there at 6pm and they brought me to the recovery room and told me to read and sign the agreement for the surgery. I was told to rest and wait on an armchair (No bed for resting) with curtain to separate in between patient. I can say there are about 15 such cubicle in that room for patient to rest or wait for the treatment. The staff are nice and ask me whether I need a drink and explain to me what I will expect later for my treatment and show me the medication I would need after my surgery.

Around 6.30pm, I was asked to walk to the surgery room (Not push using a bed). There are 2 machine there. One was to cut my cornea another was to fix my eye using laser. No pain was experience as they have numb my eyes. But the scary thing is that you can see they use a seeker to scape your eye as they need to put my cornea back after the lasik. After the surgery I have to walk back to my recovery cubicle, then they put on the eye shield for me. My eye feeling is like wind blowing onto your eye so is quite dry and you will tears, the eyes will be quite red too. But this sensation is bearable.

Later I was sent home and ate the sleeping pills they gave me as instructed. So I just sleep throughout till the next morning without feeling any discomfort. So I look myself in the mirror. GREAT! I can see clearly even though there maybe some halo around the thing I see. My eye is not red anymore and no discomfort. However I just apply eye drop as a protection. Maybe mine is the intralase technology which claim to have less side effect and prevent dry eye.

Anyway I can happily go back to Paragon for my review at 2.30pm on that day without any help as I can see clearly already. Until now everything is fine and I am happy with the result. However just an advice is that if you want good customer service, my clinic is just average as they have to handle many cases as I think they are too popular. However their skill and technology is not bad since I don't experience any discmfort.

I do not need to wait too long even though there are alot of people, so their management in timing is still not bad. I do not know how other lasik clinic works but I just don't like to walk into the surgery room myself and walk back into that small cubicle after my surgery.

Do consider lasik if you have short sightheness as the surgery is simple and fast and you can break free with your spectacles after that. However do take care your eyes after the surgery as you may be prone to eye infection after the surgery.

Highlighter will glow in UV light

Just that I am doing on something on luminescence. I saw a video where they use the chemical inside the highlighter and mix it in water. Then under UV light it will glow. I did not try out this experiment, but I just highlight a piece of paper with highlighter and see it under UV light (sometime people called it black light). True enough, it glows. So I can say if you extract out the chemical inside the highlighter and mix it in water it should be able to glow. Do give it a try and tell me whether I am correct.

Glow in the dark mountain dew does not work

I think most of you may have seen and heard about the glow in the dark mountain dew. There are other video that claim that the experiment is fake. I tried it out myself. True enough IT IS FAKE. As seen in the video, they add in baking soda, and hydrogen peroxide into 1/4 full of mountain dew.

The brand I use is different from them as Singapore does not sell those brand. I use the baking soda which comes from a red tin (forgot the brand already). I use my 20vol hydrogen peroxide that is available in my lab. As I don't see hydrogen peroxide sold commercially.

As seen in the video, I drank the mountain dew until 1/4 of it is left in the bottle. Followed by adding a bit of baking soda then 3 capful of 20 vol hydrogen peroxide. Then shake well. In the end NOTHING HAPPEN except for the bubbles created while shaking.

So don't waste your time doing this experiment and waste your mountain dew where you can drink it to quench your thrist.

The effect of acid and base on universal indicator.

I happen to see a video from steve spangler which demonstrate on the effect of milk of magnesia (a kind of liquid antacid) on acid with universal indicator. The colour change of the solution from red to purple was awesome. The video can be found in steve spangler website. The colour change slowly is because the substance in milk of magnesia dissolve slowly in acid, so it will neutralise the acid slowly instead of neutralizing the acid straight away when added.

As I was preparing for the experiment on the effect of pH on the universal indicator so I think the experiment steve spangler did will be good to show the student as a demonstration. I cannot get milk of magnesia in Singapore so I tried those antacid pill by crushing them into powder and mix in water.

To my surprise, antacid pill is acidic. I don't know why, may have to ask the manufacturer. The 2 antacid pill I tried is Wei Sen U & Gelusil Antacid. So I created something quite similar to milk of magnesia which is calcium hydroxide solution. It gives a milky appearance (like milk of magnesia) as it does not dissolve fully in water and is alkaline. Somehow it works and it can be seen in this video that is taken during the experiment. The change is quite fast, so in order to see the yellow colour in between, I reverse the reaction by adding HCl drop by drop so the colour will change slowly from purple to grey to green then yellow and finally red.

From the video, you can see that when the acid is not mixed properly, the middle is red while the side is yellow.

However calcium hydroxide do not work every time due to their solubility. So they may not be able to dissolve fully to neutralise the solution and make it turn purple. Then I tried using sodium hydroxide pellet (which is a stronger base). It works and change the universal indicator from red to purple, see this video.

It's cool right! Enjoy the video as I took a few tried in order to get such great result.

The effect of bleach on universal indicator.

I was preparing normal household reagent for the student to test on its pH. One of the reagent is bleach. I have searched in the net that bleach will gives a purple colour on the universal indicator since it is alkaline. When I tested it, it shows purple initially, but it changes from purple to green to yellow then finally colourless. This will mislead the student as they may not know what colour to record down since the colour keep on changing.

So I decided to find out why from the internet and realised that the universal indicator and any other liquid pH indicator are destroyed by bleach, rendering them useless for testing the pH. This applies to litmus paper and phenolphthalein too.

The only way to solve the problem is to adds sodium thiosulfate to the bleach solutions, it will neutralize the colour-removing effects of bleach and allow it to test with the liquid indicators. Thiosulfate reduces the hypochlorite (active ingredient in bleach) and in so doing becomes oxidized to sulfate. The complete reaction is:

4 NaClO + Na₂S₂O₃ + 2 NaOH → 4 NaCl + 2 Na₂SO₄ + H₂O

I have tried it out and it works. So in future if bleach is needed to test for its pH, neutralize it with sodium thiosulphate first before adding the liquid indicator.