Open Day Stall Activities

Friday and Saturday saw us having a lot of fun at open day this year. We had 8 demos that we repeated many times over for scholars, kids, and the curious.

Here are a few pictures of our activities:

Thembelani showing a battery made from 3 cells using Coke as the electrolyte - we got 3 volts out of it.
So you can charge your cellphone out in the bush with coke, some metals and a bit of wire all combined with a touch of electrochemistry knowledge.

Lukanyo coverts unpleasant smelling chemicals into a pineapple essence.

Here we demo polymer science - the production of insulating foam used in fridges, geysers, and as flotation in boats.

Some inspired scholars gave Chemistry the Thumbs Up.
Now for my all time favourite...

Here we demo combustion how on can change cellulose into nitrocellulose.

All in all it was great fun for learners and staff. We look forward to next year's open day.

Your Carrer in Chemistry - Open Day at NMMU

Careers day will be held on 6 and 7 May. There will be stalls for most courses at the Indoor Sports Center at South Campus.
Chemsitry will feature there - we plan to have an interactive stall with demos including some interesting chemical reactions inside the hall. If ther weather permits we will have some more exciting outside demos including a chemical volcano!!
There will be pamphlets describing our various courses and we will have staff there who can provide information on carrers in chemistry.
Hope to see you there.

Public talk by Chemistry Professor

THE ANCIENT HISTORY SOCIETY OF

PORT ELIZABETH

PRESENTS A TALK ENTITLED

“The Romans in Britain”

by Prof Peter Loyson

Prof Loyson will discuss the Roman conquest of Britain, covering the attempts of Julius Caesar, the successful expedition of the emperor Claudius, the revolt of Boudicca, the famous queen of the Iceni, and other aspects.

The Italian Sporting Club, Harold Road, Charlo

Tuesday 3 May 2011 at 19.30 pm

Refreshments and cash bar will also be available.

Enquiries: Prof Peter Loyson 041 504 2147 or 083 359 1072

Rubber Chemistry: Part 1

Rubber! You probably first encountered it when sucking on a bottle as a baby, or later in the classroom to rub out errors in your pencil work. Indirectly we encounter rubber many times a day - perhaps most noteworthy is in getting to your destinations - tyres - they are made from rubber with additives.

Try think of 10 other uses of rubber. Do it now before your read on.......

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Perhaps you saw some rubber in the video clip of my last post - on my speargun - see it even finds use in fishing! My wetsuit kept me warm. What is it made from?

I will now cover some chemistry of natural rubber.
Man has learned to make his own rubber from crude oil, but first it was taken from plants. That is the focus of this post.
Indians in South America used rubber sourced from the sap of trees to make shoes and coat the paddles of their canoes to waterproof them - the smoke of their fires cured the rubber. Explorers and early settlers in South America saw the Indians using rubber and some were intrigued sent samples home to Europe. The industrious western mind turned such rubber into big industry over two centuries.

The milky sticky sap that is found in many plants contains some form of rubber. Just the other day I was gardening (pulling out weed creepers that entangle my garden plants). I got my hands full of sticky, yukky, white "milk". Next the soil got stuck in the sap that had lodged on my hands and my hands were a mess! Soap refused to remove it - only hot water and hard rubbing with a hot rough cloth helped remove the sticky adhesion.

What type chemistry underlies this sticky sap?

Isoprene (2-methyl-1,3-butadiene) is a common, naturally occurring organic compound with the formula:CH₂=C(CH₃)CH=CH₂

Plants produce and release large amounts of isoprene into the atmosphere. Rainforests make a huge contribution. The haze one sees on a hazy day in regions where there is extensive plant life - may be partly due to isoprene. A variety of pretty complex reactions form such hazes. I will save that discussion of atmospheric chemistry for another day. Back to isoprene...

At room temperature it is a colorless liquid but it boils easily at 34 degrees Centigrade. So it is very volatile - this explains how plants can release it with relative ease.
Isoprene is the monomer of natural rubber. Monomers are molecular building blocks from which bigger building blocks are made. Just as bricks make up walls, and walls make up buildings, so isoprene units can be linked together (polymerized) into rubber.

In biological systems such as plants, the isoprene structure is found repeated in many polymers. It occurs often as dimethylallyl diphosphate (DMADP) [click on this link for more data] and its isomer isopentenyl diphosphate (IDP). An isomer is a molecule with the same formula but a different shape or structure.

Early scientists actually extracted isoprene from rubber by decomposing it and correctly assumed that rubber was made up from repeated units of isoprene. Natural rubber, or polyisoprene exists as long chains - thousands of isoprene units bound together by the carbon carbon double bonds. Some double bonds remain in the structure of polyisoprene - these can be used to change the properties of rubber.

Charles Goodyear used sulphur to harden rubber in a process called vulcanization - where sulphur is added to rubber and it is heated to harden the rubber. Vulcanization is derived from the name of the roman god of fire "Vulcan". Volcano has the same source. Sometimes Man learns from his blunders and Charles Goodyear was such a person, he had lead oxide mixed with sulphur and rubber. Accidentally some fell onto a stove and hardened and the rest is history the future of rubber had been secured.

The long, relatively strait rubber chains (polyisoprene) are secured in position by crosslinking sulphur bonds. These bonds prevent the rubber from becoming sticky and softening with heat. A clear diagram is illustrating this in the Wikipedia definition of vulkanization. 
Mr Goodyear; yes, the same name as Goodyear tyres, he developed the vulcanization process but sadly he did not make a fortune out of it and he died a poor man in 1860. Patent infringments were problematic in his endeavours. At least his name lives on in the Goodyear Tyre company.

Now that rubber had been made hard and resistant to heat it found many uses especially in the tyre industry. Here in Port Elizabeth we have a big tyre industry where rubber is vulcanized on a daily basis in the tyre factories. 

Next time you take a drive in a car or bicycle think about the polyisoprene and sulphur that hardened the rubber that supports and carries you.


 

Cement - A swim through the Coega Harbour Wall

I took this clip some time back. I was freediving on the wall - that's my speargun you see in front of the camera. You even see a few musselcracker there in the wall.
Imagine the hydration reaction calcium aluminium silicate taking water into its structure and getting stronger - and it still continues today, even through it is very slow.

The gradual hardening of cement is a true everyday reaction.

I my next chemistry post I plan to focus on rubber and a bit of chemistry related to rubber and its use.

More about cement

Last post I showed some large scale application of cement in building a harbour wall. Cement is made from limestone and shale with other components containing aluminium and iron minerals. These are carefully mixed and heated to high temperatures with coal to form a "clinker". The clinker is then crushed and its composition is adjusted by adding gypsum to control setting times. Up to 5% of other additives may be added.
The main components of cement are 3CaO.SiO2 and 2CaO.SiO2 (tricalcium silicate and dicalcium silicate). These compounds make up the majority of the cement with the iron and aluminium clinker compounds and the gypsum making up the rest.

Cement can be made to set faster or slower by adding accelerators (e.g. calcium chloride or sodium nitrate)or retarders (e.g. citric acid, sodium gluconate).

Other additives can be added depending on the desired use. E.G. adding latex makes the cement harder and improve the workability.

When this mixture that we call cement is mixed with water it reacts with the water and sets. The reaction is called a hydration reaction, and cement can be used under water - it is hydraulic. In fact it needs the water for it to work well. Plaster is a mixture of cement and fine sand that sets hard over the brick of a wall making it smooth. If your builder is impatient and tries to speed up the drying of your cement it will be weaker, or it may crack as the water needed for hydration is lost.

When I had some building done at home my wife and the builder thought I had gone insane when they found me perched on the wall watering it with then garden hose! I wanted it hydrated.

Some times you may see concrete (cement and large pieces of stone and fine sand mixed) being covered with plastic or wet rags - these cover remain on for 48 hours - this allows the hydration to further strengthen the cement or concrete before it dries. Actually cement gradually gets stronger the longer it stays wet - the strength will double from 8 hours to three days and after another 27 days the strength will double again.
From this you can see that the impatience of builders to complete the job can lead to weakened structure.

Here is a chemistry based tip for you if you build. Keep an eye on the builder and staff - they should only mix as much cement as can be used in 1 hour (the cement bag normally reminds them anyway - printed user-directions). Do not let them mix the cement sand and water just before lunch. The cement gets started reacting and the hydration reaction is well under way while they rest in the shade for that hour or so - your structure ends up being weaker if the builder violates this procedure. Two years later your plaster is falling off the wall and the builder is long gone. The same goes for tile adhesive and grouting  as these materials are also cement based.

Cement is stronly alkaline - in the manufacture the limestone breaks down to carbon dioxide gas and calcium oxide rendering it alkaline. Some alkalinity is released during hydration as well. Keep cement off your skin or it will slowly dissolve your skin.

Fact: Did you know that you can make lime Ca(OH)2 by heating sea shells or egg shells to 850 deg C?

Cement reacts with water and give off heat at the same time - in the building of large concrete structure water cooled pipes may be included to prevent cracking of the structure.

So there you have a bit of everyday chemistry - we rely on the chemical reactions of the past for our structure of the present. There is more water in your walls that you may think.

Where did you go today? Any chemistry involved?

Last week after I wrote that post I climbed into a helicopter at the PE airport and headed north east.
An internal combustion engine got me there - that combustion involved the reaction of fuel consisting mostly of carbon and hydrogen (hydrocarbon) with air which contains oxygen.
During the combustion the carbon in the fuel forms carbon dioxide. Possibly carbon monoxide will form as well, and hopefully no carbon(black smoke). The hydrogen combines with oxygen from the air to form water. Along with these gases - carbon dioxide and water vapour - comes a lot of heat. The hot gases are what drive the 4 cylinder engine in the small chopper I went up in.

Now being off the ground and a bit closer to the sun I thought of the ozone layer.

Ozone, (O₃)  is a form of oxygen that is unstable and readily reverts back to oxygen ( O₂) as we know it, and breathe it. It has a short half life - about 30  minutes. That means the concentration drops by 50% in 30 minutes. Higher up in the atmosphere (10 -50 km up) energetic radiation from the sun can break normal oxygen apart to form two free oxygen atoms that are reactive. These can then react with another normal oxygen atom to form ozone.

    O₂ + light = 2 O.  

     O  +  O₂  = O₃

This is how ozone forms in nature. The ozone layer protects us and other life forms from UV radiation by absorbing most of that harmful light. Click here for a link to how ozone is distributed in the atmosphere.

Lightning can also split apart oxygen allowing it to form ozone.
We can make ozone using sparks in a corona discharge tube. Air (or pure oxygen) is pumped through the tube and an air ozone mixture comes out.  A strong UV light will also make ozone.

Ozone is used mostly in water treatment for drinking, swimming pools, of aquaculture.  It kill bugs or oxidizes unwanted pollutants.

So that is a bit of natural chemistry (photo chemistry) that happens each day, and saves our bacon in the process. Look up, and imagine the ozone formation, or next time there is a fine electric storm - imagine the lightening forming ozone.


Now back to my flip in the chopper. About 12 km northeast of the airport I looked down at the Coega harbour.

Now there's is a big project that involved plenty of chemistry.
Obviously a lot of fuel was burned to build that wall.

Each of those dolosse (wave breaking structures) lying down there on the sides of the wall weighs about 30 tonnes. That's a lot of cement used to make the concrete!


Ah! yes, I have walls around me now, and you probably do too. Mostly these walls are made of brick and cement.

What is cement?

How is it made?

How does it get hard? Does it dry? My builder says yes, in fact he wants it to dry fast so he can paint and get on with the next job.

What does the chemistry suggest? Dry it fast?

In a subsequent post I will talk about cement manufacture and setting ; and perhaps we can have a closer look at the Coega wall - I will take you into the wall, and under the water...