Chemiluminescence!

Chemiluminescence

Chemiluminescence is the technical term given when a chemical reaction gives off light!

In year 8 we study the ‘signs that a chemical reaction has taken place’. One of the signs that a chemical reaction has occurred is that it gives off energy – typically this energy is in the form of heat, but in a few cases the energy given off can be light! Different colours are made by different amounts of energy.

Check out these chemiluminescent reactions that our science club team recently experimented with:

Just in case it’s not obvious – don’t try this at home! See here for more details about why and the details behind how glow sticks work.

Science Club is back for 2013!

We had a lot of fun this week playing with dry ice. Dry ice is the solid form of Carbon Dioxide (the colourless gas that we breathe out). Dry ice is special because unlike normal ice it doesn’t melt (and leave a puddle) instead it sublimates – it changes straight into a gas without becoming a liquid. It’s also special because it is very cold, -78.5 degrees Celsius. There’s a greater temperature difference between your hand and dry ice than your hand and boiling hot water! Dry ice is very dangerous to our bodies, it can freeze the water in our cells and the sweat on our skin (sometimes sticking to you just like when you lick a frozen ice cube or ice block and your tongue sticks to it) creating a ‘freeze’ burn or even frostbite that is potentially much worse than a regular burn.

As dry ice sublimates into a gas very quickly there are several very cool effects that it produces. Firstly, when you add dry ice to water the sublimation occurs much faster. The Carbon Dioxide gas that is produced is very cold – cold enough to cause most of the water vapour in the air condensate. The effect is that we very literally make a small cloud. However, the cloud only forms where the cool Carbon Dioxide gas is flowing. Another unusual property Carbon Dioxide has is that it is denser than air, so it’s a gas that literally ‘sinks’ in our atmosphere. This means that the cloud we make also sinks in the air and creeps along the ground.

Unfortunately I forgot my camera on the day and don’t have any new photos to share, but here’s the key effect we were experimenting with:

(A previous attempt at creating a dry ice tornado by Mr Wright and myself)

The end product we hope to use in the upcoming Wizard of Oz musical:

You can see the rest (including our big explosion) in last year’s post.

Applications now OPEN for Science Club 2013!

Applications are now open to join the 2013 science club at WCCS. This club is open to year 7 and 8 students who are interested in getting some more hands on experience with science. The aim of this group is to encourage students to develop a greater interest in and awareness of science and the amazing way our world works. We hope to bring back some of those old experiments from ‘the good old days’ that have left permanent inspiring marks on scientists around the world (and the roof of C3).

As part of this club we hope to encourage students to participate in some serious science. The club will aim to meet once a fortnight after school on a Wednesday from 3:15 – 4:15pm. Students will need to be picked up from school at this time.

Through this club we want to teach students that the cool stuff in science doesn’t solely reside in explosives and other pyrotechnics but that amazing and strange phenomena lie within all branches of science (though explosions are cool). Some areas that will be explored throughout the course of the year are:

  • Environmental Science (movement of the earth’s crust; volcanoes; effects of atmospheric pressure)
  • Biology (dissections; DNA examination)
  • Chemistry (Crystal formation; forensics; chemical based colour changes)
  • Physics (nature of soundwaves; explosives; forces and energy)

Term 4 will be a time for the students to show their true colours as we participate in the CSIRO Creativity in Science and Technology (CREST) Awards. This award is designed to help students develop skills in scientific research and inspire students to take up further studies in science.  CREST is a non-competitive science and technology award program for primary and secondary students and provides an excellent experience for training students in scientific investigation skills. As a result of completing the award students are awarded an accredited certificate from CSIRO as a record of their achievement. Completion of the CREST award will require some work from the students at home over term four, but support feedback and lots of time will be given during our regular meetings to assist students.

Entry into this club is by application as space is limited. Applications are judged on maturity of the student, demonstrated safety in a science lab, level of interest and achievement in science.  All students who have an interest in science are encouraged to apply to join this group. Students have until the end of week seven (15th March) to submit their completed application forms.

As this group is an extra-curricular activity the cost of chemical supplies will need to be covered by students. If you are offered a position in the group a $20 membership fee is required to secure your position. This money will cover all chemical and equipment costs for our regular meetings for 2013 and the registration fee for entry into the CREST program.

Please complete the application form (here) and submit to Mr R Jackson if you’re interested in this exciting opportunity by Friday week seven! Feel free to email us and ask any questions to either Mr R Jackson (jacksonr@wccs.nsw.edu.au) or Miss J Snelson who will be assisting us this year (snelsonj@willcarey.nsw.edu.au).

 

Pyrotechnic Delight!

Fireworks have many important components that come together to create the amazing effects we enjoy. To examine these components in detail we had an extended Science Club session this week.

Our first set of experiments was investigating how fireworks produce the colours that they do. Fire is actually a chemical reaction called combustion that gives off light and heat. So when we see burning wood, we’re actually seeing the light that is given off by hot gases reacting as they are boiled out of the wood. The colour of flames depends on the chemicals that are in the material being burnt. We made flammable mixtures of various salts. A salt is a simple chemical with a metal and non-metal bound together. Table salt (Sodium Chloride) is a very common salt, but is not the only kind of salt. While examining the coloured fire produced from different types of salt we were able to discover it was the metal component of the salt that determines the colour of the flame. For example, Sodium-based salts produce a strong yellow flame, Boron produced a bright green flame, Strontium was crimson red. Therefore, when we see wood burning yellow, we can conclude that it must contain Sodium-based salts (which is correct as most living tissue is rich in Sodium Chloride). Forensic scientists can use techniques based on this science to identify unknown chemicals. Pyrotechnicians use this science to mix chemicals to produce the brilliant colours in fireworks.

Combustion is a chemical reaction between a fuel and Oxygen (or more accurately, any oxidant) that produces heat and light. An explosive reaction is a sub-category of combustion reactions that occur fast enough to produce a sudden and large amount of pressure that expands outwards. We can hear this sudden change in pressure as sound. We explored the importance of Oxygen for explosive reactions in a series of reactions. Firstly we examined three balloons, one filled with Oxygen gas, one with Acetylene gas and the third with a mixture of both Oxygen and Acetylene. When we ignited the first balloon it didn’t react at all, there was no fuel and so the Oxygen merely floated away. The second balloon had plenty of fuel, but no Oxygen. However, when ignited it still reacted, as when the balloon popped the fuel could react with some of the Oxygen in the air. There wasn’t much Oxygen immediately available though and so not all of the fuel reacted. This ‘partial combustion’ produces a lot of sooty remains. The last balloon had a good mixture of Oxygen and fuel so when it was ignited all of the Acetylene reacted at once and produced a very loud explosion with no sooty remains. We demonstrated this concept again with Hydrogen gas in a Milo tin and blew the lid over the tree tops. Black powder (gun powder) and flash powder are two common explosive mixtures that rely on oxidizer-fuel reactions.

Fireworks though don’t use gaseous chemicals for their reactions. Instead they use various mixtures of powders. One powder is almost always a metal powder, this acts as the fuel for the reaction and provides the colours for the fireworks. The second powder typically contains Oxygen that is bound to other chemicals so that it stays a solid. There are many solid compounds that contain Oxygen, the ones used in fireworks are often Nitrates (the suffix ‘-ates’ tells us that this compound contains Oxygen) which is NO3. When they react the Oxygen leaves the Nitrogen and reacts with the fuel.

To demonstrate the explosive nature of some powders we produced Touch Powder. Touch powder is a solid compound of Nitrogen Tri-Iodide that can be triggered to explode by loud noises, small amounts of friction, heat from the air or even the soft touch of a feather. This compound is so easily detonated that even the Army won’t use it as the compound would explode if you tried to transport it anywhere – hence this explosive is classed as ‘sensitive’. This chemical reaction is actually quite different the typical reactions for fireworks and is NOT a combustion reaction. Instead, it is a decomposition:

2 NI3 (s) → N2 (g) + 3 I2 (g)

The Nitrogen Tri-Iodide literally blows apart producing very large amounts of gas. By rapidly producing large amounts of gas it produces a sudden increase in pressure and this is why we hear a loud explosion. Thus decomposition is a second reaction that can produce explosions (TNT, Nitroglycerin, C4 and RDX are common explosive materials that rely on decomposition reactions).
 

Here’s what we did:

Nitrate Flash and Pyrotechnics round #1

Redox reactions are the most important type of chemical reactions in pyrotechnics. Redox reactions are all about moving electrons that are fixed around one chemical to a different chemical – chemistry is all about understanding this ‘dance’ of electrons.

This week we examined one reaction in detail: The redox reaction is commonly called refered to as ‘Nitrate Flash’. Ammonium Nitrate was our ‘oxidiser’ it is strong enough to take electrons out of other chemicals. Zinc powder was the reducer, it gave up electrons to the oxidiser. The whole dance of electrons resulted in us producing Zinc Oxide, Nitrogen gas and water in the following net chemical equation:

Zn(s) + NH4NO3(s) → N2(g) + ZnO(s) + 2 H2O(g)

Notice the sub script (g) on the water molecule, that tells us that the reaction gave off enough heat to boil the water – so we actually made water in a gaseous state i.e. steam. Steam was the main gas you could see coming out of the reaction as Nitrogen gas is colourless (it makes up 78% of the air we breathe).

Notice though that in the ‘net’ chemical reaction we haven’t mentioned the water we added to start the reaction, or the Ammonium Chloride that was also included… they have a very special role called a ‘catalyst’ – look it up if you want to know more!

Here’s what we did:

To answer the question during the video, yes we did manage to set off the internal fire alarms :).

We managed to break the bin…

 

Exothermic Reactions

An exothermic reaction is any reaction that gives off energy – typically in the form of heat. The two reactions we examined today utilise the reactive properties of metal powders. In chemicals energy is stored in the bonds between atoms, when we re-arrange these bonds sometimes that energy can be released.

This week we showed how common rust (Iron Oxide) can react with Aluminum. When this reaction occurs the Oxygen atoms that were joined to the Iron, switch and join onto the Aluminum instead. As this reaction occurs a lot of heat energy is released, enough to melt the Iron. You can see clearly in this thermite reaction the molten Iron forming and the solid Aluminum oxide (rusted Aluminum) forming as a white powder. After allowing the Iron to cool and solidify we collected the solid remains, interestingly some of the Iron was very colourful and some took on a crystalline form – I wonder why that might be?

Here’s what we did:

Cold Explosions

An explosive is any material that contains a large amount of stored energy that can be released rapidly. This energy is stored as potential energy and when released transforms into a combination of heat, light, sound and kinetic energy.

This week in our first science club meeting we examined simple pressure explosives. When matter transforms into a gas the particles are trying to push away from each other, if you constrain these particles inside a container the pressure builds up. Increasing pressure is used to inflate tyres, balloons and to push water through pipes. If the pressure in a container is increased too much and the container breaks, just like popping a balloon, you can make a pressure explosion.

Here’s what we did:

Science Club 2012!

Applications are now open to join the 2012 science club at WCCS. This club is open to year 7 and 8 students who are interested in getting some more hands on experience with science. We meet together once a fortnight after school for an hour of investigations involving experiments and demonstrations that high school students typically don’t get to see.

All students in years 7 and 8 should receive an email with application forms and more details. Get your application into Mr Jackson today as members will be selected on Monday week 3!