The life and times of a younger member volunteer and medicinal chemist.

Sentinus Young Innovators 2011

First of all, let me apologise for the silence on this blog of late. As my last post indicated, things have been more than a little hectic around here of late. I did have that meeting with the RSC staff to discuss matter relating to the Younger Member’s Networks. I’m following up on those discussions with some emails back and forth, and once the picture is complete I will blog in detail on this meeting and the outcomes from it.

 1a29eac08b20ff4c66e72f644572a9c5-original-img_0059.jpgToday, I want to talk about a major event I attended in Northern Ireland: The Sentinus Young Innovators Fair. As the name implies this event encourages school children around the province to take on an extra project, in the areas of science, maths and engineering. I’m not gonna lie, I did not have any time to even peek at the presentations, as my colleagues (Kerry & Sonia, in the lab coats) and I were busy dealing with the hundreds of students who came up to us throughout the day (perhaps attracted by the loud bangs emanating from our corner!). We faced some stiff competition, from the fire-brigade, the RAF and some kind of F1 racing thing... but I think we did chemistry proud! Although we did lose to some biologists (Phil and Ben in the CRUK shirts) in a “yeast versus potassium iodide catalyst” race (sorry!).
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I thought I’d share what experiments we carried out (and what went wrong!). Our audience was mainly primary school children, so we tried to keep things simple and safe. The first few experiments require little in the way of equipment or skill, but some of the later ones... well let’s just say we brought the blast shield for a reason! Of course, you should always carry out risk and COSHH assessments in advance of the demonstration.

I'm sure lot's of people out there will have their own favourite demo's, and links to good resources so feel free to share!

  
1. Blue Bottle

Equipment and chemicals: 1 L conical flask and stopper (or parafilm), 5 g glucose, 5 g sodium hydroxide, few drops of methylene blue, 500 mL tap water.

Procedure: Dissolve the glucose and sodium hydroxide in tap water and add the methylene blue. Swirl the flask until a blue colour persists. Leave the flask to stand until the blue colour fades (stoppering the flask can speed this up a little). Repeat as required, the reaction will last several hours. As it “goes off” the solution may become pale yellow, rather than colourless, upon standing.

Chemistry: The reaction is being oxidised by oxygen in the air, converting glucose into glucuronic acid. Methylene blue acts as an indicator for the presence (blue) or absence (colourless) of oxygen.

Teaching points: This reaction demonstrates one very important physical property: the limited solubility of oxygen in water. You can ask the children why, despite oxygen being all around us, the flask needs constant swirling in order to stay blue (oxygenated). Oxygen is relatively insoluble in water, and is unable to penetrate deep into the flask without motion. If they look closely at the meniscus of the flask, they may see that it remains tinged a blue colour. This is how far oxygen can penetrate still water. Now ask them what would happen to fish in a stagnant pond? Or why the Deep Water Horizon oil spill was so disastrous for sea-life (with oil covering the water, even the motion of the sea was insufficient for oxygenation). Finally, for older students, you can link this into the reason why blood vessels (capillaries) much reach a meniscus width (or width of a fingernail) from every part of your body.

Reliability: Fool-proof. Takes a few minutes for the reaction to get started, after that works like a charm. The students may want to swirl the flask themselves, but it is a caustic solution so use your best judgement.

2. Elephant’s Toothpaste

Equipment and chemicals: Several empty Coke bottles, a basin, powder funnels, 6-10% hydrogen peroxide, dried yeast, potassium iodide, food colouring, and washing-up liquid.

Procedure: Pour about 100 mL of hydrogen peroxide into the bottle. Add a squirt of washing-up liquid and some food colouring (only if using yeast as the catalyst). Add a tablespoon of either yeast or potassium iodide using the funnel, and swirl to initiate the reaction.

Chemistry: The rate of decomposition of hydrogen peroxide into water and oxygen is greatly increased with the addition of either yeast or potassium iodide as a catalyst. The release of oxygen gas causes the washing-up liquid to foam, forming the “toothpaste”.

Teaching points: This reaction demonstrates a variety of important chemical principles. It is an irreversible, exothermic “chain-reaction”, which only occurs appreciably in the presence of a catalyst. Either a chemical catalyst or a biological catalyst (an enzyme) can be used. Usually the yeast will promote a more vigorous reaction; this is because the enzyme (catalase) is amongst the fastest and most efficient enzymes known. Hydrogen peroxide is a very toxic molecule that we make inside our bodies every day; without enzymes to degrade it to safe materials almost instantly it would do a lot of damage and make us very ill. If you don’t use food dye, you will see that the foam with yeast is white, and with potassium iodide is brown. This is because the chemical catalyst generates some iodine as a by-product, whereas the yeast only produces water and oxygen.

Reliability: Fool-proof. Just don’t forget the basin! If you do want to let the students touch the bottle or the foam (to feel the heat of the exotherm), it is best to use only yeast as the catalyst. Whilst I’m sure many readers have had iodine applied to open wounds as kids (myself included at the tender age of 21), it seems to have gone out of fashion (thanks lovely health and safety people).

3. Fire extinguisher

Unashamedly “stolen” from this great YouTube channel.

Equipment and chemicals: Jug, bowl, vinegar, bicarbonate of soda, tealight candles, spoon, lighter/matches.

Procedure: Pour about 50-100 mL vinegar into the jug. Add a tablespoon of bicarbonate of soda. Wait for the reaction to finish and for the foam to settle. Light the candles and place them in the bowl. Pour the invisible carbon dioxide gas you have made onto the candles, without pouring any of the liquid, and watch them go out “magically”.

Chemistry: This acid-base reaction coverts the acetic acid in the vinegar and the sodium bicarbonate into sodium acetate and carbon dioxide. Carbon dioxide is heavier than air, so when poured over the candles it sinks down and smothers the flame.

Teaching points: The irreversible formation of carbon dioxide gas from vinegar and bicarbonate of soda is one of the easiest reactions to carry out. Not only does this experiment show a chemical reaction occurring in a very visual way, it also allows you to demonstrate the effects invisible gases can have.

Reliability: Pretty good. Halfway through the day we had to switch from one bottle of vinegar to another brand. Despite having the same acidity (5%), this new bottle resulted in finer foam that took longer to settle. As a result we believe some gas was lost, so the demonstration did not always work. Our advice is to practice a few times beforehand, then buy sufficient quantities of the vinegar and soda for your needs.

4. Heavy Coke

Also unashamedly “stolen” from this YouTube channel.

Equipment and chemicals: Tank of water, can of Coke and diet Coke, plastic cup, sugar, spoon.

Procedure: Place the two cans in the tank. The Coke will sink, whilst the diet Coke will float. Rest the plastic cup onto of the can of diet Coke and spoon sugar in until it also sinks.

Chemistry: Diet Coke contains no sugar and as such is less dense.

Teaching points: Density, but more importantly just how much sugar there is in Coke (about 7-10 tablespoons per can)!

Reliability: Fool-proof.

Please note that from here on in, the “difficulty level” in terms of equipment and skill goes up a few notches.

5. Cool Cryogenics

Equipment and chemicals: Liquid nitrogen, dry ice, nitrile gloves (or similar), flowers, ependorf tubes, beaker of water.

Procedure: Flash freeze the gloves and flowers with liquid nitrogen and break them apart on the table or with your hands. Place some dry ice into the gloves, knot and watch them expand into “glove puppets”. Put a small amount of dry ice into an ependorf tube, close, invert and watch it shoot off as the gas expands.

Chemistry: Dry ice solidifies at -78 °C, and is one of only a few compounds that sublime. Nitrogen liquefies at -196 °C.

Teaching points: This is all about changes of state and the difference in volumes between solids, liquids and gases.

Reliability: Fool-proof. And one of the most popular demonstrations we do.

6. Hydrogen Explosion

Equipment and chemicals: Balloons of hydrogen gas on string, bamboo cane with birthday candle stuck to the top, lighter/matches.

Procedure: Light the candle and use the cane to bring it into contact with the hydrogen balloon.

Chemistry: The very exothermic reaction of hydrogen and oxygen, resulting in water and an impressive explosion.

Teaching points: You could talk about hydrogen gas as a clean fuel. Or you could just enjoy the fun!

Reliability: Fool-proof. And one of the most popular demonstrations we do. It’s also a great way to attract attention!

 
Posted by David Foley on Jun 17, 2011 7:55 PM Europe/London

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