Last week Cordie thought up a fun liver and hydrogen peroxide enzyme experiment. The idea is an interesting extension of elephant toothpaste. And it extends the chemistry learning into biology (useful for homeschool records).
When we make elephant toothpaste we use yeast as a catalyst in the breakdown of hydrogen peroxide into water and oxygen gas. By adding soap and food dye, we get oodles of colourful foam that make for a fun and memorable science lesson.
Cordie recently discovered that liver also contains a catalyst which breaks down hydrogen peroxide. She decided to try to inflate a balloon with the gas produced and to test it for oxygen. (Is it just my kids that love experiments where they get to play with fire?)
You can watch Cordie demonstrating her experiment in the video [4:39] below (with crumpet cameo from Jasper).
What you need
Liver (we used about 200g)
Hydrogen peroxide (we used about 75ml / 1/3 cup of 9% / 30 vol)
Balloon
Small plastic water bottle
Funnel
Peg or clip
Knife
If you want to test for oxygen you’ll also need:
Splint (thin piece of wood)
Lighter/matches
What you do
1. Chop the liver and put it into the bottle
2. Pour the hydrogen peroxide into the balloon via the funnel
3. Carefully put the neck of the balloon over the bottle so that the hydrogen peroxide pours onto the liver
4. Hold the balloon in place as it inflates with gas, then clip it closed
5. If you want to test the gas, light the splint then extinguish the flame. Immediately insert the still-glowing splint into the bottle
What happens
As soon as the hydrogen peroxide touches the liver, foam appears and the bottle gets warm. After a few seconds the balloon begins to inflate.
When you lower the glowing splint into the bottle, the flame rekindles. (My kids’ favourite bit!) There should be enough oxygen to do this over and over again.
What’s happening?
Just as with elephant toothpaste, the hydrogen peroxide is broken down into water and oxygen in the presence of a catalyst. (A catalyst speeds up chemical reactions without being changed itself.) The reaction is exothermic – it produces heat.
2H2O2 —-> 2H2O + O2
Liver contains a biological catalyst, the enzyme catalase.
Just as the liver in our experiment breaks down a poisonous chemical into harmless substances, an animal’s liver breaks down toxins and renders them harmless.
Take it further
Heat and cold affect how enzymes work. In Cordie’s science class she timed her experiments using boiled and frozen liver alongside liver at room temperature.
Further resources
BBC Bitesize – Webpage and video about liver, hydrogen peroxide and enzymes
Do let me know if you try this. I love hearing from you. 🙂
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Science is one of the easiest and most enjoyable subjects to learn without a curriculum. Science experiments are also surprisingly easy to strew.
What kid – big or small – can resist the temptation to find out what will happen when we add this liquid to that powder, or when we connect a battery to this strange contraption?
What’s in my unschooling science video?
In my video this week I talk about – and show you – a fun afternoon we spent experimenting. As you’ll see, my children each took the initial idea to make red cabbage indicator in a completely different direction.
And you’ll hear about the shocking discovery I made when I recently browsed a science curriculum for KS3 children (aged 11-14).
My son would (approvingly) call the previous sentence ‘click bait’. Sorry about that. I first wrote ‘surprising discovery’ but I went back and changed it because my jaw really did drop at what I saw!
I plan to compile two more mini videos from the footage of our afternoon’s science:
(1) Our demonstration of how to make red cabbage indicator, and
(2) Cordie’s liver and hydrogen peroxide experiment that I talk about in this video.
You might also like to look at my science page for other fun experiments we’ve done.
* * *
Thank you so much for all your lovely comments about my first video, and for your inspiring ideas for future videos. I did record another last week in which I talked about how we decide what to learn, but I’m not sure about it. (Perfectionism? Or fear of not being seen as a ‘proper’ unschooler? Maybe I’ll quietly put it up on YouTube anyway.)
Every summer when I declutter my science supplies cupboard I come across a few hidden treasures. (The reality: “Oops, we never did get around to making shadow leaf prints / home made light bulbs / popsicle stick trebuchets,” accompanied by a pang of guilt. Is that just me?)
The Epsom salts were bought to make bath fizzies with C(11) last Christmas. The fizzies never happened, but on the bright side, we had an unopened pack of Epsom salts when CSIRO’s cool crystals email landed in my inbox.
J(10) asked if Epsom salt was like the stuff we put on our fries, which was a good opportunity to remind ourselves what we learned about salts when we concocted our own fizzy drinks a few months back: A salt is created when an acid and a base neutralise each other.
Epsom salt is another name for magnesium sulfate. We looked up magnesium and sulfur in our book, The Elements, and noticed how very different the salt is from its constituent elements.
All you need to make quick crystals
What you need
Epsom salt (1/2 cup)
Hot water (1/2 cup)
Food colouring (optional)
Glass, spoon
What you do
Put the salt and water in the glass together with a few drops of food colouring. Stir for about five minutes, then put the glass in the fridge for at least three hours.
Dissolving the Epsom salts
What happens
After just a few hours in the fridge, you get beautiful crystals like these.
Epsom salt crystals
We carefully drained the water to get a better look at our crystals.
Taking a closer look at the crystals
How do crystals form? The scientific explanation
Epsom salt is an ionic compound. It’s made up of magnesium and sulfur ions joined together by ionic bonds. When we dissolve the salt in hot water, these bonds break and the two elements become separated .
Later, when we cool the salt solution in the fridge, the magnesium sulfate ions no longer have enough energy to move about freely. The ions begin to re-bond, first as single molecules and then – as the molecules themselves begin to join together – as crystals.
Science Kids at Home has some cool diagrams showing what’s happening at a molecular level.
Epsom salt crystals
More crystal science
Different types of molecule always the same shape of crystal, every time they form.
In the past we’ve also made crystals from table salt (sodium chloride), borax and sugar. The process for each of those is slightly more fiddly, but comparing the different shaped crystals is interesting. Borax crystals make pretty decorations, and sugar crystals are yummy!
Sugar crystalsSalt crystalsBorax crystals
And now the Epsom salt packet has been opened, we’re one step closer to making those bath bombs. 🙂
***
I’m appreciatively linking up with Weird Unsocialised Homeschoolers’ Weekly Wrap-Up and All Things Beautiful’s Science Sunday.
Close your eyes and imagine taking a long sip of your favourite soda. How does it taste? Now imagine drinking a different type of soda – Sprite, or Pepsi, maybe. What taste do the different fizzy drinks have in common? Are they salty? Acidic? Something else?
In this fun Science Buddies lab we discovered how sodas get their fizz, then we experimented to find our personal favourite soda recipes.
1. Mix 1/16 tsp baking soda with 1/4 tsp citric acid in an empty cup.
2. Add 1/4 cup of cold water and quickly stir, then taste. (You’ll probably want to have somewhere to spit out, too, especially for the first few mixtures.) Observe the reaction between the chemicals in the water, and start your timer for 1 minute.
Adding water to our fizz powder
3. Discuss (and, if you wish, record) your observations. How bubbly is the mixture, on a scale of 1-5? How ‘gritty’ is it?
4. Observe and taste again after 1 minute. Has the taste changed? Is the drink more or less bubbly? Discard any remaining liquid.
5. Repeat in a clean cup, increasing the amount of baking soda to 1/8 tsp. (The amount of citric acid stays the same throughout.) Repeat again using 1/4, then 1/2 and finally 1 tsp of baking soda.
6. Make a note of the formula that tasted best. Did everyone like the same?
7. Experiment by adding different amounts of sweetener to your preferred base recipe, beginning with 1/4, 1/2 then 1 tsp.
Nothing happens when you add the two white powders (citric acid and baking soda) together. But when you add water, bubbles are produced. More bubbles are produced when you increase the proportion of baking soda, and the reaction lasts longer.
How does it taste?
Depending on the amounts of baking soda used, our drinks ranged from fairly disgusting to reasonably palatable. J(10) hated every single unsweetened beverage, confirming our suspicion that he has only persuaded himself to endure fizzy drinks because of their ton of added sugar.
Fizzy drink flavourings (if your’e feeling brave)
We also tried adding a few flavourings. J(10) had run away to clean his teeth by this point, but C(11) was keen to try chocolate flavour soda. I suspected that if that combination worked we’d already know about it. I was right.
Vanilla soda wasn’t much better, but lemon juice worked nicely (of course, adding lemon juice also increases the ratio of citric acid to baking soda). Finally, we taste-tested our fizzy drinks against shop-bought lemonade, and decided our formula stood up pretty well against Schweppes.
Making fizzy drinks is a great demonstration how an acid and a carbonate react in the presence of water to form carbon dioxide, a salt and water.
Citric acid + Bicarbonate of soda ——> Sodium citrate (a salt)+ Carbon dioxide + Water
If you want to talk ions:acids ionise in water. This means they lose electrons, producing positively charged hydrogen ions. Meanwhile, a carbonate is a mild alkali. Alkalis in water generate negative ions, which combine with the positive ions from the acid in a neutralisation reaction.
You can also make a batch of ‘fizz powder’ by mixing citric acid, baking soda and icing (powdered) sugar. This time the reaction happens on your tongue!
We followed Science on the Shelves’ recipe. Mix 6 tsp citric acid, 3 tbsp bicarbonate of soda and 2 tbsp icing sugar, then crush with a spoon to make a fine powder.
My husband and I found the fizz powder charmingly reminiscent of the sherbet dib-dabs we’d buy with our pocket money as children, but – as you can see from the photo – our kids weren’t convinced.
Taste testing our fizz powder
More fizzy drink science
Try testing the acidity of your home-made sodas with indicator paper or a home-made indicator.
Remind your kids not to drink too many sodas by showing them the effect on their teeth – see Ticia’s What soda does to teeth.
We don’t have fizzy drinks at home but when we were in Spain C(11) and I sometimes treated ourselves to a coke at the beach cafe. J(10) has never liked anything fizzy, but while we were away he decided to overcome his aversion. The 1-minute video below shows how that turned out.
This lab appealed to us because we had been speculating, in the light of J(10)’s distaste for all fizzy drinks, what they must all contain, apart from bubbles. And I thought it would be fun to watch J(10)’s face as he taste-tested the various recipes {mwah ha ha}.
Look out for J(10)’s taste-bud theory about why C(11) and I can drink fizzy drinks, and his verdict on alcohol, which I shall be reminding him of on his 18th birthday. 😉
I’m appreciatively linking up here:
Science Sunday at All Things Beautiful
Weekly Wrap-Up at Weird Unsocialized Homeschoolers
Squishy circuits combine two of my kids’ favourite hands-on activities: play dough and electric circuits.
You can either just use conductive play dough in your circuits. Or, to extend the learning, you could mix up a batch of insulating play dough that doesn’t conduct electricity.
What you need
Conductive play dough ingredients
* Flour – 1 cup
* Salt – 1/4 cup
* Vegetable oil – 1 tbsp
* Water – 1 cup
* Cream of tartar (3 tbsp) or lemon juice (9 tbsp)
* Food colouring (optional)
Mix all the ingredients together in a pan on the stove over a medium heat, then knead to form a dough.
For more detailed instructions and other useful tips, head over to StiMotherhood.
Insulating play dough ingredients
* Flour – 1 cup
* Vegetable oil – 3 tbsp
* Sugar – 1/2 cup
* Food colouring (optional)
* De-ionised or distilled water – 1/2 cup
Mix all the insulating play dough ingredients together in a bowl, then knead. Warning – this batch will be stickier than the conductive play dough.
Apparently de-ionised water is used to prevent limescale in cars and irons. (Confession: I ordered it from Amazon and then got impatient and bought some at my local car supplies shop. Any suggestions about what to do with 5 litres of de-ionised water? ‘Do more ironing’ is not the kind of thing I mean.)
To play with the dough, you will also need a 9V battery and a battery holder with connecting wires, and some LED lights.
Before you play with your electric play dough
Before they play, show your kids what to expect and get them excited with this squishy circuits video.
The science of squishy circuits
Squishy circuits provide a perfect demonstration of how electricity takes the path of least resistance.
If an electric current has to travel through an LED bulb to complete a circuit, it will do so and light up the bulb.
But if the electricity can find an easier path (like through a piece of conductive dough), the bulb will remain unlit.
Circuit made of conductive playdough and LED bulbs
How to use the insulating play dough
Use insulating dough to bridge gaps between pieces of conductive dough.
Electricity can’t travel through the insulating dough. Instead, it has to travel through – and light up – the LED bulbs.
Squishy circuits creationsLeft: Circuit made from conductive play dough (bulb unlit). Right: Circuit with both conductive and insulating play dough (bulb lights up because electricity can’t pass through the orange insulating dough so passes through the bulb instead)
Benefit from my mistakes
I have a habit of seeing a cool activity online then gathering supplies and diving in without referring back to the original instructions. Which is why we first tried to power our squishy circuits with a couple of AA batteries.
Underpowered circuits are a bit of a dampener on kids’ enthusiasm.
Luckily J(9) and C(11) were happy to switch to regular play dough and reconvene with the conductive sort on another day, once I’d bought some 9V batteries.
AA batteries are probably fine if you have enough of them (and sufficient battery holders), but I’d recommend using 9V if you can.
Finally – do wipe down your metal wires after they’ve been in contact with the conductive play dough, so they don’t rust.
I first came across the idea of squishy circuits at StIMotherhood. Do head over there for tips on how to get the most out of squishy circuits play.
And see this great TED talk all about squishy circuits by the lady who invented them.
A note to my kind friends who are wondering what became of my next post about our Spanish adventure: This week someone with a huge Facebook following (I wish I knew who) shared my elephant’s toothpaste post, resulting in 70,000 extra visitors here.
Once I’d picked myself off the floor, I was inspired to get around to finishing this post on squishy circuits.
Scientists argued for two hundred years about whether light was a shower of tiny particles or a series of waves. Then just as the debate was settled, Einstein came along with an answer that would have set Newton’s head spinning.
We decided to explore the properties of waves and light for ourselves.
Simple wave tank with plasticine obstacles
What happens when waves meet an obstacle?
When waves meet an obstacle, they curve around it.
If light curved around an obstacle, we would expect the obstacle to cast a fuzzy shadow. But anyone who’s played shadow puppets knows that shadows can have fairly sharp edges.
When light meets obstacles, sharp shadow are created
Because of this, sixteenth century scientist Isaac Newton believed that light must be made of millions of tiny particles moving in straight paths.
Diffraction
What happens when waves pass through a small opening?
The waves spread out as they pass through, as if the opening was the source of the waves.
Seventeenth century scientist Christian Huygens pointed out that light also spreads out through an opening. If you were to put a lamp behind a wall with a small hole in it, light coming through the hole wouldn’t stay in the shape of the hole – it would spread out.
Huygens said that because light diffracts, it must be made of waves. He pointed out two other properties of light that supported his theory.
Refraction
Light appears to bend
A pencil placed in a glass of water appears to bend at the water’s surface. This is because light travels more slowly through water than it does through air.
Huygens said that if light waves travel at different speeds through different materials, the change in speed would cause the waves to bend. We call this apparent bending refraction.
We performed a cool trick to demonstrate refraction. {1 minute video below} I should have made it clear in the video that the camera stayed still throughout the demonstration!
Interference
When two sets of waves cross each other, they interact in an interesting way. In some places they cancel each other out, while in other places they add to each other and create a stronger wave. This phenomenon is called interference.
We created two sets of waves in our wave tank. (We would have observed a larger interference pattern in a bigger tank.)
In 1801 Thomas Young proved that light also produces interference patterns.
You can observe light interference patterns by looking at a source of light between two pencils.
Observing light interference patterns
When the pencils are almost touching, you can see a vertical pattern of light and dark lines. The dark lines are where the light waves are cancelling each other out.
Thomas Young was the first person to calculate the size of light waves. His measurements explained why light diffraction is so difficult to see – light waves are so small that that can only bend around the tiniest of obstacles.
Light as both wave and particle?
By the 1800’s scientists were sure that light was made of waves. But in 1900 the particle theory reappeared!
Albert Einstein and Max Planck showed that light sometimes behaves like a wave, but sometimes acts like a particle. Their discoveries led to the branch of science known as quantum physics.
We read about Einstein and Planck’s fascinating discoveries last term in the Uncle Albert books.
Veritasium has a great demonstration of wave interference, and recreates the original double slit experiment which ‘proved’ (for a while!) that light was a wave:
We’ve all been told that water is made up of hydrogen and oxygen. But how do we really know that? Can this wet substance that quenches our thirst and cools our bodies on hot summer days really be made up of two gases?
We tried to separate water into oxygen and hydrogen using electrolysis. We managed it after a series of experiments that left us with even more questions than we had before we started. Which isn’t necessarily a bad thing – curiosity is a great learning state! (See the mysterious case of the missing oxygen, below.)
You can benefit from our mistakes and perform electrolysis the quick way. Here’s how to split water into hydrogen and oxygen using electrolysis. Afterwards I’ll tell you about what we did first, which produced a different gas entirely.
See this video for detailed set-up instructions – the elastic band arrangement keeps the test tubes in place perfectly.
If you can’t watch the video, here’s the gist of it: Connect one end of each crocodile clip to a piece of graphite, and the other to the battery. Secure the graphite ends to the bottom of the tub with the graphite sticking up, and place an inverted test tube over each piece of graphite (held in place by the elastic bands). Dissolve the bicarb of soda in the water and fill the tub. Finally, remove each test tube, fill it with the water, and carefully replace it over the graphite. Any gases collected during the electrolysis will replace the water in the tubes, so make sure there are no air bubbles.
What happens
Bubbles of gas quickly start to form at each electrode. More gas collects at the negative electrode (cathode) than at the positive (anode).
How to test your gases
When you’ve collected plenty of gas at each electrode, carefully put the lids on your test tubes (while they’re still underwater).
To test for hydrogen
We hypothesised that the gas at our (negative) cathode was (positively charged) hydrogen. Hydrogen is explosive. It won’t wreck your house in these quantities, but it will make a cool popping noise in the presence of a lighted splinter of wood. You can hear it in the video below.
To test for oxygen
We test for oxygen with a glowing splint. If enough oxygen is present, the splint rekindles. The gas we collected at our anode gave a brief glow which confirmed it to be oxygen, but after the excitement of the popping hydrogen, we were a bit disappointed. We produced much more oxygen later using a different method – see below for a video of our relighting splint.
How does electrolysis work?
Water is a covalent molecule (H20) held together by shared electrons in covalent bonds.
During electrolysis, the molecules are reduced at the cathode to to hydrogen gas, and oxidised at the anode to oxygen gas.
Pure water doesn’t conduct electricity, so we need to add an electrolyte, like bicarbonate of soda. (You wouldn’t believe the number of websites that tell you to use salt. We tried it, and collected a completely different gas. More on that later.)
Twice as much hydrogen as oxygen is produced, reflecting the molecular composition of water.
If you’re looking for a more detailed explanation, see Wikipedia.
{Thank you so much, Sarah, for pointing out my earlier misunderstanding and for making this post more accurate!}
The mysterious case of the missing oxygen
(Or, what happens when you use salt as an electrolyte.)
Before we successfully split water into hydrogen and oxygen using the method above, we tried adding salt to help our water conduct electricity. And not just a pinch of salt. I decided that if a little salt would help a bit, then a lot of salt would be even better. (It works for crystals, after all.)
We set up our electrolysis using the same apparatus as above but this time with a saturated salt solution. And there we sat, eagerly looking for our bubbles of hydrogen and oxygen.
What happened? Well, plenty at our cathode. Gas quickly began to fill the test tube. We tested it and discovered it was hydrogen. And at the positive electrode? Not one single bubble of gas! What had happened to the oxygen from our water molecules?
I did a bit of research overnight.
It seems that during the electrolysis of sodium chloride (salt) solution, sodium chloride breaks down at the positive electrode to form chlorine gas and sodium hydroxide solution. (Click the link for a more detailed explanation.) Chlorine dissolves easily in water, so won’t collect as a gas until the solution is saturated and can absorb no more chlorine.
So if our positive electrode was busy attracting chlorine, and hydrogen was collecting at the cathode … what had happened to the oxygen? Or to the sodium from our sodium chloride (NaCl), for that matter? According to the chemists, the sodium and oxygen combine to make sodium hydroxide solution. Further investigation was called for.
We’d left our apparatus set up – disconnected from the battery – overnight. We decided to examine it for clues.
Further investigations
What changes had taken place as a result of electrolysis?
Our salt solution had turned a brownish colour. Was this dissolved chlorine? Broken down graphite? Corroded crocodile clip (which had been attached to the anode)?
Changes as a result of electrolysis
Filtering the solution.
Some of our positive electrode (anode) broke down, leaving black bits in the solution. We use graphite in electrolysis because it is an inert (non-reactive) metal, but perhaps the large amounts of chlorine we produced had caused it to react? We filtered the brown solution to see if any insoluble bits remained. They didn’t. But we did notice some white spots on the filter paper – the chlorine produced at our positive electrode must have bleached the paper!
Bleached filter paperAfter electrolysis our solution was slightly acidic
Testing the pH of the solution
We hypothesised that the solution would be slightly alkali due to the sodium hydroxide. But when we tested it, we found the opposite. It was slightly acidic – like chlorine. We guessed this meant the solution must contain more chlorine than hydroxide.
More fun with oxygen
I’m going slightly off topic here, but I promised to say how we created enough oxygen to successfully test for it. We got the idea from going to The Magic of Oxygen show at the Royal Institution. I’d love to share with you one of the demonstrations we saw there.
The presenters asked me if they could borrow a £10 note from me – and then they set fire to it! Here’s a video of my flaming money.
Not long afterwards the scientists returned my £10 note – completely undamaged. The trick was the scientists first soaked the money in alcohol. The alcohol burning in oxygen produces heat, light, carbon dioxide and water. The temperature the alcohol burns at is too low to evaporate the water, so the water protects the note from burning.
Unharmed £10 note
The Magic of Oxygen scientists also demonstrated how to make “elephant toothpaste” by breaking down hydrogen peroxide. We remembered how we once made our own elephant toothpaste. When we got home we decided to make elephant toothpaste again, and use a glowing splint to test for oxygen gas.
Making elephant toothpaste
When you place a glowing splint into oxygen, the splint re-lights.
Why this is my favourite way to do homeschool science
As you can tell, this was not the the kind of homeschool science demonstration where mum knows exactly what’s going to happen and why. I studied chemistry until I was sixteen – nearly thirty years ago! I didn’t know the answers to many of the questions generated by these experiments.
But not knowing what would happen made me curious and inspired to learn more, and the children were definitely caught up in my excitement. And I’m glad we made the “mistake” of using salt as an electrolyte first, because if we hadn’t we would have missed out on some very cool science!
Have you done any fun science recently?
Have you ever investigated a case of missing oxygen?
Did you know that scientists didn’t used to believe in oxygen? Oxygen in the air helps things to burn. But chemists used to think that anything that could be burned contained a mysterious element called phlogiston.
The element that weighed less than zero
Scientists thought that the red hot glow of a burning metal was evidence of phlogiston escaping. They even decided that, because metal weighs more after burning, phlogiston must weigh less than zero! (We now know that the extra weight comes from oxide that forms on metal when it’s heated.)
More phlogiston nonsense
Joseph Priestly (1733-1804) was the first scientist to trap oxygen – but he didn’t realise what he’d done. The phlogisticians thought that when they placed a burning candle under a glass, it gave off phlogiston until the air in the glass was completely saturated with phlogiston.
So when a candle burned even more brightly in the “air” Priestly collected, he reasoned that the air must not contain any phlogiston at all. He called his oxygen sample “dephlogisticated air”!
“The air Priestly thought was full of phlogiston was actually emptied of oxygen. The air he thought was entirely emptied of phlogiston, was actually full of oxygen.”
Goodbye phlogiston, hello oxygen
It was French scientist Antoine Lavoisier (1743-1794) who finally sorted things out and put phlogiston in its rightful place (the history books). How did he do it?
Lavoisier wanted to find out what really happened when a metal was heated. Was something removed from the metal and released into the air (as the phlogisticians believed), or was the reverse true – was something removed from the air and drawn into the metal?
He had the genius idea of measuring the volume of gas in his apparatus before and after the metal was heated. The result? Lavoisier found that when he heated metal, the volume of air around it decreased. Some of the air had combined with the metal!
Next, Lavoisier heated the specks that had formed on the metal and measured how much gas they gave off. Of course, it was the exact same amount as had left the air and gone into the metal previously.
Lavoisier had proved that neither phlogiston nor dephlogisticated air were real. He renamed dephlogisticated air, “oxygen”.
Even before Lavoisier’s breakthrough, scientists had begun to figure out that water was a combination of two separate things.
Henry Cavendish (1731-1810) had found that two parts of what he called”inflammable air” [hydrogen] combined with one part of “dephlogisticated air” [oxygen] made water.
But Cavendish’s inability to see beyond phlogiston got him in a bit of a pickle.
“He thought that inflammable air (hydrogen) was actually water plus phlogiston, and that dephlogisticated air (oxygen) was actually water minus phlogiston. What happens when you add water-plus-phlogiston to water-minus-phlogiston? The plus and minus phlogistons ‘cancel’ each other out, and you are left with only water!”
Thankfully Lavoisier – debunker of phlogiston – was able to put things in order. He made water by sparking oxygen with some of Cavendish’s “inflammable air”.
Now that he had proved that phlogiston didn’t exist, Lavoisier realised that inflammable air must also be an element itself. He named this gas, “hydrogen” (Greek, for water-generator).
Atomic Pancakes
The French rewarded Lavoisier for his services to science by chopping off his head. (They were a bit guillotine-crazy back then.) We decided to honour the great scientist by making atomic pancakes.
You need
Pancake batter
White chocolate chip “protons”
Dark chocolate chips “neutrons”
Small sweets e.g. M&Ms (all the same colour) – “electrons”
Chocolate sauce (and a toothpick for spreading it into “orbits”)
(We actually used red and green grapes as protons and neutrons, but we struggled to fit them all into the nucleus of our oxygen atom.)
Proton and neutron grapes, and white chocolate chip electrons
Each hydrogen atom has one proton at its centre, and one electron orbiting the nucleus.
Then we made one big pancake for our oxygen atom.
Oxygen atom
Oxygen has 8 protons and 8 neutrons in its nucleus.
Oxygen also has 8 electrons – one pair in its first orbit, and 2 more pairs in its second orbit. The second orbit also contains 2 single electrons.
To make our water molecule, we put the 2 small pancakes beside the large pancake, lining up the 2 sets of unpaired electrons.
Water molecule
In reality, electrons are really far away from the protons and neutrons. If a proton were as big as a grape, you would need to walk an hour before you set down your electron!
Putting electrons into orbit
After eating up our atomic pancakes, we moved onto making the real thing. Come back soon to find out how we made oxygen and hydrogen out of water!
CSIRO – Australia’s national science agency’s website. I came across atomic pancakes via their (free) Science by Email program.
Chemistry, a Volatile History – Fascinating BBC documentary series with a whole episode on the phlogiston blind-alley. We saw it a few years ago and would love to see it again. YouTube has clips. Please let me know if you find the whole thing available somewhere!
If you blow out a candle and then put a lighted match close to the wick (but not touching it), the wick will re-light. Most of us intuitively know this, but have you ever wondered why?
This week we did two simple experiments investigating the science of how candles burn. Both come from a free online Kitchen Chemistry course we’re enjoying.
Experiment 1 – Lighting gaseous wax
What you need
Candle
Match or lighter
What you do
Light the candle. Notice how you have to hold the match very close to the wick for a second or two before it ignites. Allow the candle to burn for a few minutes. As it burns, observe what happens to the wax.
Now blow out the candle and quickly hold a lighted match near the wick. This time the wick should easily ignite, even without the flame actually touching it.
Repeat the process a few times, experimenting with how far away from the wick you hold the match.
Lighting a candle by holding a flame near the wick
What’s happening?
When you light the candle, the solid wax melts and liquid wax is drawn up the wick. As the candle gets hotter, the liquid wax evaporates into a gas. This gaseous wax burns in the oxygen of the air.
The gaseous wax remains in the air after you blow out the candle. If you hold a lighted match near the hot wick, the wax ignites and the flame spreads to the wick. If you allow the candle to burn for long enough that it produces a visible white vapour when you blow it out, you can light the vapour from above.
Experiment 2 – Soot on a spoon
What you need
Lighted candle
Metal spoon
What you do
Briefly hold the spoon in the candle flame. Remove it and observe what you see on the spoon.
You should see black soot. You may also see a tiny bit of wax. (Don’t worry, it all washes off.)
Holding a metal spoon in a candle flame
What’s happening?
As the candle burns, solid wax becomes liquid and then evaporates to become a gas. The gaseous wax burns in oxygen to produce water, carbon dioxide, heat and light.
The burning candle also produces carbon, in the form of the black soot we see on the spoon. It is glowing soot that causes the candle give out light.
If there were enough oxygen to burn all the wax, only carbon dioxide and water would be produced and the flame would be blue, like in a gas burner.
The small amount of wax on the spoon is the unburnt gaseous wax which has condensed on the cold spoon and turned back into solid wax.
Golden gas and solid methane
These experiments are an interesting way to explore states of matter. My kids were surprised to discover that every element can exist as a solid, liquid and a gas.
C(10) wondered if gold can be a gas. The answer is yes – gold boils and evaporates at 2,800°C. And solid gold becomes a liquid at just over 1000°C.
Meanwhile J(9) wanted to know if gaseous bodily emissions can take solid form (and if so could we google photos). He phrased it differently, as you can imagine. This led us to the fascinating topic of solid methane, a source of fuel which exists in very cold conditions at the bottom of the ocean and at the poles.
Frozen methane bubbles: U.S. Geological Survey
Trick re-lighting candles
We also wondered how trick birthday candles work – the ones that re-light by themselves after you blow them out.
The “magic” ingredient is usually magnesium in the candle’s wick. When the candle is burning, the magnesium is shielded by the liquid wax being drawn up the wick. But after the candle has been extinguished, the wick is no longer hot enough to draw up the liquid wax. The magnesium is exposed to the wick, which is hot enough to ignite the magnesium The burning magnesium in turn ignites the gaseous wax. This article explains the process very clearly.
Apparently you can see tiny flecks of magnesium going off around the glowing ember of re-lighting candles. I’ve ordered some so we can observe this for ourselves.
Further Resources
Scientist Michael Faraday gave a series of children’s lectures about the chemistry of candles at the Royal Institution, London in 1860. You can read an abridged version here.
The Mystery of the Periodic Table is a wonderful living book about the history of chemistry. This week we read about the discovery of oxygen, which was the perfect background to our experiments.
Kitchen Chemistry Free online course from the University of East Anglia. (Runs until 26 May 2014.)
“What makes aeroplanes fly?” asked C(10) a few weeks ago. We’ve had fun finding out.
An aircraft flying in steady forward motion is subject to four forces: thrust, drag, lift and weight. Aviation for Kids: A Mini Course For Students in Grades 2-5 (free online) contains dozens of ideas for experimenting with these forces.
Thrust
Thrust is the force that moves a plane forward through the air. To investigate thrust, we made three different “aircraft”, each powered by a different thrust mechanism.
1. Elastic band thrust
First, we made elastic band-powered planes. We experimented with thrust by observing the distance our planes flew when we changed how far we pulled our elastic bands before we released them. {Instructions are on p3 of Aviation for Kids.}
Rubber-band powered planes
In real aircraft, of course, thrust is created by a jet engine or propeller.
2. Air pressure thrust (blowing through a straw)
Air pressure-powered planes
Our second aircraft was powered by blowing through straws, one inside the other. {For instructions see p7 of Aviation for Kids.}
We experimented with placing the wings at different points along the straw and observing the effect on our aeroplanes’ flight.
C(10) suggested a competition to knock down unifix cubes with the planes. It was more difficult than she’d expected!
3. High air pressure thrust (balloon power)
We made a balloon-powered rocket when we learned about space travel last year. The kids were delighted to recreate it as part of our investigation into thrust and drag. {See p 10 of Aviation for Kids for instructions.}
Balloon-powered plane
Newton’s third law states that for every action, there is an equal and opposite reaction – as the balloon deflates, it whizzes along the wire. It’s very cool!
Drag
Next, we investigated drag – the air resistance that slows an aircraft as it moves forward. If drag is greater than thrust, the aircraft cannot move forward.
To see the effects of drag, we attached a foam plate to the front of our balloon aircraft.
Investigating the force of drag
When it was subject to the increased drag of the plate, the balloon only managed to travel halfway across the room before it ran out of air.
Apparently it was hilarious to lie underneath the wire as the balloon zoomed to a halt.
“It’s coming at us!!”
Lift
The other pair of forces that operate on an aircraft are lift and weight. Lift is provided by the airfoil shape of an aircraft’s wings.
Whatever role it plays in helping planes fly, Bernoulli’s principle is fun to demonstrate, partly because it’s counter-intuitive. We demonstrated Bernoulli’s principle in two ways.
First we placed a sheet of paper between two books. We blew through the gap.
Investigating Bernoulli’s principle
The children had predicted that the paper would lift up as they blew underneath it. Instead, the paper sagged down. Bernoulli’s principle says that within a stream of fluid (such as air), pressure goes down as speed of flow goes up. So when we blew, the air pressure under the paper decreased and atmospheric pressure from above pushed the paper down.
Demonstrating Bernoulli’s principle with a hairdryer and ping pong balls
When the hairdryer blows fast-moving air between the ping pong balls, air pressure between the balls decreases. Atmospheric pressure outside the balls pushes them together. (This doesn’t happen when you aim directly at the ping pong balls, but J(8) had fun doing it anyway.)
How do wings produce lift?
Lift is created by the curved shape of an aeroplane’s wing. This “airfoil” shape causes air to move faster over the top of the wing than the bottom. When lift is greater than the weight of the plane, the plane will move upwards.
We made paper airfoils and attached them to thread (see p25 of Aviation for Kids).
Airfoil shape
When we ran with our airfoils, they moved up the thread.
The airfoil also lifts when you spin around very quickly. This one was repeated many times!
(Aviation for Kids also suggests pointing a hairdryer at the airfoil. We did this but found it difficult not to blow the paper wing directly up or down.)
Then we increased the plane’s weight by attaching paperclips. It was easy to see that the extra weight reduced the plane’s lift. One paperclip actually had a stabilising effect, making the plane easier to direct. Two or three clips seriously impacted our planes’ ability to stay in the air.
Investigating the force of weight
What next?
C(10) has been making notebook pages about the science of flying. She’s come up with lots more questions as she’s been writing!
C(10)’s notebook pages
Our science this month is going to focus around the exciting engineering box we’ve just received on loan from the James Dyson Foundation, but we’ll definitely be continuing with the science of flying after that.
Insulating play dough ingredients
AA batteries are probably fine if you have enough of them (and sufficient battery holders), but I’d recommend using 9V if you can.
