In the Foil Etching experiment we had copper burn a whole in the aluminium foil.
As you can see, aluminum Al is much more reactive than copper Cu, but nothing happens when aluminum foil comes into contact with the copper sulfate CuSO4 solution! How come? Unfortunately, it’s all a bit more complicated than it first looks. Being quite an active metal, aluminum Al reacts with oxygen O2 in the air, forming a very strong film of aluminum oxide Al2O3 on its surface . This film protects the metal from reacting any further.
When you add some sodium chloride NaCl, a vigorous reaction starts as Cl– ions are able to compromise the otherwise-strong Al2O3 shield. Once Cu2+ is face-to-face with the aluminum Al itself and not its Al2O3 shield, the reaction can proceed, and quite spectacularly!
In the next experiment, we obtained a magnetic substance from two non-magnetic ones, magnesium Mg and iron sulfate FeSO4, via a simple chemical reaction! The Fe2+ from the FeSO4 solution turned into metallic iron Fe on the surface of the magnesium particles, so we ended up with magnesium shavings covered with a thin layer of iron! The picture below shows how the magnesium shavings actually hold a heavy neodymium magnet in the air!
And lastly, we did what MEL Chemistry calls a “Metal Contest”, because here too, three metals (zink, copper and tin) were competing in reactivity. “If you arrange metals from more active to less active, you’ll see that zinc Zn is a more adventurous fellow than tin Sn and copper Cu. That’s why, when you put a zinc rod into a solution containing, say, copper ions Cu2+, the latter are happy to settle inside the comfortable cloud of electrons, forming metallic copper Cu on the surface of the rod. Zn ions Zn2+, in turn, go swimming in the solution. The reaction with the tin chloride SnCl2 solution is essentially the same”, MEL Science website explains.
We did two more experiments a couple days ago: Liquid Wires (creating a simple circuit using graphite and liquid glass, a sodium silicate solution) and making our own Zinc-Carbon Battery, a chemical source of electric current that relies on an oxidation-reduction (redox) reaction between manganese dioxide (MnO2) and zinc (Zn).
A redox reaction involves the transfer of electrons from one element (the reducer) to another element (the oxidizer).
Our battery is divided into two sections, separated by wadding: one section holds the oxidizer MnO2 and the other contains the reductant Zn. When the crocodile clips are connected to a diode, the circuit is closed and the reaction can begin: electrons start migrating from the zinc section to the manganese section (manganese dioxide mixed with graphite o make it a better conductor). We used ammonium chloride NH4Cl as the electrolyte.
Simon has been dreaming to try creating the Steve Mould effect, or the chain fountain phenomenon, also known as the self-siphoning beads. It’s a counterintuitive physical phenomenon, almost a magic trick, that occurs when you place a chain of beads inside a beaker and pull on one end of the chain, allowing it to fall to the floor beneath. This establishes a self-sustaining flow of the chain of beads which rises up from the jar into an arch ascending into the air over and above the edge of the jar with a noticeable gap (the higher the distance between the floor and the beaker, the higher the arch), as if being sucked out of the jar by an invisible siphon.
According to the Wikipedia page about the chain fountain phenomenon, a ball chain (or anything with rigid links) produces the best results. Indeed, we had beautiful results with a 50m long nickel ball chain, but a 1m long pearl necklace also worked, even though the links it had weren’t that rigid (just knots of cotton thread)! Anything for science, I’m a young scientist’s mom.
Simon was delighted to learn that this phenomenon has actually been officially named after one of his favourite science presenters on YouTube, Steve Mould. Mould’s YouTube video, in which he demonstrated the phenomenon of self-siphoning beads and proposed an explanation, brought the problem to the attention of academics John Biggins and Mark Warner at Cambridge University! They published their findings in Proceedings of the Royal Society A.
So what’s the scientific explanation? According to Wikipedia, the chain fountain effect is driven by upward forces which originate inside the jar. The origin of the upward force is related to the stiffness of the chain links, and the bending restrictions of each chain joint. When a link of chain is pulled upward from the jar, it rotates like a stiff rod being picked up from one end. This rotation produces a downward force on the opposite end of the link, which in turn generates an upward reactive force. It is this upward reactive force that has been shown to drive the chain fountain phenomenon. A similar effect is observed when pouring viscous fluids from a beaker, Steve Mould pointed out.
We should warn anyone who’s about to buy ball chain, however, that it’s not only the joy of watching the chain fountains flow, but the tears of spending hours of untangling the wretched thing!
Simon has always wanted to experiment with torque-induced precession (gyroscopic precession), a phenomenon usually demonstrated with a heavy wheel one can hold perpendicular to the ground as long as it keeps spinning. While we still haven’t tried it with a wheel, Simon has unexpectedly observed the same phenomenon when rotating a paper cylinder with the help of a toy drill.
Simon was trying to get a cylindrical beaker to float in water (first in bath and then in a deeper bowl), by filling it with the optimal number of marbles. “Mom, look! The center of mass is lower than the center of buoyancy, so it floats!”
Simon also recreated this experiment as a simulation using the Algodoo software:
How does a periscope work? How does light travel through a periscope? How can you make a periscope yourself? Simon answers these questions in the video:
Also tried to trace the motion of light inside the periscope using a laser beam:
Our new MEL Chemistry box arrived, containing tons of color fun! We have already tried two experiments. In the Color changing milk experiment, the soap touches the milk creating a very thin film of soap on the milk’s surface and causing the colors to spread along with it, producing a mesmerising effect. Molecules of soap and other similar substances lower the surface tension of different liquids and thus are called surface-active agents (SAA). Simon took it a notch further and created antibubbles that glide on the film of soap:
We thought this one looked like a nuclear explosion:
The second experiment we did was called Magic Liquid and felt like performing a magic trick: a yellowish liquid poured in five different cups turned five different colors, almost all the colors of the rainbow! The secret was putting a tiny bit of a different chemical substance on the bottom of every cup beforehand. The yellowish stuff was actually Thymol blue, also known as thymolsulfonephthalein (chemical formula C27H30O5S ), a pH indicator, and changed color according the acidity of the substances that were already in the cups. The larger the quantity of protons H+, the higher the acidity of the medium, while the OH– ions are responsible for the basic medium:
Thymol blue molecule visible on the iPad screen:
We also checked the pH of the substances using indicator standard teststrips:
The pH rainbow:
Simon had already been busy with colors for a few days, revisiting his Magformers collection to build this gorgeous color wheel:
We later repeated the MEL Science demos for Simon and Neva precocious friend:
“It’s so mesmerising!” Simon explains what a standing wave is and the nodes in a wave, using a Slinky. Standing waves can be polarised in any direction (horizontally, vertically or diagonally) or they can be circularly/elliptically polarised or any combination of polarisation direction. A sea wave is normally just a regular wave, but it can become a standing wave if you introduce some kind of boundary.
Caution: this is not a dessert, but ping-pong balls dumped in honey. Yes, we had to shop for a lot of honey yesterday to let Simon do the trick. It’s about a bottle rolling down a slope and stopping on the way, and rolling again. The viscous honey makes the balls super slow, this us why the bottle has uneven/unstable weight on each side. We didn’t quite succeed. The bottle did stop, but did not quite resume its motion down the slope. On other occasions it did roll well, but didn’t stop. We also tried a different bottle and a longer slope (ironing board). Perhaps, the slope still wasn’t long enough or the balls needed even more space inside the bottle?
Inspired by a Veritasium video.