Li sizzles, Na balls & K-pot explodes

Comparing the reactions of lithium, sodium and potassium with water.


A lump of potassium explodes

The alkali metals all react speedily with water and with oxygen.

For this reason they are stored in oil to limit the oxygen and water in air getting to them in the chemical store.


Lumps of lithium, sodium and potassium metals in hexane prior to dropping them into water

Students at GCSE are often asked to compare the trend in reactivity of the metals on going down the group, by comparing the observations made as each one reacts with water.

To this end experiments are sometimes carried out, demonstrating the reactions of lithium, sodium and potassium with water.

All three metals float on water and react quickly with it producing hydrogen gas.


Potassium always catches fire producing a lilac coloured flame and explodes if too big a chunk is used.


“Li sizzles, Na balls and K-pot explodes lilac”

Equations for the reactions are:

2 Li   +   2H2O  –>  2LiOH   +   H2
2 Na   +   2H2O  –>  2NaOH   +   H2
2 K   +   2H2O  –>   2KOH   +   H2

Students are also often asked to predict how rubidium and caesium metals would react with water.

The answer is that they would both react producing similar products according to the equations above, but even more vigorously than potassium, with caesium being the most reactive.

Links to movies on You Tube from which the above gif animation was made are here:

1. Short version 39 seconds

2. Longer version 2 minutes and 3 seconds


Why has no one has ever dropped a lump of Francium into water and made a movie of it?



Fresnel Thermite

We carried out some experiments recently lighting a length of magnesium ribbon with a Fresnel lens. The Fresnel lens was used to focus light rays from the sun on the magnesium. The magnesium ribbon acted as a fuse to ignite a thermite reaction mixture in which it was embedded. The experiments went rather well providing a relatively safe and unhurried way of starting this energetic reaction.


Using a Fresnel lens to start a thermite reaction


The power of the sun


We used 20g of thermite mixture made from aluminium powder (5g) and iron (III) oxide (15g) which reacts according to the following equation:

Fe2O3 + 2 Al → 2 Fe + Al2O3


Stand well back


and focus


a sample of iron can be obtained once the mixture has cooled down

The experiments were carried out in the tropics and it would be interesting to see if the same method works in a more temperate clime.

Links to movies of the experiments on You Tube can be found here:

  1. Fresnel / Thermite 1
  2. Fresnel / Thermite 2



Blue ruby

This post contains a collection of animated gifs and other pictures from experiments we have been doing recently.

First a heart made by putting copper foil into silver nitrate solution (copper is more reactive than silver and displaces silver ions from solution).


Silver heart

Next, heating a beaker of ice to water and steam.


Ice water steam

Those are anti-bumping granules you can see at the bottom of the beaker in the boiling water.

Now for a rather pretty B/Z reaction we carried out recently.


A Belousov-Zhabotinsky reaction

Captured using time-lapse mode


99 pictures at 15 seconds interval

Finally, the curious case of the colour of chromium (III) ions in water. And hence the title of this post ‘Blue ruby’.

When asked “How do you make a blue heart red?”
“With a torch and chromium (III) ions”, I said

Jim Clark, writing on notes that “The simplest ion that chromium forms in solution is the hexaaquachromium(III) ion – [Cr(H2O)6]3+.” He also goes onto say that “The hexaaquachromium(III) ion is a “difficult to describe” violet-blue-grey colour.”

Our AQA A’ level Chemistry describes [Cr(H2O)6]3+ as being ruby in colour, but our solution of chromium (III) chloride definitely looks blue to me.


chromium (III) chloride solution

That is, until one looks at it under torchlight (tungsten filament bulb), then
indeed it does appear a ruby colour.


blue or ruby?


Use a torch


shine a light


then you’ll see ruby delight


off on off


has that boiling tube got a red eye?


Sweet TLC hydrolysis

Aspartame sweetener is a modified dipeptide. When aspartame is reacted with 6M hydrochloric acid the peptide bond should be hydrolysed (broken), producing aspartic acid and phenylalanine methyl ester. The methyl ester may also be hydrolysed, depending on the severity of the conditions.


Whiteboard of the aspartame hydrolysis by my friend and colleague Tony Pluck

We carried out a hydrolysis reaction by boiling aspartame sweetener (one individual sachet) with 10ml of 6M HCl in a boiling water bath for 30 minutes. The results were analysed using thin layer silica chromatography, (silica TLC).


Running a chromatogram (silica TLC plate)

Samples of aspartame sweetener were spotted before and after the hydrolysis, together with phenylalanine and aspartic acid standards.

The plate was run in a solvent system of butan-1-ol (12ml), glacial acetic acid (3ml) and distilled water (6ml) taken from the old Nuffield A’level Chemistry textbook .

After allowing the solvent to run up to within a few cm of the top of the plate it was removed from the beaker and dried using a hot hair dryer. The TLC plate was then sprayed with ninhydrin and heated in an oven at 110 C for approximately 10 minutes.


Samples left to right, phenylalanine, hydrolysis mixture, aspartic acid and aspartame sweetener.


Same as the above with labels on the plate

Another experiment was carried out, identical to the above except with a much shorter hydrolysis time (of about 3 minutes). This was to see if the whole experiment could be done in a 55 minute period of chemistry at school.


The same again with a much shorter hydrolysis time of a few minutes

We want to run further chromatograms spotting smaller samples, as both of the above plates suffered from streaking due to sample overloading.



Tropical freeze

Cool a bottle of water in the freezer compartment of a refrigerator and it is possible to supercool the water below its freezing point for a short period of time. If one removes the bottle and gives it a sharp bang on a hard surface the rapid formation of ice crystals ensues in what is popularly referred to as the ‘instant ice’ experiment. I’ve been trying to capture the instant ice freezing experiment on camera for several weeks now without much success.

One of the biggest problems of doing this experiment in the tropics is that as soon as the bottle is removed from the fridge condensation forms on the outside of the bottle. This prevents one seeing whats going on inside.

If you try this at home I can only repeat the advice given on several You Tube movies; use as many bottles as you can and keep monitoring them to arrive at just the right moment to take them out by trial and error. My 600ml bottle took somewhere between one and a half to two hours.

Tropical freeze…


Whoosh brothers

The whoosh bottle demonstration involves setting light to methanol vapour in a thick walled 20L water bottle. By adding a few drops of water into the methanol, salts such as LiCl, NaCl and KCl can be incorporated into the ignition mixture and add colour to the resulting flame.

Here are some images of the same.

First three pictures of the experiments:


Lithium whoosh – the bottle on the right did not ignite.


Sodium whoosh – only the middle one


Potassium whoosh

Next are three animated gifs of the experiments:


What colour do you see in the flame in the bottle? Is it the characteristic flame colour from Li, Na or K?


Tried for a triple whoosh, but only the middle one worked. Was it Li, Na or K?


Better colours with the lights out? It’s usually difficult to see the colour of the flame with this shy violet. Li, Na or K?

The whoosh brothers! A composite gif animation of all the above.


Whoosh brothers!

Try as I might I could not get more than one bottle to ignite at a time. Movies uploaded to You Tube soon.



Follow appropriate safety guidelines when igniting the bottles. Methanol vapour is toxic. Only use thick walled plastic bottles. Do not try more than one ignition per bottle. Wash each bottle by filling completely with cold water after each ‘burn’. Our laboratory was ventilated with the all the windows open after the each experiment for more than an hour.


Ice to steam or I can sing a heating curve.

Can you identify the songs?

Here are some karaoke lyrics to substitute in for songs on stages of the heating curve for ice to steam (temperature against time).

Stage 1 – Song 1

“Temp low, sweet ice a lot

All the vibrations are slow

Add heat, start warming up

Vibrations mean the ice is going to go”

Stage 1 – Song 2

“Ice picking up good vibrations

Heat giving it excitations” repeat

Stage 2 – Song 3

“At nought degree C, I want to break free

To break free from your bonds takes energy

Molecules, use heat to break free”

Stage 3 – Song 4

“All the molecules liquid now

All the molecules move around

Molecules keep on moving round all night long

Heat it up, heat it up, baby heat it up

na na na na na na na na 

Temperature going up, going up, water getting hot”

Stage 4 – Song 5

“I am boiling, I am boiling

Steam again, breaking free

I am boiling, no more bonding

Temperature constant, 100 degrees C”

Stage 5 – ???



Phase change flatlines

A New Year’s Eve Chemistry Karaoke challenge. Examine the picture below which shows a heating curve for ice through to steam. The challenge is to come up with karaoke lyrics to popular songs of your choice which fit the regions on the curve 1 to 5 describing the behaviour of the water molecules. Students often have difficulty in explaining why the temperature does not increase during the regions of the curve representing phase changes; solid ice to liquid water (2.) and liquid water to gaseous steam (4.). Thus, the added challenge is to explain the reasons for these ‘flatlines’ in your karaoke lyrics.






Magnesio is magnesium in Spanish. We cut out a small figure in magnesium metal and stuck a little manganese (IV) oxide to its arms and head using Superglue.



We then dropped the figure into a luminol reaction mixture set-up in a measuring cylinder containing layers of sucrose solutions as described in March 2015. It needed a little prodding with a glass rod to get it to submerge at first, but then started bobbing up and down as shown in the animated .gifs below.


The luminol reaction mixture is in the sucrose layer between 15 – 60 ml

The bottom layer of sucrose solution solution contained some 4M hydrochloric acid so that when the magnesium sank down that far, it reacted with the acid producing bubbles of hydrogen, causing it to float up again.

When the magnesium rose up into the topmost layer, which was 0.5M iron (III) chloride, it probably got coated with the dark green iron containing precipitate formed there, which may have helped it to sink again.

The middle of the measuring cylinder contained the luminol reaction mixture, (potassium hydroxide, luminol and 6% hydrogen peroxide solution).2015_11_21_magnesio_01_20



Blue bubble ghost?



No, it’s Magnesio!


Finally, when the luminol reaction was over, Magnesio was washed out into the sink.


Luminol all used up, where’s Magnesio?


There he is, in the sink!


Relaxing after a swim on a paper towel

Maybe you will be able to see a Magnesio adventure soon.

See the movie file on You Tube

The three metals attracted to the neodymium magnet last time were nickel, cobalt and iron.