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.

P5100938_cut.mov_000017684

Using a Fresnel lens to start a thermite reaction

P5100938_cut.mov_000023823

The power of the sun

2016_05_22_Thermite_Fresnel_480_270_10.gif

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

2016_05_11_Fresnel_thermite_480_270_15

Stand well back

P5110941cut.mov_000075775

and focus

OLYMPUS DIGITAL CAMERA

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).

OLYMPUS DIGITAL CAMERA

Silver heart

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

2016_04_20_heating_ice_water_2_30

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.

2016_04_22_BZ_blue_15

A Belousov-Zhabotinsky reaction

Captured using time-lapse mode

IMG_3930_320

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 Chemguide.co.uk 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.

IMG_3956_320

chromium (III) chloride solution

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

2016_04_30_blue_ruby

blue or ruby?

IMG_3961_320

Use a torch

IMG_3962_320

shine a light

IMG_3963_320

then you’ll see ruby delight

2016_04_22_MVI_3950_33percent2.gif

off on off

2016_04_30_on_off_300

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.

2016_03_19_aspartame_whiteboard

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).

IMG_3885

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.

IMG_3889

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

2016_03_20_aspartame_expt_02

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.

2016_03_20_aspartame_expt_01

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…

2016_02_28_ice_01_20s.gif

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:

01_2016_01_31_Listill

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

02_2016_01_31_Nastill

Sodium whoosh – only the middle one

03_2016_01_31_Kstill

Potassium whoosh

Next are three animated gifs of the experiments:

2016_01_31_Liwhoosh70

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

2016_01_31_Nawhoosh70

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

2016_01_31_Kwhoosh70

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.

2016_01_31_whoosh_brothers_75

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.

 

SAFETY

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.

Flatlines

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.

20151231200458

 

 

 

Magnesio

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.

OLYMPUS DIGITAL CAMERA

Magnesio

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.

OLYMPUS DIGITAL CAMERA

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

2015_11_21_Magnesio_02_20

close_up_000104437

Blue bubble ghost?

2015_11_21_Magnesio_03_202015_11_21_Magnesio_04_202015_11_21_Magnesio_05_20.gif

close_up_000112178

No, it’s Magnesio!

2015_11_21_Magnesio_06_202015_11_21_Magnesio_07_202015_11_21_Magnesio_08_20

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

OLYMPUS DIGITAL CAMERA

Luminol all used up, where’s Magnesio?

OLYMPUS DIGITAL CAMERA

There he is, in the sink!

OLYMPUS DIGITAL CAMERA

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.

 

 

Magnetic attraction

Nickel (II) salts, like nickel (II) sulfate, are classed as category 1 carcinogens and colbalt (II) salts, like cobalt (II) chloride, are category 2 carcinogens. As such, neither of these two kinds of salts are recommended for use in experiments at school.

Setting up

Setting up

What follows is a description of some displacement reactions which were carried out on a microscale in order to minimise the hazards like the ones mentioned above. The experiments involved adding magnesium ribbon to small volumes of aqueous solutions of some transition metal salts.

Small pieces of magnesium ribbon were dropped into approximately 1.5ml of each of the following solutions:

1M manganese (II) sulfate
0.5M iron (II) chloride
1M cobalt (II) chloride
1M nickel (II) sulfate
0.5M copper (II) sulfate
and
0.5M zinc sulfate.

After several minutes a small neodymium magnet was waved over the magnesium metal strips. The results are summarised in the gif animations below.

Microscale displacement reactions using magnesium

Microscale displacement reactions using magnesium

Zinc and copper

Zinc and copper

Manganese and iron

Manganese and iron

Nickel and cobalt

Nickel and cobalt

The animations were constructed from a movie of the reactions which can be viewed on You Tube here.

Which pieces of magnesium were attracted to the neodymium magnet and why?

All the colours of a tomato

Toxic cocktail - tomato juice with a splash of bromine water

Toxic cocktail – tomato juice with a splash of bromine water

Lycopene is the molecule responsible for much of the red colour of tomatoes.

The conjugated double bonds absorb certain wavelengths of light

The conjugated double bonds absorb certain wavelengths of light

When bromine water is added to tomato juice, various addition reactions occur, with bromine molecules reacting with some of the double bonds in the lycopene molecules.

The wavelengths of light absorbed by the brominated products probably depends on the number of conjugated double bonds remaining, i.e. not reacted with bromine. In any case, many different colours are seen ranging from yellow to green and blue.

Here’s an animation of one such experiment. First bromine water is added to tomato juice in a measuring cylinder and then the mixture is stirred with a glass rod.

Re-colourising tomato juice

Re-colourising tomato juice

Almost a rainbow!

The brominated tomato juice shows various colours.

The brominated tomato juice shows a variety of colours.

We also wanted tp see what happened when chlorine water and tincture of iodine were added to tomato juice.

Before adding the halogens

Before adding the halogens

After adding the halogens to tomato juice

After adding the halogens to tomato juice

In close-up

Chlorine water + tomato juice close-up

Chlorine water + tomato juice close-up

Bromine water + tomato juice close-up

Bromine water + tomato juice close-up

Tincture of iodine added to tomato juice close-up; outside in bright sunlight

Tincture of iodine added to tomato juice close-up; outside in bright sunlight

Unsurprisingly, the chlorine water bleached the tomato juice white, whilst the tincture of iodine produced some interesting, if quite dark, green and blue colours after some time.

In summary, some interesting colours were seen in the tomato juice, although these demonstration experiments must be carried out in a fume cupboard. They can lead onto a discussion of addition reactions in alkenes and a test for alkenes, such as ethene, by decolourising bromine water.