Here’s an example of a cross-curricular puzzle. Solve the puzzle, reveal the noun and perhaps use the descriptive details as a basis for further discussion.
The puzzle:
HoHgPbSSnEsS
Description:
Is pernicious and destructive.
It destroys lives.
So why does society condone its existence?
What is it?
Lithium chloride is hygroscopic and rapidly dissolves in the water it absorbs from the atmosphere. Thus, in order to obtain some crystals of lithium chloride we placed a concentrated solution of the salt in an evaporating basin in a desiccator. Solid lithium chloride crystals were formed and when we put samples of them under the microscope, this is what we saw:
Lithium chloride crystal
More lithium chloride crystals as seen under the microscope
We did not observe a cubic structure as we had seen for sodium chloride. In fact we had not seen crystals like this with any of the sodium and potassium halides we had crystallised. See our June 2014 post for images of NaCl, NaBr, NaI, KCl, KBr, KI crystals and some other common salts.
Getting good images of lithium chloride crystals under the microscope was problematic because they started dissolving on the microscope slide as soon as they were taken out of the desiccator.
Lithium chloride crystals dissolving on the microscope slide (speeded up time lapse animation)
This is what you see looking down the microscope (speeded up of course)
Here are three samples of lithium chloride on microscope slides at three different stages of dissolution, some time after we had viewed them under the microscope:
Left to right, three samples dissolving
Here is the apparatus we used to obtain the lithium chloride crystal pictures:
Desiccator in a huge plastic bag on the right, microscope in the centre, computer screen image on the left.
Inside the desiccator
Lithium chloride crystals
We are unsure of the formula of the lithium chloride crystals produced. Lithium chloride monohydrate LiCl.H2O has been reported, as have other hydrates. Or ours may be LiCl or a mixture of the various forms.
We took multiple photos of various samples of the lithium chloride crystals under the microscope and adjusted the focus slightly between shots of each sample. We then put these images into a focus stacking freeware program called Picolay, (which can be obtained here).
Here are our results:
The pyramid
The sting
Twigs
Another spike
Can’t see the wood…
You decide
How would you describe the shapes of these lithium chloride crystals?
I wanted to see if I could create a picture by reacting aluminium foil with a solution of copper (II) chloride made at home.
The idea was to scratch the surface of the aluminium foil with a stainless steel sewing needle, thus removing the surface oxide layer and exposing the metal underneath in an etched pattern. I hoped the exposed metal would then react preferentially in a displacement reaction when brought into contact with a solution of copper (II) chloride. I envisaged that copper would be deposited at the scratched areas, ‘painting’ a picture in copper so to speak, on the surface of the aluminium foil. However, things did not turn out quite as I had expected, as can be seen in the series of images below.
Take 15cm of thin copper wire and about 25ml of bathroom cleaner containing 13% hydrochloric acid
Put the copper wire into the bathroom cleaner
Leave them to react – here is what it looked after 1 day
After about 2 days the copper had dissolved producing an acidic solution of green copper (II) chloride on the right
At this stage I scratched a pattern into the bottom of an aluminium foil pie dish, as can be seen in the picture above on the left.
I wanted the aluminium to react with the copper (II) chloride producing copper and aluminium chloride. However, the copper (II) chloride solution was still very acidic and I should have predicted what happened next.
A vigorous exothermic reaction took place, with lots of bubbles of colourless gas produced
The gas produced during the reaction created a foam with the surfactants in the bathroom cleaner – seen here after about 2 minutes
It was all over after a few minutes with the base of the pie dish completely eaten away
Plenty of copper metal had been produced as predicted – seen here after washing with water
The morning after
No etched image, although I did get the copper back
At least three chemical reactions took place in the above displacement activity.
Write balanced chemical equations for these reactions:
Answers next time.
Electrolysis can be carried out on aqueous solutions of less than 1cm3 in volume. This reduces waste, reduces risk and can be achieved in minutes. All the experiments below used approximately 0.1M solutions, except for silver nitrate and tin (II) chloride which were about 0.05M.
Equipment for carrying out micro-electrolysis
The electrolysis is carried out in the well of a spotting tile using a pencil lead cathode and a carbon fibre anode.
Close-up of the spotting tile, pencil lead and carbon fibre
The carbon fibre is moistened at one end with distilled water and then wound into a simple loop.
Carbon fibre loop
The electrolyte, carbon fibre loop and pencil lead are set-up for electrolysis in one of the wells of the spotting tile.
Copper sulfate solution ready to be electrolysed
The electrodes are connected with standard laboratory crocodile clips and leads to a d.c. power pack. When the power pack is turned on ( 6 – 12v) results can be observed in seconds.
Copper sulfate after about 1 minute of electrolysis
Tin (II) chloride
Tin (II) chloride close-up
Silver nitrate
Zinc sulfate
Lead (II) nitrate
Thanks to Bob Worley of Microchemuk for inspiration and encouragement with the development of these experiments.
Movies of various micro-electrolysis experiments can be seen by clicking on the links below:
You can test if an organic compound is an alkene by mixing it with a little bromine water and shaking or stirring the mixture. Alkenes decolourise bromine water.
Two boiling tubes containing bromine water
Alkenes turn bromine water from orange to colourless.
Which tube gets the alkene?
Cyclohexane was added to one tube and cyclohexene to the other. It is easy to tell which of the two tubes received the alkene – only one of the two tubes turned colourless.
Which tube got the cyclohexene?
Alkenes undergo addition reactions with bromine. For example, ethene reacts with bromine to form 1,2-dibromoethane and this may appear in IGCSE Chemistry exam questions.
Alkenes like ethene and cyclohexene contain a double bond and it is the double bond that reacts with the bromine. At Advanced Level we learn about the electrophilic addition reaction mechanism for the reaction of bromine with alkenes.
Last time there were some questions on the distillation of mouthwash experiment. Here are the answers to those questions:
1a Boiling occurs in the round bottomed flask. Ethanol molecules left the surface of the liquid mixture and became ethanol gas (or vapour).
1b The ethanol vapour passed down the Leibig condenser and turned back into a liquid on cooling. The gas molecules condensed into a liquid.
2 The distillate was ethanol.
3 The distillate was not pure but contained other volatile molecules from the mouthwash. You could tell this by smelling the distillate.
4 One might separate the volatile molecules from the ethanol in the distillate by carrying out fractional distillation.
A mouthwash that consists of an alcohol/water mixture can be distilled quite easily. One should be careful to heat gently when doing so as the mixture has a tendency to foam and may ‘boil over’ if heated too rapidly. A clear colourless liquid can be obtained as the major distillation product, as outlined below.
Distillation apparatus – can you name the key components?
The boiling mouthwash mixture – foaming!
What is the boiling point of the liquid distillate?
Distillation of mouthwash – I hope this doesn’t make you nauseous!
Here is a link to the movie on You Tube
Questions
1. Describe what is happening in each of the key stages of the distillation process?
2. Name the distillate
3. Is the distillate pure? Or are there other minor volatile components in the mouthwash that are distilled over with the main product? How can you tell?
4. How might one separate all the volatile components in mouthwash more efficiently by modifying the distillation apparatus?
Crush a few blueberry skins in water and a dilute solution of the skin colouring material is produced. The coloured pigments in the blueberry skin are called anthocyanins and they make a good acid/base indicator.
Alkali on the left, distilled water in the middle and acid on the right
The blueberry skins can also be smeared over filter paper producing a reddish/purple canvas on which to carry out ‘electrolysis art’.
Filter paper daubed with blueberry skin juice
First the filter paper is moistened with a few drops of brine (saturated sodium chloride solution) and placed on a thin sheet of aluminium foil.
Then using a 4.5v dc laboratory power pack the aluminium foil is connected to the positive terminal with an electrical lead and a crocodile clip.
A paper clip was held in a second crocodile clip and connected to the negative terminal of the power pack.
The supply was turned on and when the paper clip (cathode) was passed over the filter paper electrolysis of the brine took place producing bubbles of colourless gas and turning the blueberry juice blue, green and yellow.
We also experimented by adding drops of white vinegar to the filter paper and these areas turned pinky-red.
Blueberry juice electrolysis art
Can you explain the colours produced by the blueberry juice?
What other dark coloured fruits and vegetables have pigments in their skins that might be used to in the same way?
Safety advice
If you carry out an experiment such as the one described above beware of touching the filter paper with your fingers since sodium hydroxide is produced around the cathode during the electrolysis process.
Add various salts to sodium silicate solution and watch ’em grow.
Like a mysterious undersea world
Worms! Tube worms!
Aliens in the grass
Can you walk on that?
Spooky Halloween Chemistry?
Copper (II) oxide is reduced to copper by heating with carbon.
Eerie glow
What kind of a pumpkin is that?
Hot pumpkin head?
