HoHgPbSSnEsS

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?

 

Advertisements

Lithium chloride

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:

P6270533_cut

Lithium chloride crystal

P6270535_cut

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.

2018_06_30_LiCl_stage_400_300

Lithium chloride crystals dissolving on the microscope slide (speeded up time lapse animation)

2018_06_30_dissolving_02_400_300

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:

OLYMPUS DIGITAL CAMERA

Left to right, three samples dissolving

Here is the apparatus we used to obtain the lithium chloride crystal pictures:

OLYMPUS DIGITAL CAMERA

Desiccator in a huge plastic bag on the right, microscope in the centre, computer screen image on the left.

OLYMPUS DIGITAL CAMERA

Inside the desiccator

OLYMPUS DIGITAL CAMERA

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:

pysharp_sup0

The pyramid

vlcsnpicola_02

The sting

vlcsnpicola_03

Twigs

vlcsnpicola_04

Another spike

vlcsnpicola_05

Can’t see the wood…

vlcsnpicola_06

You decide

How would you describe the shapes of these lithium chloride crystals?

 

 

Displacement activity

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.

000_p

Take 15cm of thin copper wire and about 25ml of bathroom cleaner containing 13% hydrochloric acid

001_p

Put the copper wire into the bathroom cleaner

002_p

Leave them to react – here is what it looked after 1 day

003_p2

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.

004_p

A vigorous exothermic reaction took place, with lots of bubbles of colourless gas produced

005_p

The gas produced during the reaction created a foam with the surfactants in the bathroom cleaner – seen here after about 2 minutes

006_p

It was all over after a few minutes with the base of the pie dish completely eaten away

007_p

Plenty of copper metal had been produced as predicted – seen here after washing with water

008_p

The morning after

009_p

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:

  1. copper metal + hydrochloric acid
  2. aluminium + copper (II) chloride solution
  3. aluminium + hydrochloric acid

Answers next time.

 

Microelectrolysis using a carbon fibre anode

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 DSCN0209

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.

Equipment close-up DSCN0210

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 DSCN0212

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.

DSCN0154CuSO4_Start

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.

DSCN0156_CuSO4

Copper sulfate after about 1 minute of electrolysis

2018_04_30_10_640_360_SnCl2

Tin (II) chloride

IMG_1541_SnCl2

Tin (II) chloride close-up

DSCN0139_AgNO3

Silver nitrate

DSCN0153_ZnSO4

Zinc sulfate

DSCN0162_PbNO3

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:

Silver nitrate

Copper (II) sulfate

Zinc sulfate

and Lead (II) nitrate

 

 

Alkali metals in water

Here are three animations comparing the reactivity of lithium, sodium and potassium in water. Use the images to support your observations in classroom.

2018_03_23_Li_H2O_01

Lithium

2018_03_23_Na_H2O_01

Sodium

2018_03_23_K_H2O_02

Potassium

Movie clips can be viewed  here:

Lithium

Sodium

Potassium

What is the order of reactivity of the three metals?

Alkene test

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.

IMG_1304_640

Two boiling tubes containing bromine water

Alkenes turn bromine water from orange to colourless.

2018_02_28_Br2_alkene_test2

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.

IMG_1306_640

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.

 

Distilling mouthwash

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.

IMG_0965

Distillation apparatus – can you name the key components?

IMG_0972

The boiling mouthwash mixture – foaming!

IMG_0975

What is the boiling point of the liquid distillate?

2018_01_31_second

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?

 

Electrolysis Art

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.

IMG_0829

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’.

IMG_0791

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.

IMG_0795

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.

 

Crystal gardens

Add various salts to sodium silicate solution and watch ’em grow.

IMG_0498

Like a mysterious undersea world


We found iron (III) chloride produced growths in the order of seconds.

2017_11_30_FeCl3_NaSiO3_600

Worms! Tube worms!


Iron (II) sulfate (on the left below) and copper (II) sulfate (right) also gave interesting forms.

OLYMPUS DIGITAL CAMERA

Aliens in the grass


And on the surface of the beaker grew a fused larva like crust.

IMG_0504

Can you walk on that?


Crystal gardens, great fun!

Pumpkin Face Reduction

Spooky Halloween Chemistry?

Copper (II) oxide is reduced to copper by heating with carbon.

2017_10_31_Halloween_CuO_C_pumpkin_face01

Eerie glow


The mouth and eyes were made from iron (III) oxide which was not reduced under the conditions used.
2017_10_31_Halloween_CuO_C_pumpkin_face02

What kind of a pumpkin is that?


A fun experiment around Halloween.
2017_10_31_Halloween_CuO_C_pumpkin_face06

Hot pumpkin head?