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.

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:

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

Answers next time.

 

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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 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:

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.

Lithium

Sodium

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.

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.

 

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.

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?

 

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.

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.

 

Crystal gardens

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

Like a mysterious undersea world

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

Worms! Tube worms!

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

Aliens in the grass

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

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.

Eerie glow

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

What kind of a pumpkin is that?

A fun experiment around Halloween.

Hot pumpkin head?

This plastic tastes like cheese

Casein is the main protein in cows milk. It precipitates rapidly when vinegar is added to warm milk. The precipitated casein and other milk solids can be filtered, shaped and dried into a hard plastic like material frequently referred to as milk plastic.

Equipment & ingredients

Both full cream milk and low fat milk contain casein and give a good yield of product. The casein obtained from full cream milk gives a more pliable, less crumbly material, presumably due to the higher fat content. However, the solid also exudes more oily liquid during the drying stage.

We used the following recipe:
1. Heat 300ml milk to 65 C.
2. Add 20ml of white vinegar and stir.
3. Allow the precipitated casein to cool a little before filtering through a sieve.
4. Press the filtered solid between several layers of paper towel.
5. Mould the solid into the desired shape and dry in a low temperature oven or on a warm shelf near to a radiator.

Making milk plastic

Heat the milk to 65 C

Add vinegar and stir to precipitate out the casein and other milk solids.

Precipitating the casein

A closer look:

Lower the pH to precipitate the casein micelles

Cottage cheese anyone?

How do we get the cheese out?

Filter it through a sieve

Separating the milk solids from the whey

Press out the excess fluid before drying

Press between layers of paper towel

What shape will you make?

Peace dove or bunny ears?

You can add food dye to colour the milk during the heating stage

This season it’s orange

The drying stage takes several days or even weeks, until a very hard plastic-like material is produced.

Drying time, days to weeks

Hey presto! Milk plastic.

Milk plastic or dried cheese?

It’s too hard to eat, but it may still go mouldy under the right conditions.

Movies for the precipitation, filtration and shaping are on You Tube.

More information on making milk plastic and cottage cheese.

Finally, on the chemical reaction in the baking powder submarine last time

The baking powder used in the toy submarine last time contained two active ingredients, disodium diphosphate and sodium bicarbonate. These two chemicals react to produce carbon dioxide which was released as bubbles that caused the submarine to rise.

Na₂H₂P₂O₇ + 2NaHCO₃ → Na₄P₂O₇ + 2H₂O + 2CO₂

The slow release of carbon dioxide is what allows the submarine to rise and dive

This reaction tends to release carbon dioxide at a slower rate than the sodium bicarbonate reacting with an acid like vinegar.

Voyage to the bottom of the water trough

Baking powder submarines are great fun.

All you need is a submarine, baking powder and water

The baking powder provides the chemical reactants needed to produce the gas which raises the sub.

What are the key chemical reactants listed here?

At the surface the sub takes on water and sinks to the bottom of the water trough. A chemical reaction takes place producing gas inside the sub which causes it to rise back to the surface. The gas is emitted from the sub and the cycle repeats, diving and rising.

Diving and rising

A video clip from which the above animation was constructed can be viewed here.

Questions

1. What is the chemical reaction that takes place when the baking powder dissolves in water?

2. What is the gas produced that raises the sub?

Answers next time.