How Disappearing Ink Works
When the ink is sprayed onto a porous material the water in the ink reacts with carbon dioxide in the air to form carbonic acid. The carbonic acid then reacts with the sodium hydroxide in a neutralization reaction to form sodium carbonate. Neutralizaton of the base causes a color change of the indicator and the stain disappears:
Carbon dioxide in the air reacts with water to form carbonic acid:
CO2 + H2O -> H2CO3
The neutralization reaction is sodium hydroxide + carbonic acid -> sodium carbonate + water:
2 Na(OH) + H2CO3 -> Na2CO3 + 2 H2O
Here's what you need in order to make your own blue or red disappearing ink:
· 0.10 g thymolphthalein for blue ink or phenolphthalein for red ink (1/3 of 1/8 tsp)
· 10 ml (2 tsp) ethyl alcohol (ethanol) [can substitute 14 ml or 3 tsp of ethyl rubbing alcohol]
· 90 ml water
· 20 drops of 3M sodium hydroxide solution or 10 drops 6M sodium hydroxide solution [make a 3 M sodium hydroxide solution by dissolving 12 g of sodium hydroxide NaOH (1 level tablespoon of lye) in 100 ml (1/2 cup) of water.]
Here's how to make your own disappearing ink:
- Dissolve the thymolphthalein (or phenolphthalein) in the ethyl alcohol.
- Stir in 90 ml of water (will produce a milky solution).
- Add sodium hydroxide solution dropwise until the solution turns a dark blue or red (might take slightly more or less than the number of drops stated in the Materials section).
- Test the ink by applying it to fabric (cotton tee-shirt material or a table cloth works well). Paper allows less interaction with air, so the color change reaction takes more time.
- In a few seconds, the 'stain' will disappear. The pH of the ink solution is 10-11, but after exposure to air will drop to 5-6. The damp spot will eventually dry. A white residue may be visible on dark fabrics. The residue will rinse out in the wash.
- If you brush over the spot with a cotton ball that has been dampened in ammonia the color will return. Similarly, the color will vanish more quickly if you apply a cotton ball dampened with vinegar or if you blow on the spot to improve air circulation.
- Leftover ink may be stored in a sealed container. All of the materials may be safely poured down the drain.
Disappearing Ink Safety
· Never spray disappearing ink into a person's face. Particularly avoid getting the solution in the eyes.
· Preparing/handling the sodium hydroxide (lye) solution requires adult supervision, as the base is caustic. In case of skin contact, immediately rinse well with water.
How to Make Liquid Magnets - Introduction
A liquid magnet or ferrofluid is a colloidal mixture of magnetic particles (~10 nm in diameter) in a liquid carrier. The carrier contains a surfactant, so that the particles won't clump together. Ferrofluids can be either water-based (the usual form for chemistry demonstrations) or organic-based (as in oils or fluorocarbons). A ferrofluid is about 5% magnetic solids, 10% surfactant, and 85% carrier, by volume. The ferrofluid described here uses magnetite for the magnetic particles, oleic acid as the surfactant, and kerosene as the carrier fluid to suspend the particles.
When no external magnetic field is present the fluid is not magnetic and the orientation of the magnetite particles is random. However, when an external magnetic field is applied, the magnetic moments of the particles align with the magnetic field lines. When the magnetic field is removed, the particles return to random alignment. These properties can be used to make a liquid that changes its density depending on the strength of the magnetic field and that can form fantastic shapes.
Ferrofluids are used to damp high-end speakers and the laser heads of CD and DVD players. They are used in low friction seals for rotating shaft motors and computer disk drive seals. You could open a computer disk drive or a speaker to get to the liquid magnet, but it's pretty easy (and fun) to make your own.
How to Make Liquid Magnets - Materials and Safety
Safety Considerations
This procedure uses flammable substances and generates heat and toxic fumes. Please wear safety glasses, work in a well-ventilated area, and be familiar with the safety data marked on the chemical containers. Be advised that ammonia fumes are toxic. The resulting fluid is very strongly attracted to magnets and can splash, staining skin and clothing. Wear eye and skin protection when working with the ferrofluid. It is toxic - do not ingest it and keep it out of reach of children and pets.
Materials
· oleic acid (may be found in some pharmacies, craft, and health food stores)
· household ammonia
· PCB etchant (ferric chloride solution) - may be found at Radioshack
· distilled water
· steel wool
· a strong magnet
· kerosene
· heat source
· 2 pyrex beakers or measuring cups
· a plastic syringe
· coffee filters
Synthesizing Magnetite
The first step is to prepare the magnetite, which will be the source of the magnetic particles in the ferrofluid. First reduce ferric chloride (FeCl3) in PCB etchant to ferrous chloride (FeCl2), which will be used to make magnetite. Commercial PCB etchant is usually 1.5M ferric chloride, to yield 5 grams of magnetite.
- Use the plastic syringe to measure and dispense 10 ml of PCB etchant into a pyrex or kimax measuring cup. Add 10 ml of distilled water. The etchant is diluted with water because there is an additive in Radioshack PCB fluid that can cause side reactions with the iron.
- Drop a small piece of steel wool into the diluted etchant solution. Swirl the contents of the cup around until the liquid turns bright green (this is the FeCl2).
- Filter the liquid through a coffee filter to remove the particulates.
- Next, precipitate magnetite from the ferrous and ferric chloride solutions. Add 20 ml of PCB etchant (FeCl3) to the green solution (FeCl2). FeCl3 and FeCl2 react in a 2:1 ratio. The concentration of the FeCl2 just prepared is half that of the FeCl3 (because the water was added), so equal volumes will give the desired ratio.
- Add 150 ml of household ammonia, stirring continuously. The ammonia reacts with the iron salts and excess chlorine to produce the magnetite, Fe3O4, which falls out of solution, in an ammonium chloride solution.
The next step is to take the magnetite and suspend it in the carrier solution.
How to Make Liquid Magnets - Procedure for Suspending Magnetite in a Carrier
Next, the magnetic particles need to be coated with a surfactant, so that they won't stick together, even in a magnetic field, and suspended in a carrier, so the magnet will be fluid.
- Coat the magnetite particles with oleic acid by heating the solution to just below boiling, in a well-ventilated area or under a fume hood. Stir in 5 ml of oleic acid. Keep the liquid near boiling until the odor of ammonia disappears (approximately one hour). Remove the mixture from heat and allow it to cool to room temperature. The oleic acids reacts with ammonia to form ammonium oleate. Heat causes the ammonium oleate to break down, allowing the oleate ion to enter into solution, while the ammonia escapes as a gas. The oleate ion attaches to a magnetite particle and is reconverted to oleic acid.
- The coated magnetite is suspended in the kerosene carrier by adding 100 ml of kerosene to the coated magnetite suspension, again, in a well-ventilated area. Stir the suspension until most of the black coloration has left the water and has been transferred into the kerosene. Magnetite and oleic acid are insoluble in water, while oleic acid is soluble in kerosene. Stirring the mixure allows the coated particles to leave the aqueous phase in favor of the kerosene.
- Decant and save the kerosene layer. Discard the water. The magnetite plus oleic acid plus kerosene is the final product, the ferrofluid.
How to Make Liquid Magnets - Things to Do with Ferrofluid
Ferrofluid is very strongly attracted to magnets, so always maintain a barrier between the liquid and the magnet. This can mean placing a sheet of glass or a container between the magnet and the ferrofluid. Be care of splashing of the liquid, from its strong reaction to the magnet. Both kerosene and iron are toxic, so do not ingest the ferrofluid or allow skin contact (don't stir it with a finger!).
Here are some ideas for activities involving your liquid magnet ferrofluid. You can:
· Float a penny on top of the ferrofluid, using a strong magnet.
· Use magnets to drag the ferrofluid up the sides of a container.
· Bring a magnet close to the ferrofluid to see spikes form, following the lines of the magnetic field.
Explore the incredible shapes you can form using a magnet and the ferrofluid. Store your liquid magnet away from heat and flame. If you need to dispose of your ferrofluid at some point, follow your community's instructions for disposing of fuel oil or kerosene. Have fun!
http://chemistry.about.com/od/weirdscience/a/fitzroy.htm
http://chemistry.about.com/cs/demonstrations/a/aa022204a.htm
http://chemistry.about.com/cs/howtos/ht/electroslime.htm
DEMOS
In this chemistry demonstration, a blue solution gradually becomes clear. When the flask of liquid is swirled around, the solution becomes blue again. Instructions are given for performing the reaction, the chemistry is explained, and options for making red -> clear -> red and green -> red/yellow -> green color change reactions are explained. The blue bottle reaction is easy to perform and uses readily-available materials.
Materials
· tap water
· two 1-liter Erlenmeyer flasks, with stoppers
· 7.5 g glucose (2.5 g for one flask; 5 g for the other flask)
· 7.5 g sodium hydroxide NaOH (2.5 g for one flask; 5 g for the other flask)
· 0.1% solution of methylene blue (1 ml for each flask)
Procedure
- Half-fill two one-liter Erlenmeyer flasks with tap water.
- Dissolve 2.5 g of glucose in one of the flask (flask A) and 5 g of glucose in the other flask (flask B).
- Dissolve 2.5 g of sodium hydroxide (NaOH) in flask A and 5 g of NaOH in flask B.
- Add ~1 ml of 0.1% methylene blue to each flask.
- Stopper the flasks and shake them to dissolve the dye. The resulting solution will be blue.
- Set the flasks aside (this is a good time to explain the chemistry of the demonstration). The liquid will gradually become colorless as glucose is oxidized by the dissolved dioxygen. The effect of concentration on reaction rate should be obvious. The flask with twice the concentration uses the dissolved oxygen in about half the time as the other solution. A thin blue boundary can be expected to remain at the solution-air interface, since oxygen remains available via diffusion.
- The blue color of the solutions can be restored by swirling or shaking the contents of the flask.
- The reaction can be repeated several times.
Safety & Clean-Up
Avoid skin contact with the solutions, which contain caustic chemicals. The reaction neutralizes the solution, which can be disposed of by pouring it down the drain.
In this reaction, glucose (an aldehyde) in an alkaline solution is slowly oxidized by dioxygen to form gluconic acid:
CH2OH–CHOH–CHOH–CHOH–CHOH–CHO + 1/2 O2 --> CH2OH–CHOH–CHOH–CHOH–CHOH–COOH
Gluconic acid is converted to sodium gluconate in the presence of sodium hydroxide. Methylene blue speeds up this reaction by acting as an oxygen transfer agent. By oxidizing glucose, methylene blue is itself reduced (forming leucomethylene blue), and becomes colorless.
If there is a sufficient available oxygen (from air), leucomethylene blue is re-oxidized and the blue color of solution can be restored. Upon standing, glucose reduces the methylene blue dye and the color of the solution disappears. In dilute solutions the reaction takes place at 40-60°C, or at room temperature (described here) for more concentrated solutions.
In addition to the blue -> clear -> blue of the methylene blue reaction, other indicators may be used for different color-change reactions. For example, resazurin (7-hydroxy-3H-phenoxazin-3-one-10-oxide, sodium salt) produces a red -> clear -> red reaction when substituted for methylene blue in the demonstration. The indigo carmine reaction is even more eye-catching, with its green -> red/yellow -> green color change.
How to Perform the Indigo Carmine Color Change Reaction
- Prepare a 750 ml aqueous solution with 15 g glucose (solution A) and a 250 ml aqueous solution with 7.5 g sodium hydroxide (solution B).
- Warm solution A to body temperature (~98-100°F). Warming the solution is important.
- Add a 'pinch' of indigo carmine, the disodium salt of indigo-5,5’-disulphonic acid, to solution A. You want a quantity sufficient to make solution A visibly blue.
- Pour solution B into solution A. This will change the color from blue -> green. Over time, this color will change from green -> red/golden yellow.
- Pour this solution into an empty beaker, from a height of ~60 cm. Vigorous pouring from a height is essential in order to dissolve dioxygen from the air into the solution. This should return the color to green.
- Once again, the color will return to red/golden yellow. The demonstration may be repeated several times.