Monthly Archives: May 2013
One of the most spectacular chemistry demonstrations is also one of the simplest. It’s the dehydration of sugar (sucrose) with sulfuric acid. Basically, all you do to perform this demonstration is put ordinary table sugar in a glass beaker and stir in some concentrated sulfuric acid (you can dampen the sugar with a small volume of water before adding the sulfuric acid). The sulfuric acid removes water from the sugar in a highly exothermic reaction, releasing heat, steam, and sulfur oxide fumes. Aside from the sulfurous odor, the reaction smells a lot like caramel. The white sugar turns into a black carbonized tube that pushes itself out of the beaker. Here’s a nice youtube video for you, if you’d like to see what to expect.
HOW IT WORKS:
Sugar is a carbohydrate, so when you remove the water from the molecule, you’re basically left with elemental carbon. The dehydration reaction is a type of elimination reaction.
C12H22O11 (sugar) + H2SO4 (sulfuric acid) → 12 C (carbon) + 11 H2O (water) +mixture water and acid
Although the sugar is dehydrated, the water isn’t ‘lost’ in the reaction. Some of it remains as a liquid in the acid. Since the reaction is exothermic, much of the water is boiled off as steam.
If you do this demonstration, use proper safety precautions. Whenever you deal with concentrated sulfuric acid, you should wear gloves, eye protection, and a lab coat.
Oh, and by the way, consider the beaker a loss, since scraping burnt sugar and carbon off of it isn’t an easy task. Also it’s preferable to perform the demonstration outside or under a fume hood.
Black snakes, sometimes called glow worms, are small tablets that you light, using a punk or a lighter, that burn to produce long black ‘snakes’ of ash. They produce some smoke (which had a characteristic, probably toxic odor), but no fire or explosion. The original fireworks used to contain salts of a heavy metal (such as mercury), so while they were marketed for kids to play with, they really weren’t that much safer than conventional fireworks, just dangerous in a different way. However, there is a safe way to make black snakes. You can heat baking soda (sodium bicarbonate) with sugar (sucrose) to produce carbon dioxide gas that puffs up black carbon ash (see a video).
WHAT YOU NEED:
- alcohol or fuel oil (such as Heet lighter fluid)
- baking soda
- powdered sugar (must be powdered!)
WHAT TO DO:
- Mix 4 parts powdered sugar with 1 part baking soda. For example, you can use 4 tsp sugar and 1 tsp baking soda.
- Make a mound with the sand. Push a depression into the middle of the sand.
- Pour the alcohol or other fuel into the sand to wet it.
- Pour the sugar and soda mixture into the depression.
- Ignite the mound, using a lighter or match.
WHAT HAPPENS: At first, you’ll get a flame and some small scattered blackened balls. Once the reaction gets going, the carbon dioxide will puff up the carbonate into the continuously extruded ‘snake’. Actually, you don’t even need the sand. You can use baking soda and sugar in a metal mixing bowl, add the fuel, and light the mixture. It works fine. The old firework snakes had a distinct smell. These have a smell too, a bit like burnt marshmallows! If you use pure ethanol, sugar, and baking soda, then there is nothing toxic about this project. CAUTION: DO NOT add fuel to the burning snake, since you risk igniting the alcohol stream!
HOW IT WORKS:
The sugar and baking soda snake proceeds according to the following chemical reactions, where sodium bicarbonate breaks down into sodium carbonate, water vapor, and carbon dioxide gas while burning the sugar in oxygen produces water vapor and carbon dioxide gas. The snake is carbonate with black carbon particles:
2 NaHCO3 → Na2CO3 + H2O + CO2
C2H5OH + 3 O2 → 2 CO2 + 3 H2O
These instructions were adapted from a tutorial given on Boing Boing which in turn came from a defunct Russian site. The Russian site suggested two additional ways to make chemical snakes:
Ammonium Nitrate Black Snakes:
This works the same way as the sugar and baking soda snake, except you use ammonium nitrate (niter) instead of sugar. Mix one part ammonium nitrate and one part baking soda. This recipe is more like what you would see in commercial black snake fireworks, which are supposedly composed of soda with nitrated naphthalenes and linseed oil. It’s another very safe demonstration, though not safe enough to eat, like sugar and baking soda.
Ammonium Dichromate Green Snakes:
The green soda snakes are made from:
- two parts of ammonium nitrate
- one part of powdered sugar
- one part of ammonium dichromate
Mix the ingredients, add a small amount of water, and roll WITH GLOVES into a snake. Allow the snake to dry. It is easier to use a hair dryer to speed up the process. Light one end of the snake. In this case, an orange snake burns to green ash. It’s worth knowing how to do this demonstration if you have ammonium dichromate and ammonium nitrate on hand, otherwise let the Russian photos suffice and play with the sugar and baking soda snakes instead. Another (spectacular) form of black carbon snake results from reacting sugar and sulfuric acid. Visit my future post on the sugar and sulfuric acid black snake. I will post this experiment with complete instructions and write how it works.
Many have heard of the tale of King Midas and the golden touch. Everything he touched turned to gold! Now you can make your own “gold.” (Don’t tell anyone it’s just brass!) Or, if you’re not feeling your golden self, make some “silver” coins. All you need are a couple of common chemicals to turn your normal copper-colored pennies (or other mainly-copper object) from copper to silver and then to gold. No, the coins won’t really be silver or gold. The actual metal involved is zinc. This project is easy to do. While I don’t recommend it for very young kids, I’d consider it appropriate for kids ages third grade and older, with adult supervision.
WHAT YOU NEED:
- clean pennies
- zinc metal (preferably powder)
- sodium hydroxide or sodium hydroxide solution
- tweezers or tongs
- container of water
- source of heat/flame
WHAT TO DO:
- Pour a spoonful of zinc (1-2 grams) into a small beaker or evaporating dish containing water.
- Add a small quantity of sodium hydroxide.
- Alternatively, you could add zinc to a 3M NaOH solution.
- Heat the mixture to near-boiling, then remove it from heat.
- Add clean pennies to the solution, spacing them so that they are not touching each other.
- Wait 5-10 minutes for them to turn silver, then use tongs to remove the pennies from the solution.
- Rinse the pennies in water, then set them on a towel to dry.
- You can examine the pennies once you have rinsed them.
This chemical reaction plates the copper in the penny with zinc. This is called galvanization. The zinc reacts with the hot sodium hydroxide solution to form soluble sodium zincate, Na2ZnO2, which is converted to metallic zinc when it touches the surface of the penny.
How to Make the Silver Pennies turn Gold
- Grasp a silver penny with tongs.
- Gently heat the penny in the outer (cool) part of a burner flame or with a lighter or candle (or even set it on a hotplate).
- Remove the penny from heat as soon as it changes color.
- Rinse the gold penny under water to cool it.
Heating the penny fuses the zinc and copper to form an alloy called brass. Brass is a homogeneous metal that varies from 60-82% Cu and from 18-40% Zn. Brass has a relatively low melting point, so the coating can be destroyed by heating the penny for too long.
Please use proper safety precautions. Sodium hydroxide is caustic. I recommend conducting this project under a fume hood or outdoors. Wear gloves and protective eye-wear to prevent getting splashed by the sodium hydroxide solution.
Note: Supposedly you can substitute galvanized nails for the zinc and Drano™ for the sodium hydroxide, but I was unable to get this project to work using nails and drain cleaner.
Alright guys, this is a long one. I must warn you, this project is NOT for the little kiddies! This experiment includes the use of TOXIC chemicals.
Disappearing ink is a water-based acid-base indicator (pH indicator) that changes from a colored to a colorless solution upon exposure to air. The most common pH indicators for the ink are thymolphthalein (blue) or phenolphthalein (red or pink). The indicators are mixed into a basic solution that becomes more acidic upon exposure to air, causing the color change. Note that in addition to disappearing ink, you could use different indicators to make color-change inks, too.
Here’s how it 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. Neutralization 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 3 M sodium hydroxide solution or 10 drops 6 M 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; (this will produce a milky solution).
- Add sodium hydroxide solution by drops 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; (a 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
WHAT YOU NEED:
- One empty 35 mm plastic film canister and lid. These are getting harder to find, but stores that develop film should have some. (The white canisters work much better than the black ones do.) If you have trouble finding canisters, you can get them HERE.
- One fizzing antacid tablet (such as Alka-Seltzer – Get this from your parents)
- Safety goggles
WHAT TO DO:
1. Put on those safety goggles and head outside – no really, when this works, that film canister really flies! If you want to try the indoor version, do not turn the canister upside down in step 5.
2. Break the antacid tablet in half.
3. Remove the lid from the film canister and put a teaspoon (5 ml) of water into the canister.
Do the next 2 steps quickly
4. Drop the tablet half into the canister and snap the cap onto the canister (make sure that it snaps on tightly.)
5. Quickly put the canister on the ground CAP SIDE DOWN and STEP BACK at least 2 meters.
6. About 10 seconds later, you will hear a POP! and the film canister will launch into the air!
Caution: If it does not launch, wait at least 30 second before examining the canister. Usually the cap is not on tight enough and the build up of gas leaked out.
HOW IT WORKS:
There’s nothing like a little rocket science to add some excitement to the day. When you add the water it starts to dissolve the alka-seltzer tablet. This creates a gas call carbon dioxide. As the carbon dioxide is being released, it creates pressure inside the film canister. The more gas that is made, the more pressure builds up until the cap it blasted down and the rocket is blasted up. This system of thrust is how a real rocket works whether it is in outer space or here in the earth’s atmosphere. Of course, real rockets use rocket fuel. You can experiment controlling the rocket’s path by adding fins and a nose cone that you can make out of paper. Be safe and have fun!
Make it an experiment:
The project above is a DEMONSTRATION. To make it a true experiment, you can try to answer these questions:
1. Does water temperature affect how fast the rocket launches?
2. Does the size of the tablet piece affect how long it takes for the rocket to launch?
3. Can the flight path be controlled by adding fins or a nosecone to the canister?
4. How much water in the canister will give the highest flight?
5. How much water will give the quickest launch?