Chemistry at home

Fruit Battery

2011-05-18T10:54:00.001-07:00

If you have fruit, a couple of nails, and wire then you can generate electricity to turn on a light bulb. Learn how to make a fruit battery. It's fun, safe, and easy.

Here's What You Need

citrus fruit (e.g., lemon, lime, orange, grapefruit)
copper nail, screw or wire (about 2" or 5 cm long)
zinc nail or screw or galvanized nail (about 2" or 5 cm long)
holiday light with 2" or 5 cm leads (enough wire to connect it to the nails)

Make a Fruit Battery

Set the fruit on a table and gently roll it around to soften it up. You want the juice to be flowing inside the fruit without breaking its skin. Alternatively, you can squeeze the fruit with your hands.
Insert the zinc and copper nails into the fruit so that they are about 2" or 5 cm apart. You don't want them to be touching each other. Avoid puncturing through the end of the fruit.
Remove enough insulation from the leads of the light (about 1") so that you can wrap one lead around the zinc nail and one lead around the copper nail. If you like, you can use electrical tape or alligator clips to keep the wire from falling off the nails.
When you connect the second nail, the light will turn on!

Learn More

Citrus fruits are acidic, which helps their juice to conduct electricity. What other fruits and vegetables might you try that would work as batteries?
If you have a multimeter, you can measure the current produced by the battery. Compare the effectiveness of different types of fuits. See what happens as you change the distance between the nails.
Do acidic fruits always work better? Measure the pH (acidity) of the fruit juice and compare that with the current through the wires or brightness of the light bulb.

Baking Soda Stalactites and Stalagmites

2011-05-18T10:51:00.001-07:00

Stalactites and stalagmites are large crystals which grow in caves. Stalactites grow down from the ceiling, while stalagmites grow up from the ground. The world's largest stalagmite is 32.6 meters long, located in a cave in Slovakia. Make your own stalagmites and stalactites using baking soda. It's an easy, non-toxic crystal project. Your crystals won't be as big as the Slovakian stalagmite, but they will only take a week to form, instead of thousands of years!

Baking Soda Stalactite & Stalagmite Materials

2 glasses or jars
1 plate or saucer
1 Spoon
2 Paper Clips
Hot Tap Water
Piece of Yarn, about a meter long
Baking Soda (Sodium Bicarbonate)
Food Coloring (optional)

If you don't have baking soda, but you can substitute a different crystal-growing ingredient, such as sugar or salt. If you want your crystals to be colored, add some food coloring to your solutions. You might even try adding two different colors to the different containers, just to see what you get.

Grow Stalactites and Stalagmites

Fold your yarn in half. Fold it in half again and twist it together tightly. My yarn is colored acrylic yarn, but ideally you want a more porous natural material, such as cotton or wool. Uncolored yarn would be preferable if you are coloring your crystals, since many types of yarn bleed their colors when wet.
Attach a paper clip to either end of your twisted yarn. The paper clip will be used to hold the ends of the yarn in your liquid while the crystals are growing.
Set a glass or jar on either side of a small plate.
Insert the ends of the yarn, with the paper clips, in the glasses. Position the glasses so that there is a slight dip (catenary) in the yarn over the plate.
Make a saturated baking soda solution (or sugar or whatever). Do this by stirring baking soda into hot tap water until you get so much added that it stops dissolving. Add food coloring, if desired. Pour some of this saturated solution into each jar. You may wish to wet the string to start the stalagmite/stalactite formation process. If you have leftover solution, keep it in a closed container and add it to the jars when needed.
At first, you may need to keep an eye on your saucer and dump liquid back into one jar or another. If your solution is really concentrated, this will be less of a problem. Crystals will start to appear on the string in a couple of days, with stalactites growing down from the yarn toward the saucer in about a week and stalagmites growing up from the saucer toward the string somewhat later. If you need to add more solution to your jars, be sure that it is saturated, or else you will risk dissolving some of your present crystals.

The crystals in the photos are my baking soda crystals after three days. As you can see, crystals will grow from the sides of the yarn before they develop stalactites. After this point, I started to get good downward growth, which eventually connected to the plate and grew up. Depending on the temperature and rate of evaporation, your crystals will take more or less time to develop.

Cloud in a Bottle Demonstration

2011-05-18T10:50:00.000-07:00

Here's a quick and easy science project you can do: make a cloud inside a bottle. Clouds form when water vapor forms tiny visible droplets. This results from cooling the vapor. It helps to provide particles around which the water can liquefy. In this project, we'll use smoke to help form a cloud.

Cloud in a Bottle Materials

1-liter bottle
warm water
match

Let's Make Clouds

Pour just enough warm water in the bottle to cover the bottom of the container.
Light the match and place the match head inside the bottle.
Allow the bottle to fill with smoke.
Cap the bottle.
Squeeze the bottle really hard a few times. When you release the bottle, you should see the cloud form. It may disappear between 'squeezes'.

The Other Way to Do It Ok, here's the ideal gas law:

PV = nRT, where P is pressure, V is volume, n is number of moles, R is a constant, and T is temperature.
If we're not changing the amount of gas (as in a closed container) then if you raise the pressure, the only way for the temperature of the gas to be unchanged is by decreasing the container volume proportionally. I wasn't sure I could squeeze the bottle hard enough to achieve this (or that it would bounce back) and I wanted a really dense cloud for the photograph so I did the not-as-child-friendly version of this demonstration (still pretty safe). I poured water from my coffeemaker into the bottom of the bottle. Instant cloud! (... and a slight melting of the plastic) I couldn't find any matches, so I lit a strip of cardboard on fire, inserted it into the bottle, and let the bottle get nice and smoky (and melted more plastic... you can see the deformation in the photo). Dense cloud, no squeezing required, though of course it still worked.
How Clouds Form

Molecules of water vapor will bounce around like molecules of other gases unless you give them a reason to stick together. Cooling the vapor slows the molecules down, so they have less kinetic energy and more time to interact with each other. How do you cool the vapor? When you squeeze the bottle, you compress the gas and increase its temperature. Releasing the container lets the gas expand, which causes its temperature to go down. Real clouds form as warm air rises. As air gets higher, its pressure is reduced. The air expands, which causes it to cool. As it cools below the dew point, water vapor forms the droplets we see as clouds. Smoke acts the same in the atmosphere as it does in the bottle. Other nucleation particles include dust, pollution, dirt, and even bacteria.

Egg in a Bottle Demonstration

2011-05-18T10:49:00.001-07:00

The egg in a bottle demonstration is an easy chemistry or physics demonstration you can do at home or in the lab. You set an egg on top of a bottle (as pictured). You change the temperature of the air inside the container either by dropping a piece of burning paper into the bottle or by directly heating/cooling the bottle. Air pushes the egg into the bottle.

Egg in a Bottle Materials

peeled hard-boiled egg (or soft-boiled, if a yolk mess interests you)
flask or jar with opening slightly smaller than the diameter of the egg
paper/lighter or very hot water or very cold liquid

In a chemistry lab, this demonstration is most commonly performed using a 250-ml flask and a medium or large egg. If you are trying this demonstration at home, you can use a glass apple juice bottle. I used a Sobe™ soft drink bottle. If you use too large of an egg, it will get sucked into the bottle, but stuck (resulting in a gooey mess if the egg was soft-boiled). I recommend a medium egg for the Sobe™ bottle. An extra-large egg gets wedged in the bottle. Perform the Demonstration

Method 1: Set a piece of paper on fire and drop it into the bottle. Set the egg on top of the bottle (small side pointed downward). When the flame goes out, the egg will get pushed into the bottle.
Method 2: Set the egg on the bottle. Run the bottle under very hot tap water. Warmed air will escape around the egg. Set the bottle on the counter. As it cools, the egg will be pushed into the bottle.
Method 3: Set the egg on the bottle. Immerse the bottle in a very cold liquid. I have heard of this being done using liquid nitrogen, but that sounds dangerous (could shatter the glass). I recommend trying ice water. The egg is pushed in as the air inside the bottle is chilled.

How It WorksIf you just set the egg on the bottle, its diameter is too large for it to slip inside. The pressure of the air inside and outside of the bottle is the same, so the only force that would cause the egg to enter the bottle is gravity. Gravity isn't sufficient to pull the egg inside the bottle.
When you change the temperature of the air inside the bottle, you change the pressure of the air inside the bottle. If you have a constant volume of air and heat it, the pressure of the air increases. If you cool the air, the pressure decreases. If you can lower the pressure inside the bottle enough, the air pressure outside the bottle will push the egg into the container.
It's easy to see how the pressure changes when you chill the bottle, but why is the egg pushed into the bottle when heat is applied? When you drop burning paper into the bottle, the paper will burn until the oxygen is consumed (or the paper is consumed, whichever comes first). Combustion heats the air in the bottle, increasing the air pressure. The heated air pushes the egg out of the way, making it appear to jump on the mouth of the bottle. As the air cools, the egg settles down and seals the mouth of the bottle. Now there is less air in the bottle than when you started, so it exerts less pressure. When the temperature inside and outside the bottle is the same, there is enough positive pressure outside the bottle to push the egg inside.
Heating the bottle produces the same result (and may be easier to do if you can't keep the paper burning long enough to put the egg on the bottle). The bottle and the air are heated. Hot air escapes from the bottle until the pressure both inside and outside the bottle is the same. As the bottle and air inside continue to cool, a pressure gradient builds, so the egg is pushed into the bottle.
How to Get the Egg Out
You can get the egg out by increasing the pressure inside the bottle so that it is higher than the pressure of the air outside of the bottle. Roll the egg around so it is situated with the small end resting in the mouth of the bottle. Tilt the bottle just enough so you can blow air inside the bottle. Roll the egg over the opening before you take your mouth away. Hold the bottle upside down and watch the egg 'fall' out of the bottle. Alternatively, you can apply negative pressure to the bottle by sucking the air out, but then you risk choking on an egg, so that's not a good plan.

Rubber Egg & Chicken Bones

2011-05-18T10:48:00.000-07:00

A Mad Scientist can make a toy out of just about anything, including a boiled egg. Soak an egg in a common kitchen ingredient, vinegar, to dissolve its shell and make the egg rubbery enough that you can bounce it on the floor like a ball. Soaking chicken bones in vinegar will soften them so that they will become rubbery and flexible.
Rubber Egg Materials

hard-boiled egg
glass or jar, big enough to hold the egg
vinegar

Turn the Egg into a Bouncy Ball

Place the egg in the glass or jar.
Add enough vinegar to completely cover the egg.
Watch the egg. What do you see? Little bubbles may come off the egg as the acetic acid in the vinegar attacks the calcium carbonate of the eggshell. Over time the color of the eggs may change as well.
After 3 days, remove the egg and gently rinse the shell off of the egg with tap water.
How does the boiled egg feel? Try bouncing the egg on a hard surface. How high can you bounce your egg?
You can soak raw eggs in vinegar for 3-4 days, with a slightly different result. The eggs shell will become soft and flexible. You can gently squeeze these eggs, but it's not a great plan to try to bounce them on the floor.

Make Rubbery Chicken Bones If you soak chicken bones in vinegar (the thinner bones work best), the vinegar will react with the calcium in the bones and weaken them so that they will become soft and rubbery, as if they had come from a rubber chicken. It is the calcium in your bones that makes them hard and strong. As you age, you may deplete the calcium faster than you replace it. If too much calcium is lost from your bones, they may become brittle and susceptible to breaking. Exercizing and eating a diet that includes calcium-rich foods can help prevent this from happening.

Rock Candy - How to Make Rock Candy

2011-05-18T10:47:00.000-07:00

Making your own rock candy is a fun and tasty way to grow crystals and see the structure of sugar on a big scale. Sugar crystals in granulated sugar display a monoclinic form, but you can see the shape much better in homegrown large crystals. This recipe is for rock candy that you can eat. You can color and flavor the candy, too. Rock Candy Materials
Basically all you need to make rock candy is sugar and hot water. The color of your crystals will depend on the type of sugar you use (raw sugar is more golden and refined granulated sugar) and whether or not you add coloring. Any food-grade colorant will work.

3 cups sugar (sucrose)
1 cup water
clean glass jar
cotton string
pencil or knife
food coloring (optional)
1/2 tsp to 1 tsp flavoring oil or extract (optional)
Lifesaver candy (optional)
pan
stove or microwave

Make Rock Candy

Pour the sugar and water into the pan.
Heat the mixture to a boil, stirring constantly. You want the sugar solution to hit boiling, but not get hotter or cook too long. If you overheat the sugar solution you'll make hard candy, which is nice, but not what we're going for here.
Stir the solution until all the sugar has dissolved. The liquid will be clear or straw-colored, without any sparkly sugar. If you can get even more sugar to dissolve, that's good, too.
If desired, you can add food coloring and flavoring to the solution. Mint, cinnamon, or lemon extract are good flavorings to try. Squeezing the juice from a lemon, orange, or lime is a way to give the crystals natural flavor, but the acid and other sugars in the juice may slow your crystal formation.
Set the pot of sugar syrup in the refrigerator to cool. You want the liquid to be about 50°F (slightly cooler than room temperature). Sugar becomes less soluble as it cools, so chilling the mixture will make it so there is less chance of accidentally dissolving sugar you are about to coat on your string.
While the sugar solution is cooling, prepare your string. You are using cotton string because it is rough and non-toxic. Tie the string to a pencil, knife, or other object that can rest across the top of the jar. You want the string to hang into the jar, but not touch the sides or bottom.
You don't want to weight your string with anything toxic, so rather than use a metal object, you can tie a Lifesaver to the bottom of the string.
Whether you are using the Lifesaver or not, you want to 'seed' the string with crystals so that the rock candy will form on the string rather than on the sides and bottom of the jar. There are two easy ways to do this. One is to dampen the string with a little of the syrup you just made and dip the string in sugar. Another option is to soak the string in the syrup and then hang it to dry, which will cause crystals to form naturally (this method produces 'chunkier' rock candy crystals).
Once your solution has cooled, pour it into the clean jar. Suspend the seeded string in the liquid. Set the jar somewhere quiet. You can cover the jar with a paper towel or coffee filter to keep the solution clean.
Check on your crystals, but don't disturb them. You can remove them to dry and eat when you are satisfied with the size of your rock candy. Ideally you want to allow the crystals to grow for 3-7 days.
You can help your crystals grow by removing (and eating) any sugar 'crust' that forms on top of the liquid. If you notice a lot of crystals forming on the sides and bottom of the container and not on your string, remove your string and set it aside. Pour the crystallized solution into a saucepan and boil/cool it (just like when you make the solution). Add it to a clean jar and suspend your growing rock candy crystals.

How to Make Homemade Firecrackers

2011-05-18T10:44:00.000-07:00

Firecrackers are extremely easy and inexpensive to make yourself. You may want to make your own firecrackers because you are interested in learning how to make simple fireworks or it may be you are unable to obtain fireworks where you live. Fortunately, the materials needed to make your own firecrackers are very common.

Homemade Firecracker Materials

tape (e.g., transparent tape)
toy gun caps (either the tape or the rings) or black powder
fuse
pin or needle

Toy gun caps are nice because the powder used in them is easy to work with. Here's how to get the powder out of the caps:

Gently insert a pin or needle through the back of a cap through to the front.
Remove the pin and re-insert it from the front, where you made the hole. Pry the powder out of the cap, tapping it onto a sheet or paper or plate or other working surface.
Carefully work the pin around the edge of the cap to collect all of the powder. There is a very slight chance of popping the cap, so be gentle and work slowly.
How much powder you need depends on the size of firecracker you plan to make. One ring of caps is more than sufficient to create a loud bang, but you really only need powder from about 3 caps for each firecracker. For the sake of safety, it's best to make one firecracker at a time (you don't need a big pile of powder).

Now let's assemble the firecracker.

One you have all of the materials necessary to make firecrackers, you are ready to start putting the firecrackers together.

Take a piece of tape about 2" long and pick up the gunpowder on the sticky side of the tape. Evenly coat the tape until you either run out of gunpowder or else run out of stickiness.
Place the fuse (about 2 inches long) so that it sticks halfway down the tape. The fuse does not need to stick to the tape.
Roll the tape around the fuse. Take another piece of tape and tightly wrap your firecracker. Be sure to cover the bottom of the firecracker or else the opening will give you a small rocket rather than a popping firecracker.

Alternatively, you could just fold a 2-inch strip of paper in half lengthwise, pour the gunpowder into the fold of the paper, and wrap the paper around the fuse. The paper firecracker could be secured with any kind of tape.

Now that you have a homemade firecracker, you need to light it! This is basically the same as lighting any other firecracker. Make sure you light it on a firesafe surface, far from people or pets. Don't hold the firecracker in your hand when you light it. Firecrackers that you buy contain measured quantities of gunpowder. You can estimate the amount of gunpowder in your firecracker based on how many caps you used. You won't necessarily get a louder 'bang' using more gunpowder, but you will increase the potential risk of injury, so don't go crazy making big firecrackers. Have fun!

Black Snakes or Glow Worms

2011-05-18T10:42:00.000-07:00

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.
Soda & Sugar Black Snake Materials

sand
alcohol or fuel oil (I didn't have any high-proof alcohol on hand, so I used lighter fluid left over from the handheld fireballs project)
baking soda
sugar (I used powdered sugar, but you can grind table sugar in a coffee grinder)

Make Snakes

Mix 4 parts powdered sugar with 1 part baking soda. (I used 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.

How to Make a Smoke Bomb

2011-05-18T10:40:00.000-07:00

Smoke Bomb Materials

sugar (sucrose or table sugar)
potassium nitrate, KNO₃, also known as saltpeter (buy it online or you can find this at some garden supply stores in the fertilizer section, some pharmacies carry it too)
skillet or pan
aluminum foil

How to Make a Smoke Bomb

Pour about 3 parts potassium nitrate to 2 parts sugar into the skillet (5:3 ratio is also good). Measurements don't need to be exact, but you want more KNO₃ than sugar. For example, you can use 1-1/2 cups KNO₃ and 1 cup sugar. If you use equal amounts of KNO₃ and sugar, your smoke bomb will be harder to light and will burn more slowly. As you approach the 5:3 KNO₃:sugar ratio, you get a smoke bomb that burns more quickly.
Apply low heat to the pan. Stir the mixture with a spoon using long strokes. If you see the grains of sugar starting to melt along the edges where you are stirring, remove the pan from the heat and reduce the temperature before continuing.
Basically you are carmelizing sugar. The mixture will melt and become a caramel or chocolate color. Continue heating/stirring until the ingredients are liquefied. Remove from heat.
Pour the liquid onto a piece of foil. You can pour a smaller amount onto a separate piece, to test the batch. You can pour the smoke bomb into any shape, onto an object, or into a mold. The shape and size will affect the burning pattern.
If you aren't going to clean your skillet immediately, pour hot water into the pan to dissolve the sugar (or else it will be harder to clean). Clean up any residue you may have spilled out of the pan, unless you want mini-smoke bombs on your stovetop.
Allow the smoke bomb to cool, then you can peel it off the foil.

Now that you've made your smoke bomb, it's time to light it...

White Smoke Recipe

Potassium nitrate - 4 parts
Charcoal - 5 parts
Sulfur - 10 parts
Wood dust - 3 parts

Red Smoke Recipe

Potassium chlorate - 15%
para-nitroaniline red - 65%
Lactose - 20%

Green Smoke Recipe

Synthetic indigo - 26%
Auramine (yellow) - 15%
Potassium chlorate - 35%
Lactose - 26%

It's fairly easy to make colored flames by adding these chemicals to your smoke bomb recipe:
Chemicals Used to Color Flames

Red - strontium salts, most easily found in road flares
Orange - calcium chloride (laundry bleaching agent)
Yellow - sodium nitrate (common in chemistry lab)
Green - barium salts, such as barium nitrate (common in chemistry lab)
Greenish-Blue - copper sulfate (common in a chemistry lab, also found in many algicides for pool treatment) Blue - copper chloride (common in chemistry lab)
Purple - potassium permanganate (common in a chemistry lab, also used in sewage or water treatment)
White - magnesium sulfate (epsom salts, found on laundry aisle or in a pharmacy)

Burning Money - Chemistry Demonstration

2011-04-28T12:58:00.000-07:00

This is a neat 'magic trick' that illustrates the process of combustion, the flammability of alcohol, and the special qualities of the material used to make currency.

Scientific Concept behind Burning Money
A combustion reaction occurs between alcohol and oxygen, producing heat and light (energy) and carbon dioxide and water.
C₂H₅OH + 4 O₂ -> 2 CO₂ + 3 H₂O + energy
When the bill is soaked an alcohol-water solution, the alcohol has a high vapor pressure and is mainly on the outside of the material (a bill is more like fabric than paper, which is nice, if you've ever accidentally washed one). When the bill is lit, the alcohol is what actually burns. The temperature at which the alcohol burns is not high enough to evaporate the water, which has a high specific heat, so the bill remains wet and isn't able to catch fire on its own. After the alcohol has burned, the flame goes out, leaving a slightly damp dollar bill.

Here's what you need to do the demonstration...

dollar bill (higher denomination if you're brave)
tongs
matches or a lighter
salt
solution of 50% alcohol and 50% water (you can mix 95% alcohol with water in a 1:1 ratio, if desired)

Have you gathered your materials? Let's burn money...

Prepare the alcohol and water solution. You can mix 50 ml of water with 50 ml of 95-100% alcohol.
Add a pinch salt or other colorant to the alcohol/water solution, to help produce a visible flame.
Soak a dollar bill in the alcohol/water solution so that it is thoroughly wet.
Use tongs to pick up the bill. Allow any excess liquid to drain. Move the damp bill away from the alcohol-water solution.
Light the bill on fire and allow it to burn until the flame goes out.

How To Do Paper Chromatography With Leaves

2011-04-28T12:56:00.001-07:00

Most plants contain several pigment molecules, so experiment with different leaves to see the wide range of pigments.

Difficulty: Average

Time Required: 2 hours

What You Need:

Leaves
Baby Food Jars with Lids
Rubbing Alcohol
Coffee Filters
Hot Water
Shallow Pan
Kitchen Utensils

Here's How:

Take 2-3 large leaves (or the equivalent with smaller leaves), tear them into tiny pieces, and place them into small jars with lids.
Add enough alcohol to just cover the leaves.
Loosely cover the jars and set them into a shallow pan containing an inch or so of hot tap water.
Let the jars sit in the hot water for at least a half hour. Replace the hot water as it cools and swirl the jars from time to time.
The jars are 'done' when the alcohol has picked up color from the leaves. The darker the color, the brighter the chromatogram will be.
Cut or tear a long strip of coffee filter paper for each jar.
Place one strip of paper into each jar, with one end in the alcohol and the other outside of the jar.
As the alcohol evaporates, it will pull the pigment up the paper, separating pigments according to size (largest will move the shortest distance).
After 30-90 minutes (or until the desired separation is obtained), remove the strips of paper and allow them to dry.
Can you identify which pigments are present? Does the season in which the leaves are picked affect their colors?

Tips:

Try using frozen chopped spinach leaves.
Experiment with other types of paper.
You can substitute other alcohols for the rubbing alcohol, such as ethyl alcohol or methyl alcohol.
If your chromatogram is pale, next time use more leaves and/or smaller pieces to yield more pigment.

Make Ice Cream in a Baggie

2011-04-28T12:55:00.000-07:00

Materials

1/2 cup milk
1/2 cup whipping cream (heavy cream)
1/4 cup sugar
1/4 teaspoon vanilla or vanilla flavoring (vanillin)
1/2 to 3/4 cup sodium chloride (NaCl) as table salt or rock salt
2 cups ice
1-quart Ziploc^TM bag
1-gallon Ziploc^TM bag
themometer
measuring cups and spoons
cups and spoons for eating your treat!

Procedure

Add 1/4 cup sugar, 1/2 cup milk, 1/2 cup whipping cream, and 1/4 teaspoon vanilla to the quart ziploc^TM bag. Seal the bag securely.
Put 2 cups of ice into the gallon ziploc^TM bag.
Use a thermometer to measure and record the temperature of the ice in the gallon bag.
Add 1/2 to 3/4 cup salt (sodium chloride) to the bag of ice.
Place the sealed quart bag inside the gallon bag of ice and salt. Seal the gallon bag securely.
Gently rock the gallon bag from side to side. It's best to hold it by the top seal or to have gloves or a cloth between the bag and your hands because the bag will be cold enough to damage your skin.
Continue to rock the bag for 10-15 minutes or until the contents of the quart bag have solidified into ice cream.
Open the gallon bag and use the thermometer to measure and record the temperature of the ice/salt mixture.
Remove the quart bag, open it, serve the contents into cups with spoons and ENJOY!

Explanation
Ice has to absorb energy in order to melt, changing the phase of water from a solid to a liquid. When you use ice to cool the ingredients for ice cream, the energy is absorbed from the ingredients and from the outside environment (like your hands, if you are holding the baggie of ice!). When you add salt to the ice, it lowers the freezing point of the ice, so even more energy has to be absorbed from the environment in order for the ice to melt. This makes the ice colder than it was before, which is how your ice cream freezes. Ideally, you would make your ice cream using 'ice cream salt', which is just salt sold as large crystals instead of the small crystals you see in table salt. The larger crystals take more time to dissolve in the water around the ice, which allows for even cooling of the ice cream.
You could use other types of salt instead of sodium chloride, but you couldn't substitute sugar for the salt because (a) sugar doesn't dissolve well in cold water and (b) sugar doesn't dissolve into multiple particles, like an ionic material such as salt. Compounds that break into two pieces upon dissolving, like NaCl breaks into Na⁺ and Cl^-, are better at lowering the freezing point than substances that don't separate into particles because the added particles disrupt the ability of the water to form crystalline ice. The more particles there are, the greater the disruption and the greater the impact on particle-dependent properties (colligative properties) like freezing point depresssion, boiling point elevation, and osmotic pressure. The salt causes the ice to absorb more energy from the environment (becoming colder), so although it lowers the point at which water will re-freeze into ice, you can't add salt to very cold ice and expect it to freeze your ice cream or de-ice a snowy sidewalk (water has to be present!). This is why NaCl isn't used to de-ice sidewalks in areas that are very cold.

How To Do a Vinegar & Baking Soda Foam Fight

2011-04-28T12:54:00.000-07:00

This is a twist on the classic baking soda volcano, where you use the ingredients to make squirt-able fountains of foam.

Difficulty: Easy

Time Required: Mere Minutes

What You Need:

empty compressible plastic bottle - no lids
water
diswashing detergent
baking soda
vinegar
food coloring (optional)

Here's How:

First, you need bottles for everyone. The classic 2-liter bottle is nice because it's compressible and holds a large volume. Gatorade bottles are also good because they have wide mouths, so it's easier to recharge the bottle.
Fill each bottle most of the way full of warm water and add a squirt of dishwashing detergent.
Gather the rest of the materials you will need: lots of vinegar and baking soda and food coloring if you want colored bubbles. Be advised: adding food coloring could result in staining of clothing and other surfaces.
Add some baking soda to the bottle (couple of tablespoons or so). Put your hand over the bottle opening and shake it up to get the detergent water all sudsy. Drip a bit of food coloring onto the suds.
Note: if you add the food coloring before shaking the detergent water, then the dye will go into the water and the bubbles will be clear. If you add the coloring just prior to adding the vinegar then the bubbles will be deeply colored (which also increases the staining potential).
Pour in some vinegar. This starts the reaction. Feel free to give the bottle a little squeeze to help things along. Do NOT seal the bottle with a cap or lid. That basically makes a baking soda bomb, which is dangerous.
You can recharge the reaction with more baking soda and then more vinegar. If at any time you feel like shaking up the bottle only do this with your hand over the opening and never cap or seal the bottle.
The foam fight part most people figure out on their own. Have fun!

Tips:

Avoid getting the mixture into your eyes or mouth. If eye contact occurs, rinse the solution out. Don't drink the contents of the foam fight bottle.
Avoid contact with unreacted vinegar or undiluted dishwashing detergent. Both can irritate skin and mucous membranes.

Density Column

2011-04-28T12:53:00.000-07:00

Make a density column with many liquid layers using common household liquids. This is an easy, fun and colorful science project that illustrates the concept of density.

Density Column Materials

You can use some or all of these liquids, depending on how many layers you want and which materials you have handy. These liquids are listed from most-dense to least-dense, so this is the order in which you pour them into the column.

honey
corn syrup or pancake syrup
liquid dishwashing soap
water (can be colored with food coloring)
vegetable oil
rubbing alcohol (can be colored with food coloring)
lamp oil

Make the Density Column

Pour your heaviest liquid into the center of whatever container you are using to make your column. If you can avoid it, don't let the first liquid run down the side of the the container because the first liquid is thick enough it will probably stick to the side so your column won't end up as pretty. Carefully pour the next liquid you are using down the side of the container. Another way to add the liquid is to pour it over the back of a spoon. Continue adding liquids until you have completed your density column. At this point, you can use the column as a decoration. Try to avoid bumping the container or mixing its contents. The hardest liquids to deal with are the water, vegetable oil, and rubbing alcohol. Make sure that there is an even layer of oil before you add the alcohol because if there is a break in that surface or if you pour the alcohol so that it dips below the oil layer into the water then the two liquids will mix. If you take your time, this problem can be avoided.

How the Density Column Works

You made your column by pouring the heaviest liquid into the glass first, followed by the next-heaviest liquid, etc. The heaviest liquid has the most mass per unit volume or the highest density. Some of the liquids don't mix because they repel each other (oil and water). Other liquids resist mixing because they are thick or viscous. Eventually some of the liquids of your column will mix together.

How To Color Fire

2011-04-28T12:51:00.000-07:00

I know I'm not the only person who has rummaged through old magazines and newspapers, looking for highly colored pages to throw onto a fire to make colored flames. This method of coloring fire, while fun, is hit-and-miss. Have you ever wanted to know how to color the fire reliably? I've compiled a list of colorants and simple instructions for using them. Here are some of your options:

Toss dry colorants onto the flames.
Soak logs in an alcohol solution of colorants.
Soak logs in an aqueous (water) solution of colorants and allow the logs to dry.
Prepare pinecones, sawdust, or cork with colorants.

In general, there is no specific proportion of colorant to mix with the water or alcohol. Add as much powdered colorant as will dissolve in the liquid (roughly a half pound colorant to a gallon of water). Do not attempt to mix colors together - you will probably end up with a normal yellow flame. If you want multicolored fire, try adding several pinecones, each treated with a single colorant, or scatter a mixture of dried colored sawdusts across the fire.

How to Prepare Pinecones or Sawdust
It's easy! Remember to do this procedure separately for each color. You can combine dry pinecones or sawdust with different colorants later.

Pour water into a bucket. Use sufficient water to be able to wet your pinecones, sawdust, or waste cork. Skip to step 3 if you purchased your colorant in liquid form.
Stir in colorant until you can't dissolve any more. For sawdust or waste cork, you may also add some liquid glue, which will allow the pieces to stick together and form larger chunks.
Add the pinecones, sawdust, or cork. Mix to form an even coat.
Let the material soak in the colorant mixture for several hours or overnight.
Spread the pieces out to dry. If desired, pinecones may be placed in a paper or mesh bag. You can spread sawdust or cork out on paper, which will also produce colored flames.

How to Prepare Logs
Follow steps 1 and 2 above and either roll a log around in the container (big container, small log) or else pour and spread the mixture onto the logs. Wear kitchen or other protective gloves to protect your hands. Allow the logs to dry. If you make your own newspaper logs, you can smear colorant onto the paper before rolling it.
Points to Keep in Mind

The element sodium burns with the usual yellow flame. The presence of this element can overwhelm any other color. If you are making a dry mixture of colorants or colored pinecones/sawdust, you should avoid including any colorant that has sodium in it.
If you are using alcohol-based colorants: Remember that alcohol is flammable. If you don't allow it to evaporate before use, you will get a lighter-fluid effect. Use with care!
Don't color BBQ fire! The colorants may produce pretty flames, but they can also produce toxic food.
Keep the colorants away from children and handle them with the care and respect due to potentially hazardous chemicals. Read and adhere to any warnings listed on product labels.

Now, here is the list of colorants. Most can be found in a grocery or dry goods store, in the laundry or cleaner section. Look for copper sulfate in swimming pool supplies (already in water, which is fine). Potassium chloride is used as a salt substitute and may be found in the spice section. Epsom salts, borax, and calcium chloride may be found with laundry/cleaning supplies. Others, including strontium chloride, can be obtained from stores that specialize in rocketry or firework supplies.

Flame Colorants

Color	Chemical
Carmine	Lithium Chloride
Red	Strontium Chloride
Orange	Calcium Chloride (a bleaching powder)
Yellow	Sodium Chloride (table salt) or Sodium Carbonate
Yellowish Green	Borax
Green	Copper Sulfate or Boric Acid
Blue	Copper Chloride
Violet	3 parts Potassium Sulfate 1 part Potassium Nitrate (saltpeter)
Purple	Potassium Chloride
White	Magnesium Sulfate (Epsom salts)

Hot Ice or Sodium Acetate

2011-04-28T12:49:00.000-07:00

Sodium acetate or hot ice is an amazing chemical you can prepare yourself from baking soda and vinegar. You can cool a solution of sodium acetate below its melting point and then cause the liquid to crystallize. The crystallization is an exothermic process, so the resulting ice is hot. Solidification occurs so quickly you can form sculptures as you pour the hot ice.

Sodium Acetate or Hot Ice Materials

1 liter clear vinegar (weak acetic acid)
4 tablespoons baking soda (sodium bicarbonate)

Prepare the Sodium Acetate or Hot Ice

In a saucepan or large beaker, add baking soda to the vinegar, a little at a time and stirring between additions. The baking soda and vinegar react to form sodium acetate and carbon dioxide gas. If you don't add the baking soda slowly, you'll essentially get a baking soda and vinegar volcano, which would overflow your container. You've made the sodium acetate, but it is too dilute to be very useful, so you need to remove most of the water. Here is the reaction between the baking soda and vinegar to produce the sodium acetate:
Na⁺[HCO₃]^– + CH₃–COOH → CH₃–COO^– Na⁺ + H₂O + CO₂
Boil the solution to concentrate the sodium acetate. You could just remove the solution from heat once you have 100-150 ml of solution remaining, but the easiest way to get good results is to simply boil the solution until a crystal skin or film starts to form on the surface. This took me about an hour on the stove over medium heat. If you use lower heat you are less likely to get yellow or brown liguid, but it will take longer. If discoloration occurs, it's okay.
Once you remove the sodium acetate solution from heat, immediately cover it to prevent any further evaporation. I poured my solution into a separate container and covered it with plastic wrap. You should not have any crystals in your solution. If you do have crystals, stir a very small amount of water or vinegar into the solution, just sufficient to dissolve the crystals.
Place the covered container of sodium acetate solution in the refrigerator to chill.

Activities Involving Hot Ice

The sodium acetate in the solution in the refrigerator is an example of a supercooled liquid. That is, the sodium acetate exists in liquid form below its usual melting point. You can initiate crystallization by adding a small crystal of sodium acetate or possibly even by touching the surface of the sodium acetate solution with a spoon or finger. The crystallization is an example of an exothermic process. Heat is released as the 'ice' forms. To demonstrate supercooling, crystallization, and heat release you could:

Drop a crystal into the container of cooled sodium acetate solution. The sodium acetate will crystallize within seconds, working outward from where you added the crystal. The crystal acts as a nucleation site or seed for rapid crystal growth. Although the solution just came out of the refrigerator, if you touch the container you will find it is now warm or hot.
Pour the solution onto a shallow dish. If the hot ice does not spontaneously begin crystallization, you can touch it with a crystal of sodium acetate (you can usually scrape a small amount of sodium acetate from the side of the container you used earlier). The crystallization will progress from the dish up toward where you are pouring the liquid. You can construct towers of hot ice. The towers will be warm to the touch.
You can re-melt sodium acetate and re-use it for demonstrations.

Hot Ice Safety

As you would expect, sodium acetate is a safe chemical for use in demonstrations. It is used as a food additive to enhance flavor and is the active chemical in many hot packs. The heat generated by the crystallization of a refrigerated sodium acetate solution should not present a burn hazard.

How To Make Invisible Ink - Baking Soda

2011-04-28T12:37:00.000-07:00

These are instructions for making non-toxic invisible ink using baking soda (sodium bicarbonate).

Difficulty: Easy

Time Required: A Few Minutes

What You Need:

Baking Soda
Paper
Water
Light Bulb (heat source)
Paintbrush or Swab
Measuring Cup
Purple Grape Juice (opt.)

Here's How:

There are at least two methods to use baking soda as an invisible ink. Mix equal parts water and baking soda.
Use a cotton swab, toothpick, or paintbrush to write a message onto white paper, using the baking soda solution as 'ink'.
Allow the ink to dry.
One way to read the message is to hold the paper up to a heat source, such as a light bulb. The baking soda will cause the writing in the paper to turn brown.
A second method to read the message is to paint over the paper with purple grape juice. The message will appear in a different color.

Tips:

If you are using the heating method, avoid igniting the paper - don't use a halogen bulb.
Baking soda and grape juice react with each other in an acid-base reaction, producing a color change in the paper.
The baking soda mixture can also be used more diluted, with one part baking soda to two parts water.
Grape juice concentrate results in a more visible color change than regular grape juice.

Chemistry Fun with Pennies

2011-04-28T12:34:00.000-07:00

Use pennies, nails, and a few simple household ingredients to explore some of the properties of metals:

Materials

20-30 dull pennies
1/4 cup white vinegar (dilute acetic acid)
1 teaspoon salt (NaCl)
1 shallow, clear glass or plastic bowl (not metal)
1-2 clean steel screws or nails
water
measuring spoons
paper towels

Shiny Clean Pennies

Pour the salt and vinegar into the bowl.
Stir until the salt dissolves.
Dip a penny halfway into the liquid and hold it there for 10-20 seconds. Remove the penny from the liquid. What do you see?
Dump the rest of the pennies into the liquid. The cleaning action will be visible for several seconds. Leave the pennies in the liquid for 5 minutes.
Proceed to 'Instant Verdigris!'

Pennies get dull over time because the copper in the pennies slowly reacts with air to form copper oxide. Pure copper metal is bright and shiny, but the oxide is dull and greenish. When you place the pennies in the salt and vinegar solution, the acetic acid from the vinegar dissolves the copper oxide, leaving behind shiny clean pennies. The copper from the copper oxide stays in the liquid. You could use other acids instead of vinegar, like lemon juice.

Instant Verdigris!

Note: You want to keep the liquid you used to clean the pennies, so don't dump it down the drain!
After the 5 minutes required for 'Shiny Clean Pennies', take half of the pennies out of the liquid and place them on a paper towel to dry.
Remove the rest of the pennies and rinse them well under running water. Place these pennies on a second paper towel to dry.
Allow about an hour to pass and take a look at the pennies you have placed on the paper towels. Write labels on your paper towels so you will know which towel has the rinsed pennies.
While you are waiting for the pennies to do their thing on the paper towels, use the salt and vinegar solution to make 'Copper Plated Nails'.

Rinsing the pennies with water stops the reaction between the salt/vinegar and the pennies. They will slowly turn dull again over time, but not quickly enough for you to watch! On the other hand, the salt/vinegar residue on the unrinsed pennies promotes a reaction between the copper and the oxygen in the air. The resulting blue-green copper oxide is commonly called 'verdigris'. It is a type of patina found on a metal, similar to tarnish on silver. The oxide forms in nature as well, producing minerals such as malachite and azurite.

Copper Plated Nails

Place a nail or screw so that it is half in and half out of the solution you used to clean the pennies. If you have a second nail/screw, you can let it sit completely immersed in the solution.
Do you see bubbles rising from the nail or the threads of the screw?
Allow 10 minutes to pass and then take a look at the nail/screw. Is it two different colors? If not, return the nail to its position and check it again after an hour.

The copper that coats the nail/screw comes from the pennies. However, it exists in the salt/vinegar solution as positively charged copper ions as opposed to neutral copper metal. Nails and screws are made of steel, an alloy primarily composed of iron. The salt/vinegar solution dissolves some of the iron and its oxides on the surface of the nail, leaving a negative charge on the surface of the nail. Opposite charges attract, but the copper ions are more strongly attracted to the nail than the iron ions, so a copper coating forms on the nail. At the same time, the reactions involving the hydrogen ions from the acid and the metal/oxides produce some hydrogen gas, which bubbles up from the site of the reaction - the surface of the nail or screw.

How To Make a Mentos & Diet Soda Chemical Volcano Eruption

2011-04-28T12:33:00.000-07:00

Chemical volcanos are classic projects for science fairs and chemistry demonstrations. The mentos and diet soda volcano is similar to the baking soda volcano, except the eruption is really powerful, capable of producing jets of soda several feet high. It's messy, so you might want to do this project outdoors or in a bathroom. It's also non-toxic, so kids can do this project.

Difficulty: Easy

Time Required: chemical volcano takes a few minutes to set up and erupts for a few seconds

What You Need:

roll of mentos candies
2-liter bottle of diet soda
index card
test tube or sheet of paper
a mop for cleanup

Here's How:

First, gather your supplies. You can substitute another candy for the Mentos, such as M&Ms or Skittles, but ideally you want candies that stack into a neat column with minimal space between them, have a chalky consistency, and barely fit through the mouth of a 2-liter bottle.
Similarly, you could substitute normal soda for diet soda. The project will work just as well, but the resulting eruption will be sticky. Whatever you use, the beverage has to be carbonated!
First, you need to stack the candies. The easiest way to do this is to stack them in a test tube narrow enough to form a single column. Otherwise, you can roll a sheet of paper into a tube just barely wide enough for a stack of candies.
Place an index card over the opening of the test tube or end of the paper tube to hold the candies in the container. Invert the test tube.
Open your full 2-liter bottle of diet soda. The eruption happens very quickly, so set things up: you want the open bottle - index card - roll of candies so that as soon as you remove the index card, the candies will drop smoothly into the bottle.
When you're ready, do it! You can repeat the eruption with the same bottle and another stack of candies. Have fun!

How To Grow a Borax Crystal Snowflake

2011-04-28T12:32:00.000-07:00

Do real snowflakes melt too quickly? Grow a borax crystal snowflake, color it blue if you like, and enjoy the sparkle all year long!

Difficulty: Average

Time Required: Overnight

What You Need:

string
wide mouth jar (pint)
white pipe cleaners
borax (see tips)
pencil
boiling water
blue food coloring (opt.)
scissors

Here's How:

The first step of making borax crystal snowflakes is to make the snowflake shape. Cut a pipe cleaner into three equal sections.
Twist the sections together at their centers to form a six-sided snowflake shape. Don't worry if an end isn't even, just trim to get the desired shape. The snowflake should fit inside the jar.
Tie the string to the end of one of the snowflake arms. Tie the other end of the string to the pencil. You want the length to be such that the pencil hangs the snowflake into the jar.
Fill the widemouth pint jar with boiling water.
Add borax one tablespoon at a time to the boiling water, stirring to dissolve after each addition. The amount used is 3 tablespoons borax per cup of water. It is okay if some undissolved borax settles to the bottom of the jar.
If desired, you may tint the mixture with food color.
Hang the pipe cleaner snowflake into the jar so that the pencil rests on top of the jar and the snowflake is completely covered with liquid and hangs freely (not touching the bottom of the jar).
Allow the jar to sit in an undisturbed location overnight.
Look at the pretty crystals!!! You can hang your snowflake as a decoration or in a window to catch the sunlight :-)

Tips:

Borax is available at grocery stores in the laundry soap section, such as 20 Mule Team Borax Laundry Booster. Do not use Boraxo soap.
Because boiling water is used and because borax isn't intended for eating, adult supervision is recommended for this project.
If you can't find borax, you can use sugar or salt (may take longer to grow the crystals, so be patient). Add sugar or salt to the boiling water until it stops dissolving. Ideally you want no crystals at the bottom of the jar.

How To Make Slime

2011-04-28T12:30:00.000-07:00

There are lots of recipes for slime. Since most recipes are easy, look for one using ingredients you have on hand.

Difficulty: Easy

Time Required: 15 mins

What You Need:

borax powder
water
4 ounce (120 ml) glue (e.g., Elmer's white glue)
teaspoon
bowl
jar or measuring cup
food coloring (optional)
measuring cup

Here's How:

Pour the glue into the jar. If you have a big bottle of glue, you want 4 oz or 1/2 cup of glue.
Fill the empty glue bottle with water and stir it into the glue (or add 1/2 cup of water).
If desired, add food coloring. Otherwise, the slime will be an opaque white.
In a separate, mix one cup (240 ml) of water into the bowl and add 1 teaspoon (5 ml) of borax powder.
Slowly stir the glue mixture into the bowl of borax solution.
Place the slime that forms into your hands and knead until it feels dry. (Don't worry about the excess water remaining in the bowl.)
The more the slime is played with, the firmer and less sticky it will become.
Have fun!
Store your slime in a zip-lock bag in the fridge (otherwise it will develop mold).

Tips:

Use white glue, such as Elmer's brand. Most 'school glues' do not have the correct composition.
Don't eat the slime - it isn't especially toxic, but not good for you either!
Slime cleans up pretty easily. Remove dried slime after soaking with water.

How To Build a Baking Soda Volcano

2011-04-27T12:35:00.000-07:00

Okay, the baking soda volcano is the kitchen equivalent of a volcano, not a real one. It's cool all the same! The baking soda volcano is also non-toxic, which adds to its appeal.

Difficulty: Average

Time Required: 30 minutes

What You Need:

6 cups flour
2 cups salt
4 tablespoons cooking oil
warm water
plastic soda bottle
dishwashing detergent
food coloring
vinegar
baking dish or other pan
2 T baking soda

Here's How:

First make the 'cone' of the baking soda volcano. Mix 6 cups flour, 2 cups salt, 4 tablespoons cooking oil, and 2 cups of water. The resulting mixture should be smooth and firm (more water may be added if needed).
Stand the soda bottle in the baking pan and mold the dough around it into a volcano shape. Don't cover the hole or drop dough into it.
Fill the bottle most of the way full with warm water and a bit of red food color (can be done before sculpting if you don't take so long that the water gets cold).
Add 6 drops of detergent to the bottle contents. The detergent helps trap the bubbles produced by the reaction so you get better lava.
Add 2 tablespoons baking soda to the liquid.
Slowly pour vinegar into the bottle. Watch out - eruption time!

Tips:

The cool red lava is the result of a chemical reaction between the baking soda and vinegar.
In this reaction, carbon dioxide gas is produced, which is also present in real volcanoes.
As the carbon dioxide gas is produced, pressure builds up inside the plastic bottle, until the gas bubbles (thanks to the detergent) out of the 'volcano'.
Adding a bit of food coloring will result in red-orange lava! Orange seems to work the best. Add some red, yellow, and even purple, for a bright display.