How to Make Clouds in a Bottle How do clouds form? When a liquid like water evaporates, the water vapor mixes with air. Cold air can’t hold as much water vapor as warm air. So if warm air containing lots of water vapor cools off, it can’t hold on to the water vapor anymore. The water vapor condenses into tiny droplets that stick to dust, soot, or any other particles in the air. These clusters of water droplets are clouds! In the experiments below, we will use pressure to change the temperature of air. When a gas is suddenly compressed, its temperature increases. When a gas is quickly expanded, the temperature drops.

Safety Notes This is an easy way to make clouds with readily available materials. We don’t need to add any extra dust or smoke particles to the bottle for the clouds to form. In fact, rubbing alcohol is flammable, so be sure to keep it away from any open flame.

Procedure Step 1: Pour just enough rubbing alcohol into the large bottle to cover the bottom. Step 2: Seal the opening of the bottle enough that air won’t escape when you use the bicycle pump. Step 3: Pump air into the bottle until it becomes difficult to compress the pump. It might help to have someone else hold onto the bottle so it doesn’t move. Step 4: Quickly release the pressure in the bottle and watch the cloud form. Step 5: If you seal the bottle and start pumping, the cloud will evaporate as the pressure and temperature increase again.

What's Happening? In this experiment, we use some special materials to help form thicker clouds. Rubbing alcohol evaporates much more quickly than water, so we will have plenty of alcohol vapor available to condense. The bicycle pump helps us make even bigger changes in pressure and temperature than we would get by squeezing the bottle, which will cause more of the alcohol vapor to condense.

Eating Her Curds and Whey When making cheese, starter cultures, or good bacteria, are added to start the cheesemaking process. They help determine the ultimate flavor and texture of the cheese. Next, a milk-clotting enzyme called rennet is added to coagulate the milk, forming a custard-like mass. You will be curdling the milk with an acid, similarly to how the milk is coagulated by bacteria in the cheese making process.

What You Do Measure 75 mL of skim milk and pour it into the glass. Measure 2 tablespoons of vinegar and pour into the milk. Stir the vinegar and milk together then observe!

What Happened? Curds and Whey Milk is a colloid. A colloid is a mixture of substances that do not settle out over time (like a mixture of sand and water would for example). Unlike a suspension (sand and water or orange juice and pulp) that mixes together when stirred or shaken then settles into separate parts when left at rest, a colloid does not settle because the particles that make it up are extremely tiny. Looking at a glass of milk, one would not be able to see the particles that make it up, namely the curds (solid casein protein particles) and whey (liquid particles) because they are so small. (Interestingly, milk appears white even though the particles that make it up are mostly clear, because light is scattered by the tiny particles as it passes through the colloid.) The milk was “curdled” when the acidic vinegar was added and lowered the pH of the milk, causing the casein particles to come out of the solution as solid chunks of curds floating in the liquid whey. Gross—definitely don’t drink it!

Magic Milk Instructions Pour 200mL of milk into the plate. Drop one drop of each of the colors of food coloring onto the milk. Dip a toothpick in dishwashing detergent liquid.  Touch the coated toothpick to the milk in the center of the plate.  DON'T STIR THE MILK; it isn't necessary. Watch what happens!

How Magic Milk Works Milk consists of a lot of different types of molecules, including fat, protein, sugars, vitamins, and minerals. If you had just touched a clean cotton swab to the milk (try it!), not much would have happened. The cotton is absorbent, so you would have created a current in the milk, but you wouldn't have seen anything especially dramatic happen. When you introduce detergent to the milk, several things happen at once. The detergent lowers the surface tension of the liquid so that the food coloring is free to flow throughout the milk. The detergent reacts with the protein in the milk, altering the shape of those molecules and setting them in motion. The reaction between the detergent and the fat forms micelles, which is how detergent helps to lift grease off of dirty dishes. As the micelles form, the pigments in the food coloring get pushed around. Eventually equilibrium is reached, but the swirling of the colors continues for quite a while before stopping.

Oobleck This is made with one part water, two and a half parts cornstarch. PLEASE keep the Oobleck over the trays and do your best to keep it in the containers. Other classes have to use this (plus it makes a huge mess)! DO NOT pour it down the drain. Other than that, have fun!

What does non-Newtonian mean? All fluids have a property known as viscosity that describes how the fluid flows – commonly thought of as how thick or thin a fluid is. For instance, honey is much more viscous than water. When a fluid’s viscosity is constant it is referred to as a Newtonian fluid. Oobleck is an example of a fluid whose viscosity is not constant, it changes depending on the stress or forces applied to it. If you poke it with your finger and apply a large force, it becomes very viscous and stays in place. If you gently pour it, applying little force, it will flow like water. This kind of fluid is called a dilatant material or a shear thickening fluid. It becomes more viscous when agitated or compressed.

Another non-Newtonian liquid Another non-Newtonian liquid is ketchup. Ketchup behaves in just the opposite way from oobleck. It becomes less viscous when agitated. Liquids like this are called thixotropic. If you leave a bottle of Ketchup on a shelf, it becomes thicker or more viscous. Nearly everyone has experienced this while trying to pour the liquid from a new bottle – it refuses to move. If you shake the bottle or stir it up it becomes less viscous and pours easily. Why does Oobleck behave the way it does?

Oobleck Explanation The most generally accepted explanation for the behavior of Oobleck is offered by Cary Sneider in “Oobleck: What do Scientists Say?”. When sitting still the granules of starch are surrounded by water. The surface tension of the water keeps it from completely flowing out of the spaces between the granules. The cushion of water provides quite a bit of lubrication and allows the granules to move freely. But, if the movement is abrupt, the water is squeezed out from between the granules and the friction between them increases rather dramatically.

An Earth-Shattering Experience Limestone caves are hollowed out by rainwater that is slightly acid and, over thousands of years, has gradually, eventually, and greatly dissolved away the soft rock.

What to do Place 1 small piece of chalk in 150 mL of vinegar for five minutes. Place 1 small piece of chalk in 150 mL of water for five minutes. Compare the reaction from both and explain your observations.

Earth-Shattering Why? School chalk is a form of limestone, or calcium carbonate. It is made up of small bits of seashells and the mineral calcite and is similar to the soft rock caves of limestone. These caves have been formed by the rock that has been dissolved by the acids in rainwater, similar to the chalk that is dissolved by the vinegar (acetic acid). England’s famed White Cliffs of Dover are made up of great sheets of chalk, a form of calcium carbonate.

What Are You Writing? Write the title of your experiment. Write down your observations of the reaction. What is your hypothesis (educated guess) for this reaction?