You come into contact with nitrogen every day; it makes up 78% of our atmosphere. While it is very common to find nitrogen in its gaseous state, it is much more difficult to find it in its liquid state. That is because liquid nitrogen is very cold. If it gets warmer than -321°F it turns back into a gas.
Liquid nitrogen is made by compressing and expanding regular air. The air is first compressed, which makes the air warm. The compressed air is then cooled to room temperature and then released into a larger container. This transition from high pressure to low pressure results in a cooling of the air based on the ideal gas law, which you can learn morea bout here. It’s the same principle used in refrigerators or air conditioners, but is repeated many more times, allowing the nitrogen to cool off even more and separate from the other gasses in the air. We use liquid nitrogen in many of our experiments, which you can check out here!
One problem is that liquid nitrogen will slowly boil away in storage, so in the month between our fall and spring seasons, any leftover liquid nitrogen will just boil away and be wasted. Instead, we took ours to the pool!
At 86°F, the water is much warmer than the -321°F liquid nitrogen. As a result, the liquid nitrogen begins to turn into an invisible gas, which is not the interesting thing the video shows. The growing white cloud that you see is condensed water vapour from the moist humid air above the warm pool water. As the intensely cold liquid nitrogen is added, the moist, humid air almost immediately condenses, and as the cold spreads out, the cloud follows suit.
Warning: Please note this experiment should not be done with people in the pool. This is not because of the cold (it’s very hard to change the temperature of water), but because of the layer of nitrogen hovering above the pool. The nitrogen pushes the oxygen out of the way. So any swimmers will feel like they’re breathing regular air, but will not be getting vital oxygen. In fact, the room that we dispense liquid nitrogen in has to be large enough and have adequate ventilation to prevent this from happening to people standing nearby.
All you need for this at-home science is a glass, a plate, a candle, water, a match, and a bit of caution, because we are dealing with fire.
Step 1: Pour the water on the plate
Step 2: Place the candle on the center of the plate
Step 3: Light the candle (or have a guardian light it for you)
Step 4: Place the glass down over the candle, step back and watch science happen!
This experiment is all about maintaining an equilibrium of air pressures inside and outside the glass. We usually experience air pressure as the force from the atmosphere pushing down on us. Here at AstroCamp we feel about twelve PSI, or pounds per square inch, of force which is the same amount of force that the water on the plate initially feels.
The flame heats up the air on the inside, creating a higher pressure than the air on the outside. Hotter air has a higher energy and therefore exerts more air pressure. The higher pressure pushes the water down and out of the glass. You should be able to see air bubbles in the water just outside of the glass from the air forcing the water out.
Fire needs oxygen in order to continue the combustion process in the glass, but because we trapped air in the there is only a finite amount. When the flame uses up all of the oxygen it goes out, which allows the air to cool. Cold air doesn’t have as much pressure as hot air and has less pressure than the air outside of the glass. Therefore the air on the outside of the glass pushes with greater force on the water than the air on the inside so the water is able to get sucked back up into the glass! When the water level evens out that is when you know you have reached an equilibrium of air pressures again.
Have you ever been sitting inside on a rainy day and wondered how exactly rain is made? With a simple experiment, you can make it rain anywhere (anywhere that’s some kind of closed container, anyway).
To perform this experiment, you will need hot (not boiling) water, plastic wrap, ice, and a container like a glass or a bottle.
You or an adult should heat up the water to the point when it begins to steam, but not actually boil. This can be done in the microwave (about 2 minutes, depending on microwave power and amount of water) or on the stove, so long as you exercise caution. If you choose a microwave as your heat source, use a microwave-safe container. If the water is boiling, let it cool and do not put it in anything plastic.
Pour the water into your glass, bottle, etc.and stretch the plastic wrap tightly over the top. Let this sit for a minute or two.
Set ice cubes over the plastic wrap and let it sit for 6-8 minutes. As time passes, you will see condensation form on the bottom of the plastic wrap. These drops will steadily grow until raining back down. You’ve made it rain indoors!
How it works:
When the steam rises off of the hot water, it comes in contact with the ice, which cools down the steam and condenses it to a liquid. This is a scaled-down version of something called the water cycle, where water evaporates from oceans, rivers, and other bodies of water, cools down and condenses into clouds in the atmosphere, and eventually rains back down on all of us.
Dry ice is the solid state of carbon dioxide, the gas we all breathe out, but have you ever seen it in liquid form? When left at room temperature, dry ice doesn’t actually melt; it sublimates, changing directly from a solid to a gas. To understand why, let’s take a look at its phase diagram, a plot of the states of CO2 relative to temperature and pressure.
At standard pressure of one atmosphere, liquid CO2 is unsustainable and any solid carbon dioxide above -109℉, or -78℃, directly converts to a gas. In order for liquid CO2 to exist, the pressure needs to be increased to at least 5.11 atmospheres; which is where our pressure syringe comes in.
Substances tend to condense as pressure increases, changing down in state from gas to liquid or liquid to solid or at least making that state change easier. As the plunger of the pressure syringe drops, the pressure increases to the point where dry ice melts rather than sublimating and CO2 can be held in liquid form.
Just as increasing pressure aids substances in changing down in state, decreasing pressure facilitates changing up in state. At sea level, the boiling point of water is 212 degrees Fahrenheit, but if you live at 5500 feet like those of us at AstroCamp, that boiling point is decreased to 201.5 degrees. This 10.5 degree difference may not seem significant, but that’s the result of a change of less than 0.2 atm. In a vacuum chamber, water will actually boil at room temperature because of the immense drop in pressure.
We would like to thank you for visiting our blog. AstroCamp is a hands-on physical science program with an emphasis on astronomy and space exploration. Our classes and activities are designed to inspire students toward future success in their academic and personal pursuits. This blog is intended to provide you with up-to-date news and information about our camp programs, as well as current science and astronomical happenings. This blog has been created by our staff who have at least a Bachelors Degree in Physics or Astronomy, however it is not uncommon for them to have a Masters Degree or PhD. We encourage you to also follow us on Facebook, Instagram, Google+, Twitter, and Vine to see even more of our interesting science, space and astronomy information. Feel free to leave comments, questions, or share our blog with others. Please visit www.astrocampschool.org for additional information. Happy Reading!